Dr BhupinderPal Singh1, Dr Jharna Rani Sarker2, Dr Annette Cowie3, Dr Yunying Fang1, Mr Damian Collins1, Dr Warwick Badgery4, Prof Ram Dalal5

1NSW Department of Primary Industries, Elizabeth Macarthur Agricultural Institute, Menangle NSW 2568, Australia , Sydney/Menangle, Australia, 2University of New England, School of Environmental and Rural Science, Armidale, Australia, 3NSW Department of Primary Industries, Livestock Industries Centre, Armidale, Australia, 4NSW Department of Primary Industries, Orange Agricultural Institute, Orange, Australia, 5School of Agriculture and Food Sciences, The University of Queensland, St Lucia, Australia

There is a limited understanding of the impact of long-term management practices on soil organic carbon (SOC) and total nitrogen (N), sulphur (S) and phosphorus (P) concentrations in aggregates from different soils and consequent effects on SOC and nutrient storage in agro-ecosystems. Soils from long-term (16–46 years) management systems in semi-arid (Luvisol in Condobolin, NSW), Mediterranean (Luvisol in Merredin, WA) and sub-tropical (Vertisol in Hermitage, QLD) environments were collected (up to 30 cm depth). Dry- and wet-sieving techniques were used to fractionate the soils into mega-aggregates (>2mm), macro-aggregates (2–0.25mm), micro-aggregates (0.25–0.053mm), and silt-plus-clay (<0.053mm). The practices in the Luvisol were conventional (CT) and reduced tillage (RT) under mixed farming, no-till (NT) under continuous cropping, and perennial pasture (PP) at Condobolin, and stubble either retained (SR) or burnt (SB) under continuous cropping at Merredin. The practices in the Vertisol were CT, NT with either SR or SB under continuous cropping at Hermitage.

In the Luvisols, the practices had no effects on SOC and total N, S and P stocks (at all depths to 30 cm). However, in the Vertisol, the NT-SR showed higher SOC (p<0.10) and total N, S, and P (p<0.05) stocks than the other treatments at 0–10 cm only. The SOC and N concentrations were higher (p<0.05) in the wet-sieved silt-plus-clay fractions and mega-aggregates than macro- and micro-aggregates in the PP and NT at Condobolin, and SR at Merredin only (cf. other treatments at 0–10 cm). At Hermitage, SOC and N concentrations were in the order of dry- or wet-sieved silt-plus-clay ≥ micro-> mega- ≥ macro-aggregates in the NT-SR treatment only. Total S concentration was in the order of macro- ≥ micro- > mega-aggregates across all the treatments and was higher in the PP at Condobolin (0–10 cm), and in the SR at Merredin (all soil depths) than the other treatments. Further, at Merredin, both SR and SB had higher P concentration in macro- and micro- than mega-aggregates. In summary, although the PP, NT, and SR (compared with other treatments) had minimal impact on total SOC and nutrient stocks, these practices had higher SOC and/or nutrient concentrations in the finer aggregate fractions (silt-plus-clay or microaggregates). These findings suggest that sustainable farming practices such as minimal soil disturbance, stubble retention, and continual organic matter input in the systems are important for increasing SOC and nutrient storage while maintaining soil structural stability and building systems’ resilience.


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 to stakeholders, via invited lectures, field-day participation, and (inter)national conferences, underpinning improved management strategies for sustainable agriculture.

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