Can Polymer-Coated Urea Fertilizer Increase Crop Production and Reduce Nitrous Oxide Emissions?.

Information is lacking on whether polymer-coated or other controlled-release urea fertilizers can increase crop yields and/or reduce nitrous oxide (N2O) emissions for the subhumid boreal zone soils in northwestern Canada. Therefore, field studies were conducted 2003-2007 to compare polymer-coated urea (PCU) with conventional urea applied in the fall or the following spring and seeded to spring wheat, barley and canola. Seed yield and crop N uptake, and to a lesser degree, seed N concentration generally increased with N application to 90 kg N ha-1. Spring-banded PCU was more effective in two of seven sire-years than, and was as effective in the other site-years as, spring-banded urea in enhancing crop yield and N uptake. PCU tended to be superior to urea under normal to wetter than normal soil moisture conditions. Fall-applied PCU or urea generally produced lower crop yield and N uptake than spring-applied PCU or urea. Split application of urea (half each at seeding and tillering) resulted in higher seed yield and seed N concentration in three of seven site-years than did PCU and urea applied at a similar N rate. Nitrous oxide emissions from spring to fall showed few significant treatment effects: at one site, N2O loss was higher in two years with spring-banded urea and PCU (1.62 kg N ha-1) than the control (nil N) treatment (0.79 kg N ha-1). At a second site, N2O loss was 23-30% higher from urea than PCU treatments. It is concluded that, for boreal soils of the Canadian prairies, PCU applied at sowing is as effective as, and sometimes more so than, urea in increasing crop yield and N uptake, and that at one site PCU tended to reduce N2O loss.