Temporal variation of hydraulic properties for some soils with fragile structure

Abstract

At three locations in the wheat belt of N.S.W. Cowra, Junee and Tamworth, 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 were hydraulic conductivity and sorptivity at -10 and -40 mm tension. Results show that the hydraulic properties of these soils can vary significantly through the growing season. This temporal variability was attributed to tillage, plant growth, rainfall and soil settling under wetting. The soil which had the more severe tillage treatment prior to sowing, together with stubble burning (traditional tillage), had lower values of hydraulic properties at 10 mm tension than the soil with the more conservative tillage treatment of direct drilling. Results for hydraulic properties at 40 mm tension did not show consistent differences between tillage treatments, the tillage effects being dependent on the particle size distribution of the soil and aggregate stability. Overall, the hydraulic properties measured at 10 mm tension did show differences which can be attributed to tillage or soil management, and these differences are most obvious when measurements are made on a settled seedbed in the period from flowering to post harvest.