MEILING LI
RESPONSE OF TARO [Colocasia esculenta (L.) Schott] GROWTH, YIELD, AND
CORM QUALITY TO VARYING WATER REGIMES AND SOIL TEXTURES
Botucatu
2019

MEILING LI
RESPONSE OF TARO [Colocasia esculenta (L.) Schott] GROWTH, YIELD, AND
CORM QUALITY TO VARYING WATER REGIMES AND SOIL TEXTURES
T
h
Thesis presented to the Agronomical Sciences
College - campus of Botucatu, São Paulo State
University, to obtain the title of PhD in
Horticulture.
Advisor: Prof. Dr. Lin Chau Ming
Coorientator: Prof. Dr. Angélica Cristina
Fernandes Deus
Botucatu
2019
 
 
 
FICHA CATALOGRÁFICA ELABORADA PELA SEÇÃO TÉCNICA DE AQUISIÇÃO E TRATAMEN-
TO DA INFORMAÇÃO – DIRETORIA TÉCNICA DE BIBLIOTECA E DOCUMENTAÇÃO - UNESP 
– FCA – LAGEADO – BOTUCATU (SP) 
       Li, Meiling, 1988-    
L693r     Response of taro [Colocasia esculenta (L.) Schott]  
       growth, yield, and corm quality to varying water regimes  
       and soil textures / Meiling Li. – Botucatu: [s.n.], 2019  
          89 p.: fots. color., ils. color., grafs., tabs. 
                                                                   
          Tese (Doutorado)- Universidade Estadual Paulista, Fa-  
       culdade de Ciências Agronômicas, Botucatu, 2019 
          Orientador: Lin Chau Ming 
          Coorientadora: Angélica Cristina Fernandes Deus 
          Inclui bibliografia              
              
          1. Inhame - Irrigação. 2. Eficiência do uso da água.  
       3. Estresse hídrico. 4. Solos tropicais. I. Ming, Lin  
       Chau. II. Deus, Angélica Cristina Fernandes. III. Univer- 
       sidade Estadual Paulista “Júlio de Mesquita Filho” (Câm- 
       pus de Botucatu). Faculdade de Ciências Agronômicas. IV.  
       Título. 
 
Elaborada por Ana Lucia G. Kempinas – CRB-8:7310 
 
 
 
 
 
 
 
 
 
“Permitida a cópia total ou parcial deste documento, desde que citada a fonte” 
 
 
  
 
  
 
To my beloved grandmother,
Li Fan Shi,
I dedicate.

