Importance Of Soil Organic Carbon Research Articles

Drivers of the amount of organic carbon protected inside soil aggregates estimated by crushing: A meta-analysis

Given the importance of soil organic carbon (SOC) stocks and their dynamics in the regulation of climate change, understanding the mechanisms of SOC protection from decomposition is crucial. It is recognized that soil aggregates can provide effective protection of organic carbon from microbial decomposition. Currently, there is no systematic method for estimating the amount of protected carbon within aggregates. However, differences between CO2 emissions from incubation of intact versus crushed aggregates have been widely used as a proxy for SOC physical protection within aggregates. There is no global analysis on this type of experiment yet, nor on the drivers of the amount of SOC physically protected in soils. Using a meta-analysis including 165 pairs of observations from 22 studies encompassing a variety of ecosystems, climate and soil types, we investigated the crushing effects on cumulative carbon mineralization from laboratory incubation experiments. The aggregates were initially separated by either wet sieving or dry sieving before dry crushing. Our results indicated that aggregate crushing led on average to +31 % stimulation of carbon mineralization compared with intact aggregates, which represented 0.65 to 1.01 % of total SOC. This result suggests the mineralization of a previously protected pool of labile organic carbon. The linear regression analysis showed that the crushing effect on carbon mineralization depended on soil characteristics (carbon content, clay content and pH) as well as on aggregate size. Crushing aggregates stimulated carbon mineralization relative to control, up to +63 % in large aggregates (>10 mm), +38 % in large macro-aggregates (2–8 mm), +14 % in small macro-aggregates (0.25–2 mm) and +54 % in micro-aggregates (<0.25 mm). Within each aggregate size-class, the crushing effect depended on the crushing intensity. The destruction of aggregates to <0.05 mm size had a greater effect on carbon mineralization (+130–133 %) than the destruction of aggregates to >2 mm (+3 to 40 %), < 2 mm (+58 to 62 %) and < 0.25 mm (+32 to 62 %) sizes regardless of the initial aggregate size. These results suggest that macroaggregates (>0.25 mm) are less protective than microaggregates (<0.25 mm). Our dataset also show that soil physicochemical characteristics and experimental conditions influenced more the amount of protected SOC than land use and management. Contrary to our expectations the crushing effect was not affected by tillage practices nor land use. Standardizing the experimental conditions of aggregate crushing and subsequent incubation is needed to assess and compare the amount of physically protected SOC in diverse soils, and then to better understand the processes and drivers of SOC protection inside aggregates.

Digital Mapping of Soil Organic Carbon with Machine Learning in Dryland of Northeast and North Plain China

Due to the importance of soil organic carbon (SOC) in supporting ecosystem services, accurate SOC assessment is vital for scientific research and decision making. However, most previous studies focused on single soil depth, leading to a poor understanding of SOC in multiple depths. To better understand the spatial distribution pattern of SOC in Northeast and North China Plain, we compared three machine learning algorithms (i.e., Cubist, Extreme Gradient Boosting (XGBoost) and Random Forest (RF)) within the digital soil mapping framework. A total of 386 sampling sites (1584 samples) following specific criteria covering all dryland districts and counties and soil types in four depths (i.e., 0–10, 10–20, 20–30 and 30–40 cm) were collected in 2017. After feature selection from 249 environmental covariates by the Genetic Algorithm, 29 variables were used to fit models. The results showed SOC increased from southern to northern regions in the spatial scale and decreased with soil depths. From the result of independent verification (validation dataset: 80 sampling sites), RF (R2: 0.58, 0.71, 0.73, 0.74 and RMSE: 3.49, 3.49, 2.95, 2.80 g kg−1 in four depths) performed better than Cubist (R2: 0.46, 0.63, 0.67, 0.71 and RMSE: 3.83, 3.60, 3.03, 2.72 g kg−1) and XGBoost (R2: 0.53, 0.67, 0.70, 0.71 and RMSE: 3.60, 3.60, 3.00, 2.83 g kg−1) in terms of prediction accuracy and robustness. Soil, parent material and organism were the most important covariates in SOC prediction. This study provides the up-to-date spatial distribution of dryland SOC in Northeast and North China Plain, which is of great value for evaluating dynamics of soil quality after long-term cultivation.

