Soil Organic Carbon Depletion Research Articles

Impacts of plastic film mulching on crop yields, soil water, nitrate, and organic carbon in Northwestern China: A meta-analysis

In order to increase crop yield in semi-arid and arid areas, plastic film mulching (PFM) is widely used in Northwestern China. To date, many studies have addressed the effects of PFM on soil physical and biochemical properties in rain-fed agriculture in Northwestern China, but the findings of different studies are often contradictory. Therefore, a comprehensive review of the impacts of PFM on soil water content, soil nutrients and food production is needed. We compiled the results of 1278 observations to evaluate the overall effects of PFM on soil water content, the distribution of nitrate and soil organic carbon, and crop yield in rain-fed agriculture in Northwestern China. Our results showed that PFM increased soil moisture and nitrate concentration in topsoils (0–20 cm) by 12.9% and 28.2%, respectively, but slightly decreased (1.8%) soil organic carbon (SOC) content in the 0–10 cm soil layer. PFM significantly increased grain yields by 43.1%, with greatest effect in spring maize (79.4%). When related to cumulative precipitation during the crop growing season, yield increase from PFM was greatest (72.8%) at 200–300 mm, which was attributed to the large increase for spring maize and potato, implying that crop zoning would be beneficial for PFM in this region. When related to N application rate, crop yields benefited most from PFM (80.2%) at 200–300 kg/ha. A cost-benefit analysis indicated that PFM increased economic return by an average of 29.5%, with the best improvement for spring maize (71.1%) and no increase for spring wheat. In conclusion, PFM can significantly increase crop yield and economic return (especially for spring maize) in rain-fed agriculture areas of Northwestern China. Crop zoning is recommended for PFM to achieve the largest economic benefit. However, full account needs to be taken of the environmental impacts relating to N loss, SOC depletion and film pollution to evaluate the sustainability of PFM systems and further research is required to quantify and mitigate these impacts.

A Bayesian belief network framework to predict SOC dynamics of alternative management scenarios

Understanding the key drivers that affect a decline of soil organic carbon (SOC) stock in agricultural areas is of major concern since leading to a decline in service provision from soils and potentially carbon release into the atmosphere. Despite an increasing attention is given to SOC depletion and degradation processes, SOC dynamics are far from being completely understood because they occur in the long term and are the result of a complex interaction between management and pedo-climatic factors. In order to improve our understanding of SOC reduction phenomena in the mineral soils of Veneto region, this study aimed to adopt an innovative probabilistic Bayesian belief network (BBN) framework to model SOC dynamics and identify management scenarios that maximise its accumulation and minimise GHG emissions.Results showed that the constructed BBN framework was able to describe SOC dynamics of the Veneto region, predicting probabilities of general accumulation (11.0%) and depletion (55.0%), similar to those already measured in field studies (15.3% and 50%, respectively). A general enhancement in the SOC content was observed where a minimum soil disturbance was adopted. This outcome suggested that management strategies of conversion from croplands to grasslands, no tillage and conservation agriculture are the most promising management strategies to reverse existing SOC reduction dynamics. Moreover, measures implying SOC stocks were also those providing major benefits in terms of GHGs reduction emissions. Finally, climate change scenarios slightly affected management practice. Advancements in our BBN framework might include more detailed classes at higher resolution as well as any socio-cultural or economic aspect that should improve the evaluation of prediction scenarios.

