Capim marandu sob lâminas de irrigação e doses de nitrogênio: resposta agronômica e simulação do rendimento de forragem usando o modelo cropgro-perennial forage
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Data
2018-06-27
Autores
Santos, Miquéias Gomes dos [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
As pastagens representam a alternativa de maior viabilidade econômica para a alimentação de bovinos. Ainda assim, o desempenho da pecuária no Brasil é relativamente baixo, em função do manejo agrícola e planejamento agronômico inadequados das gramíneas tropicais. A exploração racional de pastagens requer cuidados principalmente quanto ao fornecimento de água e nutrientes em quantidade e proporção adequadas às plantas. A tomada de decisão quanto à adoção do manejo das pastagens pode ser auxiliada pelos modelos de simulação de culturas, capazes de gerar um grande número de informações de modo instantâneo. Neste contexto, objetivou-se quantificar a resposta de produção de massa seca e do valor nutritivo da forragem de Urochloa brizanta (Syn. Brachiaria brizantha) cv. Marandu, em função da aplicação de irrigação e de nitrogênio no nordeste do estado de São Paulo e, utilizando estes dados, testar o desempenho do modelo CROPGRO-PF em simular a produção de forragem e os balanços de água e nitrogênio da cultura. O estudo foi conduzido de setembro de 2015 a setembro de 2017. Os tratamentos incluíram cinco estratégias de aplicação de irrigação, correspondentes às reposições de 14, 44, 81, 115 e 132% da evapotranspiração máxima da cultura, combinadas com três estratégias de aplicação de nitrogênio, correspondentes às aplicações de 7,5, 15 e 30 kg ha-1, a cada tonelada de massa seca produzida. As respostas foram mensuradas durante os períodos primaveraverão e outono-inverno. O aumento da adubação nitrogenada de 7,5 para 30 kg N ha- 1 , propiciou incremento na produção de forragem na primavera-verão de 2016/2017, de cerca de 14000 para 19000 kg MS ha-1. Do mesmo modo, no outono-inverno a maior produção de forragem se deu com a estratégia de 30 kg N ha-1. O aumento da adubação nitrogenada de 7,5 para 30 kg N ha-1 também aumentou o teor de proteína bruta de 16,5% para 17,6%, de 11,8% para 19,0%, e de 12,1% para 15,7%, na primavera-verão 2015/2016 e 2016/2017, e outono-inverno de 2016, respectivamente. Além disso, proporcionou maior produtividade da água e conteúdo relativo de clorofila, entretanto, reduziu a relação folha/colmo na primavera-verão. O incremento da disponibilidade hídrica durante o outono-inverno conferiu maior produção de forragem, com aumento médio de 7716 para 10277 kg MS ha-1 em 2016, e de 4451 para 6171 kg MS ha-1 em 2017, nos tratamentos com menor e maior irrigação, respectivamente. Na primavera-verão a irrigação não propiciou aumento da produção de forragem. Independentemente do período de avaliação, o aumento da irrigação reduziu a produtividade da água. A combinação entre a adubação nitrogenada e irrigação aumentou a produção de forragem e, consequentemente, diminuiu o efeito da sazonalidade. O modelo CROPGRO-PF é capaz de simular adequadamente o crescimento do capim Marandu sob estratégias de irrigação e de adubação nitrogenada. A concordância entre as simulações e as observações de umidade do solo também demonstrou a boa performance do modelo. A parametrização dos dados de entrada do modelo mais importante consistiu na calibração da reserva de carbono passivo do solo, de grande importância para à resposta ao N, além das características de retenção de água do solo que afetaram a resposta de irrigação.
