This Is AuburnElectronic Theses and Dissertations

Investigating Soybean Test Weights for Cultivar Development




Fett, Robert

Type of Degree

Master's Thesis


Crop Soils and Environmental Sciences


Soybean test weight is a characteristic that has recently become of interest to both plant breeders and growers. The official weight of a bushel of soybean is 60 lbs bu-1 (75.7 kg hL-1). This standard is used to convert the weight displayed on screen at grain elevator to calculate the number of bushels contained in a load. Typically, when the test weight falls below 54 lbs (68.4 kg), the grower may receive a discounted payment. Due to little information being available on the components of test weight and what measurement devices would be most accurate and efficient for a breeding program, further investigation was warranted. For this thesis; i) three test weight measurement devices; a Perten Aquamatic 5200, a Mini-GAC Plus, and a Volumetric Instrument were evaluated for both accuracy and efficiency and ii) an investigation of agronomic and seed components conducted to determine their effect on test weight. Data was collected and received from cooperators, who grew the 2019 and 2020 Southern Soybean Uniform Tests, conducted by the USDA. Analysis of genotype, environment, and genotype x environment were conducted and correlations with oil, protein, seed size and plant height to determine their effect on test weight. All three instruments were found to provide adequate test weight measurements, but the Volumetric is considered the most efficient when moisture and temperature measurements are not required. The results indicated a consistent negative correlation of oil and seed size with test weight across a range of cultivars and maturity groups. Average test weights were found to be consistently less than 75.7 kg hL-1, with some individual cultivars exceeding this target. Future studies should focus on further understanding the role and interactions of oil, protein, seed size, and seed weight to develop breeding strategies for maintaining test weights while improving yield.