Changes in some soil properties due to tillage practices in rainfed hardsetting Alfisols and irrigated Vertisols of eastern Australia

Changes in soil physical and chemical properties were evaluated in several on-farm studies located in rainfed, hardsetting red Alfisols (Ferric Luvisols) and in irrigated, self-mulching Vertisols (Chromic Vertisols) of eastern Australia. The objective of the studies was to evaluate changes in soil physical and chemical properties with time under commercial farming situations where changes had been made to previously used farming systems (native pasture to wheat (Triticum sp.) cultivation in the hardsetting Alfisols; intensively tilled cotton (Gossypium sp.) monoculture to minimum tilled cotton monoculture and cotton-wheat sequences in the irrigated Vertisols), The soil physical and chemical changes in the Alfisols were caused by changing land use from native pasture to intensively tilled wheat cultivation with long fallow and stubble burning, whereas those in the Vertisols were caused by changing from intensive to minimum tillage in cotton-based cropping systems. Indicators of soil physical (tensile strength, structural stability, dispersion) and chemical (pH, electrical conductivity, organic C, total N) quality evaluated in the Alfisols indicated that a significant deterioration in soil quality, which was characterized by an increase in hardsetting behaviour and acidity, and a decrease in organic C, total N and aggregate stability had occurred. These changes were due to inappropriate tillage practices causing soil inversion and the rapid breakdown of organic matter which occurs when intensive tillage practices are imposed in previously untilled soils. In the Vertisols, however, indicators of soil physical (specific volume of air-filled pores in oven-dried clods, plastic limit, soil resilience) and chemical (pH, electrical conductivity, exchangeable sodium percentage, and soil organic C) quality indicated that while deterioration in physical quality (i.e., characterized by an increase in compaction) had occurred, chemical quality had improved. The latter was characterized by an increase in soil organic C and a decrease in exchangeable sodium percentage. These changes were due to replacing intensive tillage with minimum tillage. (C) 1999 Elsevier Science B.V. All rights reserved.