Effect of cropping rotation and input level across 18 years on the northern Great Plains.
A cropping rotation study was conducted from 1994-2012 (three 6-yr cycles) at the Agriculture and Agri-Food Canada Research Farm at Scott, Saskatchewan, Canada in a split-split-plot design with four replicates. The main plots were three levels of inputs; high (HIGH), reduced (RED), and organic (ORG) The subplots were three levels of cropping diversity (rotations); fallow-annual grains (LOW), diversified annual grains (DAG), and diversified annuals and perennials (DAP). The sub-sub plots (each 13 x 40 m) were phases of the crop rotation. Foliar disease assessments were made shortly before crop maturity each year. Across treatments and years, there was no consistent pattern of response of final disease severity to treatment. For example, level of input and cropping diversity did not affect severity on the penultimate or flag leaf of wheat in 2007 2013. In those years where there were differences in severity, severity was often highest in the high-input treatments, but organic rotations were highest in some years. However, foliar disease severity differed substantially among years. This study demonstrated that weather conditions on the northern Great Plains had a much larger impact on foliar disease severity than input levels or cropping rotation in the moderate to highly diverse rotations assessed in this 18-year study.
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