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.

Corn yield was above average in 2011, with maximum yield at about 230 bu/A. Nitrogen applied alone increased corn yield by 87 bu/A, while N and P applied together increased yield up to 139 bu/A. This is similar to the past 10 years where N and P applied together increased irrigated corn yield by about 130 bu/A. Application of 120 lb N/A (with P) was sufficient to produce 95% of maximum yield in 2011. Nitrogen fertilizer alone increased sorghum yield by about 50 bu/A, while N plus P increased yield by up to 75 bu/A. Application of 40 lb N/A (with P) was sufficient to produce about 80% of maximum yield in 2011. Potassium fertilization had no effect on sorghum yield. This is one of the few continuous, long-term crop nutrition studies in the U.S., and support is planned to continue in 2012. KS-23F