Organic Carbon and Aggregate Stability of Three Contrasting Soils as Affected by Arable Agriculture and Improved Pasture in Northern KwaZulu-Natal, South Africa

Changes in soil organic carbon (SOC) and aggregate stability as a result of agricultural practices have been extensively studied, but the extent of these changes is site and crop specific. In this study, SOC and aggregate stability were evaluated under undisturbed grassland, cultivated pasture and arable land uses in northern KwaZulu-Natal, South Africa. The soils in this study were sampled from the 0–5, 5–10 and 10–20 cm depths of a Nitisol, Stagnosol and Fluvisol, and analysed for SOC content and stocks and aggregate stability. In all soils, SOC was significantly lower under arable cultivation (range from 1.4 to 2.1%) compared to the grassland and pasture (3.4 to 4.2%) in the top 10 cm. The soil carbon stocks followed a similar trend to the SOC in all soils and under all land uses. The overall aggregate stability expressed as mean weight diameter (MWD) was also significantly lower under the arable land use (1.03 to 1.82 mm) compared to grassland (2.44 to 2.96 mm) at all depths in all the soils, except at 5–10 cm in the Stagnosol. The MWD values under grassland and pasture were equal at all depths in all the soils. The MWD increased with SOC up to a threshold of 3.0–3.9% indicating the importance of SOC in soil aggregation. The weak correlation in the Stagnosol suggests that other factors are important in this soil. The loss of SOC and decline in aggregate stability over a period of 38 years of continuous arable cultivation in the near surface layers of two of the soils are potentially problematic for soil sustainability in the longer term.

Estimation of soil organic carbon in agricultural fields: A remote sensing approach

Aim: In view of the importance of Soil Organic Carbon (SOC) in agricultural management, a study was conducted to develop a digital SOC map using remotely sensed spectral indices. The present study was conducted on the Tawdeehiya Farms, located in the central region of Saudi Arabia between Al-Kharj and Haradh cities. Methodology: Landsat-8 (L8) and Sentinel-2 (S2A) satellite images were used for the characterization of SOC stocks in the topsoil layer (0-10 cm) of the experimental fields. Soil samples were randomly collected from six (50 ha each) agricultural fields and analyzed in the laboratory for SOC (SOCA) following Walkley and Black method. While, vegetation indices (VI), such as the Normalized Difference Vegetation Index (NDVI), NDVIRedEdge, Enhanced Vegetation Index (EVI), Bare Soil Index (BSI), and Reduced Simple Ratio (RSR) were computed and subsequently used for the development of SOC prediction models. Results: Univariate linear regression technique was employed for the recognition of a suitable band/VI for SOC (SOCP) mapping. The SWIR-1 band of both L8 (R2 = 0.86) and S2A (R2 = 0.77) data was promising for predicting SOC with 16% (S2A) and 18% (L8) of BIAS. Interpretation: The NDVI and BSI (for L8 data) and BSI and RSR (for S2A data) were found most suitable VI in the prediction of SOC. The R2 values of linear regression models were 0.68 (BSI) and 0.78 (RSR), indicating that nearly 68% and 78% of the SOC could be predicted through L8 and S2A datasets, respectively.

Long term soil carbon sequestration potential of smallholder croplands in southern Ethiopia with DAYCENT model

Considering the importance of soil organic carbon (SOC) and the scarcity of data on how soil management influences its storage in the region, this study assessed the long-term impact of different soil management systems on SOC in southern Ethiopia using the DAYCENT model. The conservation management systems considered were minimum tillage, crop residue (CR) retention, fertilization and their combinations. We parameterized the model with data from studies in the literature. We then modeled conventional cropping system for smallholding farms over a 30-year period (1991–2020) as the business as usual scenario (BAU). Then we assessed the impact of alternative conservation management scenarios compared with the BAU scenario. Our results indicated that the conservation management scenarios increased SOC at 0–20 cm depth in the range 0.34–9.71 Mg C ha−1 over 30 years when compared to BAU practices. The individual effect of fertilization, CR retention or minimum tillage management practices on SOC stock were lower than the response of the combined conservation management practices. The combined 50%–75% CR retention, no-tillage (NT), and 32 kg N ha−1 fertilization provided the highest SOC sequestration. These combinations, increased SOC in the range 8.10–9.71 Mg C ha−1 over 30 years equivalent to rates of 0.27–0.32 Mg C ha−1 yr−1. While long-term empirical data from field experiments are lacking, model results suggest that the combined 50–75% CR retention, NT, and increased N fertilization have a potential to increase SOC sequestration in resource-limited smallholding croplands. The results may be useful for researchers, policy maker and other stakeholders.

