Decline In Soil Organic Carbon Research Articles

Land use effects on organic carbon storage in soils of Bavaria: The importance of soil types

Numerous studies have reported substantial changes of soil organic carbon (SOC) stocks after converting forests into agricultural land and vice versa. However, some studies suggested that agricultural soils might contain similar amounts of SOC as forest soils. Losses of SOC induced by cultivation might be overestimated due to shallow soil sampling and application of inaccurate pedotransfer functions. We investigated the impact of different land uses on total SOC storage down to the subsoil on the basis of 270 soil profiles in southeast Germany under similar climatic and pedogenic conditions using an equivalent soil mass (ESM) approach. Land use effects on SOC storage were strongly affected by soil class, which comprised soil types with similar pedogenesis. Both slightly lower (<20%) and even higher SOC stocks were found under cropland compared with forest land for different soil classes. A comparison of different soil classes under grassland and forest land also showed no considerable differences of SOC stocks. Soil cultivation may not generally be associated with a strong decline of SOC, as tillage probably promotes the formation of organo-mineral associations and a relocation of SOC with depth may decrease its decomposition. This finding should be taken into consideration when estimating and managing the emission and sequestration of C in soils. We assume that many studies based on topsoils alone may have underestimated agricultural SOC stocks, particularly when an ESM approach is used. Our results highlight the need for soil type-specific evaluations in terms of interpreting the effects of land use management on SOC stocks.

Land degradation impact on soil organic carbon and nitrogen stocks of sub-tropical humid grasslands in South Africa

Land degradation is recognized as a main environmental problem that adversely depletes soil organic carbon (SOC) and nitrogen (SON) stocks, which in turn directly affects soils, their fertility, productivity and overall quality. While it is expanding worldwide at rapid pace, quantitative information on the impact of land degradation on the depletion of SOC and SON stocks remains largely unavailable, limiting the ability to predict the impacts of land management on the C losses to the atmosphere and associated global warming. The main objective of this study was to evaluate the consequences of a decrease in grass aerial cover on SOC and SON stocks. A degraded grassland showing an aerial cover gradient from 100% (Cov100, corresponding to a non-degraded grassland) to 50–75% (Cov75), 25–50% (Cov50) and 0–5% (Cov5, corresponding to a heavily degraded grassland), was selected in South Africa. Soil samples were collected in the 0.05m soil layer at 48 locations along the aerial cover gradient and were subsequently separated into the clay+silt (2–20μm) and sand (20–2000μm) fractions, prior to total C and N analysis (n=288). The decline in grass aerial cover from 100% to 0–5% had a significant (P<0.05) impact on SOC and SON stocks, with losses by as much as 1.25kgm−2 for SOC and 0.074kgm−2 for SON, which corresponded to depletion rates of 89 and 76%, respectively. Furthermore, both the C:N ratio and the proportion of SOC and SON in the silt+clay fraction declined with grass aerial cover, which was indicative of a preferential loss of not easily decomposable organic matter. The staggering decline in SOC and SON stocks raises concerns about the ability of these acidic sandy loam soils to sustain their main ecosystem functions. The associated decrease in chemical elements (e.g., Ca by a maximum of 67%; Mn, 77%; Cu, 66%; and Zn, 82%) was finally used to discuss the mechanisms at stake in land degradation and the associated stock depletion of SOC and SON stocks, a prerequisite to land rehabilitation and stock replenishment.

Sustainability of maize (Zea mays)-wheat (Triticum aestivum) cropping system under legumes intercropping and effect of nitrogen level on light distribution, soil temperature and crop productivity

Agriculture designs for cropping system with legume intercropping for increased resource use efficiency profitability, productivity and reduced adverse environmental impact are urgently required. A three years field experiment consisting of six cropping treatments applied during both seasons was conducted during 2008-09 to 2010-11 to study the effect of nitrogen and legumes intercropping with maize (Zea mays L.) for sustainability of maize-wheat (Triticum aestivum L.) cropping system. Results indicate that the photosynthetic active radiation had highest values at noon reaching nearly 1940 µmol/m2/s for maize and 1620 µmol/m2/s for intercropped legumes. Intercropping can increase light interception, shading and reduce water evaporation as compared to sole maize. Maize intercropped had higher values of stomatal condutance and leaf temperature than sole crop. The grain yield and yield attributing characters of wheat crop increased significantly under intercropping treatments over respective check. Wheat yield significantly increased up to 160 kg N/ha. However, there was no significant increase in yield of maize beyond 120 kg N/ha.Sole maize-wheat rotation showed a decline in soil organic carbon by 3.7%,while blackgram and cowpea intercropping with maize in paired rows (2:2 row ratio) followed by wheat increased contents of percent organic carbon in soil as 0.63 and 0.67 respectively, compared to initial values of 0.54 percent. Plots treated with intercrops/FYM during the rainy season sustained the wheat yield while the check plot showed a decline in wheat yield by 4-9%.

