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The objectives of this study across the highlands of Ethiopia were: (i) to characterize the association between soil organic carbon (SOC) stocks and biophysical variables and (ii) to model and map attainable SOC sequestration associated with five improved land management practices. The spatial distribution of the SOC stock was studied using a multiple linear regression model driven by eight biophysical predictors. A widely used SOC model (RothC) was then used to model changes in SOC over the next 20–50 years of improved land management. Simulations were driven by the derived SOC stocks, pH and clay contents that are available in the ISRIC soils database at 250 m resolution and climate data from the "Enhancing National Climate Services Initiative" database. Organic carbon inputs to the model were estimated from the "Improved Crop Varieties Yield Register" of the Ministry of Agriculture and Livestock Resource and the Central Statistics Authority. After 50 years of conservation tillage with 80% of available manure applied to cultivated land, the total SOC stock increased by 169,182,174 t, which is 2.8 times higher than the stock increase with only 50% of available manure applied. Introduction of improved pasture species and measures to control soil erosion was an important source of net carbon sequestration in grasslands. Afforestation and reforestation of degraded landscapes and protection of natural ecosystems further increased soil carbon. This highlights the importance of improved land management practices to SOC sequestration, which in turn could enhance agricultural productivity, food security and sustainable development. [ABSTRACT FROM AUTHOR]

Soil amendment with organic wastes in the Highlands of Ethiopia has been greatly reduced by widespread use of dung cakes and crop residues as fuels. This study assessed the interaction between household energy and recycling of nutrients and carbon to the soil using household survey, focus group discussions, key informant interviews, direct observations and measurements between 2014 and 2015 in Kumbursa village (Central Highlands of Ethiopia). All surveyed households were entirely dependent on biomass fuel for cooking, with production and consumption rates directly related to wealth status, which significantly varied ( P < 0.001) among three farm wealth groups (poor, medium and rich). Crop residues and dung cakes accounted for 80(±3)% by energy content and 85(±4)% by dry mass weight of total biomass fuel consumption. Mean losses were 59(±2) kg ha−1 yr−1 nitrogen (109(±8) kg yr−1 per household), 13.9(±0.3) kg ha−1 yr−1 phosphorus (26(±2) kg yr−1 per household), 79(±2) kg ha−1 yr−1 potassium (150(±11) kg yr−1 per household) and 2100(±40) kg ha−1 yr−1 organic carbon (3000(±300) kg yr−1 per household). Rich farmers lost significantly more carbon and nutrients in fuel than farmers in other wealth groups. However, these losses were spread over a larger area, so losses per land area were significantly higher for medium and poor than for rich farmers. This means that the land of poorer farmers is likely to become degraded more rapidly due to fuel limitations than that of rich farmers, so increasing the poverty gap. The estimated financial loss per household due to not using dung and crop residues as organic fertilizer was 162(±8) US$ yr−1. However, this is less than their value as fuels, which was 490(±20) US$ yr−1. Therefore, farmers will only be persuaded to use these valuable assets as soil improvers if an alternative, cheaper fuel source can be found. [ABSTRACT FROM AUTHOR]

Field experiments were conducted at Gujjar Seed and Nursery Farm, Haripur, Pakistan to investigate impact of incorporating differently treated of organic manures using different tillage systems on soil carbon. Maximum increase in soil carbon was observed when the required nitrogen was applied as bioslurry produced from cattle manure by anaerobic digestion. This was significantly greater than when the required amount of nitrogen was applied as composted poultry manure or chemical fertilizer. Minimum tillage also resulted in a significant increase of soil carbon compared to conventional or deep tillage. These experimental measurements were used to evaluate a dynamic simulation model of soil organic matter turnover, RothC, which was then used to estimate future carbon sequestration. The correlation between experimental and simulated values was highly significant and the root mean square error was within experimental error, suggesting that RothC is providing an acceptable representation of the changes in soil carbon that is occurring in this experiment. The uncertainty in simulations was less than 3%. Simulations were done using future weather scenarios; these suggest that addition of the recommended rate of nitrogen in 8.4 t ha-1 y-1 bioslurry every year increases soil carbon sequestration over 100 years (2012-2112) by 24.9±0.74 t ha-1 compared to the control where no organic manure was applied. This sequesters 7.5±0.24 t ha-1 more carbon than if the same amount of nitrogen is applied as poultry manure, requiring an application rate of 7.5 t ha-1 y-1. If the same amounts of bioslurry and poultry manure are applied, carbon sequestration is still significantly greater for bioslurry than for poultry manure (4.5±0.2 t ha-1). Losses of carbon with climate change were highest under climate scenario B2 (environmental protection with regionalization) and B1 (environmental protection with globalization), followed by A1B (economic growth with globalization), with minimum losses from A2 (economic growth with regionalization). These predicted losses are likely to be more than compensated for by application of organic fertilizers at the rates needed to supply sufficient nitrogen to the crops. [ABSTRACT FROM AUTHOR]