ACKNOWLEDGEMENTS
First and foremost, loving, kindness, and faithfulness of the God in bestowing health,
strength, patience and protection throughout the study period has always praised and
with all my heart I give Thanks.
My sincere thanks is to my supervisors who assisted me through this PhD project:
Prof. Lin Chau Ming, Angélica Cristina Fernandes Deus, and Márcia Ortiz Mayo
Marques. You are all very experienced in scientific and practical work regarding my
study and I have learned a lot from you through the process and I can say I can never
finish this study without your help.
I express my gratitude to my master's supervisor Professor Danfeng Huang, who
always gives me help, support and caring.
Professor Lin Chau Ming, again thank you for encouraging and bringing me to Brazil
to start the PhD degree, thanks for all the support, caring, and help. I would like to say
Thanks for your wife Mrs. Margarete, for your son Leonardo and Rodrigo, for your
daughter in law Fabíola and your grandson Zephyr, who always give me caring,
support, and help like my another family in Brazil. My study here would be much more
stressful without you.
From the very bottom of my heart, my special thanks is to Angélica, for all your caring,
conversations, accompaniments and help. I can not imagine how could I spend these
four years without you. My sincere thanks goes to your parents Mr. Florisvaldo and
Mrs. Luzia, to your sister Silvanna and her family, to your brother Maurício and his
family, to your nephew Guilherme, Beatriz, and Giovanna, for treating me as one
member of your family, for always giving me happiness and caring when I was far
away from my own family.
I wanted to say Thanks to Priscila Dandaro with all my heart, for the caring, the
conversations, and the accompaniments, I would suffer much more if I did not have
you here as my friend.
Warmest thanks goes to Professor Dirceu Maximino Fernandes, João Carlos Cury
Saad, Almecina Balbino Ferreira, Rosemary Marques de Almeida Bertani, Gabriela s,
and Lais Lorena Queiroz Moreira, as the member of the defense team, who will
contribute a lot in improving my PhD project. I would like to forward my thanks also to
Professor Filipe Pereira Giardini Bonfim and Roberto Lyra Villas Bôas as the
members of the qualification team, who contributed a lot in improving my thesis.
Exceptional thanks also go to my friends Francisca Franciana Sousa Pereira, Aline
Mako, Marisa Aida Diogo Matsinhe, Lais Lorena Queiroz Moreira, and Gabriela
granghelli Gonçalves among the other friends for all the support and help during the
study period.
Big thanks to my colleagues in São Paulo State University, Marcos Liodorio, João
Victor and Aline Gonçalves for the contributions in the experiment, who also
elaborately helped with administration, lab work and the coordination throughout the
study period. I could not finish this project without your help. I would like to thank all
the technical personnel for help in the lab Mr. Edison, Mr. Edivaldo and all the PhD
candidates of the program for enjoyable discussions about the PhD life.
Thanks to Mrs Cristina and her family for all the help she gave to me, here I want to
say Thanks to my friends in capital São Paulo, Sharon, Ge Dan, Tina, Carla, Lia,
Jacky, Wang Sheng and so on, for all your help and caring.
I extend my sincere appreciation to all the staffs from the Department of Horticulture,
to all the staffs of the Library, and to all the staffs of the Postgraduate Section from
FCA, UNESP for their assistance and help during the study period.
I would also like to thank all the people I met in Brazil includes the ones that I would
never know their name.
For all the financially support I would like to thank the Coordenação de
Aperfeiçoamento de Pessoal de Nível Superior (CAPES). I could not finish this project
without the financial help (Process number: 88882.195706/2018-01).
Dear my parents, my sister, my brother and my nephews deeply I thank all of you for
your support and caring. All you, deserve very special thanks for your loving, caring
and motivation.
ABSTRACT
Irrigation is an important agricultural practice for the cultivation of taro, however, there
are few experimental results focus on this practice in Brazil, and there is no
information on water requirement for this crop under different soil textures in São
Paulo State. Therefore, the objective of this work was to evaluate the development,
biomass and corm quality of taro under varying water regimes and soil textures. The
experiment was conducted from 2016 to 2017 with two harvests, in a greenhouse of
Agronomical Sciences College, São Paulo State University (UNESP), Botucatu, São
Paulo, Brazil. The five irrigation levels were 20%, 60%, 100%, 140%, and 180% of
crop water requirement (ETc), with 100% ETc as the control. And three soil textures:
clay soil (CS), sandy clay loam soil (SCL) and sandy soil (SS) were used. Results
showed that plant height, petiole diameter, leaf number and area, above-ground, root,
and corm fresh/dry weight, corm number and diameter of taro were lower at 20% and
60% ETc, and higher at 140% ETc and 180% ETc when compared with 100% ETc. SS
exhibited higher leaf number at all water regimes, whereas leaf area for SS was
higher than SCL and CS at 20% ETc. For the first harvest, SCL showed higher root
fresh/dry weight, and SS exhibited higher corm dry weight than the other two soils.
The highest water-use efficiency (WUE) and index (HI) were detected at 20% ETc. For
the second harvest, SS showed higher root and corm fresh weight, corm number and
diameter. The 20% ETc had the highest WUE, whereas the lowest HI was observed at
the same water regime; The highest WUE and lowest HI were observed in SS.
Generally, reducing sugars and starch content increased with the increase in water
regime, while a different trend was observed in total soluble solids, total total titratable
acidity, and protein content in taro corm. SS was had higher total sugars, reducing
sugars, and starch content than the other two soils. Briefly, irrigation management
plays an important role in improving the growth of taro. The application of sandy soil
should be one good way for taro to adapt limited water availability conditions.
Keywords: Irrigation. Soil type. Water-use Efficiency. Canopy Size. Chemical
Composition. Water-stress.
RESUMO
A irrigação é uma prática agrícola importante para o cultivo do inhame, entretanto, há
poucos resultados experimentais focados no Brasil, e não há informações sobre a
necessidade de água para essa cultura sob diferentes texturas de solo no estado de
São Paulo. Objetivou-se com o presente trabalho avaliar o desenvolvimento,
biomassa e qualidade dos tubérculos do inhame sob diferentes lâminas de irrigação e
texturas de solo. O experimento foi conduzido de 2016 a 2017 com duas colheitas em
casa de vegetação na Universidade Estadual Paulista (FCA/UNESP), Botucatu.
Estudou-se cinco lâminas de irrigação: 20%, 60%, 100% (controle), 140% e 180% da
necessidade de água da cultura (ETc), e três texturas de solo: solo de textura argilosa
(CS), solo de textura média (SCL) e solo de textura arenosa (SS). Os resultados
mostraram que a altura da planta, diâmetro do pecíolo, número de folhas, área foliar,
peso fresco/seco da parte aérea, da raiz e do tubérculo, número e diamêtro de
tubérculo do inhame foram menores em 20% e 60% ETc e maiores em 140% and
180% ETc quando comparado com 100% ETc. SS apresentou maior número de
folhas em todas as lâminas de irrigação, enquanto a área foliar para SS foi maior que
SCL e CS em 20% ETc. Para a primeira colheita, SCL apresentou maior peso
fresco/seco da raiz, e SS apresentou maior peso seco do tubérculo do que os outros
dois solos. A maior eficiência no uso da água (WUE) e índice de colheita (HI) foram
detectados em 20% ETc. Para a segunda safra, SS apresentou maior peso fresco e
de tubérculo, número e diâmetro de tubérculo, comparados com os outros dois solos.
A 20%ETc apresentou a maior WUE, enquanto a HI menor foi observado nessa
mesma lâmina; A maior WUE e a menor HI foram observadas no SS. Geralmente,
açúcares redutores e teor de amido aumentaram com o aumento na lâmina de
irrigação, enquanto uma tendência diferente foi observada em sólidos solúveis totais,
acidez total titulável e teor de proteína no tubérculo de inhame. O SS apresentou
maiores açúcares totais, açúcares redutores e teor de amido do que os outros dois
solos. A irrigação desempenha um papel importante na melhoria do crescmento do
inhame. O solo arenoso pode ser uma boa maneira para cultivar o inhame nas
condições limitadas de disponibilidade de água.
Palavras-chave: Irrigação. Tipo de Solo. Eficiência no Uso da Água. Tamanho da
Copa. Composição Química. Estresse Hídrico.
SUMMARY
GENERAL INTRODUCTION................................................................................15
CHAPTER 1 DEVELOPMENT AND FRESH BIOMASS OF TARO (Colocasia
esculenta (L.) Schott) RESPONSE TO VARING WATER REGIMES AND SOIL
TEXTURES.......................................................................................................... 22
ABSTRACT.......................................................................................................... 22
1.1 INTRODUCTION.............................................................................................................23
1.2 MATERIALS AND METHODS..................................................................................... 24
1.3 RESULTS.........................................................................................................................29
1.4 DISCUSSION...................................................................................................................34
1.5 CONCLUSION.................................................................................................................36
ACKNOWLEDGEMENTS.....................................................................................37
REFERENCES......................................................................................................37
CHAPTER 2 RESPONSE OF TARO TO VARYING WATER REGIMES
AND SOIL TEXTURES.........................................................................................42
ABSTRACT...........................................................................................................42
2.1 INTRODUCTION.............................................................................................................43
2.2 MATERIALS AND METHODS..................................................................................... 44
2.3 RESULTS.........................................................................................................................50
2.4 DISCUSSION...................................................................................................................53
2.5 CONCLUSION.................................................................................................................55
ACKNOWLEDGEMENTS.....................................................................................56
REFERENCES......................................................................................................56
CHAPTER 3 CHEMICAL COMPOSITION AND DRY BIOMASS OF TARO
RESPONSE TO VARYING WATER REGIMES AND SOIL TEXTURES..............61
ABSTRACT.......................................................................................................... 61
3.1 INTRODUCTION.............................................................................................................62
3.2 MATERIALS AND METHODS..................................................................................... 63
3.3 RESULTS.........................................................................................................................68
3.4 DISCUSSION......................................................................................................... ........73
3.5 CONCLUSION.................................................................................................................75
ACKNOWLEDGEMENTS.....................................................................................75
REFERENCES......................................................................................................75
FINAL CONSIDERATIONS..................................................................................81
REFERENCES......................................................................................................83
15
GENERAL INTRODUCTION
Taro (Colocasia esculenta L. Schott) is known by various names, including
dasheen, eddoe, cocoyam, or tania (ONWUEME, 1999; PRAGATI; KAUSHAL, 2015;
CABI, 2017). It is a tuber crop from the family of Araceae monocot, was spreaded
from Asia to eastern of Southeast Asia and then to China, Japan, and Pacific Islands
(SINGH et al., 2007; MODI, 2007; MARE, 2009). Belonging to the subfamily of
Aroideae (LEBOT, 2009), which includes about 100 genera and 1500 widely
distributed species (MERLIN, 1982).
The above-ground (Figure 1) of taro is composed with large leaves and long
petioles (ONWUEME, 1978; PURSEGLOVE, 1972). The leaf blade ranges from 25 to
85 cm in length and 20 to 60 cm in width (PURSEGLOVE, 1972), the petioles
measured between 1 and 2 m in length (ONWUEME, 1978; PURSEGLOVE, 1972).
Taro has starchy underground stems, widely dilated, which are designated as corms
(BROUK, 1975; COURSEY, 1968; PLUCKNETT, 1970).
Figure 1 Taro leaves, petioles, roots, and corms.
Source: SCIENCE PICS, 2017
Taro corm is composed, externally, of concentric rings of scars and leaf scales
(WINTON; WINTON, 1935). It has one or more minor secondary corms that arise from
16
lateral sprouts present under each scale or leaf base (ONWUEME, 1978; WINTON;
WINTON, 1935). There are highly variable to humidity, size, color and chemical
composition for taro corm (PLUCKNETT, 1970; STRAUSS et al., 1980). The shape of
corm varies from elongated to spherical with an average diameter of 15 to 18 cm
(BROUK, 1975; ONWUEME, 1978; WINTON; WINTON, 1935). Generally, the taro
root system is adventitious and fibrous (ONWUEME, 1978; PURSEGLOVE, 1972).
Taro flowers are not common in all cultivars. One author recorded that "The taros
have been cultivated for so long while many of them never flowered and it is likely that
no civilized man has seen a viable seed of taro" (BARRETT, 1928). This led to the
supposition that taro seeds were indeed quite rare (KIKUTA, WHITNEY; PARRIS,
1938; MACCAUGHEY; EMERSON, 1913; WHITNEY, 1937; WILIMOT, 1936).
Taro growth, maturity, and harvest period depend on the cultivar. In the initial of
planting the growth rate is slow but will increase rapidly after one to two months
(ONWUEME, 1999). Taro has four physiological stages: dormancy, vegetative stage,
reproductive stage, and maturity (MARE, 2009). The dormancy and vegetative stage
is the period of root and leaf establishment (SIVAN, 1982). This stage is characterized
by sprouting and root growth. The vegetative growth is marked by an increase in plant
height, number of leaves and leaf area, and slow corm growth (TUMUHIMBISE et al.,
2009), at this stage, the leaf and petioles are the dominant collectors for
photo-assimilates (SINGH et al., 1998). The reproductive stage is the period of rapid
corm development after five months planting age (SIVAN, 1982).
At the maturity stage, the growth of corm is at the peak, with a rapid increase in
the formation of corms. This stage is a period of senescence of canopy size,
associated with decreased plant height, leaf area, and leaf number, whereas with the
continuous increase of corm size (SIVAN, 1982). At this stage there is a rapid decline
in sprout growth, and reduction in the number of active leaves, decrease in average
petiole length, total leaf area per plant, and decrease in plant height (ONWUEME,
1999; SILVA et al., 2008). According to Goenega (1995), a increase in biomass
17
occurred after obtaining maximum leaf area, and dry matter partition for the corms
remained constant from 150 days after planting. Tumuhimbise et al. (2009) also
reported that the maturity stage is a growth period in which the diameter and length of
the corm increased rapidly over the 150 days.
Taro is produced and consumed mainly in subsistence, and the surpluses are