English

Agriculture designs for cropping system with legume intercropping for increased resource use efficiency, profitability, productivity and reduced adverse environmental impact are urgently required. A three-year field experiment consisting of six cropping treatments applied during both seasons was conducted during 2008-2009 to 2010-2011 to study the effect of nitrogen and legume intercropping with maize for sustainability of maize-wheat cropping systems. Results indicate that the photosynthetic active radiation was at noon reaching nearly 1940 μmol m-2 s-1 for maize and 1620 μmol m-2 s-1 for intercropped legumes. Intercropping can increase light interception, shading and reduce evaporation as compared to sole maize. Maize intercropped had higher values of stomatal conductance and leaf temperature than pure crop. The grain yield and yield attributing characters of wheat crop increased significantly under intercropping treatments when compared with wheat only. Wheat yield significantly increased up to 160 kg N ha-1. However, there was no significant increase in yield of maize beyond 120 kg N ha-1. Sole maize-wheat rotation showed a decline in soil organic carbon by 3.7%, while black gram and cowpea intercropping with maize in paired rows (2:2 row ratio) followed by wheat had increased contents of per cent organic carbon in soil as 0.63 and 0.67, respectively, as compared to initial values of 0.54%. Plots treated with intercrops/farm yard manure (FYM) during the rainy season sustained the wheat yield while the control plot showed a decline in wheat yield by 4-9%. Key words: Sustainability, intercropping, soil temperature, crop productivity.

Modelling the impact of declining soil organic carbon on soil compaction: Application to a cultivated Eutric Cambisol with massive straw exportation for energy production in Northern France

Loss of organic matter has been recognized as being a major threat to soils in Europe with important consequences for the physical functioning of soils. We present the result of a numerical analysis of the integrated effects of changes in soil porosity and soil water status, along with decreased soil organic carbon (SOC) and the subsequent changes in the risk of compaction. This study concerns the impact of straw exportation on the risk of soil compaction. We evaluated the risk of compaction of a cultivated Eutric Cambisol in Northern France having a dominant silt loam soil texture, by simulating vehicle wheeling during sugar beet cropping for contrasting soil organic carbon contents (4.7, 11.1 and 23.4gkg−1). To do this, we coupled two models: (1) a crop model (STICS) to calculate the changes in the water content of the 0–30cm depth layer; and (2) a compaction model (COMPSOIL) to calculate soil stresses as a function of vehicle characteristics. Our study suggests that a decrease in SOC reduces the risk of topsoil deformation due to a decrease in soil water content, which tends to augment soil precompression stress. The method requires improvement in the future because it is very sensitive to input parameters for soil physical properties. Nevertheless it provides the first method for evaluating the impact of SOC decline on soil compaction. Its genericity permits it further applications to various soil management practices that decrease SOC.

Using DSSAT-CENTURY Model to Simulate Soil Organic Carbon Dynamics Under a Low-Input Maize Cropping System

Decline in Soil Organic Carbon (SOC) below the critical levels is one of the major indicators of soil fertility depletion in Sub-Saharan Africa (SSA), with the main causes being poor management practices coupled with low input use. Measures for monitoring long-term impacts of management on SOC dynamics and its restoration can be critical in enhancing sustainable soil productivity. Crop models have proved to be good tools for understanding the influence of management options on soil and crop productivity. The DSSAT-Century model was applied to simulate the influence of management practices on SOC dynamics. Using long-term datasets from Kabete, Kenya (1976-1996 maize-bean) and Kiboga-Uganda (1980-2010 maize), model calibration and evaluation showed a good fit between simulated and observed values of SOC. On simulating continuous tillage with no fertilization for the 1980-2010 antecedent period and 2010-2060 extrapolated period, the model showed high rates of SOC decline in the newly cultivated soil as compared to a degraded soil. The simulated rate of decline is 2129 kg ha -1 yr -1 for newly cultivated soil and 849 kg ha -1 yr -1 for the continuously cultivated soils. The model was sensitive to initial partitioning of SOC pools, with SOC in previously uncultivated soils declining at a higher rate than that in the cultivated ones. The model confirmed that use of continuous tillage is a major threat to SOC building and soil fertility restoration in the tropics. Adopting conservation agriculture is critical for future generations. Overall, the DSSAT CENTURY model is a potential tool for predicting SOC dynamics in low-input farming systems.

