Improving Effectiveness Of Seedrow-placed Urea With Urease Inhibitor And Polymer Coating For Durum Wheat And Canola (2003)

Seedrow-placed urea minimizes soil disturbance in reduced tillage systems, but it generally decreases emergence at nitrogen (N) rates adequate for optimum crop yield. The objective of this study was to determine the influence of coating urea fertilizer granules with a urease inhibitor or a polymer on the emergence and seed yield of durum wheat (Triticum turgidum L.) and canola (Brassica napus L.) with seedrow-placed urea, and to determine the appropriate rate of Agrotain™ coating for seedrow-placement. Protein content and N uptake in wheat seed were also determined. Field experiments were conducted at three locations using durum wheat (Aneroid) and canola (Scott and Swift Current) in Saskatchewan, Canada. The combinations of N rates (28, 56, 84, 112, and 140 kg N ha−1 for durum wheat and 34, 68, 102, and 136 kg N ha−1 for canola) and urea coatings [non-coated urea (NCU)], urea coated with Agrotain™ at full rate (Agr1, 5.2 L t−1), 2/3 rate (Agr2/3) and 1/3 rate (Agr1/3), and with polymer (Plmr, at 3% by weight) treatments were the main plots. A zero-N check was also included. There were two seed opener types (knife with 1.9 cm wide band and spreader with 7.6 cm wide band) used for the seedrow-placed urea subplots. Agrotain™ contained N-(n-butyl)-thiophosphoric triamide (NBPT) urease inhibitor at 25% by weight as active ingredient. With increase in N rate from 28 to 140 kg N ha−1 for wheat, the decline in emergence was greater for NCU (by 59.5 plants m−2) than for coated urea treatments (by 23.0 to 29.1 plants m−2); the seed yield declined in NCU and Agr1/3 treatments but increased up to 84 or 112 kg N ha−1 in Agr1, Agr2/3 and Plmr treatments. With increasing N rates, the N uptake in wheat seed was not influenced for NCU, slightly increased (by 10.3 kg N ha−1) for Agr1/3 and substantially increased (by 31.6 to 34.9 kg N ha−1) for Plmr, Agr1 and Agr2/3 treatments. The protein content in wheat seed was increased for all the coated urea treatments up to 140 kg N ha−1. Compared to the zero-N check, canola emergence with 34 kg N ha−1 declined slightly at Scott (relatively moist area) and substantially at Swift Current (relatively dry area). With an increase in the N rate from 34 to 136 kg N ha−1, the decline in canola emergence at Scott was much greater with NCU than the coated urea treatments but at Swift Current it was similar for all the urea treatments. With increasing N rate, canola seed yield declined for the NCU treatment at both sites while it increased up to 68 kg N ha−1 for Agr1, Agr2/3 and Agr1/3 at Scott, up to 102 kg N ha−1 for Agr2/3 and Agr1/3 at Swift Current, and up to 136 kg N ha−1 for Plmr at Scott and for Agr1 and Plmr at Swift Current. Both crops responded to higher rates of seedrow-placed N with coated urea compared to NCU. Polymer coating was somewhat more effective than Agrotain™ coating at the N rates used in this study. The effectiveness of Agrotain™ tended to decline with reduction in coating rate (a trend of Agr1>Agr2/3>Agr1/3). The wider spreader opener resulted in greater emergence, seed yield and N uptake than knife opener. Coating of urea was more effective than widening of the seedrow-placement band. In summary, the emergence, seed yield and N uptake were generally greater with coated urea than with NCU. The effectiveness of coating tended to increase with increasing N rate. Coating of urea was superior to widening of the seedrow-placement band, polymer tended to be better than Agrotain™ coating, and spreader was somewhat more effective than knife opener.