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 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.

The 2007 results of this project continue 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 110 bu/A, while N and P applied together increased yield by up to 180 bu/A. Application of 120 lb N/A (with P) was sufficient to produce >90% of maximum yield in 2007, which was slightly less than the 10-year average. Phosphorus fertilizer increased yield by 80 bu/A at 120 lb N/A. Application of 80 instead of 40 lb P₂O₅/A increased yields 8 bu/A. Nitrogen fertilizer alone increased sorghum yield by as much as 70 bu/A, while N plus P increased yield by as much as 90 bu/A. Application of 40 lb N/A (with P) was sufficient to produce >85% of maximum yield, although yields continued to increase up to 120 lb N/A in 2007. Potassium fertilization has had no effect on sorghum yield over the course of the study. This is one of the few continuous, long-term crop nutrition studies in the U.S.A. Support will continue in 2008. KS-23F