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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]

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]

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]

One of the main options for carbon mitigation identified by the IPCCis the sequestration of carbon in soils. In this paper we use statistical relationships derived from European long-term experiments to explore the potential for carbon sequestration in soils in the EuropeanUnion. We examine five scenarios, namely (a) the amendment of arablesoils with animal manure, (b) the amendment of arable soils with sewage sludge, (c) the incorporation of cereal straw into the soils in which it was grown, (d) the afforestation of surplus arable land through natural woodland regeneration, and (e) extensification of agriculture through ley-arable farming. Our calculations suggest only limitedpotential to increase soil carbon stocks over the next century by addition of animal manure, sewage sludge or straw (less than 15 Tg C y{sup}-1{end}), but greater potential through extensification of agriculture (~~ 40 Tg C y{sup}-1{end}) or through the afforestation of surplus arable land (~~ 50 Tg C y{sup}-1{end}). We estimate that extensification could increase the total soil carbon stock of the European Union by 17%. Afforestation of 30% of present arable land would increase soil carbon stocks by about 8% over a century and would substitute up to 30 Tg C y{sup}-1{end} of fossil fuel carbon if the wood were used as biofuel. However, even the afforestation scenario, with the greatest potential for carbon mitigation, can sequester only 0.8% of annual global anthropogenic CO{sub}2{end}-carbon. Our figures suggest that, although efforts in temperate agriculture can contribute to global carbon mitigation, the potential is small compared to that available through reducing anthropogenic CO{sub}2{end} emissions by halting tropical and sub-tropical deforestation or by reducing fossil fuel burning. [ABSTRACT FROM AUTHOR]

The purpose of this study was to characterize the soil organic carbon dynamics associated with four land-uses (cropland, grassland, shrubland, and forestland) in the upper Blue Nile Basin of the Ethiopian Highlands. We collected diverse biophysical data to allow spatial variability of soil organic carbon and factors contributing to this variation to be determined statistically, and used well established simulation models to interpret the data, predict long-term carbon dynamics and determine the potential for improvements in soil quality and mitigation of greenhouse gas emissions. The spatial variation in soil organic carbon in the 0–20 cm soil depth was significant across study areas ( P < 0.01, 21.6 g kg −1 –37.8 g kg −1 ), and between land-uses ( P < 0.05, 27.9 g kg −1 in cropland and 43.0 g kg −1 soil in forestland). In a multiple linear regression model, among the 11 explanatory variables used, four (total nitrogen, shrubs, trees and land use) showed a significant positive effect ( P < 0.01), while three (impact of grazing, impact of erosion and clay) showed a significant negative effect ( P < 0.01). Simulations using the assumption of steady state to estimate carbon dynamics suggested that plant inputs from croplands are generally lower than grass or shrublands, resulting in build-up of recalcitrant organic matter in shrublands compared to grass or croplands. Erosion results in a decline in both the absolute and relative amounts of carbon in recalcitrant pools, but the more active pools remained unchanged, meaning that the overall activity of soil organic matter is increased when the soil is eroded, and it becomes more difficult to sequester soil carbon. More rapid decrease in soil organic carbon is likely to be due to increased erosion, persistent removal of organic materials, grazing pressures, and higher rate of decompositions in cropland and grazing land-uses. Conversion to shrubland shows high potential to quickly restore eroded soils and build up a pool of recalcitrant soil carbon, suggesting that management of land using periodic 20 year exclosures, preventing cropping and grazing and allowing shrubland succession, could be beneficial in restoring degraded soils. Simulations using a calibration approach, rather than assuming steady state, corroborated these findings, suggesting that after 30 years of current management, croplands will deplete soil organic carbon by 5.6, 7.1 and 7.2 t ha −1 , and grasslands by 3.5, 3.9 and 2.7 t ha −1 , while shrublands will build-up soil organic carbon by 0.6, 0.1 and 1.3 t ha −1 at study sites. At one study site, forests, will further increase soil organic carbon by 6.7 t ha −1 after 30 years. The significant positive impact of shrubs and trees on soil organic carbon suggests the need to focus on introduction of agroforestry systems in crop and grasslands. [ABSTRACT FROM AUTHOR]