Participatory trials of on-farm biochar production and use in Tamale, Ghana

Urban agriculture is characterized by fast rotation of cropping cycles and high inputs and outputs on relatively small areas of land. Depletion of soil organic carbon and low nutrient use efficiency are severe agricultural constraints in the sandy soils of West Africa. We hypothesized that such an intensive system would provide ideal preconditions for the use of biochar, that biochar would enhance yields in urban horticulture, and that farmers would be able to produce biochar for on-farm use in Tamale, Ghana. Therefore, we studied the opportunities and challenges of biochar using a semi-participatory research approach. Working with 12 participant farmers, we defined research questions which were relevant to their livelihoods and collected qualitative and observational data, which determined the selection of variables to measure quantitatively. Different quality parameters such as leaf color and stiffness of lettuce were important to farmers and marketers when assessing the agronomic benefits of biochar. By adding biochar to their normal agricultural practice farmers were able to increase lettuce yields by 93%. This remarkable increase might be partially caused by farmers’ improved management of biochar plots: they concentrated their resources where they expected to yield the largest returns. Using a simple top-lit updraft gasifier, a special chimney for rice husk carbonization, it was relatively simple for farmers to produce biochar in the field, with an efficiency of 15–33%. These stoves’ payback times were between 1 and 2 months. Yet, rather than the efficiency of the carbonization technology, often emphasized in biochar research, the availability of feedstock and labor considerations determine the technology selected by farmers for biochar production. This is a novel approach to considering the economic realities of farmers in a semi-participatory appraisal where farmers both produce and apply biochar. This is crucial in order to understand and identify meaningful and economically viable uses of biochar.

The carbon sequestration potential of terrestrial ecosystems

T errestrial ecosystems, comprising vegetation and soil in uplands and wetlands, significantly impact the global carbon (C) cycle and, under natural conditions, are a sink of atmospheric carbon dioxide (CO2) and methane (CH4). However, conversion of natural to managed ecosystems (i.e., agroecosystems, urban lands, and mined lands) depletes ecosystem C stocks, aggravates gaseous emissions, and exacerbates radiative forcing. Thus, the onset of agriculture around 8000 BC presumably transformed these sinks into a source of greenhouse gases (GHGs) (Ruddiman 2003), mostly CO2, CH4, and nitrous oxide (N2O), and depleted the terrestrial (soil, vegetation, and peatlands) C stocks. Ruddiman (2005) estimated the depletion of the terrestrial C stock (soil and vegetation) by 456 Pg (502.65 × 109 tn) since the onset of agriculture. Of this, the historic depletion of soil organic carbon (SOC) stock is estimated at 130 to 135 Pg (143.3 × 109 to 148.8 × 109 tn) (Sanderman et al. 2017; Lal 2018). Therefore, recarbonization of some of the terrestrial biosphere (soil and vegetation) is an important strategy to mitigate the anthropogenic climate change (ACC) and enhance other ecosystem services because of the link between SOC stock and atmospheric concentration of CO2 (Trenberth and Smith 2005). Recarbonizing the terrestrial biosphere involves…

Degraded lands and their management for rehabilitation and improving crop productivity

Soil degradation causes decline in its productivity, deterioration in vegetative cover, qualitative, and quantitative decline of soil and water resources and pollution of air is widespread in India. In recent decades, the problem is greatly aggravated because of country’s increasing population, requiring marginal areas to be brought under the cultivation to meet the growing food demand. Poverty and natural resources degradation forced individuals to search for more land for food, fodder and fibre production. The main causes of degradation due to direct/indirect human intervention are deforestation and removal of natural vegetation, overgrazing, and converting forest lands to arable land, cultivating steep slopes and degrading marginal lands, other agriculture related activities and over exploitation of the vegetation for domestic purposes. Similarly, the removal or in-situ burning of crop residues, minimum addition of organic manures, and intensive cultivation are the major causes of the depletion of soil organic carbon (SOC). Potential threats to the conservation of soil resources are soil erosion both by water and air, salinization/ alkalinity, acidity, organic carbon (OC) losses, nutrient imbalance, pollution/contamination by toxic substances, and soil sealing and capping. To arrest the process of degradation, urgent measures viz., indigenous soil and land conservation practices, conservation farming, watershed management including land and water management technology, water harvesting, Integrated plant nutrient supply, (IPNS), physical, mechanical, and biological approach, soil amendments, restoration of SOC, aforestation and agro-forestry, farming system approach, and organic farming, etc. are required for rehabilitating productivity of degraded soils so that more food could be produced to provide livelihood and environmental security to the ever increasing Indian population.