Soil warming alters microbial substrate use in alpine soils

Will warming lead to an increased use of older soil organic carbon (SOC) by microbial communities, thereby inducing C losses from C-rich alpine soils? We studied soil microbial community composition, activity, and substrate use after 3 and 4 years of soil warming (+4 °C, 2007-2010) at the alpine treeline in Switzerland. The warming experiment was nested in a free air CO2 enrichment experiment using depleted (13)CO2 (δ(13)C = -30‰, 2001-2009). We traced this depleted (13)C label in phospholipid fatty acids (PLFA) of the organic layer (0-5 cm soil depth) and in C mineralized from root-free soils to distinguish substrate ages used by soil microorganisms: fixed before 2001 ('old'), from 2001 to 2009 ('new') or in 2010 ('recent'). Warming induced a sustained stimulation of soil respiration (+38%) without decline in mineralizable SOC. PLFA concentrations did not reveal changes in microbial community composition due to soil warming, but soil microbial metabolic activity was stimulated (+66%). Warming decreased the amount of new and recent C in the fungal biomarker 18:2ω6,9 and the amount of new C mineralized from root-free soils, implying a shift in microbial substrate use toward a greater use of old SOC. This shift in substrate use could indicate an imbalance between C inputs and outputs, which could eventually decrease SOC storage in this alpine ecosystem.

Reference Area Method for Mapping Soil Organic Carbon Content at Regional Scale

Soil organic carbon, the major component of soil organic matter, is very important in all soil processes. The decline in soil organic carbon (SOC) is recognized as one of the eight soil threats identified in the European Union Thematic Strategy for Soil Protection (COM (2006)231 final) (EC, 2006). The research challenge in this paper is to develop aggregation techniques which can ‘catch’ the variability at local level and being able to transfer this knowledge to larger scales. The latest developments included the research in upscaling modelling techniques which allow transferring the data values from local to regional scale. Digital Soil Mapping (DSM) and in particular regression kriging has been selected as the most appropriate modelling approach for the study. It has been successfully implemented at regional level and a soil organic carbon map was produced for the selected region (Slavkovsky Forest, 2400 km2, Czech Republic) by transferring knowledge from Lysina Critical Zone Observatory (0.40 km2). The Lysina CZO is situated in western Bohemia, the Czech Republic. Using digital soil mapping (DSM), demonstrated that it is possible to upscale the processes that take place at Critical Zone Observatories (CZOs) towards larger regions. According to the prediction results, the soil organic carbon values in the Slavkovsky Forest are ranging between 0% - 35.11%. The results of the linear regression procedure is promising, however, the statistical indicators are relatively low (R2=0.31) in the first step of the two stage model. The results of the study encourage applying similar approach at a wider scale. However, the ground data availability is still the key component to have more robust geostatistical models. The model and its outputs can be improved by using more ground data and high resolution environmental covariates.

Corn Stover Harvest Strategy Effects on Grain Yield and Soil Quality Indicators

Developing strategies to collect and use cellulosic biomass for bioenergy production is important because those materials are not used as human food sources. This study compared corn (Zea mays L.) stover harvest strategies on a 50 ha ClarionNicollet-Webster soil Association site near Emmetsburg, Iowa, USA. Surface soil samples (0 to 15 cm) were analyzed after each harvest to monitor soil organic carbon (SOC), pH, phosphorus (P) and potassium (K) changes. Grain yields in 2008, before the stover harvest treatments were imposed, averaged 11.4 Mg ha-1. In 2009, 2010, and 2011 grain yields averaged 10.1, 9.7, and 9.5 Mg ha-1, respectively. Although grain yields after stover harvest strategies imposed were lower than in 2008, there were no significant differences among the treatments. Four-year average stover collection rates ranged 1.0 to 5.2 Mg ha-1 which was 12 to 60% of the above-ground biomass. SOC showed a slight decrease during the study, but the change was not related to any specific stover harvest treatment. Instead, we attribute the SOC decline to the tillage intensity and lower than expected crop yields. Overall, these results are consistent with other Midwestern USA studies that indicate corn stover should not be harvested if average grain yields are less than 11 Mg ha-1.

