Foliar nitrogen application timing influence on grain yield and protein concentration of hard red winter and spring wheat

Foliar N applications on wheat (Triticum aestivum L.) have increased grain protein. Foliar N timing evaluations have been minimal. The objectives were (i) determine the optimal timing of foliar N for increased grain protein of hard red winter wheat (HRWW) and spring wheat (HRSW), (ii) evaluate effect of foliar N on grain yield, and (iii) determine relationship of grain protein to foliar N application and grain yield. Foliar N was applied at Feekes stage 10.0 (boot) or 10.8 (postpollination) on two cultivars of HRWW and HRSW each year from 1995 to 2000. The foliar N rate (33.7 kg N ha(-1)) was applied as 1:1 solution of urea ammonium nitrate (UAN) and water. Fertilizer N for a 3360 kg ha(-1) grain yield goal was broadcast as UAN after planting. Soil type was Estelline silt loam (fine-silty over sandy or sandy-skeletal, mixed, superactive, frigid Calcic Hapludoll). Postpollination foliar N gave the highest grain protein during all years. Grain yield was significantly reduced 5% by boot stage foliar N for HRSW. Neither timing application significantly reduced HRWW grain yield. All wheat data were pooled to relate grain yield level and protein response to foliar N. Grain protein and yield from plots without foliar N were inversely related (r(2) = 0.57). Postpollination foliar N increased protein 70% of the time when yield goal was exceeded compared with only 23% when it was not. These results show that postpollination foliar N gave higher grain protein and was most effective when planned yield goal was exceeded.