Effects of Fertilizers and Manures on Temporal Yield Variability of Winter Rye

The anticipated increases in environmental variability associated with climate change may lead to enhanced abiotic plant stresses (e.g., heat stress, drought stress, etc.) resulting in greater inter-annual yield fluctuations and higher crop production risk. While there has been increasing attention to adaptation measures, there is little evidence available on how to change agronomic management strategies to maintain stable yields in winter rye production systems in Poland. This study uses rye yields from the unique Skierniewice Long-term experiment (Poland) to examine for the first-time the long-term effects of different nutrient regimes on crop yield stability from 1966 to 2015. Yields from six combinations of mineral fertilizers and lime (CaNPK, NPK, CaPK, CaNK, CaNP, Ca), with and without additional manure, were used to estimate the temporal yield variability of winter rye. A novel statistical approach based on a mixed model approach with REML (restricted maximum likelihood) stability parameter estimation was used. The results showed that the use of additional manure in ‘sub-optimal’ mineral fertilizer treatments, such as Ca and CaPK (without mineral N), reduced the temporal yield variability of rye. In contrast, additional organic input led to more variable rye yields in already ‘optimal’ treatments including mineral N (CaNPK and NPK), compared to those with no additional manure. Winter rye given CaNPK and NPK, without additional organic manure demonstrated high yield and low temporal yield variability. In contrast, yields of treatments with no mineral N (Ca and CaPK) and no additional manure supply were low and unstable. In addition, it was found that increasing soil organic carbon resulted in larger, more stable yields. These findings highlight the importance of ensuring rye crops receive sufficient fertilizer to maintain crop production levels and yield stability, especially in dry years. They also demonstrate the importance of avoiding the excessive use of organic manures when fertilizer inputs are sufficient to meet crop demand. Overall, the study provides novel insights about how to maintain grain yields and minimize temporal yield variation of rye in arable cropping systems, which will become increasingly important in a changing climate in Poland and in other temperate climate areas. This study also highlights the importance of soil organic carbon for improving the climate resilience of winter rye, while simultaneously meeting the demand for more sustainable management of the soil.

Factors affecting sorption behaviors of tetracycline to soils: Importance of soil organic carbon, pH and Cd contamination.

The abuse of tetracycline arises the risk of antibiotic resistance genes and has been paid much attention. To understand the potential bioavailability of tetracycline (TC) in soil environments, this study explored the behaviors of TC adsorbing to six types of soils sampled from different regions of China. Moreover, the solution pH and existence of Cd2+ effect on TC sorption to soils were investigated to understand the influential factors affecting TC sorption. The results showed that the soil properties and sorption capacity of TC varied significantly with different soils. The sorption capacity of TC to soils might be largely affected by cation exchange capacity (CEC) and soil organic carbon (SOC), while the sorption rate, interaction strength and equilibrium sorption binding might be affected by soil pH, pHPZC, soil inorganic carbon (SIC) and H content. The result of solution pH effect suggested that the predominant sorption mechanism for acid soils might be hydrophobic interactions between soils and H2TC0, and the cation exchange was possibly proposed as the primary mechanism for TC sorption to alkaline soils. Furthermore, the presence of Cd2+ might increase TC sorption to acid soil, while reduce TC sorption to alkaline soil. It is expected that this study may provide important information for predicting the potential fate of TC (or similar antibiotics) in different soils, and thus helping to assess the bioavailability of TC in soils.

COMPLEMENTARY EFFECTS OF LEGUME INTEGRATION AND FERTILIZER APPLICATION ON SOIL MOISTURE AND LONG-TERM CARBON STOCKS IN MAIZE SYSTEMS OF KABETE SUB-COUNTY, KENYA