sold as production crops, which plays an important role in Fighting against hunger
(ONWUEME, 1999). The production characteristics include total weight of corms,
number of corms, and individual weight per corm and so on (MARE, 2009). In 2017,
the world production of taro reached 10.222 million tonnes in 1.724 million hectares
(ha) of land, with Nigeria accounting for about 3.901 million tonnes, followed by China
with 1.656 million tonnes, and Ghana with 1.512 million tonnes (FAO, 2019). In
addition, taro corm has a broader complement of nutrients than other tuber crops
(KAUSHAL et al., 2015; FILHO et al., 1997), it is superior to potatoes (Solanum
tuberosum), sweet potatoes (Ipomoea batatas), cassava (Manihot esculenta) and
yam (Dioscorea L.).
In Brazil, its importance is mainly linked to the center-south region of the country,
specifically in the states of Minas Gerais, Rio de Janeiro and Espírito Santo, where
most of the national taro production concentrated. Taro is associated with family
farming in producing regions, since its technological input needing is low (GONDIM et
al., 2007). For example, in the state of Rio de Janeiro, such as Cachoeiras de Macacu
and Magé, they produce more than 8,000 t/year in total, which represents
approximately 40% of the crop's production of the state (CIDE, 2007).
Compare with taro leaf and petiole, taro corms are the primary use of its
consumption, since they are sources of carotene, potassium, calcium, phosphorus
and iron (DEO et al., 2012). As good resources for infant feeding because its starch is
easily digestive, which is helpful for people with problems digestive (JOUBERT and
ALLEMANN, 1998; ONWUEME, 1999; SHANGE, 2004). They also contain higher
starch content than potatoes and sweet potatoes (TUMUHIMBISE et al., 2009), which
is suitable for gastric patients.
18
In addition, taro has a number of medicinal uses (PAUL; BARI, 2011). Taro corms
can be used as an abortifacient, as for treating tuberculous ulcers, pulmonary
congestion, fungal abscesses in animals, and as anthelmintic. Foliage is used as a
hemostasis and poultice, and the petiole is used as a treatment for wasp stings
(WILBERT, 1986) which is also a good source of dietary fiber. Additionally, high levels
of dietary fiber in foods are also advantageous for their active role in regulating
intestinal transit (WILBERT, 1986).
As an important tuber crop taro can grow in many tropical and subtropical
countries (SLOAN et al., 2016). The optimum temperature for taro growth ranges from
21°C to 27°C, and well distributed summer rains of 1000mm or more additional
irrigation is preferred (WILSON et al., 2013). However, under tropical conditions, the
crop is often subjected to unfavorable growth conditions, due to stress of water deficit,
low humidity and high temperature which may limit productivity due to their harmful
effects on taro growth (PARDALES, 1985).
Taro yield and quality fluctuate due to the differences in cultivar, irrigation
management, soil textures, planting density, levels of fertilizer application, among
other environmental factors (MANNER; TAYLOR, 2010; CHUN-FENG; KUN, 2004).
Compared to other tuber crops, the plant is characterized by the ability to grow under
adverse conditions, such as excess water, high temperature, shaded habitat, and
tropical forests (SMITH, 2006). This plasticity in adaptation has made it possible to
use taro in agroforestry systems, including intercropping, between shrub, and tree
species (ANUEBUNWA, 1992; OLIVEIRA et al., 2006), or in lines (OLIVEIRA et al.,
2007). In addition, chemical composition of tuber crops differs with different cultivars
(MARE, 2009), it is also influenced by climatic conditions, which are dependent upon
the site and planting date. Another important factor for the success of irrigated
agriculture is irrigation water management, since it is one of the major concerns
related to the agricultural system (BRITO, 2015).
19
The amount of water available with its distribution pattern results in increased
production and longer growing period. According to Daff (2011), it is important to
ensure a constant availability of water during the growing season of taro, since water
scarcity can cause water stress, which results in reduced yield, malformed and
poor-quality corms. In order to provide such water supply, irrigation should be used,
especially where there is irregular precipitation (JOUBERT; ALLEMANN, 1998). The
main methods of irrigation are by flood, furrows, sprinkler, pivots and localized (micro
sprinkler and drip irrigation). The choice of the appropriate irrigation method depends
on several factors, such as topography, soil physical properties, culture, available
water quality, among others. As one of the most efficient method used in irrigated
agriculture, drip irrigation system is able to promote higher yields with greater
efficiency in water use.
On the other hand, taro can grow in a wide variety of soil textures, from clay soils
to sandy soils (ONWUEME, 1999). However, the taro produce better when planted in
fertile soil, rich in organic matter with high capacity water retention. A slightly acid soil
with pH of 5,5 to 6,5 with moderate clay content is considered ideal (ONWUEME,
1999; SAFO-KANTAKA, 2004). Soil texture refers to the proportion of the sand, silt
and clay particles of soil, which varies according to the type and mineral composition
of the source material and the chemical weathering processes involved in soil
formation. It is an very important physical property of soil, as it influences the soil
physical and chemical behavior (BOWMAN; HUTKA, 2002), with influence on water
retention capacity and its availability, nutrient leaching and aeration (HUNT and
GILKES, 1992), thus, soil texture is also used to estimate the other soil properties,
particularly water properties related with soil. Soil texture also influences root growth
indirectly, whereas root response directly to soil textures in water, oxygen and nutrient
availability in soil, soil aeration and nutrient content (GLINSKI; LIPIEC, 1990). In
addition, the physical and chemical properties of the soil affect the quantity and the
movement of these substances essential for the growth of the plants. The first
concern in the relationship between soil texture and plant growth will be the behavior
20
of root in different soil textures (GLINSKI; LIPIEC, 1990; HILLEL, 1982).
Furthermore, as one of the most limited factor for plant growth (FISCHER;
TURNER, 1978), water availability for plants depends heavily on soil texture, which
controls hydraulic conductivity and field capacity (WALTER; STADELMAN, 1974). As
the infiltration of rainwater into coarse-textured soils is much deeper than in fine
textured soils, the evaporation of coarse-textured soils is much smaller than that of
fine-textured soils after precipitation (WALTER; STADELMAN, 1974). Thus, knowing
the textural classes of soils is an important step in using management practices that
maximize productivity and minimize environmental damage (HILLIARD; REEDYK,
2014).
However, little information is found on the water stress tolerance of taro under
different soil textures. Sivan (1995) and Sahoo et al. (2006) observed that canopy size
of taro decreased in response to water stress. Uyeda et al. (2011) evaluated the
response of taro to five irrigation levels (50%, 100%, 150%, 200%, and 250% ET0 -
reference evapotranspiration) and found maximum taro yield at 150% ET0. A study by
Buragohain et al. (2013) focus on taro quality response to 20 cultivars in Nagaland
reported that the corm length and diameter reflected wide variation among the
cultivars, as well as the starch content, corm humidity, and corm number.
Kaensombath et al. (2012) reported that the yield of taro leaves and petioles were
larger with more frequent harvesting, while corm yield was not affected by harvest
interval. Also, based on crop water requirement (ETc), Mabhaudhi et al. (2013)
investigated the effect of three water regimes on growth of taro. They found that leaf
number and leaf area decreased at 60% and 30% ETc. In addition, taro yield was
higher at optimum irrigation (100% ETc) when compared with 60% and 30% ETc,
whereas water-use efficiency (WUE) was relatively stable among water regimes.
Research on taro is still suffering from the lack of scientific information in relation
with soil texture. Filipović et al. (2016) reported that the soil with a high content of clay
significantly improved the corm number per plant of Jerusalem artichoke (Helianthus
Tuberosus L.). Martin and Miller (1983) studied the response of potato to deficit
21
irrigation under different soil textures (sandy and loam soil), they found that in sandy
soil its yield greatly increased with increase in irrigation level. Furthermore, Katerji and
Mastrorilli (2009) observed a significant reduction (22%-25%) in WUE in clay soil for
potatoes, corn (Zea mays L.), sunflowers (Helianthus annuus), and sugar beets (Beta
vulgaris), comparing with that detected in loam soil.
Chemical composition of taro corm has been well documented by previous
researches (ONWUEME, 1978; KAUSHAL et al., 2015). The proximal composition of
taro corm varies depending on variety, growing condition, soil type, moisture and
fertilizer application, maturity at harvest, post-harvest management, and storage
(ONWUEME, 1978; BRADBURY et al., 1985; BRADBURY; HOLLOWAY, 1988). Its
nutritional composition is low in protein and fat like other root crops, but high in
carbohydrate. The moisture content of taro is also very high, which generally ranges
from 60-83% (HUANG, et al., 2007). Taro starch is the most important component
(JANE, et al., 1992) of taro corm (70-80% dry weight basis). It contains about 11%
crude protein on a dry weight basis. However, the chemical composition research of
taro is still suffering from the lack of scientific information in relation with water regime
and soil texture.
It is evident from the literatures reported above that the majority of agronomical
knowledge about the crop was derived from environments outside Brazil, basic
agronomic studies on taro occurring in Brazil are still lacking. Thus, the focus of the
current study was to study the response of taro development, biomass, and corm
quality to varying water regimes and soil textures.
22
CHAPTER 1 DEVELOPMENT AND FRESH BIOMASS OF TARO (Colocasia
esculenta L. Schott) RESPONSE TO VARYING WATER REGIMES AND SOIL
TEXTURES
Meiling Li1; Angélica Cristina Fernandes Deus2; and Lin Chau Ming3
1 MS., Department of Horticulture, Agronomical Sciences College, São Paulo State University,
José Barbosa of Barros Street, 1780. Zip-Code: 18.610-307 - Botucatu, SP, Brazil. Email:
lilmeilinghappy@outlook.com. Corresponding author.
2Post Doc., Department of Soil and Environmental Resources, Agronomical Sciences College,
São Paulo State University, José Barbosa of Barros Street, 1780. Zip-Code: 18.610-307 -
Botucatu, SP, Brazil.
3 Prof., Department of Horticulture, Agronomical Sciences College, São Paulo State University,
José Barbosa of Barros Street, 1780. Zip-Code: 18.610-307 - Botucatu, SP, Brazil.
*The norm of the paper is according to “International Journal of Water Resources Development”.
ABSTRACT
In the current study, the effects of water regime and soil texture on growth and
development of taro were investigated. For this aim, the taro was grown at five water
regimes (20%, 60%, 100%, 140%, and 180% ETc - crop water requirement) in three
soil textures (clay, sandy clay loam, and sandy soil). The experiment was conducted in
a greenhouse, and two harvests of taro were analyzed. Plant height (PH), petiole
diameter (PD), above-ground fresh weight (AFW), root fresh weight (RFW), corm
number (CN), and corm diameter (CD) were lower at 60% and 20% ETc relative to
100% ETc, while 140% ETc and 180% ETc showed higher PH, PD, AFW, RFW, CN,
and CD, compared with that of 100% ETc. The 20% ETc was observed to have the
highest harvest index (HI) in the first harvest, whereas in the second harvest, 20% ETc
had the lowest HI. With respect to soil texture, a lower HI was observed in sandy soil
in the second harvest, whereas SS showed significantly greater RFW, CN, and CD,
suggesting that taro may have high potential to tolerant water stress in sandy soil.
Keywords: Irrigation, Soil type, Tuber crop, Corm number, Harvest index.
23
1.1 INTRODUCTION
Worldwide shortage of freshwater resources has focused attention on developing
innovative water-saving irrigation strategies in order to reduce the pressure on
freshwater resources (Ahmadi et al., 2011), and a rapid increase in global population
growth demands an increase in production and diversification of crops. Root and
tuber crops can play an important role in addressing this issue (Paul and Bari, 2011).
As one tuber crop, taro (Colocasia esculenta L. Schott) can survive in conditions
which considered to be adverse to the growth of other crops, due to the inherent
characteristics of most Araceae, such as tolerance to water stress, climatic stress, and
shade (Zárate et al., 2003). Taro is an important tuber crop to ensuring food security
(Melese, 2017), which is also one of the least water-efficient crops (Uyeda et al., 2011,
Daryanto et al., 2016). Both the amount of water available and its distribution have a
significant effect on taro growth, which may interfere with its yield (Daryanto et al.,
2016).
Researches on taro have been rather slow, as taro is less popular for the
researchers compared with other tuber crops (Mabhaudhi et al., 2014). It is reported
that limited water availability resulted in reduced plant growth (Hussain et al., 2008).
Lower plant height of taro was reported under limited water availability by Sivan (1995)
in taro varieties subjected to water stress. Sahoo et al. (2006) also observed
significant reductions in plant height with an increase in water stress, conversely, the
author reported a minimum reduction in yield. Mabhaudhi et al. (2013) tested taro
response to three water regimes based on crop water requirement (ETc), they found
that corm number per plant was 13% and 11% higher at 60% ETc, respectively,
compared with 100% and 30% ETc. In addition, as one trait have been extensively
utilized for yield improvement in cereals and other crops (Sinclair, 1998; Roy
Chowdhury, et al., 2012), the harvest index of taro response to irrigation treatment
and soil texture was rarely reported. Bussell et al. (1998) reported that the harvest
index of taro is generally higher in the high watering-level treatment (16 mm water/day)
compared with the low watering-level treatment (5.8 mm water/day). However, in line
24
with the observations reported by Mabhaudhi et al. (2013), the harvest index was 14%
and 7% lower at 100% ETc relative to 60% and 30% ETc, respectively.
When assessing the suitability for the cultivation of taro, soil texture is one of the
most important characteristics to be taken into account (Filipović et al., 2016). Martin
and Miller (1983) studied the response of potatoes to deficit irrigation as affected by
soil texture (sandy and loam soil), and found that potato yield increased greatly with
an increase in irrigation level (from 0% to 70% - 80% ET0) in sandy soil. Irrigation
levels above this had minimal effect, which is probably because sandy soil has a lower
water-holding capacity than loam soil. Filipović et al. (2016) reported that the soil with
a high content of clay significantly stimulated an increase in the corm number per
plant of Jerusalem artichoke (Helianthus Tuberosus L.).
However, there is no comprehensive study investigated the response of taro to
different irrigation levels under varying soil textures. As such, the aim of this study was
to evaluate the growth and development of taro to five water regimes and three soil
textures.
1.2 MATERIALS AND METHODS
Site description. The present investigation was carried out from May 31, 2016 to
March 1, 2017, in a greenhouse of the Agronomical Sciences College, São Paulo
State University (UNESP), Botucatu (22°51’S; 48°27’W), São Paulo, Brazil. The
dimensions of the greenhouse are 7 meters in width and 30 meters in length, with 6
meters in height at the highest point. During the experimental period, the average
temperature was 21.0 °C, the average ET0 was 3.56 mm/day, and the average air
humidity was 62.1%, as shown in Table 1.1.
25