We present results from modelling studies, which suggest that, at most, only about 10–20% of recently observed soil carbon losses in England and Wales could possibly be attributable to climate warming. Further, we present reasons why the actual losses of SOC from organic soils in England and Wales might be lower than those reported. [ABSTRACT FROM AUTHOR]

SummaryUnder the Kyoto Protocol, the European Union is committed to a reduction in CO2 emissions to 92% of baseline (1990) levels during the first commitment period (2008–2012). The Kyoto Protocol allows carbon emissions to be offset by demonstrable removal of carbon from the atmosphere. Thus, land-use/land-management change and forestry activities that are shown to reduce atmospheric CO2 levels can be included in the Kyoto targets. These activities include afforestation, reforestation and deforestation (article 3.3 of the Kyoto Protocol) and the improved management of agricultural soils (article 3.4). In this paper, we estimate the carbon mitigation potential of various agricultural land-management strategies and examine the consequences of European policy options on carbon mitigation potential, by examining combinations of changes in agricultural land-use/land-management. We show that no single land-management change in isolation can mitigate all of the carbon needed to meet Europe's climate change commitments, but integrated combinations of land-management strategies show considerable potential for carbon mitigation. Three of the combined scenarios, one of which is an optimal realistic scenario, are by themselves able to meet Europe's emission limitation or reduction commitments. Through combined land-management scenarios, we show that the most important resource for carbon mitigation in agriculture is the surplus arable land. We conclude that in order to fully exploit the potential of arable land for carbon mitigation, policies will need to be implemented to allow surplus arable land to be put into alternative long-term land-use. Of all options examined, bioenergy crops show the greatest potential for carbon mitigation. Bioenergy crop production also shows an indefinite mitigation potential compared to other options where the mitigation potential is finite. We suggest that in order to exploit fully the bioenergy option, the... [ABSTRACT FROM AUTHOR]

Abstract: We test the applicability of two different methods for quantifying carbon (C) stocks in five tropical peat sites in Sumatra, Indonesia; two in an intact peat swamp forest, one in a logged forest and two in an oil palm plantation. Elemental analysis is used to quantify C contents and stocks in all samples, and is the standard to which the two methods are compared. The first method, loss on ignition (LoI), underestimates sample C stocks by 4.9±0.8% compared to results from the elemental analysis across all samples. Loss on ignition is applied to three full peat cores in one of the intact forest sites and one oil palm site, using the standard factor of 1.922 to convert the organic matter (OM) result into C content. Evaluation against independent data suggests that a factor of 1.878 would be more appropriate. The second method, using the equation presented in Warren et al. (2012) for quantifying C density in peat swamp forest soils, shows no significant difference between the equation and elemental analysis derived results for the intact and logged forest sites. We suggest the use of a bulk density (BD) range to further define the limits of the equation. When applied to samples from oil palm sites, there was a significant difference in the results provided by the Warren equation and elemental analysis. Evaluation against independent data suggests that, in this land use, C density (kgCm−3) is more accurately estimated by the equation Cd =(515.44×BD)+3.01 (R2 =0.94). We also present a variable factor for the conversion of the organic matter (OM) to C content by merging the two methods. We recommend the use of the LoI method with the improved factor for conversion of OM to C content, or where bulk density is known the Warren equation for calculating accurate C density values across intact and logged forests on Indonesian peats, and our revised equation for oil palm sites. [Copyright &y& Elsevier]