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 in 2012 was well above the 10-year average, with maximum yield at 260 bu/A. Nitrogen applied alone increased corn yield by up to 84 bu/A, while N and P applied together increased yield up to 174 bu/A. Application of 120 lb N/A (with P) was sufficient to produce 82% of maximum yield in 2012, which was less than the 10-year average of 94%. The highest yield was produced with the highest N and P rates, 200 lb N and 80 lb P₂O₅/A. At this N rate, 40 lb P₂O₅ increased yield by 55 bu/A and 80 lb increased yield by 90 bu/A. Nitrogen fertilizer alone increased sorghum yield by about 70 bu/A, while N plus P increased yield by up to 100 bu/A. Application of 40 lb N/A (with P) was sufficient to produce about 79% of maximum yield in 2012. 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 2013. KS-23F