Crop production under alternate rotations on a Dark Brown Chernozemic soil at Scott, Saskatchewan

Nine rotations of fallow (F), wheat (W), barley (B), canola (C) and alfalfa hay (H) were evaluated to determine whether alternating crops in rotation on Dark Brown soils increases yield or reduces yield variability. Enhanced yield could increase economic returns, while reduced yield variability could reduce risk of economic loss in individual years. Rotations used in the study were F–W, F–C, F–W–W, F–C–W, F–W–B, F–C–B, F–C–B–H, F–C–W–B–H–H, and continuous wheat. Rotation did not affect yield of wheat or canola grown on summerfallow. Yield and quality of wheat and barley grown on stubble were influenced by rotation. Wheat yield on wheat stubble averaged 1980 and 2160 kg ha−1 in the continuous wheat and F–W–W rotations, respectively, while wheat on canola stubble averaged 2340 and 2290 kg ha−1 in the F–C–W and F–C–W–B–H–H rotations. Most of the yield reduction with wheat on wheat stubble occurred during 1987–1991, when pre-seeding tillage on stubble was minimized. Leaf disease (tan spot and septoria) increased noticeably on wheat stubble during 1987–1991 compared with 1980–1986 or with wheat on canola stubble. Presumably, reduced tillage during 1987–1991 left more infected residue on the soil surface, where it could infect a succeeding wheat crop. Yield of canola relative to wheat during 1980–1991 was much higher than reported for this study during 1972–1979; this was likely due to better seedbed preparation and more effective weed control. Coefficients of variability (CV) for yield over years were 20–25% for canola; 27–30% for wheat on fallow; 24–31% for wheat on stubble; 23–34% for barley on stubble; and 51–63% for alfalfa hay. Calculated on a rotation basis, CV tended to be high in wheat monoculture rotations, particularly where summerfallow was eliminated, but tended to be lower where a mix of crops was grown. Implications for more widespread acceptance of extended cropping are discussed. Key words: Crop rotation, wheat, barley, canola, alfalfa, rotation effect, yield variability