Table 1.1 Average maximum and minimum of temperature, air humidity and ET0 in the
greenhouse during the experiment period, São Paulo, Brazil.
Month/Year ET0 (mm/day) Tmax (℃)a Tmin (℃)b Hmax (%)c Hmin (%)d
July 2016 2.11 27.53 10.54 85.27 36.55
August 2016 2.68 28.19 13.22 79.94 38.48
September 2016 2.70 29.22 13.73 76.43 37.43
October 2016 3.28 27.77 16.57 82.06 36.26
November 2016 3.67 28.79 17.16 86.39 35.86
December 2016 3.44 29.01 18.14 86.73 33.00
January 2017 5.30 28.80 19.70 98.40 47.20
February 2017 5.30 29.20 18.40 96.10 37.10
a Temperature maximum; b Temperature minimum; c Air humidity maximum; d Air
humidity minimum.
Plant material and experimental design. The taro cultivar selected for
evaluation was ‘Chinese’. There are four physiological stages (Mare, 2009) for its
growth cycle: dormancy, vegetative stage, reproductive stage, and maturity. The
experimental design was a randomized complete block design with 15 treatments
(Figure 1.1), resulting from the combination of five water regimes (20%, 60%, 100%,
140%, and 180% ETc) and three soil textures (clay soil, sandy clay loam soil, and
sandy soil), replicated four times, with two plants per replication, for a total of 120
plants. And the 100% ETc was used as the control. Each pot (replication) had the
capacity of 25 L with one plant in it, a plant spacing in the present study was 0.6 m ×
0.5 m (Figure 1.2-A).
Figure 1.1 Experimental design.
Pump
26
Taro propagation. Taro propagation for corms commercial exploitation is
performed exclusively by planting the corm, which is the major commercial product
(Puiatti, 2001). The 400 corms weighing between 30g and 50g were selected for taro
propagation. They were sown in 400 mL plastic cups (with three holes at the bottom of
the cup), which were filled with soil and substrate. A soil to substrate ratio was 1:1 by
volume. The soil used for propagation was sandy clay loam soil (SCL). And the
substrate applied for propagation was suitable for tropical conditions and had the
following characteristics: a moisture content of 60%, a water-holding capacity of 130%
(both by weight), a bulk density of 200 kg m-3, a pH of 5.8, and an electrical
conductivity of 2.0 mS cm-1. The 120 seedlings with similar sizes (approximately three
leaves per seedling) were selected and transplanted into the pots at 48 days after
sowing.
Figure 1.2 Taros in pots in greenhouse (A) and taro corms in harvest (B).
Soils, organic compost, and water. The soils applied in the current study were
collected from the arable layer, at the 0-20 cm depth, from the farm of Agronomical
Sciences College, São Paulo State University, Botucatu, São Paulo, Brazil. For soil
fertility and texture analyses, each soil was air-dried and sieved through a 2 mm mesh.
The pH (CaCl2), organic matter (OM), P, H + Al, K, Ca, and Mg, SB (sum of bases),
CEC (cation exchange capacity), and BS (base saturation, %) were determined
according to the methodology reported by Raij et al. (2001). The particle size was
determined using the pipette method (EMBRAPA, 2006). And the soil texture was
classified according to FAO (2006). Soil analysis results are shown in Table 1.2.
A B
27
Table 1.2 Textural and chemical characteristics of soils used in the experiment.
Textural
class
Sand Clay Silt pH O.M Presinam H+Al K Ca Mg SB CEC BS%
………g/Kg …….. CaCl2 g/dm3 mg/dm3 ……..……....... mmolc/dm3……..…….......
CS 436 456 108 3.9 14 5 87 0.5 3 1 5 92 5
SCL 652 291 57 4.1 16 4 77 0.7 3 1 4 81 5
SS 957 34 9 4.7 9 4 17 1.1 7 3 10 28 38
CS = clay soil; SCL = sandy clay loam; and SS = sandy soil. m Presin is a method used
for the analysis of phosphorus in soil.
The soils were corrected using limestone before transplanting. According to the
recommendation of Bulletin 200 (Aguiar et al., 2014), the acidity correction was
calculated based on the need for liming to raise the base saturation of each soil to
60%. Based on soil fertility results and the recommendation of the Bulletin 200 (Aguiar
et al., 2014), 200 mg L-1 of P, 30 mg L-1 of N, and 40 mg L-1 of K (using triple
superphosphate, urea, and potassium chloride, respectively) were applied to each pot
before transplanting (soils were kept wet for fertilization). The amounts of corrective
and fertilizer applied per pot, in grams, were calculated considering the pot capacity
(25 L).
The compost heap was done twice (in September and December of 2016,
respectively) during the experiment with 1.5 L of organic compost (Table 1.3) applied
above the soil per pot. The irrigation water used was from Sabesp, which is
responsible for planning, executing and operating basic sanitation services throughout
the State of São Paulo of Brazil. According to the chemical characteristics of the
irrigation water, it was classified as C1S1 (Richards, 1954), and does not show
restriction for irrigation. Water analysis results are shown in Table 1.4.
Table 1.3 Chemical characteristics of organic compost used in the experiment.
O.M N P2O5 K2O Ca Mg S U-65℃ C Na Cu Fe Mn Zn
pH C/N ………........................ % ...............................……… .……… mg/Kg .………
7.7 11/1 34 1.8 1.4 0.6 1.8 0.4 0.3 13 19 609 63 10005 348 120
Table 1.4 Chemical characteristics of water used in the experiment.
N P K Ca Mg S Na B Cu Fe Mn Zn C.E
pH ........................................……. mg/L ……….............................................. µS/cm
7.3 4 1 22 18 10 5 3.80 0 0 0.16 0 0 73
28
Figure 1.3 Tension of the three soils
Irrigation system. The irrigation system used in the experiment was drip
irrigation. Irrigation was delivered using in-line pressure-compensating emitters, with a
flow rate of 2.0 L h-1, which were positioned on each pot using a micro-tube with a
connector. The time of irrigation and the volume of water to be applied were
determined by a simplified water balance, using the Class A Evaporation Pan method
(CAEP; Peixoto et al., 2010), which is a standard used to measure the water
evaporation.
In the present investigation, the irrigation management was based on the
evaporation value of the CAEP, pan coefficient (Kp), and crop factor (Kc) associated
with phenological stages of taro (Allen et al., 1998). The evaporation value of the
CAEP was measured according to Allen et al. (1998). The evaporation value and Kp
were used to calculate the ET0 (Equation 2), which differs with the change of local
climatic conditions. The value of Kp applied in the current study was 1, as
recommended by Prados (1986). The growth cycle of taro is of approximately seven
months (Lebot, 2009). Kc values of taro were as described by Fares (2008), where Kc
initial = 1.05 (two months), Kc med = 1.15 (four months), and Kc late = 1.1 (one month).
According to the values of Kc and ET0, ETc (Equation 1) was calculated using the
single crop coefficient approach, as described by Allen et al. (1998):
ETc = ET0 × Kc……………………………………………………………………………... [1]
where: ETc = crop water requirement, ET0 = reference evapotranspiration, and Kc =
crop factor; and
ET0 = CAEP × Kp……………………………………………………………………......... [2]
where: CAEP = Evaporation value of Class A Evaporation Pan, and Kp = Pan
coefficient.
29
All treatments were irrigated with 100% ET0 since July 18, 2016. Irrigation
treatments began after one month of transplanting. Irrigation was performed every
morning to ensure water availability during the peak periods of plant demand during
the day. The last irrigation occurred on February 28, 2017. The total irrigation water
applied (WUt), taking the initial watering into account, ranging from 1580 mm (180%
ETc) to 1244 mm, 908 mm, 572 mm, and 236 mm for 140%, 100%, 60%, and 20%
ETc, respectively. During the experiment, two harvests were carried out, one on
December 1, 2016 (at 135 days after transplanting), and another on March 1, 2017 (at
225 days after transplanting).
Data collection. Fifteen days after transplanting, Plant height (PH) and petiole
diameter (PD) were performed once a month until the last harvest. PH was measured
as the distance from the ground to the attachment point between the leaf petiole and
the lamina of the tallest leaf. The PD was measured in centimeters, at the base of
petioles (top of the soil) with a vernier caliper.
In the harvests, above-ground fresh weight (AFW) per plant (was measured only
in the first harvest), root fresh weight (RFW) per plant, corm number (CN) per plant,
corm diameter (CD, was measured only in the second harvest), and HI were
measured. HI was calculated by the given formula (Thokchom et al. 2018),
Harvest index = (Economic yield / Biological yield) × 100%..................................... [3]
where Economic yield - corm fresh weight per plant (Li et al. 2018), and Biological
yield - was measured by summing AFW, RFW, and corm fresh weight per plant .
Statistical analysis. Analysis of variance (ANOVA) was used to statistically
analyze data (plant height, petiole diameter, above-ground fresh weight, root fresh
weight, corm number per plant, corm diameter and harvest index) using Sigmaplot®
version 11.0 (ISI, San Jose, California, USA). The Tukey's Honest Significant
Difference test (HSD) was used for multiple comparison tests, with a significance level
of α = 0.05.
1.3 RESULTS
Effects of water regime and soil texture on plant height (PH) and petiole
diameter (PD) of taro. There was a significant difference (p < 0.001) in PH between
30
water regimes (Figure 1.4 a, c, and e), whereas there was no significant difference (p
= 0.440) between soil textures (Figure 1.5 a, c, e, g, and i). Generally, taller plants
were acquired at higher irrigation levels, 180% ETc had the tallest taro (39cm, on
average), followed by 140% ETc. The PH decreased by 25% and 36% at 60% ETc and
20% ETc (Figure 1.4 a, c, and e), respectively, compared with the control treatment
(100% ETc ). With respect to soil texture, the average PH was 32cm for the three soil
types (Figure 1.5 a, c, e, g, and i). The PH increased with an increase in planting time
until they reached a maximum plant height (which we call “PH peak”) and then
declined. In the current study, “PH peak” was reached at a different time for different
irrigation treatments. For 100%, 140%, and 180% ETc, “PH peak” was reached at 26
weeks after planting, whereas for 20% ETc and 60% ETc the peak was reached at 18
and 22 weeks after planting (Figure 1.3), respectively.
Figure 1.4 Effects of water regime on plant height and petiole diameter of taro.
Petiole diameter (PD) followed the similar trend as PH. There was a significant
31
difference in PD between water regimes (p < 0.001), no significant difference was
observed between soil textures (p = 0.603). The PD increased by 23% and 19% (on
average) at 180% and 140% ETc, respectively, and decreased by 11% and 29% at
60% and 20% ETc, respectively, compared with 100% ETc (Figure 1.4 b, d, and f).
Whereas PD for 140% ETc was not significantly different from that for 180% ETc (p =
0.335). The average PD kept relatively constant (26 mm) with respect to different soil
textures (Figure 1.5 b, d, f, h, and j).
Figure 1.5 Effects of soil texture on plant height and petiole diameter of taro.
32
Effects of water regime and soil texture on the above-ground fresh weight
(AFW), root fresh weight (RFW), corm number (CN), corm diameter (CD), and
harvest index (HI). Above-ground fresh weight (AFW) showed highly significant
differences between water regimes (p < 0.001). With respect to the differences
observed between water regimes, the trend was 180% ETc > 140% ETc > 100% ETc >
60% ETc > 20% ETc (Table 1.5). No significant difference (p = 0.062) was observed for
AFW between soil textures. There were significant differences between water regimes
(p < 0.001), as well as between soil textures (p = 0.017) for RFW in the first harvest
(Table 1.5). The interaction between irrigation treatment and soil type was also
significant (p = 0.040). Water regime of 180% ETc had the highest RFW in all soil
textures compared with the other irrigation treatments. Whereas there were no
significant differences between soil textures at 20%, 60%, 100%, and 180% ETc
(Table 1.5). The SCL soil showed higher RFW at 140% ETc in comparison with CS and
SS. In the second harvest, significant differences were observed between water
regimes (p < 0.001) as well as between soil textures (p < 0.001) for RFW (Table 1.6).
The interaction between irrigation treatment and soil type was also significant (p <
0.001). In CS, 140% ETc showed the highest value of RFW among the irrigation
treatments; In SCL, 20% and 180% ETc showed slight lower RFW compared with the
other water regimes; whereas no significant difference was observed between 100%,
140%, and 180% ETc in SS. Interestingly, in this harvest, SS showed higher RFW,
compared with CS and SCL, which is clearer at 20% ETc and 180% ETc. This is
indicating that SS may be more beneficial to the formation of taro root with long-term
water stress.
33
Table 1.5 Response of Above-ground fresh weight, root fresh weight, corm number ,
and harvest index of taro to varying water regimes and soil textures in the first harvest.
Values in table are means (n=4).
Water
regime
AFW (g plant-1) RFW (g plant-1) Corm number plant-1 Harvest index (%)
Soil texture Soil texture Soil texture Soil texture
CS SCL SS CS SCL SS CS SCL SS CS SCL SS
20% ETc 29Daa 29Da 37Da 20Da 35Ba 33Ba 4Ca 5Da 5Ba 68Aa 66Aa 63Aa
60% ETc 133Ca 102Ca 121Ca 70Ca 75Ba 72Ba 8BCa 8CDa 7Ba 46BCa 53ABa 56ABa
100% ETc 179BCa 175Ba 220Ba 84Ca 104Ba 126Aa 11Ba 10BCa 14Aa 55Ba 52ABa 52ABa
140% ETc 247Ba 248Aa 266ABa 137Bb 200Aa 144Ab 16Aa 13Ba 15Aa 55Ba 48Ba 53ABa
180% ETc 343Aa 261Aa 300Aa 201Aa 253Aa 146Aa 16Aa 20Aa 20Aa 43Ca 46Ba 46Ba
AFW = above -ground fresh weight; RFW = root fresh weight; CN = corm number; and
HI = Harvest index. CS = clay soil; SCL = sandy clay loam; SS = sandy soil. a Mean
separation between water regimes within soil texture (capital letters) and between soil
textures within water regime (lower case letters) by t-test at α = 0.05.
Regarding the corm number (CN), there were significant differences between
water regimes (p < 0.001) in both harvests, while a significant difference between soil
textures (p = 0.018) was observed only in the second harvest (Table 1.6). It is evident
from the results of Table 1.5 and Table 1.6 that CN increased significantly with
increase in irrigation level. In line with the differences observed between soil textures
in the second harvest, SS showed 6% and 32% higher CN, respectively, compared
with CS and SCL (Table 1.6). As one key yield component, the variation in the number
of corms observed in the current study may offer some meaningful information for
choosing of irrigation level and soil type to cultivate taro. There were significant
differences between water regimes (p < 0.001) and soil textures (p = 0.026) for corm
diameter (Table 1.6). Corm diameter (CD) showed a similar trend with AFW, RFW,
and CN. On average, 180% ETc had 43% and 13% higher CD, respectively, compared
with 20% and 60% ETc (Table 1.6). In line with the differences observed between soil
textures, CD for SCL (33.8 mm) and SS (34.4 mm) were similar while compared of the
CS was 7% lower than the two soils (Table 1.6).
Regarding the harvest index (HI), there were significant differences between
water regimes (p < 0.001) in the two harvests, whereas there was a significant
34
difference between soil textures (p < 0.001) in the second harvest. In the first harvest
(135 days after planting), HI ranged from 43% to 68%; And in the second harvest (225
days after planting), it ranged between 92% and 98% (Table 1.5 and Table 1.6). In
addition, in the first harvest, 20% ETc had the highest HI, while no significant
differences were observed between the other water regimes; In the second harvest,
20% ETc was observed to have the lowest HI. With respect to the differences
observed between soil textures in the second harvest, SS showed 2% and 1% lower
HI, respectively, compared with CS and SCL (Table 1.6).
Table 1.6 Response of RFW, CN, CD, and HI of taro to varying water regimes and soil
textures in the second harvest.Values in table are means (n=4).
Water
regime
RFW (g plant-1) Corm number plant-1 Corm diameter (mm) Harvest index (%)
Soil texture Soil texture Soil texture Soil texture
CS SCL SS CS SCL SS CS SCL SS CS SCL SS
20% ETc 9Bba 9Bb 11Ba 6Da 4Ca 7Ca 23Ca 27Ba 28Ca 93Ca 93Ca 94Aa
