Dr Yunying Fang1, Dr Bhupinder Pal Singh1, Dr Mark Farrell2, Dr Roger Armstrong3, Dr Lukas Van Zwieten4, Prof Chengrong Chen5, Dr Ehsan Tavakkoli6

1NSW Department of Primary Industries, Elizabeth Macarthur Agricultural Institute, Menangle NSW 2568, Australia , Sydney/Menangle, Australia, 2CSIRO Agriculture & Food, Urrbrae, Australia, 3Agriculture Research, Department of Jobs, Precincts and Resources, Horsham, Australia, 4NSW Department of Primary Industries, Wollongbar Primary Industries Institute, Wollongbar, Australia, 5Australian Rivers Institute, School of Environment and Science, Griffith University, Nathan, Australia, 6NSW Department of Primary Industries, Wagga Wagga Agricultural Institute, Wagga Wagga, Australia

Subsoil sodicity is one of the main constraints on soil functionality, productivity and sustainability, particularly in arid and semi-arid regions. In recent years, the role of organic amendments (OAs) combined with inorganic fertilizers or gypsum has received much attention for ameliorating soil physicochemical constraints and improving carbon (C) storage in sodic-subsoils. However, little is known about the effect of resource nutrient stoichiometry and gypsum on C dynamics in organic-amended sodic-subsoils. Here, we examined the role of OAs (application rate of 6.2 g OA-C kg-1 soil; C4 vegetation-derived: δ¹³C –12 to –15‰) in altering microbial C mineralization, microbial C use efficiency (CUE) and soil C priming, with and without the exogenous supply of nutrients or gypsum, in an alkaline sodic-clay subsoil (5.8 g C kg-1 soil; C3 vegetation-derived: δ¹³C –24‰).

The cumulative OA-C mineralization ranged between 70 and 630 mg CO2-C g-1 OA-C across the treatments over 270 days. The CUE of OAs was the highest in the mill mud-treated subsoil (0.25–0.80) and the lowest in the sorghum stubble-treated subsoil (0.07–0.42). The inherently balanced C-nutrient stoichiometry of OAs (such as mill mud) enhanced CUE, whereas lowering the imbalanced nutrient stoichiometry of other OAs (sorghum stubble, sugarcane bagasse) via exogenous nutrient inputs increased microbial growth but not CUE. Over 270 days, extra 0.7–8.3% of native soil organic carbon (SOC) was lost via priming across the treatments. In the first three months, the positive priming effect by the OAs was the highest in the sorghum stubble-treated subsoil, which was mainly driven by microbial co-metabolism and N mining. At the later stage, the balanced resource nutrient stoichiometry enhanced the PE. This study suggests that balancing the C-nutrient stoichiometry of OAs can increase soil functions and biological processes, such as microbial degradation of OAs, microbial growth and positive SOC priming, which may enhance nutrient availability and improve soil structure during amelioration of sodic-subsoil constraints.

Biography: Adjunct Professor Bhupinder Pal (“BP”) Singh is working as Principal Research Scientist with NSW Department of Primary Industries. His research interests are in the areas of soil science, ecology, biogeochemistry, and understanding the role of soil organic matter functionality, such as carbon and nutrient cycling in agro-ecosystems. Dr Singh disseminates his research outcomes, via invited lectures, field-day participation, and (inter)national conferences to stakeholders, underpinning improved management strategies for sustainable agriculture.

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