Effect of soil NO3-nitrogen content and nitrogen fertilizer on yield of barley and canola grown on organic soils

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Toews, Edward John.
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Twenty field experiments were conducted in 1986 and 1987 to obtain information which would be useful for making N fertilizer recommendations for barley and canola crops grown on organic soils. Nitrogen fertilizer applied as NH4NO3 at rates of 10 to 250 kg ha-1, resulted in significant yield increases in eight of twelve barley experiments and five of eight canola experiments. Maximum grain yields for all sites averaged 2811 kg ha-1 for barley and 1122 kg ha-1 for canola. Fertilizer N required to reach 90% of maximum grain yield (90%MGY) and maximum economic grain yield (MEY) ranged between 30-130 kg ha-1 and varied inversely with spring soil NO3-N levels for most sites where economic response to N fertilizer occurred. Relationsips between % yield [yield of unfertilized treatment / maximum yield of fertilized treatment) * 100] and soil NO3-N content were evaluated for the 0-15, 0-30, 0-60, 0-90, and 0-120 cm sampling depths. The relationship of % yield to soil NO3-N to a depth of 30 or 60 cm was reasonably good and was best described by quadratic regression equations for both barley (r=0.86 for the 30 cm depth) and canola (r=0.86 for the 60 cm depth). The relationship between N uptake by the crop and soil NO3-N content was described equally well by linear or quadratic equations for all depths down to 90 cm for barley, with r values ranging from r=0.80 to 0.91, whereas quadratic models fit the relationship better at all depths for canola. The relationship between seed yield and N uptake of the crop was poor and low r values were obtained for quadratic or linear regression equations for both barley (r=0.55 and 0.53, respectively) and canola (r=0.39 and 0.36, respectively). Apparent amounts of N mineralized during the growing season ranged from 7 to 73 kg N ha-1 and averaged 33.2 kg N ha-1 for soils low in NO3_N at the time of seeding. Percent utilization of fertilizer N averaged 45% for barley and 28% for canola. Soil NO3-N levels remained relatively constant from fall to spring at sites with low initial NO3-N levels.