Soybean Items of Interest No. 2--July 2025
An article titled Economic considerations of in-season potassium applications to soybean using payoff matrices by Univ. of Arkansas researchers providEs the following information.
• The response of irrigated soybean to in-season potassium [K] application was evaluated in field trials that were conducted for 3 years [2021-23] on sites with silt loam soils in Arkansas.
• Varying levels of soil test K [STK] were selected among sites in the study. Phosphorus [P] fertilizer was applied preplant to sites testing below about 40ppm in soil test P to ensure no P deficiency.
• Applications of 0, 33.2, 66.5, 99.6, and 133 lb/acre of granular K fertilizer were made within 2 days of 15, 30, and 45 days after first soybean bloom [DAR1].
• Leaf tissue analysis was used to assess K status of plants to determine the level of K deficiency that may have occurred.
• Economic analyses were performed for the 15 and 30 DAR1.
• Significant yield increases were measured at both the 15 and 30 DAR1 sample times when granular K fertilizer was applied to severely K-deficient soybean as indicated by leaf-K concentration.
• Producers can collect leaf samples to measure leaf-K concentration and use this information to determine if in-season K fertilization is needed.
• The decision to apply in-season K will be affected by both K fertilizer price and soybean commodity price. In this study, the yield increase that resulted from in-season K addition made the additional input cost of K fertilizer a sound investment. The most profitable scenario was when 66 lb/acre of K was applied to deficient plants.
• Producers can use the payoff matrices in this article as a decision support tool to make an informed decision about whether or not adding in-season K fertilizer to K-deficient soybean will increase profitability.
Click here to access a White Paper that provides details about tissue testing, and here to access a White Paper that provides critical values for soil and tissue nutrient levels for soybean.
In an article titled Soybean yield is positively linked to organic matter, but planting date remains more influential, the following information is provided.
• A study was conducted for 3 years [2019-21] using soil samples collected from 457 producer-managed fields in Arkansas, Michigan, North Carolina, and Wisconsin to assess the relationship between soybean yield and soil health indicators that included soil organic matter [SOM].
• According to models used in the study, SOM, soil test K, and planting date were significant factors in determining soybean seed yield.
• Of the indicators evaluated in this research, planting date was the most influential factor associated with seed yield.
• The authors concluded that 1) improvement in soybean yields is linked to higher SOM and early planting, 2) building/protecting SOM and soil organic carbon will likely aid in protecting future soybean yields from the occurrence of increasingly erratic weather, and 3) increasing and/or stabilizing soybean seed yield with increased SOM should be an incentive for producers to adopt practices that will increase this soil health parameter.
Composed by Larry G. Heatherly, July 2025, larryh91746@gmail.com