&lt;p&gt;&lt;strong&gt;Background.&lt;/strong&gt; Despite their immense benefits to smallholder farmers, the complementary effects of combined fertilizer sources with integration of legumes on soil moisture, soil organic carbon content, carbon stocks and their long-term projections in maize systems of Kabete sub-County, Kenya has not been fully investigated. This study will thus develop and promote a site specific technological package that will enhance maize productivity, resilience and sustainability of the smallholder farming systems. &lt;strong&gt;Objective&lt;/strong&gt;. To determine the complementary effects of legume integration and fertilizer application on soil moisture and soil carbon stocks, and carbon stock changes over a 20-year period in maize systems of Kabete sub-County, Kenya. &lt;strong&gt;Methodology.&lt;/strong&gt; The experiment was conducted at Upper Kabete field Research Station of the University of Nairobi during the long (LRS) and short (SRS) rainy seasons of 2015/2016. The experimental design was a Randomized Complete Block Design with a split plot arrangement. The main plots were integration of dolichos into maize (Z&lt;em&gt;ea mays L.&lt;/em&gt;) systems; (i) as an intercrop (dolichos - &lt;em&gt;Lablab purpureus &lt;/em&gt;(L.)/maize) and (ii) in rotation (dolichos-maize), and (iii) sole maize (without dolichos integration). The sub plots were organic and inorganic fertilizers: (i) Farmyard Manure (FYM), (ii) Triple Superphosphate (TSP)+Urea, (iii) FYM+TSP+Urea and (iv) no fertilizer input (control). Soil samples were collected at the end of each cropping season from 0-20 cm depth for determination of; soil moisture (%), soil organic carbon (SOC) content (%), and SOC stocks (t C ha&lt;sup&gt;-1&lt;/sup&gt;). The Rothamsted Carbon model (Roth-C) was used to estimate carbon stock changes over a 20-year period with 1990 as the base year. &lt;strong&gt;Results.&lt;/strong&gt; Significantly (P ≤ 0.05) high levels of soil moisture (31 and 30.1%) and SOC (2.6 and 2.5%) were respectively obtained in maize/dolichos intercrop with application of FYM and FYM+TSP+Urea during the SRS. The same trend in soil moisture and SOC was observed in the LRS. Significantly (P ≤ 0.05) high SOC stocks (t C ha&lt;sup&gt;-1&lt;/sup&gt;) were obtained in maize/dolichos intercrop with FYM (56.20 and 54.71) and TSP+FYM+Urea (54.84 and 52.91) application in the SRS and LRS, respectively.&lt;span style="text-decoration: line-through;"&gt; &lt;/span&gt;Over a 20-year period, SOC stocks maintained a significant and steady increase and were higher in maize/dolichos intercrop with FYM and FYM+TSP+urea application. The same pattern was noted in dolichos-maize rotation and sole maize systems. &lt;strong&gt;Implications.&lt;/strong&gt; Given the importance of SOC in the improvement of soil quality, incorporation of legumes into maize systems with application of FYM is thus a plausible technological package that could enhance soil fertility and consequently food and nutritional security among smallholder farmers, not only of Kabete sub-County but Kenya and other countries. &lt;strong&gt;Conclusion.&lt;/strong&gt; Significant increases in soil moisture content, organic carbon and, carbon stocks and their projections over a 20-year period were evident in maize/dolichos intercrop with FYM and TSP+FYM+Urea application in both seasons.&lt;/p&gt;

Carbon stocks in the mangrove ecosystem of Rufiji River Delta, Tanzania

Abstract. Lupembe IB, Munishi PKT. 2019. Carbon stocks in the mangrove ecosystem of Rufiji River Delta, Tanzania. Bonorowo Wetlands 9: 32-41. Carbon sequestration is one of the most important ecosystem services provided by mangrove ecosystems. Despite this, most Tanzanian carbon storage research has focused on terrestrial environments. Carbon and volume prediction models for the mangrove ecosystem in Tanzania's Rufiji River Delta were constructed in this study. The created models were utilized to calculate carbon emissions. At various depths, the importance of soil organic carbon as a carbon storage was also evaluated. Using linear regression, a damaging sample of 50 trees spanning various DBH size classes was used to create biomass and volume, prediction models. Wet oxidation was used to determine the amount of organic carbon in the soil. Biomass models for stems, branches, roots, leaves, and twigs and volume prediction models for total volume were constructed. At P0.05 and P0.001, respectively, all linear and power form models constructed were significant. At 0-15 cm, 15-30 cm, and 30-60 cm, organic carbon was 39.61 t ha-1, 28.04 t ha-1, and 32.85 t ha-1, respectively. The surface layer (0-15 cm) had considerably more soil organic carbon (39.61 t ha-1) than that at 15-30 cm (28.04 t ha-1) and 30-60 cm (32.85 t ha-1) depths (P0.05). The most biomass C was contributed by Rhizophora mucronata (39.87%), followed by Avicennia marina (39.86%). (28.06%). The smallest contributions came from Sonneratia alba (2.58%) and Lumnitzera racemosa (1.98%). Rhizophora mucronata contributed 39.3% of the overall volume, whereas Avicennia marina contributed 27.1%. Overall, soil organic carbon (61.6%) was nearly twice that of vegetation carbon (38.4%), highlighting the importance of soil as a carbon storage in mangrove ecosystems.

