A field experiment was conducted in the summer of 1996 to evaluate the supplemental irrigation needs of maize in fields located on sandy soils in eastern Ontario. Field and laboratory measurements of soil properties were made. Plow layer and deficit irrigation management approaches were evaluated. The plow layer soil depth was considered to be 300#x2002;mm, and for deficit irrigation management a soil depth of 400#x2002;mm was used. Irrigation requirements using rain and evapotranspiration data of the humid summer of 1996, as well as the drier summer of 1974, were evaluated. The results show that using a 400#x2002;mm root zone depth and 25#x2002;mm of water per irrigation led to less water losses by drainage, lower irrigation water requirements and fewer irrigations as compared to using a 300#x2002;mm root zone depth. Wilting began at 60 soil moisture depletion, thus it is suggested that irrigation begin at 50 moisture depletion to avoid costly crop stress. The principal assumptions for irrigation scheduling were that the soil is at field capacity at the beginning of June and where the summer water table is deeper than 1.6#x2002;m, the upward flux from the water table is negligible.
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