Increasing Soil Organic Carbon Through Crop Diversification in Cereal–Cereal Rotations of Indo-Gangetic Plain

Continuous practices of cereal–cereal rotations in Indo-Gangetic plain (IGP) region have emerged with several soil related issues including depletion of soil organic carbon (SOC). Crop diversification remains a conceivable option to address this issue. Here, the authors envisaged the long-term alternate-year inclusion of chickpea in upland maize–wheat and lowland rice–wheat systems on SOC, C-dynamics and C management indices under organic, inorganic, and control nutrient management. Inclusion of chickpea in rice–wheat and maize–wheat systems increased total organic C (TOC) by 6.5 and 13.4%, and particulate organic C (POC) by 94.7 and 41.3% in the surface soil (0–0.2 m), respectively. In both the production systems, enrichment of very-labile C (Cfrac1) and labile C (Cfrac2) fractions were apparent with inclusion of chickpea. Very-labile (Cfrac1) (36.6–37.9%) in upland and less-labile (Cfrac3) (29.1–31.7%) in lowland were the dominant C-fractions. Subsequently, upland conditions had higher active C-pool; conversely, lowland ecosystem enriched passive C-pool, which is desirable for long-term persistence of soil C. The higher values of TOC, POC, and C-fractions were registered in organic nutrient treatment over inorganic and control treatment. In lowland, chickpea residue C had a low rate of stabilization as compared to cereal residue. In lowland, crop diversification with chickpea increased lability-index and C-management index; however, the effect was marginal in upland. Thus, inclusion of chickpea in the cereal–cereal rotations of IGP would be a potential long-term strategy to improve SOC and to ensure production sustainability.

Traditional manual tillage significantly affects soil redistribution and CO2 emission in agricultural plots on the Loess Plateau

Traditional manual tillage using hand tools is widely used by local farmers in hilly and mountainous regions in China and many South-east Asian countries. Manual tillage could result in severe soil erosion, redistributing slopes from upslope areas (erosion) to lower slopes (deposition). This soil redistribution process may potentially affect the soil carbon cycle, but few studies have quantified soil CO2 emission under different manual tillage practices. In the present study we evaluated the soil redistribution and its effects on in situ CO2 emission as affected by manual tillage of different intensities on three short slopes representing typical cultivated landscapes on the Loess Plateau. Soils were removed at 2, 6 and 10 cm depths by three types of hand tools, namely a hoe, mattock and spade respectively, from the upslope and subsequently accumulated at the downslope to simulate soil erosion and deposition processes by traditional manual tillage. Across the tilled hillslopes, soil CO2 emission was reduced at sites of erosion but enhanced at sites of deposition. Tillage with greater intensity (i.e. hoeing < mattocking < spading) resulted in greater change in CO2 emission. This change in soil CO2 emission was largely associated with the depletion of soil organic carbon (SOC) stocks at erosion sites and the increments of SOC available for decomposition at deposition sites. Moreover, with increasing tillage intensity, soil redistribution by manual tillage shifted the hillslope from a C sink to C neutral or even a C source. Furthermore, manual tillage resulted in substantial changes in soil CO2 emission and redistributed soil in amounts that dwarf animal-powered tillage. The results of the present study imply that manual tillage-induced soil redistribution could have a large effect on the C balance across the local landscape and therefore may have considerable implications for estimates of regional and global C budgets.

Modelling the impacts of different carbon sources on the soil organic carbon stock and CO2 emissions in the Foggia province (Southern Italy)

The effects of systematic compost addition or cover cropping throughout the agricultural land of the Foggia province (Southern Italy) on the soil organic carbon (SOC) stocks and the CO2-C emissions were predicted over a period of 20years (1994–2013).Therefore, the bio-physical model RothC10N was used in combination with spatially explicit input data including soil types, soil textures, land use and climate. Actual crop successions and crop types on a grid with a resolution of 30-arc sec (1km at the equator) were included in the input data.Compost application and cover cropping were not adopted as a general input to all soils and land use classes, but according to applicability in the particular cropping systems, therefore representing a realistic input scenario under given soil use practices in the area.The results of the modelling process were spatialized with regression kriging, using soil maps, land use maps and satellite images as co-variates.While the control scenario led to a SOC depletion of 0.81 Tg and a total CO2-C emission of 21.1 Tg over 20years in the Foggia province, systematic compost addition could reduce the loss of SOC to 0.56 Tg C while slightly increasing CO2-C emissions to 21.6 of Tg C. Cover cropping led to an overall SOC accumulation of 0.61 Tg and cumulated CO2-C emissions of 24.6 of Tg. Cover cropping therefore represents the most promising tool for carbon sequestration in the Foggia province.

