Changes in soil biological and physical properties under reduced tillage systems
Interest in reduced tillage systems has increased in recent years, though important questions remain as to the impacts of such systems on soil quality and nutrient cycling. We examined the effects of tillage on soil biochemical (N and C mineralization, microbial biomass, and light fraction of organic matter) and physical (aggregate stability and size distribution) attributes at seven long-term sites in Saskatchewan, representing a range of soil types and crop rotations. Reduction in tillage increased mineralizable N at most sites, though the effect of tillage was usually not as strong as that of crop rotation (continuous cropping vs. wheat-fallow). Other indicators (microbial biomass N, light fraction N) also provided evidence of improved N fertility under reduced tillage. These findings are in apparent conflict with recent reports that adoption of reduced tillage can reduce N uptake and protein content of wheat. This anomaly remains to be resolved. Wet aggregate stability was improved by reduction in tillage and by elimination of summer fallow on a sandy loam and a silt loam, but treatment effects were small or absent in the heavy textured soils. Aggregate stability increased between spring and fall and decreased during winter. On a sandy loam, where wind erosion was a perennial threat, cropping intensity did not affect the wind-erodible fraction (aggregates < 0.84 mm) but reducing tillage did decrease erodibility of the fallow phase. Data collected between 1982 and 1994 showed that wind erodibility varied considerably from year to year, but there was no discernible relationship with weather or residue amounts from the previous crop.
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