The pastures represent the most economically viable alternative for cattle feed. Nevertheless, the performance of livestock in Brazil is relatively low, due to inadequate agricultural management and agronomic planning of tropical grasses. Rational exploitation of pastures requires care primarily in providing water and nutrients in a quantity and proportion appropriate to plants. Decision-making regarding the adoption of pasture management can be aided by crop simulation models capable of generating a large number of information instantaneously. In this context, the goal of this study was to quantify the response of dry mass production and nutritive value of the forage of Urochloa brizanta (Syn. Brachiaria brizantha) cv. Marandu to irrigation and nitrogen applications in the northeast region of the state of Sao Paulo, and with base on this data, to test the performance of the CROPGRO-PF model in simulating forage production and the water and nitrogen balances of the crop. The study was conducted from September 2015 to September 2017. The treatments corresponded to five irrigation strategies, corresponding to replenishment of 14, 44, 81, 115 and 132% of the maximum crop evapotranspiration, combined to three nitrogen application strategies, corresponding to applications of 7.5, 15 and 30 kg ha1 , for each ton of dry mass produced. Responses were measured during the springsummer and fall-winter periods. The increase in nitrogen fertilization, from 7.5 to 30 kg N ha-1 , promoted an increase in forage accumulation in the spring-summer of 2016/2017, from approximately 14000 to 19000 kg DM ha-1 . Likewise, in the autumnwinter period the highest forage production occurred with the strategy of 30 kg N ha-1 . The increase in nitrogen fertilization from 7.5 to 30 kg N ha-1 also raised the mean crude protein content from 16.5% to 17.6%, from 11.8% to 19.0%, and from 12.1% to 15.7%, in the spring-summer 2015/2016 and 2016/2017, and autumn-winter of 2016, respectively. In addition, it provided higher water productivity and relative chlorophyll content in both periods, however, it reduced leaf/stem ratio during the spring-summer. During the autumn-winter period, the increase in irrigation levels resulted in a higher forage production, with an increase from 7716 to 10277 kg DM ha-1 in 2016, and from 4451 to 6171 kg DM ha-1 in 2017. In the spring-summer period irrigation did not increase forage production. The increased irrigation reduced water productivity in all periods. The combination between nitrogen fertilization and irrigation raised the forage production, and consequently, reduced the seasonality effect. The CROPGRO-PF model can be used to simulate adequately growth of Marandu palisadegrass under different management of irrigation and N fertilization. The close agreement between simulations and field-observed soil moisture also demonstrated the good performance of the water balance module of DSSAT. The more important parameterization consisted of calibrating inputs, such as the stable soil carbon pool , which is important for accurate simulation of N response, and calibrating the soil water holding characteristics of the soil, which affected the irrigation response.
The pastures represent the most economically viable alternative for cattle feed. Nevertheless, the performance of livestock in Brazil is relatively low, due to inadequate agricultural management and agronomic planning of tropical grasses. Rational exploitation of pastures requires care primarily in providing water and nutrients in a quantity and proportion appropriate to plants. Decision-making regarding the adoption of pasture management can be aided by crop simulation models capable of generating a large number of information instantaneously. In this context, the goal of this study was to quantify the response of dry mass production and nutritive value of the forage of Urochloa brizanta (Syn. Brachiaria brizantha) cv. Marandu to irrigation and nitrogen applications in the northeast region of the state of Sao Paulo, and with base on this data, to test the performance of the CROPGRO-PF model in simulating forage production and the water and nitrogen balances of the crop. The study was conducted from September 2015 to September 2017. The treatments corresponded to five irrigation strategies, corresponding to replenishment of 14, 44, 81, 115 and 132% of the maximum crop evapotranspiration, combined to three nitrogen application strategies, corresponding to applications of 7.5, 15 and 30 kg ha1 , for each ton of dry mass produced. Responses were measured during the springsummer and fall-winter periods. The increase in nitrogen fertilization, from 7.5 to 30 kg N ha-1 , promoted an increase in forage accumulation in the spring-summer of 2016/2017, from approximately 14000 to 19000 kg DM ha-1 . Likewise, in the autumnwinter period the highest forage production occurred with the strategy of 30 kg N ha-1 . The increase in nitrogen fertilization from 7.5 to 30 kg N ha-1 also raised the mean crude protein content from 16.5% to 17.6%, from 11.8% to 19.0%, and from 12.1% to 15.7%, in the spring-summer 2015/2016 and 2016/2017, and autumn-winter of 2016, respectively. In addition, it provided higher water productivity and relative chlorophyll content in both periods, however, it reduced leaf/stem ratio during the spring-summer. During the autumn-winter period, the increase in irrigation levels resulted in a higher forage production, with an increase from 7716 to 10277 kg DM ha-1 in 2016, and from 4451 to 6171 kg DM ha-1 in 2017. In the spring-summer period irrigation did not increase forage production. The increased irrigation reduced water productivity in all periods. The combination between nitrogen fertilization and irrigation raised the forage production, and consequently, reduced the seasonality effect. The CROPGRO-PF model can be used to simulate adequately growth of Marandu palisadegrass under different management of irrigation and N fertilization. The close agreement between simulations and field-observed soil moisture also demonstrated the good performance of the water balance module of DSSAT. The more important parameterization consisted of calibrating inputs, such as the stable soil carbon pool , which is important for accurate simulation of N response, and calibrating the soil water holding characteristics of the soil, which affected the irrigation response.
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Palavras-chave
DSSAT, Urochloa brizantha, Adubação nitrogenada, Disponibilidade hídrica, Estacionalidade, Simulação