Does long-term plastic film mulching really decrease sequestration of organic carbon in soil in the Loess Plateau?

Abstract Plastic film mulching (PM) is used extensively in China to increase the productivity of food crops, especially in the arid and semi-arid regions, although a recent concern is whether the practice decreases soil organic carbon (SOC). A process-based biogeochemical model applied in the Loess Plateau, where PM is widespread, examined the status of SOC over 30 years of maize cultivation with PM. The model explained 96% of the observed variance in SOC. The root mean square error was 0.39 g kg −1 , the mean absolute error was 0.32 g kg −1 , and the bias value from the SOC simulation was −0.006 g kg −1 . The model’s projections showed that PM has no significant impact on the overall average content of SOC across the entire study area compared to the fields without mulching, or control (CK), assuming that 5% of the crop residue was ploughed back into soil. However, based on individual simulation points in the 0–50 cm soil profile after 30 years of PM, 59.29% of the points, mainly on the western parts of the Loess Plateau, showed significantly higher SOC than that in CK, 8.30% showed significantly lower, and 32.41%, mainly on the south-eastern part of the Plateau, showed no significant difference between sites with PM and without it. Mulching increased the biomass, rhizodeposition, and the speed of turnover of SOC significantly, compared to the corresponding values in CK. High biomass in PM led to more carbon (C) being retained in soil and lowered the depletion of SOC. Ploughing the crop residues back into soil increased SOC, the greater the percentage of residue thus returned to soil, the higher the SOC. For a given residue return percentage, PM could increase more SOC than the CK. At 15%, which is the current average residue return ratio in the Loess Plateau, SOC levels remained stable or even increased in 77% of the study area if it adopted PM; in CK, the corresponding figure was only 63%. In regions such as the Loess Plateau where biomass is in great demand as a fuel or animal feed, PM provides greater biomass, which also means that more of it is available to be returned to soil—PM thus promotes the sequestration of SOC.

Why does carbon increase in highly weathered soil under no-till upon lime and gypsum use?

Field experiments have been used to explain how soil organic carbon (SOC) dynamics is affected by lime and gypsum applications, however, how SOC storage occurs is still debatable. We hypothesized that although many studies conclude that Ca-based soil amendments such as lime and gypsum may lead to SOC depletion due to the enhancement of microbial activity, the same does not occur under conservation agriculture conditions. Thus, the objective of this study was to elucidate the effects of lime and gypsum applications on soil microbial activity and SOC stocks in a no-till field and in a laboratory incubation study simulating no-till conditions. The field experiment was established in 1998 in a clayey Oxisol in southern Brazil following a completely randomized blocks design with a split-plot arrangement and three replications. Lime and gypsum were surface applied in 1998 and reapplied in 2013. Undisturbed soil samples were collected before the treatments reapplications, and one year after. The incubation experiment was carried out during 16months using these samples adding crop residues on the soil surface to simulate no-till field conditions. Lime and gypsum applications significantly increased the labile SOC stocks, microbial activity and soil fertility attributes in both field and laboratory experiments. Although the microbial activity was increased, no depletion of SOC stocks was observed in both experiments. Positive correlations were observed between microbial activity increase and SOC gains. Labile SOC and Ca2+ content increase leads to forming complex with mineral soil fractions. Gypsum applications performed a higher influence on labile SOC pools in the field than in the laboratory experiment, which may be related to the presence of active root system in the soil profile. We conclude that incubation experiments using lime and gypsum in undisturbed samples confirm that soil microbial activity increase does not deplete SOC stocks under conservation agriculture.

