Selecting a nitrogen source for optimum fertilizer efficiency in no-till winter wheat
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Successful production of winter wheat (Triticum aestivum L.) on the Canadian prairies requires that the crop be no-till seeded into standing stubble so as to increase the.opportunity of trapping an insulating layer of snow. Deficiencies of soil nitrogen (N) associated with stubble fields must; be corrected by the addition of fertilizer N if optimum yields are! to be achieved. While ammonium nitrate N fertilizer has been the commonly recommended N source for application to the surface of unworked fields, it has become increasingly more difficult to obtain with the current domination of the dry fertilizer N market by urea. As a result winter wheat producers have had to consider alternate N forms for application to no-till fields. In this study replicated fields trials were established at ten locations over two years (1986-1987) to evaluate the effects of the N forms urea, ammonium nitrate, and urea ammonium nitrate (UAN) solution either early spring broadcast or surface banded on no-till fields of winter wheat. Late (i.e., 3 week delay) broadcast applications of urea and ammonium nitrate were also included in the second year of the study. Grain yield, protein concentration, and grain protein yield data was collected and analyzed for comparison of treatments. Both years of the study were characterized by early season moisture deficits and in 1986 high levels of residual soil NO3-N. While significant responses to N rate were obtained for all variables at most sites, very few significant differences were recorded among the N treatments. In general, early broadcast applications of urea and ammonium nitrate increased gra1n and protein yields over late application dates. This lower yield associated with late application was accompanied by significantly increased grain protein concentrations, indicating uptake of the N was occurring after the yield potential of the crop had been determined. Dribble bands of UAN solution produced higher grain and protein yields than surface spray applications, indicating increased losses associated with the broadcast spray to no-till fields. Calculated N recovery for treatments indicated that while the late applied treatments showed a high recovery of N in grain and grain + straw samples, this was not reflected in grain yield.
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