Urea treatment affects safe rates of seed placed nitrogen in Saskatchewan
Placing urea in close proximity to seed can cause seedling damage resulting in poor crop establishment. Plant densities are often well below the optimum, and plants that do emerge can exhibit poor vigor. Several strategies have been developed to reduce risk of seed damage from urea. Restricting the amount that is seed placed, placing urea at a safe distance and placement before or after seeding are effective but may not allow for application of adequate N or increase equipment and operating costs. Recently treatments applied to the urea granule such as Agrotain and polymer coating have been developed to slow the conversion to ammonium. Research suggests that the safe rate of N can be increased by 50% where Agrotain is used and are less clear when polymer coatings are used. To demonstrate how Agrotain and polymer treated urea affect crop establishment and yield, rates of 0, 1, 1.5, 2 and 4 times the recommended safe rate were seed placed at Scott, Swift Current, Canora and Redvers, Saskatchewan. Trials were conducted with wheat at all locations, and canola at Scott. Seed placed untreated urea was used as a check. As well, an alternate option using seed placed untreated urea followed by liquid urea ammonium nitrate dribble banded 20 to 35 days after seeding was investigated. Impact of treatments on plant density varied with rainfall across locations. Sites with lower precipitation after seeding indicated more severe damage to seedlings. Untreated urea placed with the seed had the greatest impact on plant density but, Agrotain and polymer treatments also led to decreases at high N rates. The improvement of Agrotain over untreated urea generally confirmed manufacturer recommendations that safe rates of seed placed urea can be increased by about 50%. The polymer was very effective at reducing damage from seed placed urea, but still generally resulted in fewer plants than side band at 4 times the recommended rate of N. Grain yield responses were also variable across locations. At most sites where plant stand reductions were high yield was also affected. Differences between all treatments were small at N rates up to 2 times the recommended rate but at 4 times, yield was reduced for Agrotain treated and untreated seed placed N. For treatments where liquid dribble band was compared to side banding little difference in yield was observed when soil residual N was high and precipitation was low. A reduction in yield was found when soil N and precipitation were low. Where the N supply from soil was large and precipitation higher, yield of dribble banded crop continued to respond after side banded crops had peaked.
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