Factors Affecting SOC and NPK in the Rangeland, Forest and Agriculture; Case Study Halashi Catchment, Kermanshah, Iran

Land use change causes soil disturbance and thereby considerable soil nutrients depletion and environmental impacts. This research was conducted in Halashi catchment, Kermanshah, Iran to compare the variation of soil NPK and SOC in Agricultural Lands (AL), Rangelands (RL) and Forest lands (FL). The coverage of ground surface including plant crown, stone and litter was estimated in field by using quadrate plot (1 m2). Soil sampling and the analysis were carried out for each land use during April and May, 2015. Inter-rill, rill, gully and landslide were found as the dominant erosion features. The ANOVA analysis explored no considerable differences for soil texture, pH and Electrical Conductivity (EC). High clay and silt content induced clayey and silty soil that means Soil Organic Carbon (SOC) level in the AL, RL and FL were 1.14%, 1.45% and 2.13%, respectively, showing significant (p ≤ 0.05) different from each other among them. The respective values of total N in the AL, RL and FL were 0.14, 0.14 and 0.18 mg/kg, indicating significant decrease in the AL and RL. The respective mean avails P and exch. K in the AL, RL and FL were 15.72, 11.44, 11.38; 342.5, 375.0 and 374.5 mg/kg. Crop residues burning and tillage practicing cause depletion of SOC and NPK in AL, while as compared with FL, lower vegetation canopy and litter in the RL promotes soil nutrients and SOC lost due to overgrazing and converting to rain-fed lands. As a conclusion, rangeland was the intermediate site in terms of soil nutrient and SOC stock in the Halashi.

Soil organic carbon losses by water erosion in a Mediterranean watershed

Soil organic carbon (SOC) is one of the primary elements required in the functioning of ecosystems. Soil erosion, a major mechanism of land degradation, removes SOC and transfers it to the hydrosphere or the atmosphere, thereby affecting key ecosystem functions and services. The Mediterranean region is highly susceptible to land degradation because of erosion due to heavy rains following long, dry, hot summers. Although the Mediterranean landscape typically has a high altitude and incline, the soil is brittle and soft and is easily washed away by rain. Thus, vast regions in Turkey have been afflicted by this type of soil degradation. This study aimed to (1) estimate the temporal distribution of water erosion in the Seyhan River Basin, (2) assess the spatial distribution of SOC and (3) estimate the depletion of SOC through soil erosion using the Pan-European Soil Erosion Risk Assessment model, a physically based, regionally scaled soil erosion model. The annual amount of soil eroded from the Seyhan River Basin is estimated to be 7.8million tonnes per hectare (tha–1year–1). The amount of fertile soil loss from agricultural areas is ~1.2million tonnes per year. The maximum amount of soil erosion occurs in maintenance scrubland and degraded forest areas, contributing to 68% of erosion, followed by that in agricultural land, contributing to 27% of erosion, with the remaining in forests and urban areas.

CO2 emission pattern of eroded sloping croplands after simulated rainfall in subtropical China

Soil water erosion can profoundly affect soil properties, especially their integration with serious cultivation. The mobilization and depletion of soil organic carbon (SOC) are likely to respond to this disturbance, which may profoundly change the patterns of ecosystem carbon cycles. The effects of water erosion on SOC mineralization within tillage (TT) and no-tillage (NT) sloping lands were examined in this study through the simulation of one-hour rainfall and field observation of CO2 emission. During the rainfall, the estimated soil loss rates induced by erosion in NT and TT amounted to 0.72 and 0.05×103gm−2 respectively, and the corresponding SOC loss rates amounted to 10.83 and 0.84gm−2. Most of the measured soil properties showed significant difference between NT and TT after erosion. The cumulative CO2 productions of the three sub-plots in NT were lower than that of the control plot, while this observation was not detected in TT. NT also had larger variability in CO2 evolution rate than TT. The potentially mineralizable C showed a pattern of increase from up slope to down slope in both NT and TT. Redundancy analysis results illustrate that soil bulk density, moisture and dissolved organic carbon were the major physical factors controlling erosion-induced carbon mineralization among the measured soil properties, and that a complex interplay between the above three factors and silt content could best explain the variability of the cumulative CO2 productions. Together, these results suggest that patterns of CO2 emission from sloping croplands are closely related to the changes of soil properties induced by erosion, and tillage practices may profoundly affect those patterns by inducing shifts in the erosion-resistance response of soil texture to rainfall. Moreover, tillage practices could slow SOC mineralization under the influence of a single rainfall event more than no-tillage practices in the hilly red soil region of subtropical China.

