Late-Season Nitrogen Applications Increase Soybean Yield and Seed Protein Concentration

Abstract

Low seed and meal protein concentration in modern high-yielding soybean [Glycine max L. (Merr.)] cultivars is a major concern but there is limited information on effective cultural practices to address this issue. In the objective of dealing with this problem, this study conducted field experiments in 2019 and 2020 to evaluate the response of seed and meal protein concentrations to the interactive effects of late-season inputs [control, a liquid Bradyrhizobium japonicum inoculation at R3, and 202 kg ha−1 nitrogen (N) fertilizer applied after R5], previous cover crop (fallow or cereal cover crop with residue removed), and short- and full-season maturity group cultivars at three U.S. locations (Fayetteville, Arkansas; Lexington, Kentucky; and St. Paul, Minnesota). The results showed that cover crops had a negative effect on yield in two out of six site-years and decreased seed protein concentration by 8.2 mg g−1 on average in Minnesota. Inoculant applications at R3 did not affect seed protein concentration or yield. The applications of N fertilizer after R5 increased seed protein concentration by 6 to 15 mg g−1, and increased yield in Arkansas by 13% and in Minnesota by 11% relative to the unfertilized control. This study showed that late-season N applications can be an effective cultural practice to increase soybean meal protein concentration in modern high-yielding cultivars above the minimum threshold required by the industry. New research is necessary to investigate sustainable management practices that increase N availability to soybeans late in the season.

Regional analysis of planting date and cultivar maturity recommendations that improve soybean oil yield and meal protein concentration

“…Lastly, seed and meal protein concentration showed the largest percentage of variability associated to random factors and to unaccounted sources of variation in our analysis ( Figure 2 ). Low repeatability in seed protein concentration is consistent with results by Dardanelli et al (2006) and suggests that other site-specific factors may be driving variation in seed and meal protein concentrations, such as soil fertility and management practices that affect crop N availability ( Bosaz et al, 2021 ; Chiluwal et al, 2021 ). However, we did find some significant effects and clear trends that provide new understanding on the interactive effect of planting date and cultivar maturity that can help increase oil yield and manage risk of deficient meal protein concentration.…”

“…Where Oil and Protein are concentration in mg g –1 of oil and protein in whole seeds with 130 mg g –1 moisture, respectively. This approach to estimate meal protein concentration was previously used by others (e.g., Mourtzinis et al, 2018 ; Chiluwal et al, 2021 ) and provided similar values compared to calculating meal protein concentration by subtracting oil concentration ( y = 0.9967x−2.7557, R 2 = 0.99) but 0.2–1.5% lower due to inefficiencies in the crushing and oil extraction process.…”

“…In the study by Alsajri et al (2020) , the relatively low seed oil concentration may be caused by fertilizing plants with inorganic N fertilizer throughout the study, which likely increased seed protein concentrations ( Figure 6B ). Chiluwal et al (2021) found that N fertilizer applications during seed growth increased seed protein and decreased seed oil concentration, compared to an unfertilized control.…”

Agronomic characteristics of soybean cultivars with late-season nitrogen application in supplementation to the inoculation of Bradyrhizobium spp.

“…In this sense, there is no way to generate a definitive and comprehensive conclusion on this agricultural practice. On the other hand, other research has shown that N fertilization can improve plant growth and soybean grain yield (Barranqueiro;Dalchiavon, 2017;Moreno et al, 2018;Chiluwal et al, 2021). Therefore, this agricultural practice can be a viable alternative in some soybean production systems, especially with late N application, to optimize grain filling and protein concentrations.…”

“…Late N application in supplementation to Bradyrhizobium spp. inoculation has been used by some Brazilian soybean farmers to increase soybean yield and grain protein concentration, especially in modern highyielding cultivars, which have low protein concentrations in their grains (Chiluwal et al, 2021). The importance of N availability to soybean during reproductive growth is indicated by its high rates of N accumulation in the seed during the grain filling phase (Hungria;Mendes, 2015;Moreno et al, 2018).…”