Soil carbon and nutrient services under Australian apple production systems

Increasing soil carbon can mitigate climate change and enhance soil water and nutrient retention. To improve soil function and sustainability, a better understanding of the links between soil carbon, nutrient availability, and soil microbial communities is required. We conducted a survey of soil carbon and soil functioning in the main apple orcharding regions of Australia, with the objectives of establishing the soils’ current carbon status and determining the relationships between soil carbon and soil function. Orchard soils were sampled in five depth increments to 70 cm. Analyses were performed for total and labile pools of organic carbon and nitrogen, microbial activity and pH. Surface soil samples were further analysed by anaerobic incubation to measure the potentially mineralisable nitrogen pool, and by qPCR to assess soil microbial biodiversity and the genes involved in the nitrogen cycle. The measured parameters varied widely among sites. Soil carbon stocks to 1 m ranged from 7 to 26 kg C m^-2. All characteristics decreased rapidly with depth in the soil profile. Strong positive relationships were observed between various soil health parameters. Hot-water carbon, total nitrogen, dehydrogenase activity and potential nitrogen mineralisation were strongly correlated with each other. These soil functioning parameters serve as potential indicators for soil carbon regulation and nutrient supply in orchard production systems.