Information
Key findings (brief)
Project 1
Turpin et al. (1998) concluded that leaching losses were strongly influenced by land management practices that either increased mineral nitrogen levels, or infiltration within the soil. A significant relationship was observed at the Hermitage site between zero tillage and stubble retention on the depth of chloride infiltration. Zero tillage and stubble retention increased chloride infiltration with the peak chloride concentration occurring at 4.5m within the zero tillage sites. This is 2m deeper than in the other trial sites. Undisturbed soils also showed a significant influence on chloride infiltration rate with the Virgin Hermitage site chloride concentration peaking around 1m, 1.5m higher than all other sites.
The Hermitage study indicated that leaching losses in Vertosols of the Darling Downs can be up to 377kg N/ha over 20 years. Stubble burning, increased infiltration, while increasing nitrogen in the top soil for plant uptake. However, as the chloride concentrations had shown, zero – tillage increased infiltration through the soil. When nitrogen application rates were increased in either zero tillage - stubble retained, or zero tillage – stubble burnt soils, nitrogen concentrations would peak at shallower depths but then rapidly decrease due to transportation through water infiltration.
Project 2
Turpin et al. (1999) concluded that the same land management practices performed in the long-term fallow management trial also strongly influenced aggregate stability and pore continuity within black Versotol soils. Zero tillage and stubble retained soils were found to have better aggregate stability , pore continuity, and resistance to compaction through the reduction of traffic and retention of straw. Whereas, aggregates in soils that had conventional tillage - stubble burned were found to have less stability. This was caused by smearing of the aggregate surfaces during tillage practices and stubble removal resulting in massive peds up to 20cm across.
Under dry and moist conditions, when the soil is cracked, all tillage treatments had similar conductivities but in wet conditions zero tillage - stubble retention soils maintained structure resulting in a greater volume of large pores improving conductivity. Infiltration rates are far greater within zero tillage – stubble retained soils making them susceptible to nutrient leaching.
Key tables and figures extracted from data, literature and miscellaneous publications