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Efficiency of nitrogen fertilization in the soil-soybean system in tropical and subtropical environment

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Author(s):
Clovis Pierozan Junior
Total Authors: 1
Document type: Doctoral Thesis
Press: Piracicaba.
Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
Defense date:
Examining board members:
José Laercio Favarin; Heitor Cantarella; Jackson Kawakami; Paulo Sergio Pavinato
Advisor: José Laercio Favarin
Abstract

The soybean yield in the world has been increasing for decades, due to the cultivation techniques, the cultivars, and the advancement of science in improving the biological nitrogen fixation (BNF), nutrient required in large quantities for soybeans. There is hypothesis that the quantity of nitrogen (N) provided by the BNF and soil are not enough to continue to increase yields today achieved (3 Mg ha-1), or N would be the limiting factor for soybeans. This hypothesis is reinforced when we consider that soybean cultivation is carried out in soils with low N supply, and suboptimal conditions for BFN. In this scenario, it would be the use of nitrogen fertilizer to supplement the soybean demand for N? The demand of N by soybeans may even be supplemented via fertilization. However, it only makes sense if there is (NUE) o damage to the BFN, a process that should always be prioritized. Many experiments with supply of mineral N have been conducted. Some tested negative, others positive. Producers are also conducting nitrogen fertilization in soybean, without proper knowledge of the subject. This study aimed to evaluate the production of soybean response, and understand the reaction of the plant to nitrogen fertilization, with regard to the use of N fertilizer and its influence on BFN. For that, two years of experiments were performed in tropical environment (Cerrado, Mato Grosso) and subtropical (southern state of São Paulo). The experimental variation sources were nitrogen rates, and fertilizer application times, using N marked with the 15N isotope. The application of nutrients has been tried in the soil, and also in soybean leaves. Verified productive soybean response to the supply of N in the Cerrado where the amount of N available to the crop is low. However such response is achieved under certain environmental conditions or N supply is no guarantee production increase, and the response is uncertain. The BFN is reduced, if not in absolute terms (kg ha-1 de N fixed by FBN), in percentages (% of N at plant from atmosphere). The total N extraction was always higher with fertilization in R3, and the Cerrado environment the application at this stage caused increased yeld, but only in one crop season. Increasing Number of shoot with the application in R3 in Primavera do Leste, accompanied the increase in productivity, but this increase was not caused by N fertilizer (Ndff). The N use efficiency showed values close to 50% and was similar between the two N application timing in both environments. In the tropical environment NUE decreased with increasing N rate. In subtropical environment NUE was constant. The supply of leaf N did not increase productivity, although the NUE is high, averaging 64%. (AU)

FAPESP's process: 13/06515-2 - NITROGEN FERTILIZATION EFFICIENCY ON SOIL-SOYBEAN SYSTEM IN TROPICAL AND SUBTROPICAL ENVIRONMENT
Grantee:Clovis Pierozan Junior
Support Opportunities: Scholarships in Brazil - Doctorate