60% ETc 9Bb 14ABab 18Ba 9CDa 10BCa 11BCa 30Bb 35Aa 34Ba 96Ba 94BCa 95Aa
100% ETc 9Bb 20Aab 29ABa 14BCa 12ABa 17ABa 34ABa 36Aa 34Ba 97Aa 95BCa 94Aa
140% ETc 13Ab 14ABab 26ABa 18Bab 13ABb 20Aa 35Aa 35Aa 38Aa 97Aa 97ABab 95Ab
180% ETc 9Bb 10Bb 37Aa 24Aa 18Aa 21Aa 37Aa 36Aa 39Aa 98Aa 98Aa 92Ab
RFW = root fresh weight; CD = corm diameter. a Mean separation between water
regimes within soil texture (capital letters) and between soil textures within water
regime (lower case letters) by t-test at α = 0.05.
1.4 DISCUSSION
Results observed above showing reduced plant height (PH) under lower limited
water availability (20% and 60% ETc) were consistent with reports by Mabhaudhi et al.
(2013) and Sahoo et al. (2006). In addition, kinds of literature suggested that PH of
taro increased (until the “plant height peak”) during the early growth stages before
gradually declining (six months after planting) as they approached maturity
(Fa’amatuainu, 2016; Noor et al., 2015; Tumuhimbise et al., 2009; Onwueme, 1999).
In the current study, the time of “PH peak” was reached at different time with respect
to water regime. The “PH peak” was reached at eight and four weeks earlier at 20%
and 60% ETc, respectively, compared with the other water regimes. PD was also
affected negatively by water stress as reported above in the current study (Figure 1.4
35
b, d, and f). As a prevention strategy for drought (Levitt, 1979; Turner, 1986), plants
tend to cope with limited water availability and escape from water shortage through
reducing its size (plant height and petiole diameter). Results reported above proved
that plants tend to complete their life cycle earlier than normal to avoid drought
damage (Onwueme, 1999).
Results of above-ground fresh weight (AFW) was only for the first harvest as in
the second harvest there was almost no more fresh leaf or petiole. In this period,
water played an important role in biomass accumulation of the above-ground, while
soil texture had no effect on biomass accumulation. Soil water content and soil
physical properties affect root growth of taro (Parker et al., 1989; Bowen, 2003), yet
there is little information focus on how irrigation level and soil texture influence on root
fresh weight (RFW) in taro production. Generally, a well-developed root system was
built to enhance the capture of soil water under water-limited conditions (Passioura,
2006; Vurayai et al., 2011). The RFW of taro decreased with the decrease in water
availability in the first harvest, which was inconsistent with the reports by Sivan (1995),
who observed that the root/shoot in taro increased subjected to water stress. We can
only hypothesis that the daily drip irrigation may have kept the root zone reasonably
moist enough to discourage root growth. In addition, soil texture has influenced root
growth as SS showed the highest RFW in the second harvest. That may be because
of that the sand content of SS is more than 90% (Table 1.2), which is much easier to
handle and more suitable for root growth (Filipović et al., 2016).
The CN showed the similar trend with CD with respect to water regime (Table 1.6).
In line with the observations of soil texture, SS showed more CN, compared with CS
and SCL (a similar trend with corm weight, Li et al., 2019), while for CD, there was no
significant difference between SS and SCL. We speculate that soil texture had
affected corm shape of taro. In SCL we could get more rounded corms, compared
with that of CS and SS, as with higher CD in SCL, the corm fresh weight (Li, et al.,
2019) and CN did not increase significantly. However, further investigation (for
example corm length) is needed. Results for CN were inconsistent with the
36
investigation of Jerusalem artichoke by Filipović et al. (2016), they reported that
composition with high clay content stimulated an increase in CN, while in the current
study, SS showed the higher CN in both harvests.
Harvest index (HI) has been extensively utilized in cereals and other crops for
yield improvement (Hay, 1995; Sinclair, 1998), it can be used as a target trait in
biomass improvement of taro. Results for HI in the current study were inconsistent
with the reports by Thokchom et al. (2018) who observed that the HI of taro was
ranged from 57% to 83% with 120 days after planting, while it ranged between 43%
and 68% with 135 days after planting (Table 1.5). This is out of expecting, generally,
the HI increased with increase in growth age, which was proved in the study of
Mabhaudhi et al. (2013), they reported that the HI was 14% higher with 8 months of
growth age than 6 months. In addition, the contrary behavior of HI shown at 20% ETc
for the two harvests (Table 1.5 and Table 1.6) indicates that HI was not only
significantly influenced by water regime, growth age also affects greatly on HI, but it
may also influence the effect of water stress on HI. Soil texture had influenced
significantly on HI. The SS was observed to have lower HI, compared with CS and
SCL, although SS were observed to have significantly higher corm weight (Li et al.,
2019) and RFW in the second harvest. It is indicating that the difference for corm
weight between soil textures was lower than for RFW, as SS showed significantly
lower HI than the other soil textures. Which proved that in SS taro could create a
strong root system to have high ability to use water under water stress conditions, and
ultimately increase the yield.
1.5 CONCLUSION
The research conducted here show that limited water availability caused the
reduced plant height, petiole diameter, as well as reduced above-ground, root fresh
weight, corm number per plant, and corm diameter. A contrary trend was observed in
the two harvests for harvest index, as the highest harvest index was observed at 20%
ETc in the first harvest, while the lowest harvest index for the second harvest was
observed at the same irrigation level. Which indicating lower water availability could
37
improve harvest index, while there is a limit of duration of water stress, when the
irrigation treatment last more than this limit could negatively affect on taro harvest
index and ultimately on its growth and biomass accumulation. In the second harvest,
sandy soil was shown to have significantly higher root fresh weight, corm number, and
corm diameter, while a lower harvest index, compared with clay and sandy clay loam
soil. It is suggesting that under limited available water conditions, taro may be better
adapt in sandy soils, as in which it shown to have higher biomass accumulation, and
stronger root system to avoid or reduce water stress damage.
ACKNOWLEDGEMENTS
Funding for this research was provided in part from the Coordination of
Improvement of Higher Level Personnel (CAPES), Brazil. Thanks go to Marcos
Liodorio, João Victor and Aline Gonçalves for the contributions in the experiment.
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42
CHAPTER 2 RESPONSE OF TARO TO VARYING WATER REGIMES AND SOIL
TEXTURES*
Meiling Li1; Angélica Cristina Fernandes Deus2; and Lin Chau Ming3
1 MS., Department of Horticulture, Agronomical Sciences College, São Paulo State University,
José Barbosa of Barros Street, 1780. Zip-Code: 18.610-307 - Botucatu, SP, Brazil. Email:
lilmeilinghappy@outlook.com. Corresponding author.
2Post Doc., Department of Soil and Environmental Resources, Agronomical Sciences College,
São Paulo State University, José Barbosa of Barros Street, 1780. Zip-Code: 18.610-307 -
Botucatu, SP, Brazil.
3 Prof., Department of Horticulture, Agronomical Sciences College, São Paulo State University,
José Barbosa of Barros Street, 1780. Zip-Code: 18.610-307 - Botucatu, SP, Brazil.
* The norm of the paper is according to “Journal of Irrigation and drainage engineering”.
ABSTRACT
Taro [Colocasia esculenta (L.) Schott] is a major root crop widely distributed in the
tropics and subtropics. However, little information is found on its water stress
tolerance under different soil textures. Therefore, this study aimed to evaluate the
effects of five water regimes (20%, 60%, 100%, 140%, and 180% ETc - crop water
requirement) and three soil textures (clay, sandy clay loam, and sandy soil) on growth,
yield, and water-use efficiency of taro. The experiment was conducted in a
greenhouse, and two harvests of taro were analyzed. In both harvests, leaf number
(LN), leaf area (LA), and corm yield (Yc) were lower at 20% and 60% ETc when
compared with 100% ETc, and higher at 140% ETc and 180% ETc when compared
with 100% ETc. Sandy soil (SS) exhibited higher LN at all water regimes than clay (CS)
and sandy clay loam (SCL) soils. For LA, the values found in SS were higher at lower
water regimes (20% and 60% ETc). In the three types of soil, water-use efficiency
(WUE) was significantly higher at 20% ETc, i.e., 1.00 kg m−3 and 0.51 kg m−3,
respectively, in the first and second harvest when compared with the other water
regimes. In the second harvest, WUE and Yc were significantly higher in SS when
compared with CS and SCL, indicating that SS has a higher potential to improve WUE
43
of taro under limited water availability conditions.
Keywords: Irrigation, Soil types, Corm yield, Canopy size, WUE.
2.1 INTRODUCTION
Despite being a renewable resource, water availability varies. Nearly every
country in the world experiences water shortages during certain periods of the year
(Gleick, 1993), and more than 80 countries currently suffer from severe water
shortage (Jin et al., 2007; Long et al., 2009). Owing to the competing demands for
fresh water from various sectors of human enterprises, the increase in irrigation
water-use efficiency is required for the sustained global food security (Saseendran et
al., 1991, 2015).
Taro is a major root crop of the Araceae family and is widely distributed in the
tropics and subtropics (Lebot, 2009). It is considered an undemanding plant regarding
cultural practices, such as the use of fertilizers and pesticides (Gondim et al., 2007).
Taro is also one of the least water-efficient crops (Uyeda et al., 2011, Daryanto et al.,
2016). Both the quantity and distribution of the available water have a significant effect
on taro growth, which may ultimately interfere with taro yield. The crop is fundamental
to ensuring food security and rural development (Melese, 2017). Globally, taro is
ranked the 14th most productive plant among staple crops, with a yield of
approximately 12 million tons from approximately two million hectares of land (Rao et
al., 2010).
However, little information is found on the water stress tolerance of taro under
different soil types. Sivan (1995) developed a study focused on the breeding of more
water-tolerant taro varieties and observed that stomatal conductance, leaf number
(LN), and leaf area (LA) of two cultivars decreased in response to water stress. Sahoo
et al. (2006) observed a significant reduction in LN and LA with an increase in water
stress; conversely, the author reported a minimum reduction in yield. Uyeda et al.
(2011) evaluated the response of taro varieties to five irrigation rates (50%, 100%,
150%, 200%, and 250% ET0 - reference evapotranspiration) and found maximum taro
yield at 150% ET0. Also, Mabhaudhi et al. (2013) tested the response of taro to three
44
water regimes based on crop water requirement (ETc) to evaluate its growth, yield,
and water-use efficiency. They found that LN and LA decreased by between 5% and
19% at 60% and 30% ETc, respectively. In addition, taro yield was 15% and 46%
higher at optimum irrigation (100% ETc) when compared with 60% ETc and 30% ETc,
whereas water-use efficiency (WUE) was relatively stable among water regimes.
The effects of soil texture on WUE are often neglected, even in the most recent
studies on water-use efficiency (for some examples, check Tränkner et al., 2016; Ren
et al., 2017; and Huang et al., 2017). Martin and Miller (1983) studied the response of
potato yield to deficit irrigation under different soil textures (sandy and loam soil) and
found that potato yield greatly increased in sandy soil with the increase in irrigation
levels (from 0% to 70%-80% ET0). Irrigation levels higher than 70% and 80% ET0 had
minimal effect, which is probably because sandy soil has a water-holding capacity
lower than loam soil. Furthermore, Katerji and Mastrorilli (2009) observed a significant
reduction (22%-25%) in WUE in clay soil for potatoes, corn, sunflowers, and sugar
beets, comparing with that detected in loam soil.
Thus, the response of taro to varying water regimes and soil textures must be
evaluated. Such information would allow more efficient application of agricultural
water by improving and applying existing irrigation technologies. Therefore, this study
aimed to evaluate the growth, yield, and water-use efficiency of taro under five water
regimes (20%, 60%, 100%, 140%, and 180% ETc) in three soil textures (clay, sandy
clay loam, and sandy soil).
2.2 MATERIALIS AND METHODS
Site and treatment description. The experiment was conducted from May 31,
2016 to March 1, 2017, in a greenhouse (7.0 × 30 × 6 m), in the experimental area of
the Agronomical Sciences College, São Paulo State University (UNESP), Campus of
Botucatu (22°51’S; 48°27’W), state of São Paulo, Brazil. During the experimental
period, the average temperature was 21.0 °C, the average ET0 was 3.56 mm/day, and
the average air humidity was 62.1%, as shown in Table 2.1.
45
Table 2.1 Average maximum and minimum of temperature, air humidity, ET0 and Kc in
the greenhouse during the experiment period, São Paulo, Brazil.
a Temperature maximum; b Temperature minimum; c Air humidity maximum; d Air
humidity minimum.
A factorial experimental design was performed with two factors (irrigation level
and soil type), replicated four times, with two plants per replication, for a total of 120
plants. Five irrigation levels (20%, 60%, 100%, 140%, and 180% ETc) were applied,
and 100% ETc was used as the control. Three soil types (clay soil, sandy clay loam
soil, and sandy soil) were used. The experiment was carried out in a randomized
complete block design (Figure 2.1). Each pot (replication) had the capacity of 25 L,
with a plant spacing of 0.6 m × 0.5 m (Figure 2.2 A).
Irrigation treatments began on August 18, 2016 (at 30 days after transplanting)
and were applied daily, using drip irrigation. Two harvests were conducted, one on
December 1, 2016 (at 135 days after transplanting), and another on March 1, 2017 (at
225 days after transplanting).
Month/Year ET0 (mm/day) Kc Tmax (℃)a Tmin (℃)b Umax (%)c Umin (%)d
July 2016 2.11 1.05 27.53 10.54 85.27 36.55
August 2016 2.68 1.05 28.19 13.22 79.94 38.48
September 2016 2.70 1.05 29.22 13.73 76.43 37.43
October 2016 3.28 1.15 27.77 16.57 82.06 36.26
November 2016 3.67 1.15 28.79 17.16 86.39 35.86
December 2016 3.44 1.15 29.01 18.14 86.73 33.00
January 2017 5.30 1.15 28.80 19.70 98.40 47.20
February 2017 5.30 1.10 29.20 18.40 96.10 37.10
46
Figure 2.1 Experimental design.
Plant materials. The taro cultivar selected for evaluation was ‘Chinese’. Taro
growth cycle has four physiological stages (Mare, 2009): dormancy, vegetative stage,
reproductive stage, and maturity. Taro propagation for corms commercial exploitation
is performed exclusively by planting the corm, which is the major commercial product
(Puiatti, 2001). Before sowing, 400 corms weighing between 30g and 50g were
selected for seedling preparation. They were sown in 400 mL plastic cups (with three
holes at the bottom of the cup), which were filled with soil and substrate. With a soil to
substrate ratio of 1:1 by volume. Sandy clay loam soil (SCL) was used as the soil. The
substrate was suitable for tropical conditions and had the following characteristics: a
moisture content of 60%, a water-holding capacity of 130% (both by weight), a bulk
density of 200 kg m-3, a pH of 5.8, and an electrical conductivity of 2.0 mS cm-1. At 48
days after sowing, 120 seedlings with similar sizes (approximately three leaves per
seedling) were selected and transplanted into the pots.
Pump
47
Figure 2.2 Taro in pot in the greenhouse and taro corms in harvests (“C” is the
corm of first harvest, “D” is the corm of second harvest).
Soils. The three types of soil used in this study were collected from the arable
layer, at the 0-20 cm depth, from the Agronomical Sciences College Farm, São Paulo
State University, Campus of Botucatu (22°51’S; 48°27’W), state of São Paulo, Brazil.
