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

Non-Peer ReviewedLate-season application of nitrogen fertilizer is of interest for increasing grain protein concentration in Canadian Western Red Spring wheat. The objective of this study was to determine the relative effectiveness of foliar versus soil application of urea solution fertilizer (15N enriched) at anthesis in increasing grain uptake of fertilizer nitrogen and grain protein content. Urea fertilizer treatments containing the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) and/or the surfactant Agral 90 were included to show any additional effects of fertilizer additives on nitrogen uptake efficiency. Growth chamber studies were conducted in 1997 and 1998 with Pasqua and AC Barrie wheat, respectively. Nitrogen uptake from soil-applied urea ranged from two to five times that of foliar-applied urea, irrespective of fertilizer additions. Recovery of unamended foliar and soil applied urea-N averaged 6% and 10.5% versus 35% and 65% for Pasqua and Barrie, respectively. Best urea-N uptake from foliar application was achieved using the surfactant with urea (23-27%). Fertilizer N recovery was highest for soilapplied urea treated with NBPT (Pasqua: 54% average; Barrie: 69% average). Grain protein content was significantly higher when urea-N was soil-applied than foliar-applied (P < 0.05). Results of this study indicate an increase in grain protein content is better attained by late-season soil application of urea-N than late-season foliar application of an equal rate of urea-N