Contrasting Effects of Agricultural Management on Soil Organic Carbon Balance in Different Agricultural Regions of China

Improving management of soil organic carbon (SOC) has been considered as a substantial mitigation strategy to climate change. Management such as stubble retention (SR), conservation tillage (ZT), and fertilization are recommended for both promoting production and accumulating SOC. However, whether such management practices can cause net increase in SOC or just a slow-down of SOC decline largely depends on the current status of SOC for a given region. This paper synthesized the available SOC data in the croplands of China, and analysed the change of SOC in the top 20 cm soil as a result of management change. The results showed that, on average, SOC increased by 18.3% through SR, by 9.1% through ZT, and by 12.4%, 36.9% and 41.5% through application of inorganic (IF), organic (OF) and combined inorganic and organic fertilizers (IOF), respectively, compared to those under stubble removal, conventional tillage and no fertilization. Under SR, ZT, IF, OF and IOF, SOC increased by 16.0%, 10.2%, 8.2%, 32.2% and 41.3%, respectively, at the end of the trials compared with the initial values at the start of the trials. Our analysis also showed that in Northeast and Northwest China, SOC in agricultural soils is still decreasing due to cultivation. In North and South China, however, SOC appears to have reached a new equilibrium of low SOC state after a long cultivation history, and soils have greater potential to sequester C. Our analysis highlights the need of taking account of the baseline status to assess the net soil C balance over time and space.

Temporal Variation of SOC Enrichment from Interrill Erosion over Prolonged Rainfall Simulations

Sediment generated by interrill erosion is commonly assumed to be enriched in soil organic carbon (SOC) compared to the source soil. However, the reported SOC enrichment ratios (ERSOC) vary widely. It is also noteworthy that most studies reported that the ERSOC is greater than unity, while conservation of mass dictates that the ERSOC of sediment must be balanced over time by a decline of SOC in the source area material. Although the effects of crusting on SOC erosion have been recognized, a systematic study on complete crust formation and interrill SOC erosion has not been conducted so far. The aim of this study was to analyze the effect of prolonged crust formation and its variability on the ERSOC of sediment. Two silty loams were simultaneously exposed to a rainfall simulation for 6 h. The ERSOC in sediment from both soils increased at first, peaked around the point when steady-state runoff was achieved and declined afterwards. The results show that crusting plays a crucial role in the ERSOC development over time and, in particular, that the conservation of mass applies to the ERSOC of sediment as a consequence of crusting. A “constant” ERSOC of sediment is therefore possibly biased, leading to an overestimation of SOC erosion. The results illustrate that the potential off-site effects of selective interrill erosion require considering the crusting effects on sediment properties in the specific context of the interaction between soil management, rainfall and erosion.

Implication of erosion on the assessment of decomposition and humification of soil organic carbon after land use change in tropical agricultural systems

Soil organic carbon decline after land use change from forest to maize usually leads to soil degradation and elevated CO2 emissions. However, limited knowledge is available on the interactions between rates of SOC change and soil erosion and how SOC dynamics vary with soil depth and clay contents. The 13C isotope based CIDE approach (Carbon Input, Decomposition and Erosion) was developed to determine SOC dynamics on erosion prone slopes. The aims of the present study were: (1) to test the applicability of the CIDE approach to determine rates of decomposition and SOC input under particular considerations of concurrent erosion events on three soil types (Alisol, Luvisol, Vertisol), (2) to adapt the CIDE approach to deeper soil layers (10–20 and 20–30 cm) and (3) to determine the variation of decomposition and SOC input with soil depth and soil texture. SOC dynamics were determined for bulk soil and physically separated SOC fractions along three chronosequences after land use change from forest to maize (up to 21 years). Consideration of the effects of soil erosion on SOC dynamics by the CIDE approach yielded a higher total SOC loss (6–32%), a lower decomposition (13–40%) and a lower SOC input (14–31%) relative to the values derived from a commonly applied 13C isotope based mass balance approach. Comparison of decomposition between depth layers revealed that tillage accelerated decomposition in the plough layer (0–10 cm), accounting for 3–34% of total decomposition. With increasing clay contents SOC input and mass of sand sized stable aggregates increased. In addition, decomposition increased with increasing clay contents, too, being attributed to decomposition of labile SOC which was attached to clay particles in the sand sized stable aggregate fraction. In conclusion, this study suggests that in situ SOC dynamics on erosion prone slopes are commonly misrepresented by erosion unadjusted approaches leading to an overestimation of SOC input and underestimation of SOC loss.