After collection, each soil sample was air-dried and sieved through a 2 mm mesh for
soil fertility and texture analyses (Table 2.2). The pH (CaCl2), organic matter (OM), P,
H + Al, K, Ca, and Mg, SB (sum of bases), CEC (cation exchange capacity), and BS
(base saturation, %) were determined according to the methodology described by Raij
et al. (2001). The particle size was determined using the pipette method (EMBRAPA,
2006). Soil texture was classified according to FAO (2006).
Table 2.2 Textural and chemical characteristics of soils used in the experiment.
a P resin is an method used for analysis of phosphorus in the soil. CS=clay soil;
Textural
class
Sand Silt Clay pH O.M Presina H+Al K Ca Mg SB CEC BS%
………..g/Kg………. CaCl2 g/dm3 mg/dm3 .............................. .mmolc/dm3 ..................................
CS 436 108 456 3.9 14 5 87 0.5 3 1 5 92 5
SCL 652 57 291 4.1 16 4 77 0.7 3 1 4 81 5
SS 957 9 34 4.7 9 4 17 1.1 7 3 10 28 38
A
DC
B
48
SCL=sandy clay loam; SS=sandy soil.
Before transplanting, the pH of the three soil types was corrected using limestone.
The acidity correction was calculated based on the need for liming to raise the base
saturation of each soil to 60%, according to the recommendation of Bulletin 200
(Aguiar et al., 2014).
Based on soil fertility results and the recommendation of the Bulletin 200 (Aguiar
et al., 2014), 200 mg L-1 of P, 30 mg L-1 of N, and 40 mg L-1 of K (using triple
superphosphate, urea, and potassium chloride, respectively) were applied to each pot
before transplanting (soils were kept wet for fertilization). The amounts of corrective
and fertilizer applied per pot, in grams, were calculated considering the pot capacity
(25 L).
Figure 2.3 Tension of the three soils
Irrigation system. Irrigation was delivered using in-line pressure-compensating
emitters, with a flow rate of 2.0 L h-1, which were positioned on each pot using a
microtube with a connector. The time of irrigation and the volume of water to be
applied were determined by a simplified water balance, using the Class A Evaporation
Pan method (CAEP; Peixoto et al., 2010), which is a standard used to measure the
water evaporation.
Irrigation scheduling was based on the evaporation value of the CAEP, pan
coefficient (Kp), and crop factor (Kc) associated with phenological stages (Allen et al.,
1998). The evaporation value of the CAEP was determined using the method
proposed by Allen et al. (1998). The evaporation value and pan coefficient (Kp) were
applied to determine the ET0 (Equation 2), which varies according to local climatic
conditions. In the present study, the value of Kp was 1, as recommended by Prados
(1986). The growth cycle of taro is of approximately seven months (Lebot, 2009). Kc
values of taro were as described by Fares (2008), where Kc initial = 1.05 (two months),
49
Kc med = 1.15 (four months), and Kc late = 1.1 (one month). Based on the values of Kc
and ET0, ETc (Equation 1) was calculated using the single crop coefficient approach,
as described by Allen et al. (1998):
ETc = ET0 × Kc............................................................................................................ [1]
where: ETc = crop water requirement, ET0 = reference evapotranspiration, and Kc =
crop factor; and
ET0 = CAEP × Kp....................................................................................................... [2]
where: CAEP = Evaporation value of Class A Evaporation Pan, and Kp = Pan
coefficient.
During the first month after transplanting, all treatments were irrigated with 100%
ET0. Thereafter, irrigation treatments were imposed. Irrigation was performed every
morning to ensure water availability during the peak periods of plant demand during
the day. The last irrigation occurred on February 28, 2017. The total irrigation water
applied (WUt), taking the initial watering into account, ranged from 1580 mm (180%
ETc) to 1244 mm, 908 mm, 572 mm, and 236 mm for 140%, 100%, 60%, and 20%
ETc, respectively.
Data collection. LN and LA evaluations began at 15 days after transplanting.
Data were collected once a month until the second harvest. Only fully-expanded
leaves with at least 50% green leaf area were considered in the LN evaluation. The
first harvest was conducted at approximately 19 weeks after transplanting, and the
second harvest occurred at approximately 32 weeks after transplanting, during which
the fresh weight of corms was recorded (Figure 2 B & C).
Leaf area was measured by the non-destructive method developed by Chapmam
(1964), which was adapted to the ‘Chinese’ taro by Nolasco et al. (1984), using the
following equations:
Y = 242.0 × X 0.6656 .................................................................................................... [3]
X = AA' × AB × AB'/1000 .......................................................................................... [4]
Where: AA′ = distance from the insertion of the petiole to the extremity of the leaf
blade, AB = distance from the right end of the leaf blade to the petiole insertion, and
AB′ = distance from the left end of the leaf blade to the petiole insertion.
Corm yield was calculated by summing the fresh weight of taro corms per plant
(corms are shown in Figure 2 C and D), and WUt was calculated by summing the daily
50
water applied. Water-use efficiency (WUE) was calculated according to the following
equation (Mabhaudhia et al., 2013):
WUE = Yc/WUt........................................................................................................... [5]
Where: WUE = water-use efficiency in kg m-3, Yc = sum of the fresh weight of corms in
kg, and WUt= total water applied in m3.
Statistical analysis. Data (leaf number, leaf area, corm yield, and water-use
efficiency) were subject to the analysis of variance (ANOVA), using the Sigmaplot®
(Version 11.0, ISI, USA). The Tukey's Honest Significant Difference test (HSD) was
used for multiple comparison tests, with a significance level of α = 0.05.
2.3 RESULTS
Effects of water regime and soil texture on LN and LA of taro. Leaf number
(LN) showed a highly significant difference (p < 0.001) between irrigation treatments
(Figure 2.4 a, c, e), as well as between soil textures (Figure 2.5 a, c, e, g, i). The
interaction between irrigation treatment and soil type was also significant (p < 0.05).
Leaf number increased by 18% and 14% at 140% and 180% ETc, respectively, and
decreased by 3% and 44% at 60% and 20% ETc, respectively, when compared with
the control treatment (100% ETc). In CS (clay soil) and SS (sandy soil), LN was
slightly higher for 140% ETc than 180% ETc (Figure 2.4 a, e); conversely, for SCL
(sandy clay loam), LN exhibited a consistent decline with a decrease in water regimes,
although no statistically significant differences were detected between 60%, 100%,
140%, and 180% ETc. LN for CS (6.09 plant-1) and SCL ( 6.10 plant-1) were similar,
whereas LN for SS was 22% higher than that of the other soil types. LN was slightly
higher for SCL when compared with that of CS at 20%, 60%, and 100% ETc. On the
other hand, LN for CS was higher than that of SCL at 140% and 180% ETc. A closer
look at the results showed that LN for SCL (6.98 plant-1) at the maximum water regime
(180% ETc) was lower than that observed for SS at 60% ETc (8.35 plant-1). At lower
water regimes (20%, 60%, and 100% ETc), LN was slightly higher for SCL than for CS;
conversely, LN was lower for SCL than for CS at higher water regimes (Figure 2.5 a, c,
e). Overall, results showed that LN for SS was higher at all water regimes, comparing
51
with those of the other soil textures.
Figure 2.4 Response of taro leaf area (cm2) and leaf number per plant by water
regime.
Highly significant differences were observed for LA (p < 0.001) between irrigation
treatments; however, no significant differences (p > 0.05) were detected between soil
textures (Figure 2.5 b, d, f, h, j). The interaction between irrigation treatment and soil
type was significant (p < 0.05). Leaf area decreased by 54% and 22% at 20% and
60% ETc, respectively, and increased by 24% and 42% at 140% and 180% ETc,
respectively, when compared with 100% ETc (Figure 2.4 b, d, f). Since LN showed the
highest value at 140% ETc, individual leaves were smaller when compared with those
at 180% ETc, which resulted in a smaller LA at 140% ETc. Also, LA for SS was 42%
and 30% higher than that of SCL and CS, respectively, at 20% ETc. Conversely, at
100% ETc, CS showed the highest LA among the three soil types. At 60%, 140%, and
180% ETc, no statistically significant differences were detected between soil types
52
(Figure 2.5 d, h, j). Overall, LA showed to be significantly affected by changing the
water availability in all types of soils; SS showed a higher LA regulation under limited
water conditions when compared with SCL and CS. Nevertheless, LA was not
significantly affected by soil types at higher water regimes.
Figure 2.5 Response of taro leaf area (cm2) and leaf number per plant by soil texture.
Effects of water regime and soil texture on Yc and WUE of taro. Yc showed
highly significant differences between water regimes (p < 0.001). In the first harvest,
53
Yc of different water regimes exhibited the following trend: 140% ETc > 180% ETc >
100% ETc > 60% ETc > 20% ETc. Conversely, in the second harvest, the trend was:
180% ETc > 140% ETc >100% ETc > 60% ETc > 20% ETc (Table 2.3). No significant
differences were detected in Yc among the soil types in the first harvest. However, a
significant difference (p < 0.05) was observed in the second harvest. Yc of SS was
significantly higher than that of SCL and CS by 19% and 10%, respectively. Results of
LN and LA revealed that SS was better for taro yield accumulation.
Table 2.3 Effects of water regime and soil texture on mean taro Ycn and WUEo by
harvest. Values in table are means (n=4).
WUt m (m3) Yc (Kg) WUE (kg m-3)
Harvests Water
Regimes
Soil texture Soil texture Soil texture
CS SCL SS CS SCL SS CS SCL SS
First
Harvest
20%ETc 0.12 0.12 0.12 0.10aCa 0.13aD 0.12aD 0.83aA 1.10aA 1.04aA
60%ETc 0.36 0.36 0.36 0.18aC 0.20aCD 0.24aC 0.50aB 0.56aB 0.69aB
100%ETc 0.60 0.60 0.60 0.31aB 0.31aBC 0.38aAB 0.53aB 0.52aB 0.64aB
140%ETc 0.84 0.84 0.84 0.46aA 0.41aAB 0.46aA 0.56aB 0.50aB 0.55aB
180%ETc 1.08 1.08 1.08 0.41aA 0.45aA 0.36aB 0.39aB 0.42aB 0.34aC
Second
Harvest
20%ETc 0.25 0.25 0.25 0.11aE 0.11aD 0.16aD 0.44bA 0.44bA 0.64aA
60%ETc 0.61 0.61 0.61 0.25bD 0.27bC 0.34aC 0.38bA 0.45bA 0.55aAB
100%ETc 0.98 0.98 0.98 0.43aC 0.45aB 0.47aB 0.44aA 0.43aA 0.48aBC
140%ETc 1.34 1.34 1.34 0.53aB 0.50aAB 0.56aAB 0.40aA 0.35aA 0.42aC
180%ETc 1.70 1.70 1.70 0.69aA 0.60aA 0.65aA 0.40aA 0.35aA 0.39aC
a Mean separation between water regimes within soil texture (capital letters) and
between soil textures within water regime (lower case letters) by t-test at α = 0.05; m
Total water use; nYield of corms; oWater-use efficiency.
Water-use efficiency (WUE) also showed highly significant differences (p < 0.001)
between water regimes in both harvests; however, a highly significant difference (p <
0.001) between soil types was observed only in the second harvest (Table 2.3). For
both harvests, the highest WUE was reported at 20% ETc, and no statistically
significant differences were observed in WUE among the four highest water regimes.
In the second harvest, WUE for CS (0.41 kg m-3) and SCL (0.40 kg m-3) were similar,
whereas WUE for SS was 22% higher than that of the other two soil textures (Table
2.3).
2.4 DISCUSSION
54
Results show that limited water availability (20% and 60% ETc) reduced LN and
LA (Figure 2.4). In contrast, over-irrigation (180% ETc) could negatively influence LN,
although it may be beneficial in increasing LA. The lower LN observed under limited
water availability was consistent with reports of Mabhaudhi (2013) and Sahoo et al.
(2006). Mabhaudhi (2013) documented 5% and 12% reduction in leaf area index (LAI)
at 30% ETc and 60% ETc, respectively, when compared with that of 100% ETc. The
lower LA observed under limited water availability in the present study also
corroborates the results of Sivan (1995), who observed reduced growth in taro subject
to drought stress.
Leaf area (LA) and leaf number (LN) represent the canopy size, as well as the
surface area available for transpiration (Mabhaudhi et al., 2013). Plants cope with
reduced water availability by reducing the canopy size (Mitchell et al., 1998). Leaf
area reduction has previously been ascribed to photosynthesis reduction under
water-limited conditions (Anjum et al., 2011), which reduces leaf expansion.
Additionally, LN reduction is caused by leaves premature senescence, which affects
WUE. Hypothetically, a plant that shows a moderate reduction in the canopy size is
capable of striking a balance between minimizing water loss and continuing
reasonable biomass production (Blum, 2005, 2009). In this regard, SS was efficient in
achieving both aspects. Although the crop canopy size reduced under water-limited
conditions, it was more moderate in SS when compared with that of CS and SCL,
resulting in a higher yield in SS than in the other two soil textures.
The response of Yc to the irrigation applied (WUt) in the present study is similar to
that recently reported by Uyeda et al. (2011), Mabhaudhi et al. (2013), and Vieira et al.
(2015). The authors stated that Yc of taro decreased with a reduction in the applied
irrigation. In addition, Daryanto et al. (2016) performed a meta-analysis on the effects
of drought on root and tuber production, and their results indicated that taro generally
suffered a greater production loss under water deficit conditions. Furthermore, Uyeda
et al. (2011) found that while 150% ET0 could maximize taro yield, increasing the
irrigation level up to 250% ET0 did not result in a higher yield. Therefore, determining
55
whether the increase in yield is worth the increase in water cost is fundamental, and
SS may be an option to improve taro Ycwith less water application.
The trend of WUE in the present study (Table 2.3) was inconsistent with the
reports of Bussell and Bonin (1998), who found WUE to be generally higher at high
watering-level treatments than at low water-level treatments. Vieira et al. (2015) found
that an increase in the applied water depth resulted in an increase in WUE to a
maximum value of 2.78 kg m-3 at 75% ETc. However, they also found a decrease in
WUE at higher water regimes (100% and 125% ETc). Additionally, drought has been
shown to increase WUE in peanuts (Aranyanak et al., 2008), cassava (Olanrewaju et
al., 2009), common beans, green gram (Webber et al., 2006), and Jerusalem
artichokes (Janket et al., 2013). A reduction in WUt should increase WUE and
ultimately improve yield (Blum, 2005; Jones, 2004). A reduction in the canopy size
(lower LN and LA) in response to the limited water availability is an attribute of
increased WUE; however, this reduction should not be excessive since canopy size is
directly correlated with reduced biomass production and yield (Blum, 2005, 2009). In
the present study, soil texture influenced WUE in the second harvest; WUE was
significantly lower in CS and SCL than in SS (Table 2.3). According to Katerji and
Mastrorilli (2009), soil texture can affect the WUE of potatoes, considering that heavier
soil textures decrease WUE. The positive effect of SS on WUE recognized by Turner
(2004) was confirmed in the present study for taro and was evident in the second
harvest (Table 2.3). WUE was higher for SS at lower water regimes, indicating that it is
probably wiser to improve WUE of taro by correctly choosing the soil type before
increasing the irrigation water unilaterally.
2.5 CONCLUSION
The reasonable control of the irrigation applied and the correct selection of the
soil type are key factors that need to be considered for taro production. These facts
would help improve water-use efficiency and possibly yield. The present research
showed the reduced canopy size (leaf number and leaf area) of taro under conditions
of limited water availability. The reduction in the canopy size was greater for clay and
56
sandy clay loam soil than sandy soil, especially at lower water regimes for leaf area.
Furthermore, canopy size and corm yield increased by increasing water regimes in all
the soil textures. The highest water-use efficiency was observed at 20% ETc, whereas
