Jeff Moore1, Randy Killorn2, and Marianela Gonzalez1. (1) Iowa State Univ, Dept of Agronomy, Ames, IA 50011, (2) Iowa State Univ, Agronomy Dept, 3208 Agronomy Hall, Ames, IA 50011-1010
Nitrogen (N) application to corn has been proven to increase yields, but concerns about nitrate-N in ground and surface water have led to investigation of controlled-release N fertilizer. The objective of these experiments is to compare corn grain response to controlled-release urea (ESN) and conventional urea. Two field studies are being conducted at two locations in Iowa and corn yield data will be reported from 2003-2005. All N treatments were hand broadcast in 34 kg N ha-1 increments from 0 kg N ha-1 to 202 kg N ha-1, then incorporated into the soil using standard tillage practices for the area. In the spring study, grain yield increased with N rate at all locations every year and there were significant differences due to N material at four of five site-years. Average grain yields were 9.5 Mg ha-1 for the ESN and 9.2 Mg ha -1 for the conventional urea. In the fall study, grain yield increased with N rate at all locations every year and there were significant differences due to N material at two of three site-years. On average, grain yields were 9.6 Mg ha-1 for the fall applied conventional urea, 9.8 Mg ha-1 for the fall applied ESN, and 10 Mg ha-1 for the spring applied conventional urea.