Carbon Depletion by Plowing and its Restoration by No‐Till Cropping Systems in Oxisols of Subtropical and Tropical Agro‐Ecoregions in Brazil

AbstractThe continuous use of plowing for grain production has been the principal cause of soil degradation. This project was formulated on the hypothesis that the intensification of cropping systems by increasing biomass‐C input and its biodiversity under no‐till (NT) drives soil restoration of degraded agro‐ecosystem. The present study conducted at subtropical [Ponta Grossa (PG) site] and tropical regions [Lucas do Rio Verde, MT (LRV) site] in Brazil aimed to (i) assess the impact of the continuous plow‐based conventional tillage (CT) on soil organic carbon (SOC) stock vis‐à‐vis native vegetation (NV) as baseline; (ii) compare SOC balance among CT, NT cropping systems, and NV; and (iii) evaluate the redistribution of SOC stock in soil profile in relation to soil resilience. The continuous CT decreased the SOC stock by 0·58 and 0·67 Mg C ha−1 y−1 in the 0‐ to 20‐cm depth at the PG and LRV sites, respectively, and the rate of SOC sequestration was 0·59 for the PG site and ranged from 0·48 to 1·30 Mg C ha−1 y−1 for the LRV site. The fraction of C input by crop residues converted into SOC stock was ~14·2% at the PG site and ~20·5% at the LRV site. The SOC resilience index ranged from 0·29 to 0·79, and it increased with the increase in the C input among the NT systems and the SOC sequestration rates at the LRV site. These data support the hypothesis that NT cropping systems with high C input have a large potential to reverse the process of soil degradation and SOC decline. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Soil carbon and nitrogen stocks under chronosequence of farm and traditional agroforestry land uses in Gambo District, Southern Ethiopia

Conversion of forests to farm lands with- out trees and farm lands with scattered trees (tradi- tional agroforestry systems) may lead to decline of soil organic carbon (SOC) and N stocks provided that they have similar original status. This study was conducted on soils with the age chronosequences of 12, 20, 30, 40, 50 years of farm (F), traditional agroforestry (AF) and the adjacent natural forest (NF) lands. We studied the changes in the concentration and stocks of SOC, total N and their distribution in the soil profile of an Andic Paleustalfs in Gambo District, Southern Ethi- opia. Soil samples were collected at 10, 20, 40, 60, 100 cm depth interval from pits of 1 m depth in all land use types and they were analyzed for their SOC and N stock. The results showed that the greater proportion of SOC and N was concentrated in 0-20 cm depth and that their concentration in AF and F land uses was significantly lower than that under the NF. Soils in traditional agroforestry land use showed a trend of higher SOC stocks in all chronosequences than those under the corresponding farm lands. The SOC stock under the chronosequence of 12-50 years of AF and F land uses varied from 28.2 to 98.9 Mg ha -1 or 12 to 43 % of the stock under the NF. The SOC was less by 6.2 Mg ha -1 year -1 for AF12 and 0.9 Mg ha -1 year -1 for AF50 compared with NF. The corresponding values for farm lands were 6.6 and 1.3 Mg ha -1 year -1 . The N values of all land uses were also less than that of the NF. The SOC and N stocks tended to be less in farm lands than in the traditional agroforestry. However, the SOC stocks were not significantly higher with AF compared with F suggesting that the parkland systems as practiced is not sufficient to overcome other effects of cultivation.

