High-Yielding Soybean: Genetic Gain x Fertilizer Nitrogen Interaction.

The U.S. and Argentina account for more than 50% of the global soybean production. Soybean yields are determined by the genotype, environment and management practices (G x E x M) complex interaction. An unanswered scientific knowledge gap is still related to the ability of the biological nitrogen (N) fixation (BNF) process to satisfy soybean N demand at varying yield levels. The overall objective of this project is to study the contribution of N via utilization of varying N strategies under historical and modern soybean genotypes. Three field experiments were conducted during the 2015-16 seasons: Ottawa (East Central KS, US), Ashland Bottoms (Central KS, US) and Oliveros (Argentina, herein termed as ARG). Different soybean genotypes were utilized (1990’s = non-RR, 2000’s = RR-1 and 2010’s = RR-2) in US and a wide-variety of historical non-RR and modern RR-1 genotypes in ARG, all tested under three N management strategies (S1 = non-N applied, S2 = all N provided by fertilizer, and S3 = late-N applied). At Ottawa, the study was planted in an area without previous soybean history with yields ranging from 1.4 to 2.1 Mg ha^-1. Modern genotype RR-2 increased 15% over the other varieties evaluated. As related to the N management approach, higher soybean yields occurred when N nutrition was based on S2 (10% increase). At Ashland Bottoms, yields ranged from 3.2 to 4.4 Mg ha^-1, where the oldest genotype (non-RR) increased yield by 13% over the rest. There was not statistical significance between N management strategies at this location. For both US sites, it can be concluded that the field where soybean has not been previously planted (Ottawa) had a lower yield capacity compared to the site with a soybean history (Ashland). At ARG, seed yield ranged from 3.0 to 4.6 Mg ha^-1, where modern cultivars (released after 2010) increased yield 34% over the rest. No interaction between release year and N fertilization strategy was observed. However, S2 increased seed yield by 5% over N fertilization strategies S1 and S3. In ARG, yield levels were similar to that in Central KS, but larger yields were observed with modern cultivars.