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

IPNI-1991-USA-KS23

15 Jan 2007

2006 Annual Interpretive Summary


This long-term western Kansas study was initiated in 1961 to evaluate responses of irrigated continuous corn and grain sorghum to N, P, and 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, thus 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. Nitrogen alone increased corn yield by as much as 70 bu/A, while N and P applied together increased yield by up to 160 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 maximum yield in 2006. Phosphorus fertilizer increased yield by 134 bu/A at 120 lb N/A... from 68 bu/A with the zero P control to 202 bu/A with the application of 80 lb P2O5/A. Corn yield was higher (26 bu/A) with 80 compared to 40 lb P2O5/A. Nitrogen fertilizer alone increased sorghum yield by as much as 50 bu/A, while N plus P increased yield by as much as 65 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. Support will continue in 2007. KS-23F