UPTAKE OF POINT-INJECTED NITROGEN BY WINTER-WHEAT AS INFLUENCED BY TIME OF APPLICATION

Conventional methods of N application to winter wheat often lead to low fertilizer-use efficiency. Point injection may improve fertilizer efficiency but the optimum time of application has not been established. A field experiment was conducted during two growing seasons at Lethbridge, AB, Canada, on a Typic Haploborall sandy clay loam to determine N-15-fertilizer uptake as a function of application time and method. The experiment included a factorial of three methods (point-injected urea-NH4NO3, broadcast urea, and broadcast NH4NO3,) and four application times (at seeding, late fall, early spring, and late spring) along with two banding treatments (urea and NH4NO3) applied at seeding and a control. For all methods of application, efficiency of fertilizer tended to be highest when applied in early spring. In the point-injection treatments, average recovery of applied N by wheat was 32% for the seeding, 43% for late fall, 56% for early spring, and 29% for late spring applications. At the optimum time of application, point injection exhibited significantly higher fertilizer recovery than broadcast applications, probably because of direct placement of N into the rooting zone. Fertilizer recovery from banding treatments applied at seeding was lower than from early-spring point injection, presumably because of overwinter N losses. The results suggest that point injection can significantly enhance fertilizer-use efficiency and that optimum time of injection is in the early spring just prior to the period of maximum N assimilation by the crop.