The effect of granular fertilizer N-form, placement, and time of application on yield and quality of no-till winter wheat

Non-Peer ReviewedThe introduction of a practical snow management system, which utilizes no-till seeding into standing stubble immediately after harvest of the previous crop ("stubbling-in") has allowed for expansion of the North American winter wheat (Triticum aestivum L.) production area to include most of the western Canadian prairies. Soil nitrogen (N) deficiencies are usually associated with this production system and N fertilization is normally required to maximize grain yield and maintain acceptable grain quality. The present study summarizes twenty-one broadcast ammonium nitrate fertilizer field trials conducted from 1976 to 1986 in Saskatchewan with the objectives of determining the effect of date of N fertilizer application on grain yield, grain protein yield and grain protein concentration of stubbled-in hard red winter wheat. Dates of N application considered were early fall, late fall, early spring and late spring. Date of N application had significant influence on total grain yield, grain protein yield and grain protein concentration in 33, 33 and 29 % of the trials, respectively. Reduced grain and grain protein yields, attributed primarily to denitrification losses, and immobilization, were observed with fall N applications in four trials located in the northeastern part of the agriculture region of Saskatchewan. Reductions in grain protein concentration accompanied these N losses. In contrast, a prolonged dry period, following spring N applications resulted in a temporary stranding of fertilizer N on the soil surface at one location thereby delaying its availability to the plant until after early spring N deficiencies had seriously limited the yield potential of the crop. Delays in N application had the same effect. Reduced grain and grain protein yield and increased grain protein concentration were also observed for fall and early spring N applications in trials that experienced spring environmental conditions favorable to plant growth followed by prolonged drought. This sequence of environmental conditions resulted in maximum grain protein concentrations that ranged from 14.5 to 20 % compared to approximately 13 % under normal growing conditions for this region. An additional nine field trials were conducted from 1982 to 1986 with the objectives of determining the influence of fertilizer formulation and placement method on N response of stubbled-in winter wheat. Reduced grain and grain protein yield responses indicated large N losses due to volatilization of broadcast urea in three of the nine trials. Comparison with yield response curves for ammonium nitrate indicated that the losses with broadcast urea could be in excess of 50 % of the added N. Fall banding prior to seeding was effective in reducing losses with urea, but did not outperform broadcast ammonium nitrate applied at the same time. Yield losses, which were probably due to denitrification, were observed for both urea and ammonium nitrate broadcast in the late fall at one location