Effects of conservation tillage and rotation on water infiltration in two soils in south-eastern Australia

The infiltration of water under long-term (8-10 years) conservation tillage (zero and subsurface tillage with stubble retention) and conventional tillage (frequent tined tillage with no surface residues) systems was compared on a grey cracking clay and a sandy loam soil in south-eastern Australia. Potential infiltration rates were higher under conservation tillage on both soil types. On the grey clay soil, stubble retention and zero tillage produced up to an 8-fold increase (from 12-33 to 145-206 mm/h) in saturated hydraulic conductivity (K-s) compared with the conventional practice of removing stubble by burning or grazing, followed by frequent tillage to control weeds. An annual application of nitrogen at 20-60 kg/ha had no significant effect on K-s. Similarly, on the sandy loam soil a 2-fold increase in K-s was observed from conservation tillage. Increases in K-s from approximately 46 to 96 mm/h occurred in rotations which included an 18-month fallow with conservation tillage (stubble retention and zero tillage) compared with conventional tillage (stubble removed and frequent tillage). A continuous rotation of pasture and wheat under conventional tillage had a significantly lower K-s of 22-23 mm/h which was increased to 47-49 mm/h with stubble retention and zero tillage. These differences in K-s explain an important mechanism for increased water storage on these soil types under reduced tillage.