Surface hydraulic properties of a red earth under continuous cropping with different management practices

Abstract

Differences in surface soil hydraulic properties after 10 years of different tillage (direct drilled (DD) versus conventional tillage (CT)) and stubble management practices (stubble retained (SR) versus stubble burnt (SB)) were measured in a lupin/wheat rotation on a red earth at Wagga Wagga, NSW. Sorptivity and hydraulic conductivity measurements using a disk permeameter under negative matric potential (-40 mrn) was complicated by water repellence found under SR as compared to SB treatments. Using water, K-40 of SR/DD was only 40% of SB/CT. However, using a wetting agent instead of water increased K-40 of SR/DD by >400% but did not significantly change that of SB/CT such that K-40 was similar for the two treatments. Despite similar bulk density, hydraulic conductivity under ponded infiltration of SR/DD was 4.1 times that of SB/CT. Differences in hydraulic conductivity between -40 mm and under ponded conditions suggest the presence of significantly more transmitting macropores >1.5 mm in diameter under direct drilling. Dye infiltration results indicated that tillage significantly reduced the number of transmitting macropores (>1 mm) even though the total number of macropores remained similar amongst the different treatments. 65% of the macropores were transmitting under SR/DD compared to 1% under SB/CT. A significant correlation (r2=0.82**) was found between transmitting pores (>1.0 mm) and the earthworm population. Tillage but not stubble burning significantly reduced earthworm population.