Effect of Long-term Nitrogen, Phosphorus and Potassium Fertilization of Irrigated Corn and Grain Sorghum

IPNI-1991-USA-KS23

24 Mar 2015

2014 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, 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.

Nitrogen applied alone in 2014 increased corn yield by up to 58 bu/A, while N and P applied together increased yield up to 152 bu/A compared with the unfertilized control. This is slightly above the 10-year average, where N and P fertilizer together increased yields up to 146 bu/A. Application of 120 lb N/A (with P) was sufficient to produce 91% of maximum yield in 2014, which is similar to the 10-year average. The highest yield (238 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 60 bu/A, and 80 lb increased yield by 94 bu/A. Nitrogen fertilizer alone increased sorghum yield by 49 bu/A, while N plus P increased yield by up to 81 bu/A. Application of 40 lb N/A (with P) was sufficient to produce about 87% of maximum yield in 2014. Potassium fertilization had no effect on sorghum yield, as has been the case throughout the study. This is one of the few continuous, long-term crop nutrition studies in the U.S., and support is planned to continue in 2015.