Urea-based fertilizer as an efficient nitrogen source in perennial cool-grass forage production

Urea-N fertilizers are widely used in agriculture but the efficiency of different forms has yet to be quantified for cool-season forage grasses grown in northern areas. In a study conducted in eastern Canada during three growing seasons (2014-2016), polymer-coated controlled release urea (PCU), a blend of 50% PCU and 50% urea, and urea treated with an inhibitor of urease (Urea+NBPT) broadcast in early spring were compared with calcium ammonium nitrate (CAN) broadcast in spring (60%) and after the first harvest (40%) on two timothy (Phleum pratense L.) fields with contrasting soil textures (clay and loam). Fertilizers were added at rates of 50, 100, 150, and 200 kg N ha-1 and compared with an N-unfertilized control. The three urea-based fertilizers resulted in similar annual forage dry matter (DM) yields than CAN on the two soil types but in different forage DM yield seasonal distribution. The highest DM yield in spring growth was achieved with PCU/Urea and Urea+NBPT, while DM yields were the lowest with PCU in spring growth but highest in summer regrowth. Annual forage DM yields increased with increasing N rates for all fertilizers in both soils. Concentrations of forage N, nitrates, and non-protein fractions were highest in spring growth after the spring application of 200 kg N ha-1 as Urea+NBPT in both soils. The N sources did not affect forage digestibility and neutral detergent fiber (NDF) concentration. Economic return was the highest for Urea+NBPT and PCU/Urea. Therefore, these urea-based fertilizers constitute valuable alternatives to CAN for grass-based forages under eastern Canada conditions.