Dynamics of nitrogen partitioning in a historical set of soybean cultivars

Abstract

Dynamics of nitrogen partitioning in a historical series of soybean cultivarsIn the soybean crop, nitrogen (N) is one of the most important nutrients. However, this element has been little explored in relation to changes that occurred in the species during the improvement and selection of cultivars. Thus, the aim of this study was to evaluate how soybean breeding in Brazil in the last 50 years has impacted soybean N accumulation, N partitioning to grains, and grain protein concentration. Two experiments were carried out, one in the field in two growing seasons (Experiment I) and the other in a greenhouse (Experiment II). Experiment I was conducted for two years, the 2016/2017 and 2017/2018 growing seasons, and Experiment II in one growing season. In both experiments a randomized block design was used. Seeds of representative cultivars launched in the period between 1965 and 2016 were obtained, and for Experiments I and II, 26 and 25 cultivars were used, respectively. In Experiment I the plants were sampled during the beginning of grains formation (R5) and at harvest (R8), while in Experiment II they were sampled when the plant was with 4 vegetative nodes (V4), at flowering (R1), in the beginning of pod formation (R3), in addition to R5 and R8. During crop growth, N accumulation in biomass, N concentration, N utilization efficiency, and N partitioning were evaluated. For Experiment I, N accumulation increased throughout the year of release of the cultivars (YOR) in plant and grain biomass while the residual N (remaining in the straw) decreased. The N concentration decreased in grains, biomass and residue along the YOR. There was a greater efficiency of N utilization in modern cultivars compared to older ones, and the ratio of nitrogen harvest index (NHI) to harvest index (HI) decreased with the YOR. For Experiment II, dry mass showed a positive trend for grains and biomass along the YOR and negative for the residue, the N accumulation showed the same trend as Experiment I but it was non-significant. The N concentration decreased along the YOR in grains and residue and increased slightly in biomass. The N utilization efficiency increased and there a negative relationship between the NHI:HI ratio and the YOR. Thus, it was concluded that there was an increase in the grain N content of more modern cultivars, but there was a more intense increase in the grain dry mass, which caused a dilution in the amount of total N present especially in the grain, a greater efficiency in use. of N and a smaller ratio between the NHI: HI and the YOR ratio.