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Background: Indigenous fire management in northern Australian savannas (beginning at least 11,000 years ago) involved frequent, small, cool, early dry season fires. This fire regime changed after European arrival in the late 1700s to unmanaged fires that burn larger areas, late in the dry season, detrimental to carbon stocks and biodiversity. Aims: Test the hypothesis that significant sequestration of pyrogenic carbon in soil accompanies the reimposition of an Indigenous fire regime. Methods: Savanna soils under the same vegetation, but with the number of fires varying from 0 to 13 (irrespective of the season) between 2000 and 2022 were sampled. Organic and pyrogenic carbon stocks as well as carbon isotope composition of the 0–5 cm soil layer were determined along sample transects with varying fire return intervals. Key results: An average increase of 0.25 MgC ha−1 was observed in soil pyrogenic carbon stocks in transects with ≥5 fires, compared to transects with 0–4 fires, with a small increase in soil organic carbon stocks that was not significant. Conclusions: A return to more frequent fires early in the dry season has the potential to sequester significant pyrogenic carbon in northern Australian savanna soils on decadal timescales. The reimposition of an Indigenous fire regime (frequent, small, cool, early dry season fires) has the potential to sequester significant pyrogenic carbon in northern Australian savanna soils on decadal timescales. We observed an increase of 0.25 MgC ha−1 in transects with ≥5 fires over a 22-year period. [ABSTRACT FROM AUTHOR]

Tidal marshes, mangrove forests, and seagrass meadows are important global carbon (C) sinks, commonly referred to as coastal "blue carbon". However, these ecosystems are rapidly declining with little understanding of what drives the magnitude and variability of C associated with them, making strategic and effective management of blue C stocks challenging. In this study, our aims were threefold: (1) identify ecological, geomorphological, and anthropogenic variables associated with 30 cm deep sediment C stock variability in blue C ecosystems in southeastern Australia, (2) create a predictive model of 30 cm deep sediment blue C stocks in southeastern Australia, and (3) map regional 30 cm deep sediment blue C stock magnitude and variability. We had the unique opportunity to use a high-spatial-density C stock dataset of sediments to 30 cm deep from 96 blue C ecosystems across the state of Victoria, Australia, integrated with spatially explicit environmental data to reach these aims. We used an information theoretic approach to create, average, validate, and select the best averaged general linear mixed effects model for predicting C stocks across the state. Ecological drivers (i.e. ecosystem type or ecological vegetation class) best explained variability in C stocks, relative to geomorphological and anthropogenic drivers. Of the geomorphological variables, distance to coast, distance to freshwater, and slope best explained C stock variability. Anthropogenic variables were of least importance. Our model explained 46 % of the variability in 30 cm deep sediment C stocks, and we estimated over 2.31 million Mg C stored in the top 30 cm of sediments in coastal blue C ecosystems in Victoria, 88 % of which was contained within four major coastal areas due to the extent of blue C ecosystems (∼87 % of total blue C ecosystem area). Regionally, these data can inform conservation management, paired with assessment of other ecosystem services, by enabling identification of hotspots for protection and key locations for restoration efforts. We recommend these methods be tested for applicability to other regions of the globe for identifying drivers of sediment C stock variability and producing predictive C stock models at scales relevant for resource management. [ABSTRACT FROM AUTHOR]

Rotational grazing management strategies have been promoted as a way to improve the sustainability of native grass-based pasture systems. From disturbance ecology theory, rotational grazing relative to continuous grazing can increase pasture productivity by allowing vegetation to recover after short intense grazing periods. This project sought to assess whether soil organic carbon (SOC) stocks would also increase with adoption of rotational grazing management. Twelve pairs of rotationally and continuously grazed paddocks were sampled across a rainfall gradient in South Australia. Pasture productivity approximated as the normalized difference vegetation index (NDVI) was on average no different between management categories, but when the data from all sites were aggregated as log response ratios (rotational/continuous) a significant positive trend of increasing NDVI under rotational grazing relative to continuous grazing was found (R2 = 0.52). Mean SOC stocks (0–30 cm) were 48.3 Mg C ha-1 with a range of 20–80 Mg C ha-1 across the study area with no differences between grazing management categories. SOC stocks were well correlated with rainfall and temperature (multiple linear regression R2 = 0.61). After removing the influence of climate on SOC stocks, the management variables, rest periods, stocking rate and grazing days, were found to be significantly correlated with SOC, explaining 22% of the variance in SOC, but there were still no clear differences in SOC stocks at paired sites. We suggest three reasons for the lack of SOC response. First, changes in plant productivity and turnover in low-medium rainfall regions due to changes in grazing management are small and slow, so we would only expect at best small incremental changes in SOC stocks. This is compounded by the inherent variability within and between paddocks making detection of a small real change difficult on short timescales. Lastly, the management data suggests that there is a gradation in implementation of rotational grazing and the use of two fixed categories (i.e. rotational v. continuous) may not be the most appropriate method of comparing diverse management styles. [ABSTRACT FROM AUTHOR]

