Manejo da adubação nitrogenada no algodoeiro cultivado em sistemas de rotações de culturas

Abstract

No-tillage is essential to enable agricultural production in sandy soils with low fertility, and in these environments, in addition to water restriction, the low N content in the soil limits crop yields, especially when there is rotation with grasses. high C: N ratio with non-leguminous crops, such as cotton. As a result, a field trial was conducted for two seasons (2018/2019 and 2019/2020) in order to evaluate the dynamics of nitrogen (soil / plant) and the yield of cotton in production systems with different crop rotations, doses and sources of mineral N. Crop rotation systems were implemented in 2016, and consisted of the absence of cover crops and combinations of grasses and legumes, single or in consortium. Three doses of N (70, 100 - recommended dose - and 130 kg ha-1) and two sources of N (conventional urea and controlled-release urea) were used. The use of controlled-release urea associated with a greater diversity of cover crops in the off-season resulted in higher yield and quality of cotton fiber, without the need to increase nitrogen fertilization in systems with cover crops, but in fallow it was necessary to increase fertilization. 30% in the year with high productive potential. The increase in the dose of N increased the concentration of bolls and yield in the upper part, reducing the precocity of the plant, mainly in systems with legumes, in addition to the controlled-release urea improving the yield allocated in the upper plant. Cover crops and controlled-release urea increase the N stock in the soil and reduce the leaching of inorganic nitrogen, and although higher doses of N increase the N stock in the soil, they also increase leachate losses. The greater diversity of cover crops and moderate dose of N improves the microbial activity of the soil, and the glomalin content is higher after the use of grasses associated with the recommended dose of N. Our results show that there is no need to increase nitrogen fertilization in cotton in this production environment, and as long as cover crops are used, controlled-release urea can be an ally to improve N efficiency in the soil-plant system and reduce the use of nitrogen fertilizer.