Long-term effects of tillage systems and rotation on selected soil properties in cropping zone of Southern NSW, Australia

Different tillage and cropping practices can change soil properties which in turn can affect crop growth and the environment. The objective of this study was to investigate the effect of different tillage and pasture rotation systems on pH, soil organic matter (SOC), total N (TN) and selected physical properties of the surface layer (0-5 cm) of 3 soils in Wagga Wagga, New South Wales, Australia. In 0-5 cm layer, % 2mm water stable macro-aggregates, soil organic carbon (SOC), and total nitrogen (TN) were significantly higher in the treatments of direct drilled/stubble retained (DD/SR), perennial pasture (PP) and nature pasture (NP), than the corresponding contrasting treatments of conventional cultivation/stubble burnt (CC/SB), pasture/crop rotation (PPC) and conventional cultivation (CT) respectively. At all 3 experiment sites, conservation tillage had the effect of changing the nature of organic carbon resulting in higher labile and slow organic carbon fractions. Soil organic carbon concentration was significantly related to total nitrogen(r=0.994 ,n=6). At each experiment site, SOC was significantly positively correlated with % 2 mm macro-aggregates but there was no correlation when data of all 3 sites were combined. This indicated that SOC was not the only factor affecting soil aggregation, other factors like clay content were also involved.The effects of tillage practice on bulk density (BD) and porosity varied at different experiment sites. At one of the sites, BD was significantly higher and 60 μm porosity was significantly lower under conventional tillage practice compared to conservation tillage.However, results of the other two sites were inconsistent. Field capacity water content was significantly affected by tillage practices and significantly correlated with SOC within 3 soils ( r=0.996 ,n=6). This suggested that soil water holding capacity was mainly affected by SOC. Stubble burning and gypsum application significantly altered exchangeable Ca2+、Mg2+、K+, and topsoil pH. Adoption of conservation tillage and/or perennial pasture can improve topsoil SOC and structural stability and therefore long-term soil fertility.