NO-TILL WINTER-WHEAT DRY-MATTER AND TISSUE NITROGEN RESPONSE TO NITROGEN-FERTILIZER FORM AND PLACEMENT

Expansion of winter wheat (Triticum aestivum L.) production into the high winterkill risk regions of the Canadian prairies has been achieved by no-till seeding into standing stubble immediately after harvest of the previous crop. Seven field trials were conducted in Saskatchewan to evaluate the seasonal pattern of dry matter and N accumulation of no-till winter wheat. The fertilizer treatments included the currently recommended early (20 April) spring broadcast ammonium nitrate (AN) and early spring broadcast and surface band applied urea and urea-ammonium nitrate (UAN) solution. In four of the seven trials, late (12 May) AN and urea were also applied. Nitrogen fertilizer was applied at 0, 34, 67, 101, and 202 kg N ha-1. Mean maximum dry matter and N yields were established by Zadoks Growth Stage 65 (ZGS65) and ZGS45, respectively. Subsequent losses of both dry matter and N were observed under conditions of high evaporative demand and low precipitation. When rainfall was more favorable and N supply abundant, N and dry matter yields increased through the growing season to harvest. Increased N rates increased N uptake and amplified plant-N and dry matter losses. Growing season environmental conditions and plant-available-N levels also played an important role in determining the efficiency of N translocation to the seed. Early broadcast AN produced larger dry matter and N-yield responses than all other fertilizer treatments. While surface band applied urea showed no advantage over early broadcast urea, surface band applied UAN increased dry matter yield and N uptake over broadcast sprayed UAN. Average dry matter (N) yield-N response for early broadcast urea, surface band applied urea and surface band applied UAN treatments were 93 (89%) of those recorded for early broadcast AN. The broadcast sprayed UAN treatment dry matter and N yield-N responses were 81% of early broadcast AN. Compared with early broadcast AN and urea, late broadcast AN and urea produced lower dry matter yields and delayed N uptake. Average late broadcast AN and urea dry matter (N) yield-N responses were 63 (85%) of those recorded for early broadcast AN and urea. These observations indicate that differences in dry matter and N-yield responses for different N forms and placement methods are established early in the growing season and maintained through to maturity.