TEMPORAL VARIATION OF HYDRAULIC-PROPERTIES FOR SOME SOILS WITH FRAGILE STRUCTURE

At three locations in the wheat belt of N.S.W. Cowra, Junee and Tamwor th, soil hydraulic properties were measured through the growing season on hardsetting soils with different tillage histories, namely direct drilling and traditional tillage. The hydraulic properties measured we re hydraulic conductivity and sorptivity at -10 and -40 mm tension. Re sults show that the hydraulic properties of these soils can vary signi ficantly through the growing season. This temporal variability was att ributed to tillage, plant growth, rainfall and soil settling under wet ting. The soil which had the more severe tillage treatment prior to so wing, together with stubble burning (traditional tillage), had lower v alues of hydraulic properties at 10 mm tension than the soil with the more conservative tillage treatment of direct drilling. Results for hy draulic properties at 40 mm tension did not show consistent difference s between tillage treatments, the tillage effects being dependent on t he particle size distribution of the soil and aggregate stability. Ove rall, the hydraulic properties measured at 10 mm tension did show diff erences which can be attributed to tillage or soil management, and the se differences are most obvious when measurements are made on a settle d seedbed in the period from flowering to post harvest.