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Soybean Seed Protein Concentration: Current Status and Way Forward Dr. Anuj Chiluwal, Assistant Professor of Agronomy, Kentucky State University

Soybean (Glycine max [L.] Merr.) is the main source of protein in livestock and poultry feed in the world. Soybean meal, which is a by-product after oil extraction from its seed is used for protein source in most of the poultry and livestock farms in the U.S. and all around the world. The U.S. National Oilseed Processors Association has set a minimum threshold of 44% protein concentration in non-dehulled soybean meal for high quality animal feed to support proper growth and development of poultry and livestock (NOPA, 2024). Soybean seed with 18 - 19% oil concentration (average oil concentration in the U.S. soybean seed) should contain 34 - 35% protein concentration to produce a meal with 44% protein concentration. Soybean yield in the U.S. has gradually increased over the past few decades but consistent decline in seed protein concentration has also occurred during the same period. Average soybean yield in the U.S. was 3412 kg/ha in 2024 after gradually increased from 2241 kg/ha in 1986 (Figure 1). However, in the meantime seed protein concentration has steadily decreased from 35.8% in 1986 to 34% in 2024 (Figure 1). Due to the constant decline in soybean seed protein concentration over the years, soybean meal produced in some U.S. locations is struggling to meet the high-quality animal feed standard. Soybean produced in northern U.S. states contains comparatively less seed protein concentration than southern states. As a result, recent soybean seed produced in some northern states in the U.S. is struggling to produce high quality soybean meal (Chiluwal, 2025). If the trend of declining soybean seed protein concentration continues, it could be a widespread problem across the nation in the future. Therefore, the declining seed protein concentration has become one of the concerns for the U.S. soybean industry. The U.S. is the second largest soybean exporter in the world hence it is important to improve soybean seed protein concentration to make U.S. soybean competitive in the global feed market.

widespread problem across the nation in the future. Therefore, the declining seed protein concentration has become one of the concerns for the U.S. soybean industry. The U.S. is the second largest soybean exporter in the world hence it is important to improve soybean seed protein concentration to make U.S. soybean competitive in the global feed market.

Soybean obtains nitrogen (N) from two sources – inorganic N from the soil and organic N from the biological N fixation. Soybean requires a very high dose of N during its seed filling stage. Soil inorganic N will mostly be depleted when soybean reaches seed filling stage and crops rely heavily on biological N fixation. Under the high-yielding environments, only biological nitrogen sources alone may not be able to meet the high N demand during the seed filling phase. As a result, low soybean seed protein concentrations are more common under high yielding environments. Recent studies have shown N limitations during seed filling phase as the major reason for declining soybean seed protein concentration in modern high yielding cultivars (La Menza et al., 2017; Ortez et al., 2018; Chiluwal et al., 2021).