高寒草原土壤有机碳及土壤碳库管理指数变化研究

The alpine steppe plays a vital role in the stability of alpine ecosystem. To understand the variation of soil organic carbon( SOC) and active soil organic carbon( ASOC) in alpine steppe,and the influence of grassland degradation on soil carbon pool,We initially investigated the SOC and ASOC in the surface soil( 0—10 cm) and subsurface soil( 0— 20 cm) in normal steppe,light degraded steppe,severely degraded steppe in The Northern Tibet Plateau. The results showed that:( 1) The SOC and ASOC all declined with different degree in each layer soil in mildly degraded steppe and severely degraded steppe. The decline of SOC in surface soil were much higher than that in subsurface soil in these degraded steppe,and the decline of SOC in each layer soil decreased with the steppe degradation.. But the decline of ASOC in surface soil was much lower than subsurface soil,and which in severely degraded steppe was much higher than that in mildly degraded steppe.( 2) The distribution ratio of ASOC in surface soil in normal steppe,mildly degraded steppe and severely degraded steppe were 16. 8%,21. 3% and 16. 6%,respectively,and which in the subsurface were 21. 8%, 18. 1 and 16. 0%,respectively. Besides that,the variation tendencies of soil carbon pool activities were consistent with the distribution ratio of ASOC. So that,the SOC in the surface soil in the mildly degraded steppe is unstable.( 3) The soil carbon management index( CMI) in the surface soil and subsurface soil all significantly declined in degraded steppe,the decline of CMI in surface soil much lower than subsurface soil. The CMI in each layer soil of mildly degraded steppe were much higher compared to severely degraded steppe.( 4) The negative correlation was observed between SOC and ASOC in each layer soils in normal steppe,mildly degrade steppe and severely degraded steppe in alpine grassland. This result suggests that the effects of soil microorganism on SOC,ASOC might be different.

Estimating the soil organic carbon content for European NUTS2 regions based on LUCAS data collection

Under the European Union Thematic Strategy for Soil Protection, the European Commission Directorate-General for the Environment and the European Environmental Agency (EEA) identified a decline in soil organic carbon and soil losses by erosion as priorities for the collection of policy relevant soil data at European scale. Moreover, the estimation of soil organic carbon content is of crucial importance for soil protection and for climate change mitigation strategies.Soil organic carbon is one of the attributes of the recently developed LUCAS soil database. The request for data on soil organic carbon and other soil attributes arose from an on-going debate about efforts to establish harmonized datasets for all EU countries with data on soil threats in order to support modeling activities and display variations in these soil conditions across Europe.In 2009, the European Commission's Joint Research Centre conducted the LUCAS soil survey, sampling ca. 20,000 points across 23 EU member states. This article describes the results obtained from analyzing the soil organic carbon data in the LUCAS soil database. The collected data were compared with the modeled European topsoil organic carbon content data developed at the JRC. The best fitted comparison was performed at NUTS2 level and showed underestimation of modeled data in southern Europe and overestimation in the new central eastern member states. There is a good correlation in certain regions for countries such as the United Kingdom, Slovenia, Italy, Ireland, and France. Here we assess the feasibility of producing comparable estimates of the soil organic carbon content at NUTS2 regional level for the European Union (EU27) and draw a comparison with existing modeled data. In addition to the data analysis, we suggest how the modeled data can be improved in future updates with better calibration of the model.

Rothamsted carbon model reveals technical options to maintain soil organic carbon under semi-arid climate

Soil organic matter in the Sahel is severely reduced by continuous cultivation. Reductions of soil organic matter decrease in turn soil productivity. Nonetheless, reports show that organic matter application in the Sahel improves crop yield. However, long-term effects of organic matter application on soil fertility have not been fully studied. In particular, it is essential to get information on organic matter decomposition and annual carbon requirement. Model simulation is suitable for evaluating long-term sustainability. The Rothamsted carbon model is convenient and has been recently validated for use in Sahelian conditions. Here, we studied the annual carbon requirement for sustainable soil organic carbon management in the Sahelian zone using datasets of short-term trials conducted in the Sahel. We estimated the long-term effect of various agricultural managements on soil organic carbon dynamics as one of the soil fertility indices. The 10-year soil organic carbon value changes were predicted by the Rothamsted carbon model for 59 treatments. Results show that, contrary to previous short-term experiments that indicated crop yield enhancement, these technical options also cause a decline in soil organic carbon if enough organic resource is not applied. Soil productivity should therefore decrease. The annual carbon requirement to maintain the soil organic carbon level is approximately 0.8 tons of carbon per hectare.

