Evaluation of Polymer‐Coated Urea and Urease Inhibitor for Winter Wheat in Southern Alberta

Abstract

Nitrogen fertilization of winter wheat (Triticum aestivum L.) in the drier regions of the Canadian prairies is currently accomplished by banding urea or anhydrous ammonia at seeding or broadcasting urea in early spring. This study was conducted to determine if the efficacy of urea could be improved by using polymer‐coated urea (PCU) or treatment with urease inhibitor N‐(n‐butyl) thiophosphoric triamide (NBPT). Two field experiments were conducted for 3 yr on wheat stubble and on fallow at Bow Island and at Lethbridge. Grain yield and protein concentration response of winter wheat was determined for noncoated urea (NCU) and PCU banded in the soil at seeding at seven rates from 30 to 210 kg N ha−1 (Exp. 1) and for four N fertilizer types broadcast on the soil surface in early spring at rates of 30, 60, and 90 kg N ha−1 (Exp. 2): NCU, ammonium nitrate (AN), NBPT‐treated urea (NTU), and PCU. When N fertilizer was banded at seeding, grain yield was higher for PCU than NCU, but differences were small (<100 kg ha−1, <5%) and likely not due to reduced N losses. Grain protein concentration was unaffected by fertilizer type. When N fertilizer was broadcast on the soil surface in the spring, grain yield and protein concentration were similar for NCU, AN, and NTU, but reduced for PCU due to excessive delay in N release. The negligible impact of polymer coating or treatment with NBPT on urea efficacy reflects the low risk of urea N loss in this region.