Effect of Long-term Nitrogen, Phosphorus and Potassium Fertilization of Irrigated Corn and Grain Sorghum

This western Kansas study was initiated in 1961 to determine responses of continuous corn and grain sorghum grown under flood irrigation to N, P and K fertilization. No yield benefit to corn from K fertilization was observed in the first 30 years, and soil K levels remained high so the K treatment in the corn study was discontinued in 1992 and replaced with a higher P rate.

This research continues to show that P and N fertilizer must be applied to optimize production of irrigated corn and grain sorghum in western Kansas. When averaged across the past eight years, corn yields were increased more than 100 bu/A by N and P fertilization, up to 90 bu/A in 2000. Application of 160 lb

N/A generally is sufficient to maximize yields. At this N rate, 80 lb P₂O₅/A increased yield by about 60 bu/A in 2000. Application of 40 lb P₂O₅/A has been adequate for corn until this year, when yields were increased by the higher P rate. Grain sorghum yields averaged across eight years were increased 50 bu/A by N and 20 bu/A by P fertilization. Application of 80 lb N/A was sufficient to maximize yields in most years. At this N rate, 40 lb P₂O₅/A increased yield by 31 bu/A in 2000. Potassium fertilization had no effect on sorghum yield. This project has generated excellent long-term yield response and environmental data that have been used extensively. KS-23F