Effect of simulated erosion on canola productivity

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Kenyon, Brian Edward
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Simulated soil erosion sites were developed on six soil types in Manitoba to assess the effect of topsoil removal on canola productivity. The soil types studied ranged from a Reinland loamy very fine sand to a Pembina clay loam. Plots were developed on a completely randomized split plot design with topsoil removal being the main plot treatment and fertilizer additions being the subplot treatment. Levels of topsoil removal were: 0 (control), 5, 10, and 20 cm. Each topsoil removal treatment was replicated 4 times. Each topsoil removal level was then treated with no fertilizer (control), recommended rate of fertilizer (based on soil test), and approximately twice the recommended rate of fertilizer. Data from 1985 and 1986 indicated that, in general, canola yields decreased where 5, 10, and 20 cm of topsoil were removed and no fertilizer was added. For the fine textured soils, additions of fertilizer at the recommended rate usually mitigated the yield loss associated with topsoil removal in both years. Applications above the recommended rate of fertilizer did not significantly increase yields any further. Yield reduction where topsoil was removed was likely nitrogen related as the canola plants exhibited typical nitrogen deficiencies. For the coarse textured soils, applications of fertilizer at the recommended rate, where 20 cm of topsoil had been removed, were not able to increase yields over those of the control (no topsoil removed, no fertilizeer added). In some instances, even twice the recommended rate of fertilizer did not increase yields over that of the control. For these soils, some other factor, other than fertility, was limiting crop growth. It is possible that the subsoil possessed some characteristics, either physical or chemical, which were limited to crop growth. For the Waskada VFSCL site, applications of the recommended rate and twocie the recommended rate of fertilizer, where 10 and 20 cm of topsoil had been removed, did not increase yields over the control where no fertilizer had been added and no topsoil was removed. A layer consisted of gravel and coarse material existed approximately 20-30 cm below the soil surface. Exposure of this layer or increasing its proximity to the soil surface by the removal of topsoil likely restricted the root growth of canola and therefore limited yields on these subplots. As the level of topsoil removed increased and no fertilizer was added, straw yields decreased. As well, nutrient concentration of the straw also decreased. Additions of fertilizer increased straw yield production and also increased the concentration of nutrients in the straw.