COMPARISON OF CROP ROTATIONS FOR SORGHUM PRODUCTION IN SOUTHERN ALBERTA

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