Importance of soil organic carbon in near-surface soil water content estimation: A simple model comparison in dry-end Canadian Prairie soils

The relationship of soil organic carbon (SOC) to soil water content (SWC) is primarily included in hydrological models through porosity where SOC is known to influence soil structure. The Soil Moisture Active Passive Validation Experiment 2012 (SMAPVEX12) field sampling campaign in southern Manitoba provided both SWC and SOC data over three soil textural classes and a range of soil wetness conditions. Linear regressions were developed to predict time-averaged SWC from SOC in the surface 5 cm of 50 cropland fields during SMAPVEX12 when averaged across three wetness ranges. The prediction of SWC from SOC was tested on fields in the same vicinity as SMAPVEX12 that were sampled for SWC in 2008 when soils were very dry. The measured SWC on the five sampling dates in 2008 was compared to SWC estimated for those dates from (1) the single-parameter regression equation from SOC during SMAPVEX12 dry days (1pSOC); (2) a ‘decay’ formula (5% reduction of a declining balance) (2pDM); and (3) a model based on field mean SOC with daily computation (3pSOCM). Both daily iteration models (2 and 3) required initial field capacity and rainfall data from 1 April. Models were compared with root-mean-square error (RMSE) and delta Akaike information criterion (∆AIC). The two-parameter model (2pDM) had the lowest RMSE and most favorable ∆AIC scores for mean SWC of the five sampling dates over all fields. The single-variable SOC equation was equally viable in RMSE and ∆AIC to the other models on sand soils. On clay soils, 3pSOCM was advantageous on some sampling dates, demonstrating a benefit of including SOC with field capacity and precipitation. The predictive ability of SOC to explain time-averaged SWC variability in dry soils would be valuable for SWC model initialization and as a covariate for geostatistical downscaling from satellite SWC scales.

A soil carbon proxy to predict CH4 and N2O emissions from rewetted agricultural peatlands

The temporal and spatial variations in greenhouse gas (GHG) emission estimates in wetlands impede our ability to predict and upscale total emissions; thus, a scalar parameter is needed to predict GHG emissions. We investigated the importance of soil organic carbon (SOC) in the prediction of methane (CH4) and nitrous oxide (N2O) emissions in rewetted agricultural peatlands, positing that both CH4 and N2O production are explained by the quantity and turnover of SOC. Field CH4 and N2O fluxes, along with other edaphic and environmental variables, were monitored in rewetted peatlands with a range of SOC (6%, 11%, and 23%) that were recently converted from row crops to flooded rice cultivation to reverse soil subsidence. Nitrogen (N) fertilization reduced annual CH4 emission by 77.2% in the 6% C field, but this effect was not found in other fields. Annual N2O emissions were not affected by N fertilization and averaged 8.9, 5.2, and 1.9kgN2O-Nha−1 for the 6%, 11%, and 23% C fields, respectively. SOC was the dominant factor controlling both CH4 and N2O emissions. The annual emission for both CH4 and N2O was accurately described by a decaying power regression with increasing SOC contents (R2>0.49). This relationship was also observed after splitting total annual emission of CH4 and N2O into growing and fallow seasons. Nitrogen fertilization and the seasonality in CH4 and N2O emissions did not change the relationships. The inverse correlation between SOC and CH4 and N2O emissions was likely caused by different chemical composition of SOC in various soils. Our results suggest that SOC can be a potential proxy to predict CH4 and N2O emissions in rewetted peatlands to better define GHG predictions of wetland restoration efforts.

Soil carbon storage and stratification under different tillage/residue-management practices in double rice cropping system

The importance of soil organic carbon (SOC) sequestration in agricultural soils as climate-change-mitigating strategy has become an area of focus by the scientific community in relation to soil management. This study was conducted to determine the temporal effect of different tillage systems and residue management on distribution, storage and stratification of SOC, and the yield of rice under double rice (Oryza sativa L.) cropping system in the southern China. A tillage experiment was conducted in the southern China during 2005–2011, including plow tillage with residue removed (PT0), plow tillage with residue retention (PT), rotary tillage with residue retention (RT), and no-till with residue retention on the surface (NT). The soil samples were obtained at the harvesting of late rice in October of 2005, 2007 and 2011. Multiple-year residue return application significantly increased rice yields for the two rice-cropping systems; yields of early and late rice were higher under RT than those under other tillage systems in both years in 2011. Compared with PT0, SOC stocks were increased in soil under NT at 0–5, 5–10, 10–20, and 20–30 cm depths by 33.8, 4.1, 6.6, and 53.3%, respectively, in 2011. SOC stocks under RT were higher than these under other tillage treatments at 0–30 cm depth. SOC stocks in soil under PT were higher than those under PT0 in the 0–5 and 20–30 cm soil layers. Therefore, crop residues played an important role in SOC management, and improvement of soil quality. In the 0–20 cm layer, the stratification ratio (SR) of SOC followed the order NT>RT>PT>PT0; when the 0–30 cm layer was considered, NT also had the highest SR of SOC, but the SR of SOC under PT was higher than that under RT with a multiple-year tillage practice. Therefore, the notion that conservation tillage lead to higher SOC stocks and soil quality than plowed systems requires cautious scrutiny. Nevertheless, some benefits associated with RT system present a greater potential for its adoption in view of the multiple-year environmental sustainability under double rice cropping system in the southern China.

