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The inorganic soil C pool is a major source of CO2 emission into the atmosphere along with the soil respiratory CO2 fluxes but is comparatively less studied than the organic C mineralisation processes. This study aims to understand how soil available carbonates influence the soil C dynamics under different tillage, mulching and temperature regimes. A 90-day incubation experiment was conducted by adding calcite nodules to soils (10% w/w) collected from an agricultural field maintained with or without 5 t ha−1 mulching under no-till (NT) or conventional tillage (CT) systems. Environmental Scanning Electron Microscope (ESEM) examination indicated greater morphological changes in the calcite nodules incubated with CT than NT soils. Soil samples incubated with calcite and mulching recorded 6.3% greater CO2 evolution than the un-mulched condition. Under the CT system, the overall CO2 emission rate was higher in the control treatment (43%), followed by a combined treatment of 5 t ha−1 mulch + CaCO3 (10% w/w) (29.2%), 5 t ha−1 mulch only treatment (27.9%), and 10% CaCO3 (w/w) (16.5%) treatment, with a rise in incubation temperature from 22 °C to 37 °C. Kinetic model calculations for CO2 emission indicated a greater half-life of easily mineralisable C pools in the NT system at 22 °C. Microbial biomass carbon (MBC) results further verified that the high temperature and disturbed soil conditions limit the availability of soil MBC under the CT systems, indicating a higher decomposition rate. Eventually, these results indicated that agricultural management practices, including tillage shift, explicitly influence the different functional components of soil organic matter (SOM). Refereed/Peer-reviewed

Background and aims: Carbon (C) cycling in terrestrial ecosystems is influenced by the distribution of photo-assimilated C in the plant-soil system. Photo-assimilated C allocation in a wheat cropping system was examined to identify the links between soil fertility, C partitioning and soil C sequestration. Methods: A pulse labelling experiment was conducted where 14CO2 was introduced to wheat plants grown in two groups of soils of varying fertility: arable soils spiked with nutrients, and soils with differing land-use histories. Wheat shoot, root and soil samples were taken 1, 14 and 28 days after pulse labelling to examine the fluxes of 14C in the plant-root-soil system. Results: The partitioning of 14C in wheat plant-root-soil system was found to vary with time, nutrient spiked soil fertility and land-use history. At the end of the experiment using spiked soils, a positive correlation was observed between the allocation of 14C in the shoots and soil fertility, whereas in the roots, this relationship was negative.The overall allocation of 14C in the plant-root system differed significantly between the land-use histories; while in the spiked arable soils 14C allocation in the shoots and roots systematically followed their fertility status. Conclusions: There was a weak relationship between C allocation and soil fertility in the soils of different land-use history compared to the strong relationship in the spiked arable soils. This suggests that other factors in the soils under different land uses were more important than nutrient status alone in driving photo-assimilated C allocation. This study demonstrated that soil fertility and land-use history have a crucial role in the allocation of photo-assimilated C in the plant-soil system and are important factors by which C sequestration in soil may be impacted. Refereed/Peer-reviewed

International audience; Co-composting biowastes such as manures and biosolids can be used to stabilize carbon (C) without impacting the quality of these biowastes. This study investigated the effect of co-composting biowastes with alkaline materials on C stabilization and monitored the fertilization and revegetation values of these co-composts. The stabilization of C in biowastes (poultry manure and biosolids) was examined by their composting in the presence of various alkaline amendments (lime, fluidized bed boiler ash, flue gas desulphurization gypsum, and red mud) for 6 months in a controlled environment. The effects of co-composting on the biowastes' properties were assessed for different physical C fractions, microbial biomass C, priming effect, potentially mineralizable nitrogen, bioavailable phosphorus, and revegetation of an urban landfill soil. Co-composting biowastes with alkaline materials increased C stabilization, attributed to interaction with alkaline materials, thereby protecting it from microbial decomposition. The co-composted biowastes also increased the fertility of the landfill soil, thereby enhancing its revegetation potential. Stabilization of biowastes using alkaline materials through co-composting maintains their fertilization value in terms of improving plant growth. The co-composted biowastes also contribute to long-term soil C sequestration and reduction of bioavailability of heavy metals.

Thesis (PhD)--University of South Australia, 2013. Includes bibliographical references (leaves 144-174) Climate change due to increasing carbon dioxide (CO2) emission, a major greenhouse gas is considered a major threat to society. From the time of industrial revolution, the CO2 emission into the atmosphere has increased rapidly. Therefore, it is imperative to take steps to reduce the CO2 emissions and increase the atmospheric carbon (C) storage in a C reservoir such as soil. Indeed, soil C sequestration is an important option not only to mitigate climate change but also to enhance soil fertility and the productivity of agroecosystems.In addition to increasing plant C inputs, strategies for increasing Csequestration in soils include minimizing cultivation and other soil disturbances through conservation tillage, application of organic wastes such as bio-solids and composts, and improved crop rotation involving cover crops. The study aimed to investigate the effect of nutrients on C sequestration in agricultural soils. The specific objectives were to: (i) demonstrate the effect of stubble removal on C storage in soil as affected by nutrient addition; (ii) examine the effect of nutrients on the decomposition of organic compounds in soil; (iii) examine the priming effect (PE) of soil organic matter (SOM) due to added organic substrate as affected by nutrient availability and (iv) examine the photo-assimilated C distribution in plant-soil system as affected by nutrient addition. The effects of nutrients on C dynamics in stubble retention systems, decomposition of organic compounds, PE and management, and redistribution of photoassimilated C were examined using a number of analytical techniques including chemical C fractionation, 14C-labelled compounds and 14C pulse labelling.