Response of Residual Soil Available N Level to Polymer-Coated Urea (ESN) Application in a Canola-Barley Cropping System.

ABSTRACT

Efficient use of N fertilizer is important in achieving optimal crop yield and minimizing environmental impacts. Our study addresses the question of whether there are any differences in the soil residual N levels between urea and polymer coated urea (ESN) in a canola-barley cropping system. Canola (Brassica napus L.) and barley (Hordeum vulgare L.) were grown in rotation on a Grey Luvisol (Haplocryalf) at Beaverlodge, a Black Chernozem (Haplocryoll) at Lacombe and a Dark Brown Chernozem (Haplustoll) at Lethbridge from 2005 to 2008. Both phases of the rotation were present each year. Urea and ESN were applied at 1 and 1.5 times (x) the recommended agronomic rate. Soil samples were collected to 120 cm depth (0-5, 5-15, 15-30, 30-60, 60-90, and 90-120 cm) in 2005 prior to and in 2008 after four years of fertilizer treatments. Soil samples were analyzed for available N (AN: NO₃^- + NH₄⁺-N) using 2M KCl extraction (1:5 solid liquid ratio). The amount of soil AN in the soil profile (0-120 cm) was calculated based on AN concentration and bulk density. When applied at the recommended agronomic rate, there were no differences (P>0.05) in the residual soil AN levels between the urea and ESN treatments for all three soil types. When applied at the 1.5x recommended agronomic rate, residual soil AN levels were higher (P<0.05) in urea than in ESN for Haplocryalf and Haplocryoll, but similar (P>0.05) for Haplustoll. For both urea and ESN, residual AN was higher when applied at 1.5x agronomic rate (P<0.001) than at the recommended rate and residual soil AN values with the 1.5 x ESN (urea) were 149% (201%), 150% (152%) and 157% (136%) those from the recommended rate ESN (urea) for Haplocryalf, Haplocryoll and Haplustoll, respectively. Compared to initial soil AN values (before fertilizer treatment was imposed), the residual AN in the 1.5 x ESN and urea were higher in Haplocryalf, with all other treatments lower or similar to the initial values. Our study suggests that ESN fertilizer could reduce the amount of nitrogen left in the soil but the amount of reduction depends on soil type. Applying fertilizer at higher than the recommended agronomic rate should be avoided, particularly for Haplocryalf where more residual AN left in soil could negatively impact the environment through runoff and leaching losses.