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 response of irrigated continuous corn and grain sorghum to nitrogen (N), phosphorus (P), and potassium (K) fertilization. Furrow irrigation was used through 2000, and sprinkler irrigation since 2001. There was no yield benefit to corn from K fertilization 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. For both crops, N treatments were 0, 40, 80, 120, 160, and 200 lb N/A and P treatments 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 2016 increased corn yield by up to 85 bu/A, while N and P applied together increased yield up to 164 bu/A (compared with unfertilized control). Maximum yield for corn (238 bu/A) was obtained with the addition of 160 lb N and 80 lb P₂O₅/A._. At the same N rate, 40 lb P₂O₅ increased yield by 84 bu/A (from 142 bu to 226 bu/A) over no P application (P control), while 80 lb P₂O₅ increased yield by 96 bu/A. At the rate of 160 lb N, the addition of 80 lb P₂O₅/A doubled apparent fertilizer N recovery in grain (from 26 to 51%) over the zero-P control. Nitrogen fertilizer alone increased sorghum yield by 71 bu/A, while N plus P increased yield by up to 93 bu/A.

Application of 80 lb N/A (with P) was sufficient to produce about 89% of maximum yield in 2016. At the 80 lb N/A rate, the addition of P fertilizer increased the apparent fertilizer N recovery in grain from 49 to 60%. At the next highest N rate (120 lb/A) the addition of P increased apparent N recovery in grain from 33 to 48%. While K fertilization resulted in increased yield in several treatment sets, on average it had no effect on sorghum yield which has been the case throughout the study.

This remains one of the few continuous, long-term crop nutrition studies in the U.S. Support for the project is planned to continue in 2017.