no statistically significant differences were detected between 60%, 100%, 140%, and
180% ETc in both harvests. Sandy soil showed to have significantly higher water-use
efficiency and corm yield in the second harvest, suggesting that, under conditions of
limited water availability, taro may be better adapted to sandy soils.
ACKNOELEDGEMENTS
Funding for this research was provided in part from the Coordination of
Improvement of Higher Level Personnel (CAPES), Brazil. Thanks go to Marcos
Liodorio, João Victor and Aline Gonçalves for the contributions in the experiment.
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61
CHAPTER 3 CHEMICAL COMPOSITION AND DRY BIOMASS OF TARO
RESPONSE TO VARYING WATER REGIMES AND SOIL TEXTURES
Meiling Li1; Angélica Cristina Fernandes Deus2; and Lin Chau Ming3
1 MS., Department of Horticulture, Agronomical Sciences College, São Paulo State University,
José Barbosa of Barros Street, 1780. Zip-Code: 18.610-307 - Botucatu, SP, Brazil. Email:
lilmeilinghappy@outlook.com. Corresponding author.
2Post Doc., Department of Soil and Environmental Resources, Agronomical Sciences College,
São Paulo State University, José Barbosa of Barros Street, 1780. Zip-Code: 18.610-307 -
Botucatu, SP, Brazil.
3 Prof., Department of Horticulture, Agronomical Sciences College, São Paulo State University,
José Barbosa of Barros Street, 1780. Zip-Code: 18.610-307 - Botucatu, SP, Brazil.
*The norm of the paper is according to “Agricultural Water Management”
ABSTRACT
The chemical composition and dry mass accumulation of taro (Colocasia esculenta L.
Schott) response to water regime and soil texture were investigated in the present
study. For this aim, an experiment with five water regimes (20%, 60%, 100%, 140%
and 180% ETc - crop water requirement) and three soil textures (clay, sandy clay loam,
and sandy soil) was conducted in a greenhouse. Results showed that corm humidity
(CH), above-ground dry weight (ADW), root dry weight (RDW), and corm dry weight
(CDW) of taro corm increased with increase in water regime. Generally, reducing
sugars (RS), and starch content (SC) showed a increased trend with increase in water
regime, while the different trend was observed in total soluble solids (TSS) and total
titratable acidity (TTA) in taro corm. However, TTA in taro leaf was increased with
increase in water regime. In addition, protein content (PC) of taro corm was higher at
20% and 60% ETc relative to 100% ETc, while 140% ETc and 180% ETc showed lower
PC, compared with 100% ETc. In taro corm, sandy soil (SS) exhibited higher TSS,
TTA, RS, SC, total sugars (TS), and CDW, while higher RDW was observed in SCL.
CH was 6.2% higher in clay soil (CS), compared with sandy clay loam (SCL) and SS,
while it was relatively constant (64%) in the latter two soils. In addition, a higher TTA
62
was also observed in SS in taro petiole. Overall, results reported in the present study
suggested that higher water regime was more beneficial to improve corm quality, and
SS could be more suitable for taro cultivation under water stress.
Keywords: Irrigation, Soil type, Corm quality, Water stress, Tuber.
3.1 INTRODUCTION
Colocasia esculenta is popularly known as "taro" and belongs to the Araceae
family (Castro et al., 2017). As a tuber crop largely produced for its underground corm,
it is mainly consumed in the tropical and sub-tropical countries (Matthews et al., 2017).
The plant performs well with a temperature between 21 and 27°C and 1500-2000 mm
of rainfall and does best in a soil with a pH of 5.5-6.5 and a moderate clay content
(Onwueme, 1999).
The chemical composition of taro corm has been well documented by previous
researches (Onwueme, 1978; Kaushal et al., 2015). It has a broader complement of
nutrients than other tuber crops (Kaushal et al., 2015; Filho et al., 1997), it is superior
to potatoes (Solanum tuberosum), sweet potatoes (Ipomoea batatas), cassava
(Manihot esculenta) and yam (Dioscorea L.). In addition, the nutritional compounds of
its corm vary significantly between cultivars and the differences are also well known
from consumers and traders (Alcantara et al., 2013). There is also a variation between
the proximal, central and distal parts of taro corm according to the chemical analyses
complex (Mergedus, 2015; Kristl et al. 2016 ).
However, the chemical composition research of taro is still suffering from the lack
of scientific information in relation with water regime and soil texture, in spite of that
some researchers focused on the effect of variety, harvest interval and drying
methods on chemical composition of taro corm (see, for example, Arıcı et al. 2016;
Lebot et al. 2017; Castro et al. 2017; Kaensombath et al. 2012). It was recorded that
the variations in CH (55.8% to 74.4%), SC (20.0% to 35.1%), and PC (0.5% to 2.1%)
between taro cultivars (Agbor-Egbe and Rickard, 1990). Kaensombath et al. (2012)
reported that effects of harvesting intervals on the chemical composition of taro leaf
differed little. In addition, the storage temperature influences the quality of harvested
63
commodities (Kader and Rolle, 2004). Low storage temperature leads to developing
more RS and decreasing SC of corm; while high storage temperatures, on the other
hand, causes sprouting and weight loss ( Pal et al., 2008).
Some researchers investigated the effect of water stress on the growth of taro
(Sivan et al., 1995; Sahoo et al., 2006; Uyeda et al., 2011; Mabhaudhi et al., 2013),
however, they mainly focused on taro water-use efficiency, corm yield and canopy
size. Miller and Martin (1987) compared the response of potato to irrigation treatment
under sandy and loam soil. They reported that in sandy soil, daily irrigation increased
corm yield, number of corms, but decreased average corm weight, compared to
irrigation every four days. While the responses to water regime were small in loam soil.
In another work published by them which studied the response of potato yield and
quality to irrigation treatment in sandy soil, they reported that irrigation treatment had
no effect on the number of corms, the yield reduction of potato was due largely to
reduced corm size (Miller and Martin, 1987).
Thereby, there is a need to evaluate the response of chemical composition of taro
to water regime and soil texture. The aim of the present study was to evaluate the
response of pH, TSS, TTA, CH, TS, RS, SC, and PC of taro to five water regimes and
three soil textures.
3.2 MATERIALS AND METHODS
Site description and meteorological conditions. The experiment was carried
out in the experimental area of Agronomical Sciences College, São Paulo State
University (UNESP), Botucatu (22°51′S; 48°27′W), São Paulo, Brazil. The taro was
grown in a greenhouse with dimensions of 7.0 x 30 x 6.0 m, from May 31, 2016 to
December 1, 2016. This region has a subtropical climate with the average
temperature during the experimental period was 21.0°C, the average ET0 was 2.98
mm/day, and the average air humidity was 59.5 % as shown in Table 3.1.
64
Table 3.1 Average maximum and minimum of temperature, air humidity, and ET0 in
the greenhouse during the experiment period, São Paulo, Brazil.
a Temperature maximum; b Temperature minimum; c Air humidity maximum; d Air
humidity minimum.
Experimental design and plant materials. The experiment was conducted
according to the randomized complete block design (Figure 3.1) with two factors
(irrigation level and soil texture). Five water regimes (20%, 60%, 100%, 140%, and
180% ETc) and three soil types (clay soil, sandy clay loam soil, and sandy soil) were
applied, and 100% ETcwas used as the control. Replicated four times, for a total of 60
plants. The taro was grown in the pot, each of which had the capacity of 25 L, with a
plant spacing of 0.6 m × 0.5 m (Figure 3.2). In the experiment, the taro cultivar
selected for investigation was ‘Chinese’. It has four physiological stages for growth
cycle (Mare, 2009): dormancy, vegetative stage, reproductive stage, and maturity.
Figure 3.1 Experimental design.
Taro propagation. The taro was rapidly propagated vegetatively (Puiatti, 2001)
Month/Year ET0 (mm/day) Kc Tmax (℃)a Tmin (℃)b Hmax (%)c Hmin (%)d
July 2016 2.11 1.05 27.53 10.54 85.27 36.55
August 2016 2.68 1.05 28.19 13.22 79.94 38.48
September 2016 2.70 1.05 29.22 13.73 76.43 37.43
October 2016 3.28 1.15 27.77 16.57 82.06 36.26
November 2016 3.67 1.15 28.79 17.16 86.39 35.86
December 2016 3.44 1.15 29.01 18.14 86.73 33.00
Pump
65
with 400 corms weighing between 30g and 50g for seedling propagation. They were
sown in 400 mL plastic cups (with three holes at the bottom of the cup), which were
filled with soil and substrate. With a soil to substrate ratio of 1:1 by volume. Sandy clay
loam soil (SCL) was used as the soil. The substrate was suitable for tropical
conditions. At 48 days after sowing, 60 seedlings with similar sizes (approximately
three leaves per seedling) were selected and transplanted into the pots.
Figure 3.2 Taro in pot in the greenhouse (A) and taro corms in harvest (B).
Preparation of soils, organic compost, and water. The soils used in the
current investigation were collected from the Agronomical Sciences College Farm,
São Paulo State University, Botucatu, São Paulo, Brazil. The three soils were taken
from the depth of 0-20 cm. The determination of the content of sand, silt, and clay in
the three soil samples was performed by pipette technique (EMBRAPA, 2006),
whereas their textural class was defined according to FAO (2006). The chemical
characteristics of soils were determined according to the methodology described by
Raij et al. (2001). Soil analysis results are shown in Table 3.2.
Table 3.2 Textural and chemical characteristics of soils used in the experiment.
a P resin is an method used for analysis of phosphorus in the soil.
According to Bulletin 200 (Aguiar et al., 2014), the pH of the three soils was
Textural
class
Sand Silt Clay pH O.M Presina H+Al K Ca Mg SB CEC BS%
………..g/Kg………. CaCl2 g/dm3 mg/dm3 .............................. .mmolc/dm3 ..................................
CS 436 108 456 3.9 14 5 87 0.5 3 1 5 92 5
SCL 652 57 291 4.1 16 4 77 0.7 3 1 4 81 5
SS 957 9 34 4.7 9 4 17 1.1 7 3 10 28 38
A B
66
corrected using limestone before transplanting. The acidity correction was calculated
based on the need for liming to raise the base saturation of each soil to 60%. Based
on the analysis of the soils and the recommendation of Bulletin 200 (Aguiar et al.,
2014), 200 mg L-1 of P, 30 mg L-1 of N, and 40 mg L-1 of K (using triple superphosphate,
urea, and potassium chloride, respectively) were applied to each pot. The amounts of
corrective and fertilizer applied per pot, in grams, were calculated considering the pot
capacity (25 L).
During the experiment period, compost heap was done twice (in September and
December of 2016, respectively), 1.5 L of organic compost was applied above the soil
per pot. The irrigation water resource was from Sabesp, State of São Paulo, Brazil.
According to the chemical characteristics of the irrigation water, it was classified as
C1S1 (Richards, 1954), and does not show restriction for irrigation. Organic compost
and water analysis results are shown in Table 3.3 and Table 3.4, respectively.
Table 3.3 Chemical characteristics of organic compost used in the experiment.
O.M N P2O5 K2O Ca Mg S U-65℃ C Na Cu Fe Mn Zn
pH C/N ………........................ % ...............................……… .……… mg/Kg .………
7.7 11/1 34 1.8 1.4 0.6 1.8 0.4 0.3 13 19 609 63 10005 348 120
Table 3.4 Chemical characteristics of water used in the experiment.
N P K Ca Mg S Na B Cu Fe Mn Zn C.E
pH ........................................……….. mg/L ……….............................................. µS/cm
7.3 4 1 22 18 10 5 3.80 0 0 0.16 0 0 73
Figure 3.3 Tension of the three soils
Irrigation system. The irrigation system used was drip irrigation, which was
delivered using in-line pressure-compensating emitters, with a flow rate of 2.0 L h-1. It
is connected by a 4 mm microtube on lateral line (16 mm) and branch line (25 mm).
The system is pressurized by an irrigation pump (0.5 HP of power) and a gauge height
of 30 mca. The time of irrigation and the volume of water to be applied were
67
determined by using the Class A Evaporation Pan method (CAEP; Peixoto et al.,
2010).
Irrigation management was based on reference evapotranspiration (ETo) and a
crop factor (Kc ) (Allen et al., 1998). The ETo was obtained from the values of CAEP
and pan coefficient (Kp) (Equation 2), which varies according to local climatic
conditions. In the current investigation, the value of Kp was 1, according to Prados
(1986). The growth cycle of taro is of approximately seven months (Lebot, 2009). The
Kc values of taro were: Kc initial = 1.05 (two months), Kc med = 1.15 (four months), and Kc
late = 1.1 (one month), respectively, as described by Fares (2008). Based on the Kc
and ET0, ETc (Equation 1) was calculated using the single crop coefficient approach,
as described by Allen et al. (1998):
ETc = ETc × Kc……………………………………………………………………….......... [1]
where: ETc = crop water requirement, ET0 = reference evapotranspiration, and Kc =
crop factor; and
ET0 = CAEP × Kp………………………………………………………………………...... [2]
where: CAEP = Evaporation value of Class A Evaporation Pan, and Kp = Pan
coefficient.
At the beginning of the study, all treatments were irrigated with 100% ET0. One
month after transplanting, irrigation treatments were imposed. Irrigation was applied
during the mornings to ensure water availability during peak periods of demand in the
day. The last irrigation occurred on November 30, 2016. Taking into consideration the
initial watering, the total actual amount of water applied (WUt) was ranged from 946
mm (180% ETc) to 751 mm, 556 mm, 360 mm and 165 mm for 140%, 100%, 60%,
and 20% ETc, respectively.
Data collection. The harvest was conducted approximately 135 days after
transplanting. In the harvest, pH, total soluble solids (TSS), and total titratable acidity
(TTA) were determined in taro corm, leaf, and petiole. pH of homogenized extracts of
taros was measured using the Digimed DMPH-2 potentiometer, as recommended by
Adolfo Lutz Institute (1985). For TSS determination, the juice extracted from a slice of
the corm was used, then it was placed on the prism of an electronic refractometer;
The o Brix was then read directly by ABBE refractometer, brand ATAGO - N1,
according to the recommendations by A.O.A.C (1970). To determine TTA, 5g of fresh
68
taro were used and diluted in 95 mL of deionized water. The titration was performed
with a standard solution of 0.1 N sodium hydroxide and the indicator used was
phenolphthalein (Adolfo Lutz Institute, 1985). The results were expressed as percent
of malic acid.
Total sugars (TS), reducing sugars (RS), starch content (SC), protein content
(PC), and corm humidity (CH) were determined in taro corm. TS and RS obtained by
alcohol extraction, according to Instituto Adolfo Lutz, which was quantified by
spectrophotometry with Somogyi-Nelson reagents, at 500 nm wavelength, in
Spectrum 70 Bausch & Lomb apparatus, as described by Aued et al. (1989). The SC
was determined on the residue of the alcoholic extract after hot acid hydrolysis by the
Lane-Eynon method, with the Fehling reagent, according to Instituto Adolfo Lutz
procedure. For PC, the micro Kjeldahl method was used to estimate the total nitrogen,
using the factor 6.25 to convert it into protein content, according to A.O.A.C (1970).
CH was determined by greenhouse gravimetric method at 105°C, as described by
Instituto Adolfo Lutz. The above-ground, root and corm of taro was dried at 105°C until
the constant weight, and the above-ground dry weight (ADW), root dry weight (RDW),
and corm dry weight (CDW) were calculated by summing its dry weight per plant.
Statistical analysis. Analysis of variance (ANOVA) was used to statistically
analyze data (pH, total soluble solids, total titratable acidity, total sugars, reducing
sugars, starch content, and protein content, corm humidity, above-ground dry weight,
root dry weight, and corm dry weight) using Sigmaplot® version 11.0 (ISI, San Jose,
California USA). The Tukey's Honest Significant Difference test (HSD) was used for
multiple comparison tests, with a significance level of α = 0.05.
3.3 RESULTS
Effects of water regime and soil texture on pH, total soluble solids (TSS),
total titratable acidity (TTA) of taro corm, leaf, and petiole. pH demonstrated a
