Project Leaders: Dan Schaefer, Illinois Fertilizer and Chemical Association; Jason Solberg, Illinois Fertilizer and Chemical Association; Eric Miller, Piatt County Farmer; Giovani Preza Fontes, University of Illinois

Purpose: In most corn-soybean rotations, fertilizer applications are typically made to maximize corn yields, with less consideration of its impact on soybean yields. This project tests how direct soybean fertilization affects yields and evaluates the potential return on investment compared to conventional soybean production.

Approach:  On-farm trials in central Illinois were conducted in 2023 and 2024 to test yield response to controlled-release N, P, K, and S fertilizers in a strip-till system. Products tested included controlled-release urea with a 140-day delay before release, along with potash, Mosaic Aspire, Mosaic MESZ, and pelletized gypsum. The trials also compared 15” and 30” row spacing. The plot followed an omission-style layout to evaluate each fertilizer’s contribution to yield. The treatments in 2024 were modified to add more combinations as a result of 2023 yield results. This study was funded by the Illinois Soybean Checkoff program.

Results:

• Row spacing and fertilizer had little consistent impact on soybean yields.
• In 2023, with a dry, warm spring, untreated 15” soybeans (95.4 bu/a) yielded highest compared to 30” regardless of fertilizer products (92.8-93.9 bu/a).
• In 2024, lowest yields came from untreated 15” soybeans (72.9 bu/a), while the two highest yields were from 15” rows (77.3 bu/a) and 30” rows (77.1 bu/a). Both had all fertilizer products. These were closely followed by the untreated 30” rows (76.5 bu/a).
• In 2024, April and May were very wet and prevented timely planting. This impacted yields, emphasizing the importance of planting as early as possible (April 1^st for Central Illinois).

 Key Takeaway: Use 15” rows and do not spend money for additional fertilizer if the soil tests are in the recommended range for pH, P1, and K.

Soybeans grown in 15” rows without fertilizer in 2023 yielded 2 bu/a more than fertilized soybeans in 30” rows. However, in 2024, the lowest yielding treatment was unfertilized soybeans grown in 15” rows.