Nitrogen fertilizer management for maximum economic yields of spring wheat in southwestern Saskatchewan
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The effects of snow trapping by means of alternative cereal stubble heights, and of N fertilizer management in terms of rates, times of application, and methods of placement on soil moisture conservation, grain yields, and economic returns for zero tilled continuous spring wheat were examined over a 6-year period on a loam soil at Swift Current, Saskatchewan. The trap strips consisted of a portion of stubble 40-60 cm tall by 30 cm wide spaced every width of the swather (6 m) and perpendicular to the prevailing winds. Short stubble was cut at a uniform standard height of 15-20 cm. The water equivalent of snow trapped over the fall and winter periods averaged 85 mm in tall stubble and 45 mm in short stubble treatments; however, water conserved averaged only 11 mm higher in tall than in short stubble, and ranged from 6 mm lower to 27 mm higher. Efficiency of meltwater intake averaged 45 % (range 13-66 %) for tall stubble and 33 % (range 22-43 %) for short stubble. The low soil moisture conserved and low efficiency of meltwater intake in some years was due to high runoff losses caused by rapid melting of the snowpack in late winter by Chinook winds. The effect of stubble height and fertilizer management treatments on grain yields and economic returns varied with the level of growing season rainfall. In dry years, wheat yields on tall stubble areas averaged 166 kg/ha higher (655 vs 489 kg/ha ) than on short stubble areas, in moist years the yield advantage on tall stubble was 35 kg/ha (1566 vs 1531 kg/ha), while in wet years the yield advantage of tall stubble was 68 kg/ha (2493 vs 2425 kg/ha ). Wheat yields were increased with N fertilizer in years with favorable moisture reaching a maximum at 75-100 kg/ha. Furthermore, in years of favorable moisture, yields were generally greater for spring applied than for fall applied urea N, and for deep banded than for broadcast N. In contrast, in dry years wheat yields did not respond to N fertilizer or to the method of fertilizer management used. The overall relative yield ratings for spring band, fall band, spring broadcast and fall broadcast were 100, 198, 94, and 91, respectively. In dry years, net return averaged $15-25 ha-1 higher on tall than short stubble; but, only $4-8 ha-1 higher in moist years and no difference in wet years. The economic benefit of snow trapping increased with the price for wheat and decreased with the cost for N fertilizer. In the dry years, fall broadcasting of N fertilizer provided the greatest profit due largely to the lower costs for fertilizer N and labor in the fall compared to spring period and to the lower energy and equipment ownership costs for broadcasting compared to banding fertilizer. In years with favorable moisture, there was generally little difference in net returns among the fertilizer management systems.
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