THE EFFECTS OF CONSERVATION TILLAGE ON POTENTIAL GROUNDWATER RECHARGE

Measurements of soil water and chloride made in a 10-year-old tillage experiment in north-western Victoria, Australia, at Dooen, were used t o calculate the effect of different tillage methods of fallowing in a fallow-wheat rotation on drainage below the root zone and hence potent ial recharge to groundwater. The soil type was a grey cracking clay (c hromic vertisol) and the tillage methods included: stubble-retained ze ro-tilled fallows (SRNT), stubble-retained subsurface tilled fallow (S RST) and conventional fallow (no stubble fully tilled)-wheat rotation (NSCT). Calculations of potential recharge rate over the 10 year perio d of the tillage experiment in two fields showed between 18.5 and 18.6 mm year(-1) additional recharge occurring owing to SRNT fallowing on this soil compared with NSCT fallow. The SRST fallow, which disturbs t he soil below the surface (5-15 cm) without significant inversion, sho wed significantly less potential recharge of 2.2-3.8 mm year(-1) compa red with NSCT fallow. Both SRST and NSCT fallow appear to have similar water flux rates.