Water and bromide movement in a Vertosol under four fallow management systems

Recent work on the Hermitage long-term fallow management found increased ra tes of anion movement under zero tillage systems compared with conventional tillage. Four separate experiments have been used to determine relative ra tes of water movement through different fallow management treatments on the Hermitage long-term fallow management trial and the causes of any differen ces. Photography of the aggregation patterns at the depth of tillage (approx. 15 cm) showed that conventional tillage combined with stubble burning has led to the formation of large massive peds up to 20 cm across below the tillag e layer, whereas zero-tillage with stubble retention has maintained much sm aller aggregates in this zone. Measurements of hydraulic conductivity at 15 cm under both dry and moist conditions indicated that, when the soil is dr y and cracked, all tillage treatments have similar conductivities, but when the soil swells and cracks close, zero tillage-stubble retention maintains a greater volume of large pores and thereby greater conductivity. This ere ct was further demonstrated when a bromide tracer solution was applied to a relatively wet soil by ring infiltrometer, where only 15% of the solution moved below 15 cm in conventional tillage-stubble burning compared with 26% and 38% in zero tillage-stubble retention. In the final experiment, which followed the movement of surface applied bromide over a 6-month fallow, the re were no significant differences in rates of leaching between management treatments.