Illinois Fertilizer & Chemical Association
Supply · Service · Stewardship

Utilizing Inhibitors For Increased Efficiency Of N From Fall Vs. Spring Fertilizer Dap Or App Applications To Corn In A Corn-Soybean Rotation

S. A. Ebelhar, F. G. Fernandez, and K. D. Greer
Recent research by Ebelhar, et al. (2009) showed significant losses of N from fall applied DAP to wheat, with implications toward significant losses when DAP is fall applied to crop land prior to corn planting in the spring. These findings were substantiated by Fernández, et al. (2010) who found only about one-third of fall applied N in DAP carried over to the spring for next year’s corn crop. In a typical corn-soybean rotation in southern Illinois where corn averages 150 bu/acre and soybeans averages 45 bu/acre, maintenance (removal) rates of DAP (18-46-0) would provide 25% of the needed N for the corn crop and losses of this N from fall application could result in significant yield loss.

There are several inhibitors being marketed to improve N efficiency from fertilizer N sources, but little research exists on utilizing these inhibitors to reduce N losses from DAP or liquid ammonium poly-phosphate (APP, 10-34-0 or 11-37-0) applications. Our study will be looking at Agrotain®, AgrotainPlus®, Instinct® and potassium thiosulfate (KTS) inhibitors.

As an alternative to fall or spring applications of DAP or APP, the best management practice of sidedressing these N sources could increase the efficiency of N utilization and therefore grain yields, but may also increase the utilization efficiency of P and K in these materials. As fertilizer prices continue to rise, there could be an economical advantage to sidedressing P and K fertilizers to improve nutrient efficiency.

The objectives of this study are to 1) evaluate the effects of inhibitors added to DAP or APP fertilizer applications on N utilization by corn; 2) compare inhibitors added to fall vs spring DAP or liquid APP applications to corn; and 3) evaluate the effectiveness of sidedress P and K fertilizer applications.