Produtividade e qualidade do algodão em função da adubação nitrogenada sob restrição luminosa
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Data
2019-05-31
Autores
Raphael, Juan Piero Antonio [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
A limitação de luz reduz a produtividade do algodoeiro (Gossypium hirsutum L.). Não há, porém, indicações do efeito de doses de N sobre plantas nessa condição. O objetivo deste trabalho foi avaliar o desempenho agronômico da cultura do algodoeiro em função da adubação nitrogenada sob restrição luminosa. Quatro experimentos de campo foram conduzidos para avaliar a produtividade, os componentes de produção, a distribuição de capulhos e a qualidade da fibra durante os anos de 2016 e 2017 no Brasil: Primavera do Leste/MT (I); Itapeva/SP, em áreas não irrigada (II) e irrigada (III); e Chapadão do Sul/MS (IV). Nos experimentos III e IV, estudou-se também a precocidade das plantas a partir da distribuição da produção de capulhos segundo a escala fenológica. Em todos os experimentos, sombreamento foi imposto no início do florescimento, mantendo-se uma tela de cor preta (42% de redução de radiação global) sobre as plantas por um período entre 16 e 25 dias dependendo do experimento; e foram realizadas duas adubações de N em cobertura, uma durante a fase dos primeiros botões florais e outra no início do florescimento. Nos experimentos I, II e III, testaram-se as doses de N em cobertura de 0, 60, 120 e 180 kg ha-1 em combinação com presença ou ausência de sombreamento, em delineamento de blocos ao acaso em esquema fatorial 2 x 4. No experimento IV, os cultivares FM 983 GLT (de ciclo tardio) e EB 1405 GLT (de ciclo precoce) foram testados nas doses de N em cobertura de 0, 80 e 160 kg ha-1, na presença ou ausência de sombreamento, com delineamento de blocos ao acaso e esquema fatorial 2 x 3 x 2. O sombreamento diminuiu a produtividade de fibra em 10,1 e 11,6% nos experimentos I e IV, como resultado da redução do número de capulhos no terço inferior de 24,0 e 31,8%, respectivamente. No experimento II, não houve efeito do sombreamento sobre a produtividade final de fibra nem sobre a distribuição de capulhos nas plantas. No experimento III, as plantas foram muito responsivas ao N, e o sombreamento reduziu a produtividade de fibra apenas na ausência de adubação, em 10,0%, observando-se uma diminuição de 18,6% no número de capulhos no terço inferior. O sombreamento afetou a massa média de capulho apenas em Primavera do Leste, onde resultou em aumento de 5% e, em geral, não afetou de modo consistente a qualidade de fibra. A produtividade de fibra e o número de capulhos foram aumentados até as doses de N de 60 kg ha-1 (II), 80 kg ha-1 (IV) e 120 kg ha-1 (I e III). O aumento das doses de N reduziu o índice micronaire em todos os experimentos. No entanto, não foram observados resultados consistentes para comprimento, resistência, uniformidade de comprimento e índice de fibras curtas. No experimento IV, os cultivares precoce e tardio não diferiram entre si quanto à produtividade de fibra. No entanto, EB 1405 GLT apresentou, em média, 59,3% mais capulhos no terço inferior; e FM 983 GLT, 80,7 e 63,0% mais capulhos no terço superior nas doses de N de 80 e 160 kg ha-1, respectivamente. O genótipo tardio também apresentou fibras com maior comprimento e resistência. O estudo da precocidade revelou que o sombreamento aumentou os valores de posições fenológicas até a produção em caroço cumulativa de 10 e 30% nos experimentos III e IV, respectivamente, devido à forte redução do número de frutos nos primeiros sítios de frutificação, mas não influenciou a precocidade final. A precocidade, porém, foi reduzida pelo aumento da dose de N, devido à maior produção cumulativa em sítios de frutificação tardios. De modo geral, os efeitos negativos da restrição luminosa sobre a produtividade final foram maiores na ausência de N, indicando que a adubação nitrogenada possibilita compensações parciais ou totais das perdas iniciais. Esse padrão de resposta indica que a adubação insuficiente de N leva à capacidade mais restrita da planta de recuperar-se de perdas provocadas pelo sombreamento. Por outro lado, a adubação de N em doses suficientes para altas produtividades minimiza os riscos de perdas após período de limitação de luz durante o florescimento.
