Uptake of Point‐Injected Nitrogen by Winter Wheat as Influenced by Time of Application

Abstract

AbstractConventional 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 15N‐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.