Uptake of foliar or soil application of 15N-labelled urea solution at anthesis and its affect on wheat grain yield and protein

Two growth chamber experiments were conducted to determine the effect of N-15-labelled urea solution foliar- or soil-applied at anthesis on recovery of fertilizer N in grain, grain protein and grain yield of Canadian Western Red Spring wheat (Triticum aestivum L.). Recovery of N-15-labelled urea-N in grain ranged from 4.5 to 26.7% with foliar application, and from 32.3 to 70.1% with soil application. Amending the urea solution with the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) improved recovery of soil-applied N in exp. I only and did not increase N recovery from foliar applications. Nitrogen recovery of foliar-applied urea was increased on average from 10.6 to 25.0% by adding nonyl phenol ethoxylates (NPE), a non-ionic surfactant, to the urea solution. Grain protein was higher when urea was applied to the soil than when applied to the foliage. Addition of N at planting increased both grain protein and yield while only protein was enhanced with fertilizer N applied at anthesis. Although wheat cultivar, soil type and growing environment differed in the two experiments, protein content consistently increased with N application at anthesis, indicating the effect of N applied at anthesis is constant across a range of conditions.