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 2008 results of this project continue to demonstrate that P and N fertilizer inputs are important to the optimization of irrigated corn and grain sorghum production in western Kansas. Nitrogen alone increased corn yield by as much as 60 bu/A, while N and P applied together increased yield by up to 120 bu/A. Application of 120 lb N/A (with P) was sufficient to produce >90% of maximum yield in 2008. Phosphorus fertilizer increased corn yield by over 80 bu/A at 120 lb N/A. Application of 80 instead of 40 lb P₂O₅/A increased yields by only 3 bu/A. Nitrogen fertilizer alone increased sorghum yield by 54 bu/A, while N plus P increased yield by 72 bu/A. Application of 40 lb N/A (with P) was sufficient to produce >80% of maximum yield, although yields continued to increase with higher N rates. Potassium fertilization had no effect on sorghum yield in 2008, nor has it had any effect on sorghum yield over the course of the study. This is one of the few continuous, long-term crop nutrition studies in the USA. Support will continue in 2009. KS-23F