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

This long-term western Kansas study was initiated in 1961 to evaluate responses of irrigated continuous corn and grain sorghum to nitrogen (N), phosphorus (P), and potassium (K) fertilization. Furrow irrigation was used through 2000, and sprinkler irrigation since 2001. 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. Nitrogen treatments for corn and grain sorghum were 0, 40, 80, 120, 160, and 200 lb N/A. Phosphorus treatments for corn and grain sorghum were 0, 40, and 80 lb P₂O₅/A, and 0 and 40 lb P₂O₅/A, respectively. The K treatments for grain sorghum were 0 and 40 lb K₂O/A.

This project continues to show that P and N fertilizer inputs are critical to the optimization of irrigated corn and grain sorghum production in western Kansas. Corn yields in 2004 were considerably higher than the 10-year average. Nitrogen alone increased corn yield in 2004 by as much as 95 bu/A, while N and P applied together increased yield by up to 173 bu/A. Historically, 160 lb N/A has been the economic optimum N rate for corn. However, 120 lb N/A was required to obtain greater than 95% of maximum yield in 2004. Phosphorus fertilizer increased yield by as much as 131 bu/A at 120 lb N/A…from 103 bu/A with the zero P control to 234 bu/A with the rate of 80 lb P₂O₅/A. Corn yield overall tended to be only slightly higher with 80 compared to 40 lb P₂O₅/A. Grain sorghum yields were slightly less in 2004 than the 10-year average. Nitrogen fertilizer alone increased yield by as much as 43 bu/A, while N plus P increased yield by as much as 63 bu/A. Potassium fertilization has had no effect on sorghum yield over the course of the study.

This is one of the few long-term crop nutrition studies in the U.S. The results of such experiments are becoming increasingly valuable as nutrient use comes under greater scrutiny. Since this project continues to generate excellent long-term yield response and environmental data, support will continue in 2005. KS-23F