Update:
Farmers have raised concerns that test weight is on a long-term decline. In the early 1900s the test weight of soybean was standardized as 60lbs/Bushel, and it is still the standard today. The US Soybean Quality Annual Report, based on a four-year average from 2017-2020, reported the actual test weight of the US crop as only 56.7lbs/Bushel. Thus, low test weight is not just a problem for one particular growing region of the US, but for the entire US. Since lower test weight means less beans in a given volume, lower test weight can increase transportation and storage costs. In addition, lower test weight can decrease processing efficiency for the crushers and lead to inferior animal feed quality. So, as we begin working towards increasing test weight, improvements to protein and other nutritional factors could also be possible. The goal of this research is to identify management and genetic factors that can reverse the decline in test weight. We will determine the impact of increased test weight on seed protein content, nutritional quality, market value and develop breeding strategies which will simultaneously incorporate improved test weight and protein content into high yielding varieties. Over 500 breeding lines were evaluated in 2021 for test weight. Testing included multiple planting dates, multiple harvest dates and multi-state collaborations. Multiple planting and harvest dates were evaluated because seed quality, which may have an impact on test weight, is normally a concern based on how long mature plants remain in the field and when the plants matures. Often times unfavorable harvest conditions, i.e. increased rainfall, shorter day lengths and milder temperatures, occur later in the season. These tests included genotypes with a significant range of seed protein and oil (35-42% protein and 18-21% oil on 13% moisture basis) and substantial differences in seed sizes (7-20g per 100-seed). Harvest and data analysis of 2021 trials are on ongoing. A significant relationship between test weight and seed weight was reported from analyzing over 2,000 samples, test weight ranged from 54 lbs/Bu to 64 lbs/Bu. However, seed size was found only to contribute 13% of the variation in test weight. Protein was shown only to contribute 2% of the variation in test weight. This in contrast to what has been reported. These studies were conducted in two separate growing regions in the US. However, there does not appear to be a tradeoff between test weight and increasing protein, whereas there does appear to be a penalty when increasing oil above 20%. Further investigation is ongoing to determine what variation is due to genetics compared to environmental effects. The preliminary data does suggest that higher test weights are achievable no matter what your target seed composition. New populations are under development. In addition, our preliminary results suggest harvest date does impact test weight, but planting date does not significantly impact test weight. Also, sulfur treatments and planting densities did not affect test weight. However, drought stress did have a significant impact on test weight. Finally, a genome wide association study (GWAS) diversity panel, comprising of more than 300 MG 5 lines was selected based on seed composition traits, seed size and country of origin for analysis in 2021. This panel was planted in two replications under both irrigated and rain fed conditions. Test weights, protein and oil analysis, sugar content, amino acid and fatty acid composition will be measured once harvest is complete.