statistically significant difference between water regimes for taro corm (p = 0.03) and
leaf (p = 0.003). The lowest pH was obtained at 60% ETc, on average, 6.4 and 6.2,
respectively, for corm and leaf (Figure 3.4 a, b), whereas there was no significant
69
difference between the other irrigation treatments. No significant difference (p > 0.05)
was observed between soil textures in its corm, leaf or petiole. With respect to soil
texture, the average pH was 6.5, 6.3, and 6.1, respectively, for corm, leaf, and petiole
(Figure 3.5 a, b, c).
For total soluble solids (TSS), the interaction between irrigation treatment and soil
texture was significant in taro corm (p < 0.001) and petiole (p = 0.033). In taro corm,
TSS was higher at 60% ETc (7.5%) and 100% ETc (7.0%) in SCL, whereas 20% ETc
and 140% ETc showed higher TSS in SS, and there was no significant difference
between water regimes in CS (Figure 3.4 d); With respect to soil texture, at 140% and
180% ETc, SCL was observed to have significantly lower TSS compared with SS and
CS; while at 20% ETc, TSS was significantly higher (8.28%) in SS (Figure 3.5 d). For
petiole, SS showed the highest TSS (5.4%) at 140% ETc (Figure 3.4 f), and there was
no significant difference among the other treatments. No significant differences were
detected between water regimes (p = 0.847) or soil textures (p = 0.499) for TSS in taro
leaf (Figure 3.4 e and Figure 3.5 e).
Figure 3.4 Response of pH, TSS, TTA of taro corm, leaf, and petiole to varying water
regimes.
70
The interaction between irrigation treatment and soil type was significant for total
titratable acidity (TTA) in taro corm (p = 0.005, Figure 3.3 g and Figure 3.4 g) and
petiole (p = 0.020, Figure 3.4 i and Figure 3.5 i). In taro corm, water regime of 20%
ETcwas observed to have the highest TTA, 0.62% and 0.78%, respectively, in CS and
SS; whereas 60% ETc showed the highest TTA in SCL (Figure 3.4 g). At 60% ETc,
SCL showed higher TTA (0.62%), while SS exhibited a higher TTA, 0.78% and 0.65%,
respectively, at 20% and 100% ETc (Figure 3.5 g). In taro petiole, SS showed highest
TTA at 100% ETc (0.6%) and 140% ETc (0.7%), no significant difference was
observed among the other treatments (Figure 3.5 i ). While for taro leaf, a significant
difference (p = 0.008) was observed between water regimes (Figure 3.4 h). The
lowest TTA (0.8%) was observed at 60% ETc, there were no significant differences
among the other irrigation and soil treatments (Figure 3.4 h and Figure 3.5 h).
Figure 3.5 Response of pH, TSS, TTA of taro corm, leaf, and petiole to varying soil
textures.
71
Effects of water regime and soil texture on chemical composition of taro
corm. Significant differences (P < 0.05) were observed between irrigation treatments
as well as between soil textures for total sugars (TS). The trend observed was 140%
ETc > 60% ETc > 180% ETc > 20% ETc > 100% ETc (Table 3.5). On average, TS of CS
(2.20%) and SCL (2.15% ) was similar, while it was 18% lower compared with that of
SS. Reducing sugars (RS) was shown to be significantly influenced by irrigation
treatment as well as by soil type (Table 3.5). The interaction between irrigation
treatment and soil type was also significant (P < 0.001). In the three soil types, RS
showed an obvious decline at 20% ETc, compared with the other water regimes (Table
3.5). However, there was no consistent increase with an increase in water availability
from 60% ETc to 180% ETc. In SCL, 180% ETc showed higher RS in comparison with
that of 100% ETc,whereas no significant difference was observed between 100% ETc
and 180% ETc in CS and SS. With respect to soil texture, at 20% and 100% ETc, SCL
had significantly lower RS compared with CS and SS; At 60% ETc, RS for SS was
16% and 17% lower, respectively, in comparison with CS and SCL. In addition, at
140% ETc, CS showed lower RS compared with the other two soil types; Whereas at
180% ETc there was no significant difference in RS between soil textures. Overall,
results pointed to SS having higher sugar accumulation in response to water stress.
Starch content (SC) of taro corm was significantly influenced by irrigation
treatment as well as by soil texture (Table 3.5). There was also a significant difference
(P < 0.001) of the interaction between irrigation treatment and soil texture (Table 3.5).
In CS and SCL, 20% ETc showed lower SC in comparison with 60%, 100%, and 140%
ETc, whereas in SS, 100% ETc was observed to have the lowest SC, followed it was
20% ETc. In addition, at 100% ETc, SC of SS was 30% and 13% lower than that of CS
and SCL, respectively. At 20%, 60%, and 180% ETc, SS was observed to have the
highest SC, compared with CS and SCL.
In line with the observations of protein content (PC) of taro corm, significant (p <
0.001) differences were observed between irrigation treatments (Table 3.5). Generally,
PC was increased with decrease in water availability (see, for example, 140% ETc <
72
180% ETc < 100% ETc < 60% ETc < 20% ETc). Whereas 180% ETc showed slightly
higher (6% higher) PC compared with that of 140% ETc, however, it was lower than
that of the other three irrigation treatments (20%, 60%, and 100% ETc). No significant
differences were observed for PC between soil textures (Table 3.5).
Table 3.5 Effect of water regime and soil texture on chemical composition of taro corm.
Values in table are means (n=4).
Water
regime
Total sugars (%) Reducing sugars (%) Starch content (%) Protein content (%)
Soil texture Soil texture Soil texture Soil texture
CS SCL SS CS SCL SS CS SCL SS CS SCL SS
20% ETc 2.0Bba 2.0BCb 2.5Ba 0.39Ca 0.30Cb 0.44Da 17Cb 17Cb 21Ca 2.8Aab 3.0Aa 2.7Ab
60% ETc 2.4Aa 2.3ABa 2.6Ba 0.62Aa 0.63Aa 0.52Cb 20Bb 19Bb 26Ba 1.8Bc 2.0Bb 2.3Ba
100% ETc 2.3ABa 1.7Cb 2.4Ba 0.62Aa 0.49Bb 0.69Aa 23Aa 22Aa 16Db 1.8Ba 1.7CDa 1.9Ca
140% ETc 2.1ABc 2.4Ab 3.1Aa 0.52Bb 0.60Aa 0.59BCa 20Bb 23Aab 25Ba 1.7Ca 1.5Da 1.7CDa
180% ETc 2.4Aa 2.3ABa 2.4Ba 0.62Aa 0.61Aa 0.64ABa 19BCb 18BCb 29Aa 1.8BCa 1.8Ca 1.7Da
CS = clay soil; SCL = sandy clay loam; SS = sandy soil. a Mean separation between
water regimes within soil texture (capital letters) and between soil textures within
water regime (lower case letters) by t-test at α = 0.05.
Effect of water regime and soil texture on dry biomass accumulation of taro.
Highly significant differences were observed between water regimes for above-ground
(ADW, p < 0.001), root (RDW, p < 0.001), and corm dry weight (CDW, p < 0.001) of
taro (Table 3.6). Which were increased constantly with the increase in water regime
(Table 3.6). Soil texture had no significant effect on ADW, whereas it influenced
significantly on RDW (p = 0.041) and CDW (p = 0.011). SCL showed the highest RDW
(22g plant-1, on average), while for CDW, SS exhibited the highest value (56g plant-1,
on average). The interaction between irrigation treatment and soil type was significant
for corm humidity the interaction (p = 0.017). The variation of CH was ranged from
41% to 78% (Table 3.6). And a trend of decline with decrease in water availability was
observed in the three soil textures. It was decreased by 39% and 9% at 20% ETc and
60% ETc, respectively, relative to 100% ETc. There was a significant difference for CH
between soil textures at 100% ETc, CS showed slight higher CH than that of SCL and
SS (Table 3.6).
73
Table 3.6 Effects of water regime and soil texture on corm humidity, above -ground,
corm, and root dry weight of taro. Values in table are means (n=4).
Water
regime
Above-ground dry weight
(g plant-1)
Root dry weight
(g plant-1)
Corm dry weight
(g plant-1)
Corm humidity (%)
Soil texture Soil texture Soil texture Soil texture
CS SCL SS CS SCL SS CS SCL SS CS SCL SS
20% ETc 12Cba 11Bb 13Ca 9Db 10Cab 11Ca 29Da 32Ba 29Ca 46Ca 41Da 42Ca
60% ETc 15Ca 13Bb 15Ca 15Ca 16Ca 16BCa 33CDa 37Ba 42Ca 65Ba 60Ca 67Ba
100% ETc 19BCa 17Ba 20Ba 20Ba 18Ca 20Ba 49BCa 51Aa 58Ba 78Aa 68Bb 68Bb
140% ETc 26Aa 25Aa 26Aa 25Aa 30Ba 21Ba 68Aa 62Aa 70Ba 76Aa 76Aa 74Aa
180% ETc 32Aa 24Aa 27Aa 28Aa 38Aa 27Aa 60ABb 58Ab 83Aa 77Aa 78Aa 73Aa
a Mean separation between water regimes within soil texture (capital letters) and
between soil textures within water regime (lower case letters) by t-test at α = 0.05.
3.4 DISCUSSION
The chemical composition of taro corm has been well documented (Onwueme,
1978; Bradbury et al., 1985), while little information was recorded about pH, total
soluble solids (TSS), and total titratable acidity (TTA) in taro corm, leaf, and petiole. In
the current study, pH taro corm, leaf, and petiole were slightly above of 6.0, it can be
observed that the taro was in a good state of maturation and conservation since lower
pH values are better for the action of enzymes which degrade starch (Nardin, 2009).
The values for pH in taro corm in the current study were higher than those reported by
Feltran et al. (2004) in potato, while which were similar to those verified on potato by
Nardin (2009) and Fernandes et al (2010). In the current study, 20% ETc (7.0%) and
60% ETc (7.3%) showed higher TSS in taro corm compared with the other irrigation
treatments (Figure 3.4 d). In a study conducted by Robles (2003) who observed the
value of TSS ranged from 5.88 to 5.93% in potato. However, according to the
research of Pereira (1987), lower TSS is not indicative of poor corm quality. Little
variation was observed for TTA with respect to water regime, but higher variations
were observed between soil textures for taro corm and petiole. Sandy soil (SS)
showed higher TTA in taro corm and petiole, compared with that of CS and SCL
(Figure 3.4 g, i). Overall, higher water regime was more suitable for the behavior of
this variable, and SS may be more possible to get higher TTA under the same level of
74
irrigation treatment, which may affect ultimately the flavor of taro.
One of the most important components in taro corm is carbohydrates (Kaur et al.
2011). Starch as the main carbohydrate in taro corm, is also one of the most important
sources of carbohydrates in food and is gaining more and more attention because of
its health benefits (Bezerra et al., 2013, ). In the current study, starch content (SC)
ranged between 16% and 20%, TS ranged from 1.7% to 3.1%, PC varied from 1.5%
to 3.0%, which are similar to the investigation by Onwueme (1994), whereas higher
than those reported on taro by Kaur et al. (2011) and Himeda (2014). According to the
results in Table 3.5, worthy of note here is that higher water availability is more
beneficial to the accumulation of SC rather than that of PC. As with increase in water
regime, the PC reduced, whereas SC was increased in response to the augment of
water regime. In addition, SS had a positive effect on SC (Table 3.5). As a good
source of carbohydrate for infant weaning diets (Kaushal et al., 2015), the content of
carbohydrates and protein influence the quality and flours of taro corm. Experiments
conducted to clarify the relationships between the chemical composition and
consumers’ preferences indicate that taro corm with high dry matter and starch
content but with low total sugars are preferred (Lebot et al. 2004, 2011).
It is clear that the ADW, RDW, and CDW per plant were depressed by lower water
regimes. Similar results were reported by Mabhaudhi et al., (2013) and Bussell et al.,
(1998), they reported that taro leaf dry weight and corm dry weight were increased
with increase in irrigation level. In the present study, we got a higher CDW in sandy
soils (SS). It is well known that SS has a lower ability to hold water which leads to low
fertility as its light texture and loose structure. But with organic matter, sandy soil is
good for growing many varieties of vegetables and is well suited to tuber crops (Fry,
https://living.thebump.com/properties-sandy-soils-9588.html). The compost heap was
done twice during the experiment with 1.5 L of organic compost per pot (Table 3.3),
the application of organic compost may have a positive effect on the dry mass
accumulation of taro in SS. Corm humidity (CH) is very high and varies with variety,
growth condition, and harvest time. Generally, the moisture of taro corm ranges
75
between 63 and 85% (Kaushal et al., 2015). Results reported above demonstrated
that limited water availability resulted in reduced CH. CS had higher CH compared
with SCL and SS, which was also proved indirectly by the fact that SS obtained higher
SC and PC.
3.5 CONCLUSION
Results described here confirmed that irrigation treatment and soil texture
affected significantly on chemical composition behavior of taro corm. Higher water
regime had a positive effect on taro corm humidity, reducing sugars, starch content,
root dry weight, and corm dry weight, whereas had a negative effect on total soluble
solids, total titratable acidity, and protein content. In addition, sandy soil may be more
suitable to cultivate taro, as total soluble solids, total sugars, protein, starch content,
and corm dry weight were observed higher in this soil in comparison with the other soil
textures. Though the sandy soil also showed higher total titratable acidity content,
which is inadequate to the flavor of taro corms, that we can try to increase the water
regime to control the total titratable acidity content. Additionally, results of dry biomass
of taro proved again that higher water regime and sandy soil were more beneficial to
the growth of taro. Briefly, adequate control of water regime may improve the quality of
taro corm, and the application of sandy soil to cultivate taro may be a good way to
improve its quality under water limited conditions.
ACKNOWLEDGEMENTS
Funding for this research was provided in part from the Coordination of
Improvement of Higher Level Personnel(CAPES), Brazil. Thanks go to Marcos
Liodorio, João victor and Aline Gonçalves for the contributions in the experiment.
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81
FINAL CONSIDERATIONS
Taro growth, its corm production and corm quality response to irrigation level and
soil texture were discussed in the present study. Based on issues related to botany,
environmental requirement, and the importance of taro cultivation presented
throughout the general review, the canopy size (leaf number and leaf area), water-use
efficiency, and corm yield of taro were discussed in the first chapter; the plant height,
petiole diameter, fresh biomass, corm diameter, corm number, and harvest index of
taro were analyzed in the second chapter; and the analysis of chemical composition
and dry biomass of taro response to water regime and soil texture was done in the last
chapter.
With the results reported above, it is possible to conclude that, reasonably
controlling the amount of irrigation applied and correctly selecting the soil texture
should be key objectives for taro production. Doing so would be helpful to improve its
water-use efficiency, corm quality, and possibly corm yield. The taro physiological
parameters, yield parameters, and chemical composition parameters responded
differently to water regime and soil texture. It is evident that higher water regime
played a positive effect on growth and yield of taro, despite that water-use efficiency
was higher at 20% ETc, compared with the other irrigation treatments. It is not
necessary to applied irrigation level with 180% ETc, as higher water regime could
decrease water-use efficiency and protein content. In addition, 140% ETc was
observed to have the highest corm yield rather than 180% ETc as reported above. It is
considered to select soil texture correctly to guarantee taro yield and its corm quality
with less water applied. The response of taro chemical composition parameters to the
treatment in the present study was relatively irregular, it was not simply increased or
decreased with the increase or decrease in water regime. Additionally, there was no
one soil texture was more beneficial to all the chemical compositions parameters of
taro corm, whereas the sandy soil was observed to have higher total sugars, starch
content, and total soluble solids than the other two soils. Briefly, adequate control of
82
water regime may improve growth, corm yield, water-use efficiency, and corm quality
of taro. The application of sandy soil to cultivate taro may be a good way to improve its
quality under limited water availability conditions.
83
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