EFFECT OF INTENSITY OF CROPPING ON THE EFFICIENCY OF WATER USE

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Abstract
An experiment conducted at Brandon, Manitoba, during the years 1955–1959 inclusive, indicated that the proportion of the total rainfall lost to the atmosphere from plant and soil surfaces on cropped land during the growing season (hereafter referred to as evapotranspiration) was highly dependent on the intensity of cropping. Evapotranspiration accounted for only 38.3 per cent of the total rainfall in a wheat-summerfallow rotation. The remaining 61.7 per cent was lost by percolation, run-off and/or evaporation during the non-crop period of the rotation. Decreasing the frequency of summer-fallow in the rotation increased the percentage of the total rainfall used by evapotranspiration. This percentage increased to 78.5 when wheat was grown continuously. Evapotranspiration accounted for 90.8 per cent of total rainfall with alfalfa. Evapotranspiration by wheat grown on summer-fallow tended to decrease when fertilizer was used and increased when third crop wheat was fertilized. The changes resulting from fertilizer were small, relative to the changes resulting from the intensity of cropping. The use of fertilizer increased the number of bushels of wheat produced per inch of evapotranspiration. This was determined mainly by the fact that fertilizer increased the yield and not because of decreased evapotranspiration. Summerfallow was not necessary to conserve moisture for wheat production during the experimental period.