Deforestation impacts on soil organic carbon stocks in the Semiarid Chaco Region, Argentina

Land use change affects soil organic carbon (SOC) and generates CO2 emissions. Moreover, SOC depletion entails degradation of soil functions that support ecosystem services. Large areas covered by dry forests have been cleared in the Semiarid Chaco Region of Argentina for cropping expansion. However, deforestation impacts on the SOC stock and its distribution in the soil profile have been scarcely reported. We assessed these impacts based on the analysis of field data along a time-since-deforestation-for-cropping chronosequence, and remote sensing indices. Soil organic C was determined up to 100cm depth and physically fractionated into mineral associated organic carbon (MAOC) and particulate organic C (POC). Models describing vertical distribution of SOC were fitted. Total SOC, POC and MAOC stocks decreased markedly with increasing cropping age. Particulate organic C was the most sensitive fraction to cultivation. After 10yr of cropping SOC loss was around 30%, with greater POC loss (near 60%) and smaller MAOC loss (near 15%), at 0–30cm depth. Similar relative SOC losses were observed in deeper soil layers (30–60 and 60–100cm). Deforestation and subsequent cropping also modified SOC vertical distribution. Soil organic C loss was negatively associated with the proportion of maize in the rotation and total crop biomass inputs, but positively associated with the proportion of soybean in the rotation. Without effective land use polices, deforestation and agricultural expansion can lead to rapid soil degradation and reductions in the provision of important ecosystem services.

Sensitivity of soil carbon fractions and their specific stabilization mechanisms to extreme soil warming in a subarctic grassland.

Terrestrial carbon cycle feedbacks to global warming are major uncertainties in climate models. For in-depth understanding of changes in soil organic carbon (SOC) after soil warming, long-term responses of SOC stabilization mechanisms such as aggregation, organo-mineral interactions and chemical recalcitrance need to be addressed. This study investigated the effect of 6years of geothermal soil warming on different SOC fractions in an unmanaged grassland in Iceland. Along an extreme warming gradient of +0 to ~+40°C, we isolated five fractions of SOC that varied conceptually in turnover rate from active to passive in the following order: particulate organic matter (POM), dissolved organic carbon (DOC), SOC in sand and stable aggregates (SA), SOC in silt and clay (SC-rSOC) and resistant SOC (rSOC). Soil warming of 0.6°C increased bulk SOC by 22±43% (0-10cm soil layer) and 27±54% (20-30cm), while further warming led to exponential SOC depletion of up to 79±14% (0-10cm) and 74±8% (20-30) in the most warmed plots (~+40°C). Only the SA fraction was more sensitive than the bulk soil, with 93±6% (0-10cm) and 86±13% (20-30cm) SOC losses and the highest relative enrichment in 13 C as an indicator for the degree of decomposition (+1.6±1.5‰ in 0-10cm and +1.3±0.8‰ in 20-30cm). The SA fraction mass also declined along the warming gradient, while the SC fraction mass increased. This was explained by deactivation of aggregate-binding mechanisms. There was no difference between the responses of SC-rSOC (slow-cycling) and rSOC (passive) to warming, and 13 C enrichment in rSOC was equal to that in bulk soil. We concluded that the sensitivity of SOC to warming was not a function of age or chemical recalcitrance, but triggered by changes in biophysical stabilization mechanisms, such as aggregation.