Light limitation decreases cotton (Gossypium hirsutum L.) yield. However, there are no reports of N fertilization effects on cotton plants under these conditions. The objective of this work was to evaluate the agronomic performance of the cotton crop as a function of N rates under light restriction. Four experiments were conducted in Brazil in 2016 and 2017 seasons: Primavera do Leste/MT (I); Itapeva/SP, in non-irrigated (II) and irrigated (III) areas; and Chapadão do Sul/MS (IV). In experiments III and IV, crop earliness was also studied from boll distribution data according to the phenological scale. In all experiments, shading was imposed at the early flowering phase by placing a black shade fabric (42% reduction in global radiation) on plant’s canopy for a period ranging from 16 to 25 days, depending on the experiment; and two topdressing N applications were made, the first at early squaring and the second at early flowering. In experiments I, II and III, N rates of 0, 60, 120 and 180 kg ha-1 in combination with or without shading were tested in complete randomized blocks arranged in a 2 x 4 factorial scheme. In experiment IV, the cultivars FM 983 GLT (late-cycle) and EB 1405 GLT (early-cycle) were subjected to N topdressing rates of 0, 80 and 160 kg N ha-1, with or without shading, in complete randomized blocks arranged in a 2 x 3 x 2 factorial scheme. Shading decreased lint yield by 10.1 and 11.6% in experiments I and IV, as a result of the reduction in boll number at the lower third of the plant by 24.0 and 31.8%, respectively. In experiment II, shading had no effects on lint yield and boll distribution. In experiment III, the plants were highly responsive to N, and the shade treatment reduced the number of bolls at the lower fruiting branches by 18.6%, but the respective effect in reducing lint yield was only verified at 0 kg N ha-1, by 10.0%. Shading affected the average boll weight only in Primavera do Leste, resulting in a 5% increase and, in general, did not have consistent effects on fiber quality. Lint yield and number of bolls were increased as a function of nitrogen rates up to 60 (II), 80 (IV) and 120 (I and III) kg ha-1. Increasing N rates reduced micronaire values in all experiments. However, results were inconsistent for length, strength, length uniformity and short fiber content. In experiment IV the early- and late-cycle cultivars did not differ from each other for lint yield. However, EB 1405 GLT showed an average increase in boll number at lower fruiting branches of 59.3%; and FM 983 GLT showed increases of 80.7% and 63.0% in boll number at the upper branches at 80 and 160 kg N ha-1, respectively. The late-cycle cultivar FM 983 GLT genotype also showed higher fiber length and strength values. The earliness study revealed that shading increased phenological position values up to 10 and 30% of accumulated seed cotton yield in experiments III and IV, respectively, due to the marked decline in the number of bolls at early fruiting sites, but did not affect the final crop earliness. However, earliness was decreased by high N rates due to higher cumulative yield at later fruiting sites. Overall, negative effects of light limitation on cotton yield seemed to be higher in the absence of N, indicating that nitrogen fertilization enables partial or total compensation of early-boll losses. Such response pattern indicates that insufficient N supply leads to a more restricted ability of the plant to recover from damages caused by shading. Conversely, N rates recommended for high yields minimize the risk of loss after a period of light limitation during the flowering phase.
Light limitation decreases cotton (Gossypium hirsutum L.) yield. However, there are no reports of N fertilization effects on cotton plants under these conditions. The objective of this work was to evaluate the agronomic performance of the cotton crop as a function of N rates under light restriction. Four experiments were conducted in Brazil in 2016 and 2017 seasons: Primavera do Leste/MT (I); Itapeva/SP, in non-irrigated (II) and irrigated (III) areas; and Chapadão do Sul/MS (IV). In experiments III and IV, crop earliness was also studied from boll distribution data according to the phenological scale. In all experiments, shading was imposed at the early flowering phase by placing a black shade fabric (42% reduction in global radiation) on plant’s canopy for a period ranging from 16 to 25 days, depending on the experiment; and two topdressing N applications were made, the first at early squaring and the second at early flowering. In experiments I, II and III, N rates of 0, 60, 120 and 180 kg ha-1 in combination with or without shading were tested in complete randomized blocks arranged in a 2 x 4 factorial scheme. In experiment IV, the cultivars FM 983 GLT (late-cycle) and EB 1405 GLT (early-cycle) were subjected to N topdressing rates of 0, 80 and 160 kg N ha-1, with or without shading, in complete randomized blocks arranged in a 2 x 3 x 2 factorial scheme. Shading decreased lint yield by 10.1 and 11.6% in experiments I and IV, as a result of the reduction in boll number at the lower third of the plant by 24.0 and 31.8%, respectively. In experiment II, shading had no effects on lint yield and boll distribution. In experiment III, the plants were highly responsive to N, and the shade treatment reduced the number of bolls at the lower fruiting branches by 18.6%, but the respective effect in reducing lint yield was only verified at 0 kg N ha-1, by 10.0%. Shading affected the average boll weight only in Primavera do Leste, resulting in a 5% increase and, in general, did not have consistent effects on fiber quality. Lint yield and number of bolls were increased as a function of nitrogen rates up to 60 (II), 80 (IV) and 120 (I and III) kg ha-1. Increasing N rates reduced micronaire values in all experiments. However, results were inconsistent for length, strength, length uniformity and short fiber content. In experiment IV the early- and late-cycle cultivars did not differ from each other for lint yield. However, EB 1405 GLT showed an average increase in boll number at lower fruiting branches of 59.3%; and FM 983 GLT showed increases of 80.7% and 63.0% in boll number at the upper branches at 80 and 160 kg N ha-1, respectively. The late-cycle cultivar FM 983 GLT genotype also showed higher fiber length and strength values. The earliness study revealed that shading increased phenological position values up to 10 and 30% of accumulated seed cotton yield in experiments III and IV, respectively, due to the marked decline in the number of bolls at early fruiting sites, but did not affect the final crop earliness. However, earliness was decreased by high N rates due to higher cumulative yield at later fruiting sites. Overall, negative effects of light limitation on cotton yield seemed to be higher in the absence of N, indicating that nitrogen fertilization enables partial or total compensation of early-boll losses. Such response pattern indicates that insufficient N supply leads to a more restricted ability of the plant to recover from damages caused by shading. Conversely, N rates recommended for high yields minimize the risk of loss after a period of light limitation during the flowering phase.
Descrição
Palavras-chave
Gossypium hirsutum L., Nitrogênio, Estresse luminoso, Fisiologia das plantas cultivadas, Nitrogen, Light stress, Crop physiology