THE EFFECT OF SPRING AND FALL APPLICATION OF N ON YIELD AND QUALITY OF BARLEY (Hordeum vulgare L.) AND RAPESEED (Brassica campestris L.)

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Abstract
Application of N fertilizer in the fall as opposed to spring has been a controversial recommendation for cereal crops grown in Western Canada. Also, oilseed crops such as rapeseed may not respond to N in the same way as cereals. To investigate spring and fall application of N on barley and rapeseed, fractorial split plot experiments were designed with three N treatments of 45, 90 and 134 kg N ha-1 and four P treatments of 0, 9.4, 18.8 and 28.2 kg P ha-1, as main plots. A control without fertilizer was included and the subplots were spring and fall times of broadcast application of ammonium nitrate fertilizer. Barley (Hordeum vulgare L.), cultivar Conquest and rapeseed (Brassica campestris L.) cultivar Arlo were seeded at the test crops over a 5-yr period and a 6-yr period, respectively, at separate sites on Melfort silty clay soil to determine the difference in yield and quality of grain between spring and fall applied N. In some years yield response to N fertilizer was greater when applied in the spring and in other years when applied in the fall, resulting in a significant time of N .times. year interaction effect on yield. However, on the average, there was no significant difference in yield of barley or rapeseed grain between fall and spring applied N, 3.51 vs. 3.59 and 1.39 vs. 1.41 t ha-1, respectively. Nitrogen and P fertilizer increased yield as much as 2.17 t of barley and 0.76 t of rapeseed ha-1 although the concentration of mineralized ammonium- and nitrate-N in the soil was rated medium according to provincial soil test standards. The difference in yield response of barley (Y, t ha-1) between spring and fall applied N among years was related to the rainfall (X, mm) in May by the equation Y = -0.22 + 0.0135X, R2 = 0.74 and for rapeseed: Y = -0.061 + 0.0069 X, R2 = 0.58. Because N was applied relatively late in the fall, the available soil N was medium and the conditions for N loss in these experiments minimal, differences in barley and rapeseed yield response to N fertilizer between spring and fall applied N were small. When P fertilizer were applied at heavy rate, fall application of N produced a higher yield of rapeseed than spring application in all years.