A spatially explicit life cycle assessment midpoint indicator for soil quality in the European Union using soil organic carbon

Improving land use assessment in life cycle assessment (LCA) is a priority. Recently, soil organic carbon (SOC) depletion has been proposed as a transformation and occupation midpoint indicator to estimate impacts on biotic production potential (BPP). SOC depletion is recommended by the European Union in the International Reference Life Cycle Data System (ILCD) Handbook as a land use indicator. There is a consensus method to calculate SOC depletion in LCA, and ILCD proposes a set of characterization factors (CFs), but these lack geographical discrimination. Our method of calculation for midpoint CFs follows Brandao and Mila i Canals (Int J Life Cycle Assess 18:1243–1252, 2013). We operationalize the method using SOC stocks from the LUCASOIL database of field measurements in Europe. We use potential natural vegetation (PNV) as the reference situation. CFs were calculated on a cell basis for 23 countries in Europe and grouped in three spatial scales (an administrative classification, NUTS II, and two biophysical classifications, ecoregion and climate region) according to soil type and land cover following a consensus map of cover classes. To evaluate the method’s results, CFs were applied in a case study. SOC stocks of European soils were obtained according to land use and soil type classes (excluding non-European Union countries) for the three spatial scales. A database of European transformation and occupation CFs is also presented and analyzed. The aggregation of CFs at biophysical scales (ecoregion and climate region) is similar, but NUTS II aggregation of CFs is problematic. The application of the CFs in the case study revealed significant differences compared to the outcome of using CFs collected from other land use models. This paper is the first operationalization using field measurements of an updated version of the ILCD-recommended model for land use impacts in LCA. We obtained CFs for SOC depletion in Europe that can be nested within CFs suggested by ILCD since our results possess better spatial resolution but are only for European Union countries. The case study application highlighted the need for inventories to improve the spatial resolution of the life cycle processes to match the detail of LCIA models.

Overgrazing decreases soil organic carbon stocks the most under dry climates and low soil pH: A meta-analysis shows

Grasslands occupy about 40% of the world’s land surface and store approximately 10% of the global soil organic carbon (SOC) stock. This SOC pool, in which a larger proportion is held in the topsoil (0–0.3m), is strongly influenced by grassland management. Despite this, it is not yet fully understood how grassland SOC stocks respond to degradation, particularly for the different environmental conditions found globally. The objective of this review was to elucidate the impact of grassland degradation on changes in SOC stocks and the main environmental controls, worldwide, as a prerequisite for rehabilitation. A comprehensive meta-analysis was conducted using 55 studies with 628 soil profiles under temperate, humid, sub-humid, tropical and semi-arid conditions, to compare SOC stocks in the topsoil of non-degraded and degraded grassland soils. Grassland degradation significantly reduced SOC stocks by 16% in dry climates (<600mm) compared to 8% in wet climates (>1000mm) and Asia was the most affected continent (−23.7%). Moreover, the depletion of SOC stock induced by degradation was more pronounced in sandy (<20% clay) soils with a high SOC depletion of 10% compared to 1% in clayey (≥32% clay) soils. Furthermore, grassland degradation significantly reduced SOC by 14% in acidic soils (pH≤5), while SOC changes were negligible for higher pH. Assuming that 30% of grasslands worldwide are degraded, the amount of SOC likely to be lost would be 4.05Gt C, with a 95% confidence between 1.8 and 6.3Gt C (i.e. from 1.2 to 4.2% of the whole grassland soil stock). These results by pointing to greater SOC losses from grasslands under dry climates and sandy acidic soils allow identification of grassland soils for which SOC stocks are the most vulnerable, while also informing on rehabilitation measures.

The effect of straw and wood gasification biochar on carbon sequestration, selected soil fertility indicators and functional groups in soil: An incubation study

