Applied Fertility Management for Irrigated Soybean Production

Although irrigated soybean yields in North Central Kansas have trended upward in recent years, producers in the area are largely unsatisfied with yield performance. Past research from the Kansas State University (KSU) North Central Kansas Experiment Field near Scandia demonstrated that more intensive fertility management, including direct application of P and K, has the potential to significantly improve irrigated soybean yield. Despite these findings soybean producers have been slow to adopt more intensive fertility management programs.

This project, initiated in 2012, seeks to expand upon previous soybean fertility work by performing both a small plot study and a farmer field strip trial to increase awareness of irrigated soybean yield potential with proper fertility management. The small plot work was conducted at the KSU Irrigation Experiment Field, and the field scale study on a producer’s field in the same region. Small plot treatments included a zero fertilizer control, and all combinations of 30 and 80 lb P₂O₅/A, and 80 and 120 lb K₂O/A. The effects of N and S were evaluated at the higher P and K rates.

Soil test P in the small plot study was low (6.9 ppm Bray 1), and K was high (542 ppm). The zero fertilizer control yield was 53 bu/A, and yield with fertilizer input ranged from 59 to 63 bu/A. The effect of fertilizer treatments over the control was significant, but there was no significant difference among the fertilizer treatments. The field scale design was simpler, with a zero fertilizer control, one P (30 lb P₂O₅) and one K (80 lb K₂O) rate and a combination of the two. Yield monitor data were collected by the grower, and at the time of this report were being processed. KS-41