Impact of soil tillage and land use on soil organic carbon decline under mediterranean conditions

Soils under Mediterranean climate conditions frequently have low to very low levels of soil organic matter (SOM), as a result of low biomass production under the predominantly rainfed conditions and the intensive tillage operations commonly practiced. In order to assess both short and long-term impacts of soil tillage and land use on soil organic carbon, two sets of experiments were performed. One consisted in the identification and soil analysis of 3 pairs of sites under different soil types and land use over 5 to 30 years; in the second experiment a long-term fallow area was repeatedly submitted to different types of soil tillage management (mouldboard plough + disc harrow; non-inversion tine cultivation; no-till) over 3 years. Soil texture, bulk density and SOM were analysed along the whole soil profile in the first experiment, whereas bulk density and SOM to a depth of 30 cm was measured before the first tillage operations and at the end of the observation period in the second experiment. The results clearly indicate that tillage based land use, irrespective of the type of land use, caused a considerable decline in SOM content in the tilled soil layer. Very small and inconsistent differences in SOM between paired soil profiles were observed in the lower part of the profiles. In the second experiment with three types of tillage systems, SOM content decreased with tillage intensity. Avoidance of soil disturbance is an important step towards halting SOM decline under Mediterranean climate conditions.

Spatial Variability of Soil Organic Carbon and Related Factors in Jiangsu Province, China

Soil organic carbon (SOC) plays a key role in the global carbon cycle. In this study, we used statistical and geostatistical methods to characterize and compare the spatial heterogeneity of SOC in soils of Jiangsu Province, China, and investigate the factors that influence it, such as topography, soil type, and land use. Our study was based on 24 186 soil samples obtained from the surface soil layer (0–0.2 m) and covering the entire area of the province. Interpolated values of SOC density in the surface layer, obtained by kriging based on a spherical model, rang ed between 3.25 and 32.43 kg m−3. The highest SOC densities tended to occur in the Taihu Plain, Lixia River Plain, along the Yangtze River, and in high-elevation hilly areas such as those in northern and southwest Jiangsu, while the lowest values were found in the coastal plain. Elevation, slope, soil type, and land use type significantly affected SOC densities. Steeper slope tended to result in SOC decline. Correlation between elevation and SOC densities was positive in the hill areas but negative in the low plain areas, probably due to the effect of different land cover types, temperature, and soil fertility. High SOC densities were usually found in limestone and paddy soils and low densities in coastal saline soils and alluvial soils, indicating that high clay and silt contents in the soils could lead to an increase, and high sand content to a decrease in the accumulation of SOC. SOC densities were sensitive to land use and usually increased in towns, woodland, paddy land, and shallow water areas, which were strongly affected by industrial and human activities, covered with highly productive vegetation, or subject to long-term use of organic fertilizers or flooding conditions.

LONG-TERM EFFECT OF PULSES AND NUTRIENT MANAGEMENT ON SOIL ORGANIC CARBON DYNAMICS AND SUSTAINABILITY ON AN INCEPTISOL OF INDO-GANGETIC PLAINS OF INDIA

SUMMARYContinuous cultivation of rice–wheat cropping system in the Indo-Gangetic plains is under threat with decline in soil organic carbon (SOC), total factor productivity and overall sustainability. Pulses, an important component of crop diversification, are known to improve soil quality through their unique ability of biological N2 fixation, leaf litter fall and deep root system. Therefore, the effect of inclusion of pulses in the puddled rice system under organic and inorganic amendments on SOC pool and its management indices were evaluated in a long-term experiment after seven cropping cycles. The results indicated that inclusion of pulses in the rice-based system improved the SOC content, being greater in surface soil (0–20 cm) and declining with soil depth. Among the four carbon fractions determined, less labile carbon fraction (Cfrac3) was the dominant fraction in the puddled rice system, particularly under organic treatments, indicating that it is possible to maintain organic carbon for longer time in this system. The rice–wheat–mung bean system resulted in 6% increase in SOC and 85% increase in soil microbial biomass carbon as compared with the conventional rice–wheat system. Application of crop residues, farm yard manure (5 t ha−1) and biofertilisers had greater amount of carbon fractions and carbon management index (CMI) over control and the recommended inorganic (NPKSZnB) treatment in the soil surface, particularly in the system where pulses are included. Interestingly, in the puddled rice system, passive carbon pool is more in surface soil than deeper layers. The relative proportion of active carbon pool in surface layer (0–20 cm) to subsurface layer (20–40 cm) was highest in rice–wheat–rice–chickpea (1.14:1) followed by rice–wheat–mung bean (1.07:1) and lowest in the rice–wheat system (0.69:1). Replacing wheat with chickpea either completely or during alternate year in the conventional rice–wheat system also had positive impact on SOC restoration and CMI. Therefore, inclusion of pulses in the rice-based cropping system and organic nutrient management practices had significant impact on maintaining SOC in an Inceptisol of the Indo-Gangetic plains of India.