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ARS Home » Southeast Area » Raleigh, North Carolina » Soybean and Nitrogen Fixation Research » Research » Research Project #445344

Research Project: Determining the Causes of Declining Test Weight of Soybean and Utilizing Breeding to Increase Test Weight

Location: Soybean and Nitrogen Fixation Research

Project Number: 6070-21220-070-039-R
Project Type: Reimbursable Cooperative Agreement

Start Date: Oct 1, 2023
End Date: Sep 30, 2024

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/bu, and it is still the standard today. According to the U.S. Soybean Quality Annual Report, based on a four-year average from 2017-2020, the actual test weight of the crop is now only 56.7lbs/bu. Since lower test weight means fewer beans in a given volume, lower test weight decreases processing efficiency for crushers and can lead to inferior animal feed quality. So, research on increasing test weight may also improve seed composition traits, e.g., protein and oil contents. The goal of this research is to identify what factors impact test weight and how to obtain a test weight of 60lbs/bu in soybean. We will determine the impact of increased test weight on seed protein and oil contents, nutritional quality and develop breeding strategies which will simultaneously incorporate improved test weight and optimum protein and oil contents into high yielding varieties. Objectives to which ARS investigator will contribute: 1. Develop new breeding lines with increased test weight and high yield. 2. Implement coordinated multi-state trials to determine the impact of genetics and geography on test weight using an array of extreme soybean types and extreme environments. 3. Determine the relation of test weight to seed size, seed quality, protein and oil content, sucrose concentration and yield.

Objective 1: Initial crosses involving elite breeding lines and lines with high test weight were made in 2022 and were advanced from F1 to F2 in a winter nursery in Puerto Rico. Then in the summer of 2023, F2 seed will be advanced in NC using the modified single seed descent breeding method and advanced from F3 to F4 at a winter nursery. Selection will begin in 2024 based on visual agronomic performance and test weight. Additional crosses will be made in 2023 and 2024 to improve test weight, while also improving seed protein and sucrose content. New material will be incorporated into the breeding process as new sources of high test weight are identified. Objective 2: In NC and AL two tests will be grown in 2024 that will be harvested at three different dates. 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 will be included that vary in protein and oil content, seed size and genetic diversity. Each test will consist of 26 USDA elite breeding lines and 4 yield checks and will be evaluated for yield, seed size, seed quality, sucrose content and test weight across 3 replications. Test weight will be analyzed using a Grain Analysis Computer (GAC 2500-UGMA). Sucrose content will be measured using HPLC. The same two tests will be grown in 2023. Objective 3: We will investigate maturity group (MG) V-VIII USDA breeding lines with high protein or high oil, providing a significant range of seed protein and oil (35-42% protein and 18-21% oil on a 13% moisture basis). Also, genotypes will be evaluated that have substantial differences in seed sizes (13 – 18g per 100-seed). All lines will be evaluated in replicated yield trials. For evaluation in 2024 all lines will be planted in 12’ 4-row plots with 4 replications. After harvest a GAC 2500-UGMA will be used to assess test weight. Seed oil and protein content will be analyzed with a Perten 7250 Near Infrared Reflectance (NIR).