Long and short-term variability of aggregate size distribution in tillage and chemical fallow
Size distribution of aggregates is one of the most important factors which affect soil erodibility with respect to wind erosion. A long-term study was established in 1968 to investigate the influence of tillage and chemical fallow systems on aggregate size distribution. The cropping systems involved fallow with herbicides only, herbicides in combination with one or two tillage operations, and tillage alone. Significant differences in aggregate size distribution were found between years during the period between 1968 and 1986. It was clear that in some years Melfort soils were highly erodible. In 1991, aggregate size distribution was measured at 5 times during the fallow season in order to evaluate the effects of the different cropping systems, determine aggregate size distribution with depth, and to compare variability over the long and short term. The percentage of aggregates at the surface in the 0 to 0.5 mm size fraction decreased after tillage with a double disk, and increased with time thereafter despite further cultivation with a field cultivator, but remained relatively constant under chemical fallow. During the period of this study it was clear that there were two distinct sources of variability in soil erodibility. Both sources of variability should be taken into account if soil erodibility is to be predicted over the long term.
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