Urea fertilizer forms affect grain corn yield and nitrogen use efficiency.

Controlled-release urea may be a good management strategy to increase the efficiency of N fertilizers. In a 3-yr study (2008-2010) conducted on a clay soil near Québec City, Canada, we compared the effect of polymer-coated urea (PCU), nitrification inhibitor urea (NIU), dry urea and urea ammonium nitrate 32% (UAN) on corn yield, plant N accumulation and soil NO₃₋N remaining at harvest. Corn was fertilized with urea and PCU at 50, 100 and 150 kg N ha⁻¹ in addition to an unfertilized control (0 N), and NIU and UAN at 150 kg N ha⁻¹. Urea, PCU, and NIU were pre-plant broadcast whereas UAN was side-banded at the six-leaf stage of corn. Response to N fertilization occurred in all years, but the magnitude of the response varied with years. In wet years (2008 and 2009), PCU and NIU resulted in higher grain yield than urea, but the increase was greater for PCU (+0.8 to 1.6 Mg ha⁻¹) than for NIU (+0.3 to 0.6 Mg ha⁻¹). In a dry year (2010), no significant difference was found between urea, PCU and NIU. Yields and apparent N recovery were comparable for PCU and UAN except in the dry year, when plant N accumulation was much higher for the UAN treatment. At harvest, soil NO₃₋N was increased by PCU in all years. Economic analysis revealed that despite 30% higher cost, PCU gave comparable net returns at equivalent N rate than UAN in wet years. We conclude that controlled-release urea, particularly PCU, would be an additional option to farmers instead of sidedressed UAN application for fertilizing corn grown in eastern Canada.