Annual removal of crop residues may lead to depletion of soil organic carbon and soil degradation. Gasification biochar (GB), the carbon-rich byproduct of gasification of biomass such as straw and wood chips, may be used for maintaining the soil organic carbon content and counteract soil degradation if applied to soil. This study investigated the effect of straw removal and GB addition on soil biological, chemical and physical properties in a 22-months soil incubation study with a temperate sandy loam soil.Soil application of wood and straw GB (WGB and SGB) resulted in very low CO2 emissions, confirming the stability of the material against microbial degradation. Both GBs increased total organic carbon, cation exchange capacity and pH of the soil. The application of SGB and WGB did not affect aggregate stability, whereas SGB did not affect and WGB decreased clay dispersibility. In contrast, the addition of straw resulted in a high soil respiration rate, and about 80% of the added carbon was respired at the end of the incubation. However, the addition of straw increased aggregate stability and decreased clay dispersibility. Results from Fourier transformed infrared photoacoustic spectroscopy revealed a lower content of O–H and aliphatic C–H together with a higher content of aromatic groups in soils amended with GB compared to soils amended with straw. This suggested that the improvement in aggregate stability in straw treatments could be related to microbial derived aliphatics and simple sugars, and that increased stability against microbial degradation in biochar amended soil was related to highly condensed aromatic groups. Addition of nutrients (N, P and S) together with straw resulted in higher soil respiration compared to the straw treatment, but did not cause differences in other soil processes.Results from this study suggest that GB has a potential for increasing soil carbon sequestration, CEC and pH. However, the straw turnover process plays a vital role for aggregate stability and clay dispersibility. Thus, annual straw removal on loamy soil needs to be considered with care in order to avoid soil degradation and risk of soil compaction or erosion.

Effect of Terrain Characteristics on Soil Organic Carbon and Total Nitrogen Stocks in Soils of Herschel Island, Western Canadian Arctic

Permafrost landscapes experience different disturbances and store large amounts of organic matter, which may become a source of greenhouse gases upon permafrost degradation. We analysed the influence of terrain and geomorphic disturbances (e.g. soil creep, active-layer detachment, gullying, thaw slumping, accumulation of fluvial deposits) on soil organic carbon (SOC) and total nitrogen (TN) storage using 11 permafrost cores from Herschel Island, western Canadian Arctic. Our results indicate a strong correlation between SOC storage and the topographic wetness index. Undisturbed sites stored the majority of SOC and TN in the upper 70 cm of soil. Sites characterised by mass wasting showed significant SOC depletion and soil compaction, whereas sites characterised by the accumulation of peat and fluvial deposits store SOC and TN along the whole core. We upscaled SOC and TN to estimate total stocks using the ecological units determined from vegetation composition, slope angle and the geomorphic disturbance regime. The ecological units were delineated with a supervised classification based on RapidEye multispectral satellite imagery and slope angle. Mean SOC and TN storage for the uppermost 1 m of soil on Herschel Island are 34.8 kg C m-2 and 3.4 kg N m-2, respectively. Copyright © 2015 John Wiley & Sons, Ltd.

Potential of fallow chronosequence in shifting cultivation to conserve soil organic carbon in northeast India

Secondary forest in shifting cultivation might influence soil organic carbon (SOC) stock. However, information with respect to SOC accumulation or depletion in fallow stand with secondary forest in shifting cultivation is insufficient. We, therefore, undertaken this experiment with the objective to evaluate the impact of secondary forest on SOC stock and its allocation into pools of different oxidizability [very labile (CVL), labile (CL), less labile (CLL) and nonlabile C (CNL)] along soil depth using three fallow chronosequences of shifting cultivation located in subtropical mid-hills of northeast India. Results showed that SOC content in 0–0.45m depth increased with age of the fallow stand [the values being 78.4, 91.5 and 102.8Mgha−1 in young (5–9years), mid-aged (18–20years) and old (28–33years) secondary forest, respectively] after land clearing (slashing and burning of forest) and exhaustive cropping (75.9kgha−1). There was a decrease in SOC content with increasing soil depth, constituting 49.0, 27.8 and 23.2% of the total (for 0–0.45m) for 0–0.15, 0.15–0.30 and 0.30–0.45m, respectively. Among the analyzed C pools CVL, CL and CLL were influenced by the fallow period and the active pools (CVL+CL) constituted 65.7% of the SOC. Most of the SOC pools were significantly correlated with each other and with fallow age. Results thus indicate that soil in shifting fallow conserves increasing amount of organic C during regeneration of forest vegetation and majority of the SOC is in active or labile pools of shorter residence time.