Update:
Over 500 breeding lines were evaluated in 2020 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. Planting and harvest dates were approximately two weeks apart. Harvesting occurred approximately 1 week after maturity when the center row was harvested, then approximately 2 and 4 weeks later the right and left outside rows were harvested, respectively. All plots have been harvested and are currently being processed for test weight, moisture, seed size, seed quality, fatty acid content, protein, oil and amino acid content. These tests include genotypes with high protein or high oil and there is 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). As these seed traits can potentially impact test weight, the results from the study should be valuable for making improvements to test weight in soybean. In addition, test weight is being collected all Southern Uniform Tests and USB Diversity Tests grown by collaborators for test weight. We hope to have data collection complete by the end of the year and data analysis complete by the end of February. This study will be repeated in 2021.
Update:
According to the Soybean Seed Quality Report the average test weight in the US has fluctuated from 56.1 to 57.1 over the last three years, from 2018-2020. The variation in test weight is probably largely contributed to environmental conditions, but the overall decrease in test weight is likely due to genetics. Over 500 breeding lines were evaluated in 2020 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. Based on the results in MO in 2020, test weight was not affected by planting dates, either in clay soil or in loam soil for both MG 4 and MG 5. Planting date did not make any notable change in seed quality for both maturity groups. For yield, earlier planting showed higher yield in clay soil for both groups of soybeans but the result was inclusive for loam soil. However, the overall yield in clay soil was higher than loam soil in both group 4 (51 vs. 45 b/a) and group 5 (61 vs.53 b/a). In NC the largest test weight of 60lbs/Bu was recorded from a line with meal protein content of only 48% and a seed size of 6g per 100 seed. The lowest test weight of 56.2lbs/Bu was from a line with 47% meal protein and a seed size of 14g per 100 seed. However, a similar test weight of 56.8lbs/Bu was recorded for a line with 51% meal protein and a 14g seed size. The line with the highest meal protein content of 54% had a test weight of 59.1lbs/Bu and a seed size of 24.2g per 100 seed. In MN, test weight was measured on 2,238 samples from the regional trials and Minnesota statewide variety trials. There was substantial variation in test weight among samples, ranging from 63.4 to 54.5 lb/bu. Notably, average test weight of the samples was 59 lb/bu, and the median was also 59, meaning about half the samples had test weights below 59 lb/bu. There was a significant relationship, although it was weak, identified with seed size only explaining about 13% of the variation in test weight. We also plotted the relationship between protein and test weight, which was basically non-existent, with protein only explaining less than 2% of the variation in test weight. A similar result was found for protein+oil. These results suggest there is variation for test weight is independent of variation in seed size, protein, and oil. In AL, samples from a diversity panel of >300 lines have been sent off for oil and protein, amino acid and sugar profiles will have to be done in 2022 due to limited seed. In GA, DNA extraction has been completed for advance breeding lines varying in test weight, which will be used for genotyping with SoySNP6k Infinium chips. They are in the process to analyze the correlation of test weight with the seed composition, agronomic traits and yield. Once genotyping is completed, genome-wide analysis will be performed to understand the genetic control of test weight.
Update:
When talking with soybean producers about test weight, one common comment I receive is that with soybeans obtaining a test weight of more than 57 lbs/Bu is tough and often times it’s lower. The standard test weight for soybeans is 60 lbs/Bu. Ironically, obtaining a test weight of 57 lbs/Bu is common with corn, when the standard test weight for corn is 56 lbs/Bu. Determining what factors impact test weight and determining how to obtain a test weight of 60 lbs/Bu in soybean is the premise of this project. Planting in 2021 is almost complete. Extreme weather conditions have caused a few delays in planting. In 2021, we will be evaluating ~500 breeding lines varying in seed size and composition across a wide range of environmental conditions. Multiple harvest and planting dates will be evaluated. In NC and AL we are growing two tests that will harvested at three different dates, a repeat of what was grown in 2020. The first harvest date will be 1-2 weeks after the plants reach maturity and subsequent harvests will be delayed by 2-3 weeks. In these two tests, lines vary in protein and oil content, seed size and genetic diversity. In 2020, the difference in test weight between the first harvest date and the last harvest date varied. In general test weight ranged from 56-58 lbs/Bu, with extremes of 55 and 60 lbs/Bu. Most lines in the test were able to maintain test weight across harvest dates, but for some of the lines test weight decreased significantly. Interestingly, the data suggests that test weight can vary for high protein lines and for both large and small seeded lines. Also, the average yield decline across harvest dates in AL was 90%, with some lines only yielding 60% on the third harvest date compared to the first harvest date. In NC, the average yield reduction was 70% across harvest dates, with some lines decreasing in yield by 50% on the third harvest date compared to the first harvest date. In MO, a total of 33 Missouri elite breeding lines of MG4 and MG5 and one Mississippi soybean line have been included in two separate tests. The tests have been planted using two planting dates, 20-30 days apart in two locations/soil conditions. In AL, a diversity panel, evaluating differences in test weight and seed composition, was planted. Collaborative tests with MO and NC were also planted. A graduate student will join the program in August and will take on the TW harvest date trials and relationship between TW and seed composition. In GA, analyses of test weight, seed composition, and seed size is complete and once a new model is developed it will be used to normalize the test weight to a standard 13% moisture basis. Fifty new elite advanced lines with diverse pedigrees were selected for planting at two different planting dates. Test weight, seed composition and agronomic trait data will be collected. DNA extraction was done using SoySNP6k Infinium chips and SNP allele calls are currently being completed. Once completed, genome-wide analyses will be performed to understand the genetic control of test weight.