Pedometric Mapping of Soil Organic Carbon Loss Using Soil Erosion Maps of Tripura

Importance of soil organic carbon (SOC) in maintaining soil productivity and natural ecosystem has been a major concern throughout the globe. SOC in the humid tropical climate becomes more important in view of undulating hilly terrain in the northeastern region of India. The major concern in such landscape is soil erosion and the necessary conservation practices. In the present study, we discuss the technique of pedometric mapping to link SOC and soil loss. The best-fit semi-variogram model for SOC was found to be exponential model (R 2 = 0.90). The best fit semivariogram models for soil and SOC losses are spherical (R 2 = 0.95) and exponential (R 2 = 0.77) respectively. The spatial distribution of SOC, soil and SOC loss was found to be related with topography and different land-use types and showed moderate spatial dependence. With the help of 196 grid observations, the present study shows a threshold limit of 150 kg ha -1 year -1 SOC loss above which the areas are to be considered as susceptible demanding immediate conservation measures. Pedometric mapping using SOC and soil loss can, thus, be a tool to prioritize areas in humid tropical climate for conservation agriculture.

天山北坡城市群非渗透面下的土壤有机碳特征

Existence of impervious surface areas(ISA) in cities strongly influences the physical and chemical characteristics of regional soil, therefore, has profound impact on ecosystem carbon cycle at multiple scales.However, due to the inaccessibility of soil sample beneath urban ISA, we know little about the biochemical properties and distribution pattern as well as the importance of soil organic carbon under urban ISA(SOCISA). To clarify this issue, 100-cm-depth soil profiles from 27 paired ISA and pervious surface areas(PSA) sites in northern Tianshan urban cluster in a dryland environment of northwestern China were taken. In order to estimate total soil carbon storage, urban land cover was retrieved from cloud-free Landsat8 images. Based on the data of land cover area and SOC, the soil carbon storage of this urban cluster was calculated.(1) averaged 100-cm-depth SOCISAof the northern Tianshan urban cluster is 5.74±0.39 kg C· m-2, which is significantly lower than the paired soil organic carbon of PSA(SOCPSA) of 8.69±0.75 kg C· m-2, about 52% of the latter(p0.01); averaged soil bulk density(BD) under ISA BDISA=1.58 ± 0.02 g · cm-3, which is significantly higher than its paired BD of PSA of1.51±0.02 g· cm-3, about 5% of the latter(p0.01).(2) SOC and BD of both ISA and PSA declines with depth.The results of linear fitting between SOC, BD, and depth show that SOCISAand BDISAhave significantly declining trends, however, SOCPSAand BDPSAdoes not show such clear trend. In addition, SOCPSAat the 60~100 cm soil layers is significantly higher than SOCISAbut there is no stable correlation between them.(3) Carbon storage hidden under ISA of northern Tianshan urban cluster is 68% of the total urban carbon storage and for individual cities this percentage is higher than 50%, therefore, SOCISAis the main part of the urban SOC storage. By revealing the SOCISAand its distribution, this study can facilitate the understanding of biochemical characteristics of soils beneath urban ISA, which is significance for estimating carbon cycling in both urban and global ecosystems.

Stabilization of Organic Carbon via Chemical Interactions with Fe and Al Oxides in Gley Soils