On-farm activities that reduce GHG emissions or sequester carbon from the atmosphere to compensate for anthropogenic emissions are currently being evaluated by the Australian Government as carbon offset opportunities. The aim of this study was to examine the implications of establishing and grazing Kikuyu pastures, integrated as part of a mixed Merino sheep and cropping system, as a carbon offset mechanism. For the assessment of changes in net greenhouse gas emissions, results from a combination of whole farm economic and livestock models were used (MIDAS and GrassGro). Net GHG emissions were determined by deducting increased emissions from introducing this practice change (increased methane and nitrous oxide emissions due to higher stocking rates) from the soil carbon sequestered from growing the Kikuyu pasture. Our results indicate that livestock systems using perennial pastures may have substantially lower net GHG emissions, and reduced GHG intensity of production, compared with annual plant-based production systems. Soil carbon accumulation by converting 45% of arable land within a farm enterprise to Kikuyu-based pasture was determined to be 0.80 t CO2-e farm ha-1 yr-1 and increased GHG emissions (leakage) was 0.19 t CO2-e farm ha-1 yr-1. The net benefit of this practice change was 0.61 t CO2-e farm ha-1 yr-1 while the rate of soil carbon accumulation remains constant. The use of perennial pastures improved the efficiency of animal production almost eight fold when expressed as carbon dioxide equivalent emissions per unit of animal product. The strategy of using perennial pasture to improve production levels and store additional carbon in the soil demonstrates how livestock should be considered in farming systems as both sources and sinks for GHG abatement. [ABSTRACT FROM AUTHOR]

Abstract: In many important agricultural regions, soil inorganic carbon (SIC) stocks can rival the amount of carbon found in organic form. Land management practices, including irrigation, fertilization and liming, have the potential to greatly alter the soil inorganic carbon cycle thus creating an important feedback to atmospheric CO2 concentrations. However, the current literature is less clear regarding the direction and magnitude of this feedback. Application of irrigation water, for example, can increase the rate of soil carbonate precipitation, but depending on the source of calcium and bicarbonate, the net reaction can be an atmospheric carbon sink, a carbon source or carbon neutral. Similarly, the accelerated dissolution of soil carbonates due to various acidifying processes can act as a net sink or source of atmospheric CO2 depending on the spatial and temporal frame of reference. While SIC stocks in agricultural soils have been found to increase or decrease by as much as 1.0tCha−1 yr−1, given the need to account for both the supply and fate of reactants and reaction products, ascribing these stock changes as a net sink or net source activity is difficult. This review paper provides an overview of the major inorganic carbon transformations in soils as affected by agricultural management, including the practice of liming to raise soil pH, and when these transformations should be considered a net atmospheric carbon source or sink. [Copyright &y& Elsevier]

Anthropogenically induced change in soil redistribution plays an important role in the soil organic carbon ( SOC) budget. Uncertainty of its impact is large because of the dearth of recent soil redistribution estimates concomitant with changing land use and management practices. An Australian national survey used the artificial radionuclide caesium-137 (137Cs) to estimate net (1950s-1990) soil redistribution. South-eastern Australia showed a median net soil loss of 9.7 t ha−1 yr−1. We resurveyed the region using the same 137Cs technique and found a median net (1990-2010) soil gain of 3.9 t ha−1 yr−1 with an interquartile range from −1.6 t ha−1 yr−1 to +10.7 t ha−1 yr−1. Despite this variation, soil erosion across the region has declined as a likely consequence of the widespread adoption of soil conservation measures over the last ca 30 years. The implication of omitted soil redistribution dynamics in SOC accounting is to increase uncertainty and diminish its accuracy. [ABSTRACT FROM AUTHOR]

Policies aiming to preserve vegetated coastal ecosystems (VCE; tidal marshes, mangroves and seagrasses) to mitigate greenhouse gas emissions require national assessments of blue carbon resources. Here, we present organic carbon (C) storage in VCE across Australian climate regions and estimate potential annual CO 2 emission benefits of VCE conservation and restoration. Australia contributes 5-11% of the C stored in VCE globally (70-185 Tg C in aboveground biomass, and 1,055-1,540 Tg C in the upper 1 m of soils). Potential CO 2 emissions from current VCE losses are estimated at 2.1-3.1 Tg CO 2 -e yr -1 , increasing annual CO 2 emissions from land use change in Australia by 12-21%. This assessment, the most comprehensive for any nation to-date, demonstrates the potential of conservation and restoration of VCE to underpin national policy development for reducing greenhouse gas emissions.