SOIL HYDRAULIC-PROPERTIES OF AN ORTHIC BLACK CHERNOZEM UNDER LONG-TERM TILLAGE AND RESIDUE MANAGEMENT

The effects of tillage on soil hydraulic properties are unclear from t he literature and residue effects are little reported. The hydraulic p roperties of an Orthic Black Chernozem under three tillage-residue sys tems in central Alberta - tillage with straw incorporated (till-straw) or removed (till-straw) - and no tillage with straw on the surface (n o till+straw) - were studied for 2 yr. Measurements began in the 9th y ear of continuous barley (Hordeum vulgare L.). Plant-available water c apacity differed among treatments only in the 0-2.5 cm layer, due to d ifferences in water retention at -1500 kPa. Pore size partitioning rev ealed relatively high macroporosities (14-18% of total porosity) and r esidual porosity (34-41% of total porosity), but no treatment differen ces in the tillage layer. Saturated hydraulic conductivity (K-sat), in filtration rate and cumulative infiltration at 1 h followed the trend: no till+straw > till+straw > till-straw. Infiltration characteristics and hydraulic conductivity had considerable temporal variation. Inter estingly, field and laboratory measurements gave the same order of mag nitude of transmission characteristics. The common similarity of the n o till+straw and the till+straw treatments and their usual difference from the till-straw treatment, especially in the water transmission ch aracteristics, indicate the importance of the return of residue to the soil. The influence of straw on soil hydraulic properties does not ap pear to depend on whether it was incorporated or not.