The importance of soil organic carbon (SOC) stabilization via chemical interactions with Fe and Al oxide minerals within gley soils remains unclear. Changes in the proportions of Fe/Al oxides and SOC and N contents associated with Fe/Al oxides within the profiles of gley soils under contrasting hydrological regimes and freely draining control soils from Harwood Forest (northeast England) were investigated. Sequential selective dissolution techniques were used to measure Fe/Al oxide crystallinity and explore whether crystallinity differed between gleyed and freely draining soils. Extracts were analyzed using Fourier transform infrared spectroscopy to investigate the chemical characteristics of organic matter (OM) associated with Fe/Al oxides. Strongly crystalline Fe oxides were the dominant (∼50%–80% of total Fe oxides present) mineral phase in gley mineral soils. Contrasting gley soil hydrological regimes influenced total subsoil Fe and total and weakly crystalline Al oxide concentrations. Also, within-profile changes in strongly crystalline Fe oxide concentrations were linked to differences in hydrological and redox conditions. A large proportion of SOC (generally 70%–90% of total) seemed to be associated with Fe/Al oxides. Correlation plots, however, indicated that SOC contents were not linearly related to amounts of total Fe and Al oxides, weakly crystalline Fe and Al oxides, or strongly crystalline Fe oxides. The lack of linear correlations observed for these acidic soils may be caused by contributions from other extractable soil components and factors such as high organic loadings and insufficient amounts of Fe/Al oxides for interaction with SOC in topsoils and variable surface loadings of different organic inputs at different soil depths. Subsoil C/N ratios (∼18–21) were higher than those in extracted subsoil residues (∼9–17), suggesting that minerals other than Fe/Al oxides preferentially adsorbed N-rich microbially processed compounds. The OM associated with weakly and strongly crystalline Fe/Al oxides was chemically different, the latter generally having greater hydroxyl, aliphatic, carboxylate, and /or phenolic character and less carbohydrate character than the former. This research shows that interactions between Fe/Al oxides and SOM in redox-dynamic gley soils under different hydrological regimes are complex, and further investigations of SOC stabilization in these systems using selective dissolution and other complementary techniques are required.

Changes in soil organic carbon and nitrogen as affected by tillage and residue management under wheat–maize cropping system in the North China Plain

The importance of soil organic carbon (SOC) and nitrogen (N) sequestration in agricultural soils as climate-change-mitigating strategy has received robust attention worldwide in relation to soil management. This study was conducted to determine the temporal effects of different tillage systems and residue management on distribution, storage and stratification of SOC and N under wheat (Triticum aestivum L.) – maize (Zea mays L.) cropping systems in the North China Plain (NCP). Four tillage systems for winter wheat established in 2001 were: moldboard plow tillage with maize residues removed (PT0), moldboard plow tillage with maize residues incorporated (PT), rotary tillage with maize residues incorporated (RT), and no-till with maize residues retained on the soil surface (NT). Compared with PT0 and PT, significantly higher SOC and N concentrations were observed in the surface layer (0–10cm depth) under NT and RT. In 2004, the SOC stocks were lower (P<0.05) under NT and RT than under PT and PT0, however, the opposite trend was observed in 2012. Compared with 2001, the net profile (0–30cm) SOC sequestration rate was 10.60, 13.95, 13.65, and 14.92Mgha−1 in 2012 under PT0, PT, RT, and NT, respectively. As for SOC stocks in the 0–50cm profile, no significant differences (P<0.05) were observed among NT, RT, and PT. The trends in N stocks in profile (0–30, 0–50cm depth) were NT>RT>PT>PT0 in both years. Compared with other treatments, SOC and N stocks were the lowest (P<0.05) under PT0. Therefore, crop residues play an important role in SOC and N management, and improvement of soil quality. The higher SOC stratification was observed under NT and RT than under PT and PT0, whereas the C:N ratio was higher (P<0.05) under PT and PT0 than under NT and RT systems. Therefore, the notion that NT leads to higher SOC stocks than plowed systems requires cautious scrutiny. Nonetheless, some benefits associated with NT present a greater potential for its adoption in view of the long-term environmental sustainability under wheat–maize double-cropping system in the NCP.

Estimating change in soil organic carbon using legacy data as the baseline: issues, approaches and lessons to learn

The importance of soil organic carbon (SOC) in maintaining soil health is well understood. However, there is growing interest in studying SOC with an emphasis on quantifying its changes in space and time. This is because of the potential for soil to be used to sequester atmospheric C. There are many issues which make this difficult, for example shortcomings in sampling designs, and differences in vertical and lateral sampling supports between surveys, particularly if legacy data are used as the baseline survey. In this study, we systematically work through these issues and show how a protocol can be developed using design-based and model-based statistical approaches to estimate changes in SOC in space and time at different spatial supports. We demonstrate this protocol in a small subcatchment in the upper Namoi valley for estimating the change in SOC over time, whereby the baseline dataset was collected during 1999–2001 and is compared with a dataset from November 2010. The results from both design-based and model-based approaches revealed a drop in SOC across the catchment between the two survey periods. A 0.26% drop in SOC was reported globally across the catchment. Nevertheless, the change in SOC reported for both approaches was not statistically significant.

