Influence of N fertilization method on weed growth, grain yield and grain protein concentration in no-till winter wheat

Applying polymer-coated urea (PCU) instead of uncoated urea may benefit winter wheat (Triticum aestivum L.) production by reducing weed growth or increasing grain yield and protein concentration. Field trials were conducted for 3 yr under rainfed and irrigated conditions in Lethbridge and 2 yr under rainfed conditions in Lacombe to determine potential benefits of substituting urea with PCU for typical winter wheat production practices in Alberta. Four factors were included in each experiment: (1) urea type (urea, PCU and a 50:50 blend of urea and PCU), (2) application method (fall side-band vs. spring broadcast), (3) N rate (1×and 1.5×recommended N rate), and (4) herbicide application (none vs. full). Herbicide application substantially reduced weed biomass at all site-years, but only increased average grain yield by 9%. Dicot weed biomass was not affected by fertilizer treatment, but monocot weed biomass was less for fall banded than spring broadcast application and less for urea than PCU or blend at the 1×N rate. Over all site-years, substitution of 50 or 100% of urea with PCU increased grain yield by an average of 4.3% and reduced protein concentration by 1.3%. Substitution of urea with PCU had the largest impact at the site-year with most severe drought stress, indicating that PCU benefits were probably due to factors other than reduced N loss. Further study is required to evaluate potential benefits from substitution of urea with PCU over a wide range of environmental conditions.