As soybean [Glycine max (L.) Merr.] yields reach record highs, more nutrients are required to maintain these production levels. This study was conducted to evaluate the effect of S and N on soybean yield in diverse environments across the United States. Data were collected from a total of 52 sites in 10 states over 2 yr (2019 and 2020) for this study. A factorial arrangement of three S rates (11, 22, and 33 kg S ha −1 ) using two sources (ammonium sulfate [AMS] and calcium sulfate [CaSO 4 ]) were broadcasted by hand at planting. Additionally, to examine the impact of N on soybean yield, urea was applied at 10, 20, and 29 kg N ha −1 to equal that supplied by AMS. A zero-fertilizer control treatment was also included. Soil samples prior to fertilization as well as grain yield at R8 were collected and analyzed to understand what environmental conditions favor soybean response to S additions. Results

Soybean is widely recognized as a valuable crop and plant protein source due to its ideal amino acid profile. However, deficient methionine content in soybean seeds limits the nutritional utility. Therefore, a genome-wide association study (GWAS) utilizing 311 soybean accessions from maturity groups IV and V was performed alongside genomic prediction models to determine genetic underpinnings and breeding potential. Additionally, sulfur fertilization source and rate were evaluated for their impact on methionine content in soybean seeds. Across four environments, 23 novel single nucleotide polymorphisms (SNPs) were identified as being associated with methionine content, and average prediction accuracy (r2) ranged from 0.03 to 0.62 for genomic prediction models. Across six locations, soybean plots treated with ammonium sulfate (AMS) exhibited statistically increased methionine content when compared to other sulfur fertilizers. When combined, these results highlight the complex genetic and environmental controls for methionine content in soybean seeds and will positively contribute to protein quality improvement in soybean.

As United States farmers adapt soybean (Glycine max) production methods from oilseed to vegetable (edamame), key management practices will need to be considered. The key objective of this study was to determine the optimal nitrogen (N) rate and N application timing for edamame in the mid-Atlantic coastal plain system. The study was conducted for three years in Painter, VA, USA on sandy loam soils. A factorial arrangement of four N rates was applied with two application timing strategies: at-planting, and split application. Leaf tissue samples were collected and analyzed at R1. At harvest, the Normalized Difference Vegetation Index (NDVI) was measured, whole pods were mechanically collected, and yield was recorded. Additionally, pod and bean physical and chemical quality were assessed. Nitrogen fertilization significantly increased pod yield in two out of three years. R1 leaf N and sulfur (S) concentrations correlated to the yield, and R1 leaf and R6 whole-plant N concentrations correlated to the total N uptake. None of the tested parameters indicated that N fertilizer decreased yield or quality. In conclusion, we found that N fertilizer applied at planting may aid edamame yield and profit for sandy loam soils in the mid-Atlantic, USA.