| Summary: | In southern Manitoba moisture and nitrogen are frequently limiting factors in the production of cereal and oilseed crops. Variations in the severity of limitations among years result in large year to year variations in yield and quality of crops grown. Fertilizer trials were established in 1972 to determine the severity of the variations. A total of 58 field experiments, 29 on fallow and 29 on stubble were conducted over six years to determine the effect of selected soil and climatic parameters on the response of wheat (Triticum Aestivum cv. Neepawa, Glenlea), barley (Hordeum Vulgare cv. Conquest, Fergus), canola (Brassica Napus cv. Tower), and flax (Linum Usitatissium cv. Dufferin) to applied fertilizer nitrogen. Regression analysis was used to quantify the importance of soil NO3-N, fertilizer N, nitrogen supply (Ns), water supply (Ws), and growing degree days (Gdd) on yield and grain protein percentage of the cereal and oilseed crops. A technique using normalized standard partial regression coefficients was used to assess the relative contribution of soil and fertilizer N in the determination of yield and grain protein percentage. Stepwise regression analysis was used to select significant independent variables for entry into yield and protein prediction equations. Grain yield of cereal crops was increased when N fertilizer was applied to nonfallow sites. A small increase in yield was also obtained on fallow sites when N fertilizer was applied. Both varieties of wheat and barley indicated significant positive responses to fertilizer N and soil NO3-N. Soil NO3-N was almost two times more important than fertilizer N in the determination of final grain yield of cereals. Seed yield of oilseed crops was increased when N fertilizer was applied to nonfallow sites. A small increase in seed yield was also obtained on fallow sites when N fertilizer was applied. Soil NO3-N and fertilizer N were less significant in explaining the variation in grain yields of flax and canola than for the cereal crops. Fertilizer N was three times more important than soil NO3-N in the determination of seed yields of canola and flax....
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