COMPARISON OF CROP ROTATIONS FOR SORGHUM PRODUCTION IN SOUTHERN ALBERTA

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Abstract
Grain sorghum (Sorghum bicolor L. Moench.) was evaluated in six rotations under rainfed conditions at the Lethbridge Research Station from 1978 to 1984. The rotations included continuous sorghum, sorghum-fallow, sorghum-barley, sorghum-spring wheat-fallow, sorghum-fallow-spring wheat and sorghum-fallow-winter wheat. The highest total production was achieved with the sorghum-barley rotation. This was followed by the continuous sorghum and sorghum-fallow-winter wheat rotations. The 3-yr rotations were not significantly different from each other but the sorghum-fallow-winter wheat rotation appeared to be the best. The 2-yr rotation, sorghum-fallow, was the least productive. Variability in yields was adequately accounted for by variability in annual rainfall. Water use efficiencies were 1.30 and 1.35 kg m−3 for sorghum and wheat grown on fallow and 1.11 and 1.12 kg m−3 when seeded into stubble. Therefore, it was concluded that sorghum was no more drought-resistant than wheat. Bioassay of soils from the crop rotation study indicated that residual atrazine toxicity should not be a significant limitation to wheat grown in rotation with sorghum. Economically, sorghum was at a disadvantage despite comparable yields in wheat because of its lower price. It was concluded that the inclusion of sorghum in crop rotations in southern Alberta cannot currently be recommended.Key words: Spring wheat, winter wheat, atrazine, adaptation