Impact of management on soil carbon and nutrient cycling and storage under contrasting farming systems

Abstract

For this research, soils were collected from three long-term (16–46 years) management systems in semi-arid (Luvisol, at Condobolin, NSW), Mediterranean (Luvisol, at Merredin, WA) and sub-tropical (Vertisol, at Hermitage, QLD) environments in Australia from 0–10 cm, 10–20 cm and 20–30 cm depths. The practices at Condobolin comprised conventional (CT) and reduced tillage (RT) under mixed crop-pasture rotation, no-till (NT) under continuous cereal–cover crop rotation, and perennial pasture (PP). The practices at Merredin comprised stubble either retained (SR) or burnt (SB) under direct-drilled continuous wheat–legume rotation. The practices at Hermitage comprised a factorial combination of CT, NT, SR, SB, with either 0 (0N) or 90 kg urea-N ha-1 (90N) under continuous wheat–wheat rotation. To see soil aggregate stability, and SOC and nutrient stocks across the three long-term sites, dry and wet sieving techniques were performed to fractionate mega- (> 2 mm), macro- (2–0.25 mm), micro-aggregate (0.25–0.053 mm) and silt-plus-clay (< 0.053 mm) fractions. Further, to understand SOC and nutrient (N, P and S) mineralisation dynamics in bulk soil and soil aggregates, soils with or without crop residues were incubated for 126 days. To understand the allocation dynamics of newly assimilated C and N in a canola crop–soil system with different tillage and N fertilisation treatments, a field-based 13C15N isotopic study was performed at Wagga Wagga, NSW. The results showed that long-term management practices influenced carbon and nutrient (N, P and S) concentrations in soil aggregates, although had minimal impact on soil carbon and nutrient storage and aggregate stability. Soil organic matter was shown as a ready source of plant-available nutrients with variations across management practices. Crop stubble input in tilled (cf. no-till) systems caused a greater release of available nutrients. Further, tillage enhanced newly-assimilated carbon input into a soil system, leading a greater crop nitrogen uptake. These novel findings enhanced understanding of the impact of management practices on soil carbon and nutrient storage and nutrient availability in agro-ecosystems.