Potencial de produtividade em soja limitada por nitrogênio em ambiente subtropical

Abstract

Soybean ia a key crop in world agriculture, being the second largest supplier of vegetable oil for human consumption and the main source of protein, about 40%, to feed animals and people. Rio Grande do Sul, located in Southern Brazil, is the third largest soybean producer, with approximately 17% of national production. Meeting the demand for soybean in the existing agricultural area for a global population of 9.7 billion people by the year 2050 implies closing the gap between average production and production potential (PP). Thus, for pursuit of crop PP, nitrogen (N) availability cannot be a limiting factor, as it is an essential element for most crops, as it is a constituent of several molecules important for their development. As Brazil is the 2nd largest soybean producer world wide, studies with new methodologies in Brazil that aim or increase the studies, as or what it does, comes a new limit of knowledge about Nitrogen fertilization in Brazil. The objective of this study was to determine if nitrogen is a limiting factor for high soybean yields in the Subtropical environment of Brazil. Following the a curve of N uptake by soybean, N (as urea) was applied at 5 times: V2, V4, R1 R3 and R5. The experiments were carried out during the 2017/2018 and 2018/2019 grpwing seasons in soybean crops with high production potential in the counties of Cruz Alta, Júlio de Castilhos, Santa Maria, Uruguaiana and Pelotas, in the State of Rio Grande do Sul. The results showed that cultivars with GMR ≤ 5.5 had the highest yields with applied N. Cultivars with GMR > 5.5 did not respond to aplied N. Protein contetn in the grains were higher where N is applied, especially in the environments with the lowest yields. The oil content was little affected and slightly, decreased with protein content increase in the grains. This study selected a framework for assessing nitrogen limitations in soybeans with different relative maturity groups. In the present study, we followed a nitrogen fertilization protocol, ensuring that N was not limited to a potential soybean potential. The protocol was implemented with several GMRs that represent the majority, as well as most used in the state of Rio Grande do Sul.