Tillage translocation and tillage erosion in the complex upland landscapes of southwestern Ontario

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Authors
Lobb, David Allen
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University of Guelph
Abstract

Tillage translocation and tillage erosion are suspected of dominating the redistribution of soil within the complex upland landscapes of southwestern Ontario, resulting in soil degradation and affecting soil variability. This study was initiated to examine in detail the processes of tillage translocation and tillage erosion to gain a better understanding of the processes and of their roles in soil redistribution. The study consisted of a field experiment on tillage translocation and tillage erosion and, based on these results, the development and assessment of models for tillage translocation and tillage erosion. Tillage translocation and tillage erosion were measured throughout the complete sequence of slope positions of the topographically complex landscapes of two fields in the uplands of southwestern Ontario. Translocation of soil by tillage was measured by labelling plots of soil with Cl and measuring its forward displacement in response to single passes by four tillage implements (mouldboard plough, chisel plough, tandem disc and field cultivator). For all four tillage implements, tillage translocation varied considerably in topographically complex landscapes. Based on measurements of translocation, net translocation, net downslope translocation, and the tracer distributions, it was concluded that all four tillage implements were erosive. Relationships (linear regression) were observed between tillage translocation and slope gradient and between translocation and slope curvature. Relationships also existed between translocation and tillage depth and speed, and between tillage depth, tillage speed, slope gradient and slope curvature. The tractor-implement match and the responsiveness of the tillage operator were presumed to affect significantly soil translocation and its variability. A tillage erosion model was developed for the topographically complex landscapes of southwestern Ontario based on the relationships between tillage translocation and slope gradient and slope curvature. Two field sites were used for validation of the model. For both sites, past tillage practices were known and past soil erosion was determined using \sp137Cs as an indicator of soil redistribution. The tillage erosion model accurately predicted the pattern of soil redistribution within the two field sites. Severe soil loss was observed and predicted on convex landscape positions and soil accumulation on concave landscape positions. These findings support the conclusions of previous studies that tillage erosion is a major cause of soil redistribution and the major cause of severe soil loss within topographically complex landscapes of southwestern Ontario and, therefore, is the primary cause of increased soil variability. Step, linear-plateau and exponential functions were assessed for their ability to characterize tillage translocation. The exponential and linear-plateau models provided accurate estimations of the magnitude of soil translocated by tillage. The pattern of soil redistribution within the till-layer was more accurately estimated and predicted by the exponential model. The exponential model was concluded to be the preferred model of tillage translocation.

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Keywords
tillage translocation, tillage erosion, soil redistribution, upland landscapes, southwestern Ontario
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