Importance of soil organic carbon on surface soil water content variability among agricultural fields

Summary Improvements to the downscaling estimates of soil water content (SWC) from passive microwave retrievals require detailed knowledge of field scale influences on SWC variability. The Soil Moisture Active Passive Validation Experiment (SMAPVEX-12) field campaign provided SWC and physical properties from 50 cropland fields to assess the influence of soil organic carbon (SOC) on SOC variability in a range of SOC, SWC and soil textural class over a 6 week period. Field average SWC over the duration of the experiment was optimally predicted by combination of soil texture and SOC in all soil wetness conditions, although either %Sand or SOC separately also expressed 82% of variance in SWC over all fields covering three soil textural groups. Soil OC explained greater variance in SWC than texture in dry conditions, while texture predominated in moist conditions. The high correlation between SOC and SWC suggests soil OC may contribute to the initiatives to downscale SWC estimates from satellite to field scale where SWC data are sparse or inaccurate.

A new baseline of organic carbon stock in European agricultural soils using a modelling approach

Proposed European policy in the agricultural sector will place higher emphasis on soil organic carbon (SOC), both as an indicator of soil quality and as a means to offset CO2 emissions through soil carbon (C) sequestration. Despite detailed national SOC data sets in several European Union (EU) Member States, a consistent C stock estimation at EU scale remains problematic. Data are often not directly comparable, different methods have been used to obtain values (e.g. sampling, laboratory analysis) and access may be restricted. Therefore, any evolution of EU policies on C accounting and sequestration may be constrained by a lack of an accurate SOC estimation and the availability of tools to carry out scenario analysis, especially for agricultural soils. In this context, a comprehensive model platform was established at a pan-European scale (EU+Serbia, Bosnia and Herzegovina, Croatia, Montenegro, Albania, Former Yugoslav Republic of Macedonia and Norway) using the agro-ecosystem SOC model CENTURY. Almost 164000 combinations of soil-climate-land use were computed, including the main arable crops, orchards and pasture. The model was implemented with the main management practices (e.g. irrigation, mineral and organic fertilization, tillage) derived from official statistics. The model results were tested against inventories from the European Environment and Observation Network (EIONET) and approximately 20000 soil samples from the 2009 LUCAS survey, a monitoring project aiming at producing the first coherent, comprehensive and harmonized top-soil data set of the EU based on harmonized sampling and analytical methods. The CENTURY model estimation of the current 0-30cm SOC stock of agricultural soils was 17.63Gt; the model uncertainty estimation was below 36% in half of the NUTS2 regions considered. The model predicted an overall increase of this pool according to different climate-emission scenarios up to 2100, with C loss in the south and east of the area (involving 30% of the whole simulated agricultural land) compensated by a gain in central and northern regions. Generally, higher soil respiration was offset by higher C input as a consequence of increased CO2 atmospheric concentration and favourable crop growing conditions, especially in northern Europe. Considering the importance of SOC in future EU policies, this platform of simulation appears to be a very promising tool to orient future policymaking decisions.

Energy sorghum biomass harvest thresholds and tillage effects on soil organic carbon and bulk density

Bioenergy feedstock production systems face many challenges, among which is the lack of guidelines on sustainable biomass harvest thresholds and tillage cropping systems that maintain soil quality and productivity. We used the ALMANAC crop model to evaluate four biomass removal rates, 0%, 50%, 75% and 100%, and four tillage cropping systems, continuous No Till (NT), and Conventional Till (CT), and periodically plowed or subsoiled NT lands at Shorter, AL, for a Lynchburg loamy sand soil, over 51 yr of actual weather data: 1960–2010. Farmers periodically plow or subsoil NT lands to alleviate problems of drainage, pests, and soil compaction. Given the importance of soil organic carbon (SOC) as a soil quality indicator, we premised sustainability upon the maintenance of SOC at or above the initial SOC levels. As expected, NT had the highest SOC and lowest bulk density (BD) across the four biomass removal rates and gained the highest percent SOC over the 51-yr simulation period. For this study, the 75% biomass removal rate was applied sustainably on NT energy sorghum production systems, giving an annual harvestable biomass yield of 18.0±0.9, residue biomass, 6.2±0.3, and a root biomass of 7.2±0.4Mgha−1. However, the 75% removal rate also significantly increased soil bulk density, a critical indicator of soil compaction, by 30%. Compared to conventional tillage, subsoil tillage maintained SOC and better alleviated soil compaction in NT systems, but at the reduced biomass removal threshold of 50%. Long-term biomass removal resulted in reduced total biomass yields over time due to nutrient depletion as reflected by increased N stress days on subsequent crops. We attributed the N stress to N immobilization by the decomposing residues, reduced mineralization and N losses. Additional inputs will be needed to avoid increased N uptake from the soil which could result in soil mining.