Effect of Long-term Nitrogen, Phosphorus and Potassium Fertilization of Irrigated Corn and Grain Sorghum
IPNI-1991-USA-KS23
29 Apr 2016
2015 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, so 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.
Nitrogen applied alone in 2015 increased corn yield by up to 70 bu/A, while N and P applied together increased yield up to 129 bu/A. This is below the 10-year average, where N and P fertilizer together increased yields up to 144 bu/A. Application of 120 lb N/A (with P) was sufficient to produce about 98% of maximum yield in 2015, which is higher than the 10-year average (93%). The highest yield (221 bu/A) 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 52 bu/A, and 80 lb increased yield by 59 bu/A. Nitrogen fertilizer alone increased sorghum yield by 66 bu/A, while N plus P increased yield by up to 92 bu/A. Application of 40 lb N/A (with P) was sufficient to produce about 88% of maximum yield in 2015. Potassium fertilization had no effect on sorghum yield, as has been the case throughout the study.
This remains one of the few continuous, long-term crop nutrition studies in the U.S., and support is planned to continue in 2016.