Higher Soil Organic Carbon Stocks Research Articles

Soil Organic Carbon Fractions and Stocks as Affected by Organic Fertilizers in Rice Paddy Soil

This research evaluated the effect of different organic fertilization (OF) on soil organic carbon (SOC) stock and fractions in rice paddy soil. The OF system consisted with NPK, NPK+Rice straw (NPK+RS), NPK+Cow compost (NPK+CC), NPK+Swine compost (NPK+SC) and no-fertilization (Control). Labile organic C fractions and humification rates were characterized and SOC stock was determined with bulk density and SOC content. Application of OF significantly SOC content by 7-12% and 23-33% over the NPK and control, while it decreased bulk density by 2-6% and 11-14%. The lowest bulk density was found in RS, which indicated the improvement of soil physical property. The highest SOC stock (38-39 kg C ha-1) was observed in SC and CC treatments. The SOC stock showed significant negative correlation with bulk density (p < 0.001), and positively correlated with humification rate, grain yield (p < 0.01) and HWEC and straw yield (p < 0.05), indicating key roles of SOC on soil quality. These results showed that the OF application largely increased SOC stocks, rice yield, and concentration of labile C and stable C. Therefore, application of OF is recommendable for suitable soil management strategy to improve soil fertility and increase crop yield in rice paddy field. Correlation analysis between soil organic carbon fractions under different fertilization system. Parameter SOC† Bulk density HA FA HA/FA§ HR¶ HA/SOM∮ FA/SOM∮ WEC∫ HWEC∫ Grain Straw SOC stock 1 B. density - < 0.001***† 1 HA 0.103 0.070 1 FA 0.013* 0.027* 0.008** 1 HA/FA 0.754 0.512 < 0.001*** 0.801 1 HR 0.008 - 0.010** < 0.001*** < 0.001*** 0.021* 1 HA/SOM 0.032* - 0.026* < 0.001*** 0.004** 0.001*** 0.001*** 1 FA/SOM 0.001*** - 0.007** 0.009** < 0.001*** 0.787 0.001*** 0.003** 1 WEC < 0.001 - 0.001*** 0.214 0.026* 0.986 0.035* 0.099 0.006** 1 HWEC 0.047* - 0.039* 0.431 0.045* 0.680 0.153 0.310 0.030* 0.07 1 Grain 0.011* - 0.004** 0.157 0.450 0.206 0.105 0.093 0.254 0.10 0.060 1 Straw 0.043* - 0.004** 0.433 0.857 0.360 0.356 0.315 0.586 0.039* 0.207 < 0.001*** 1 †*, **, and *** denote significance at the 5, 1, and 0.1% levels, respectively.†SOC: Soil organic carbon§HA/FA: Ratio of humic acid content and fulvic acid content¶HR: Humification rate∮HA/SOM and FA/SOM: Proportion of humic acid to SOM content and Proportion of fulvic acid to SOM content∫WEC and HWEC: Water extractable carbon and hot water extractable carbon

Maize Straw Returning Approaches Affected Straw Decomposition and Soil Carbon and Nitrogen Storage in Northeast China

The characterization of straw decomposition and the resulting carbon (C) and nitrogen (N) release is crucial for understanding the effects of different straw returning methods on the immobilization and cycling of soil organic carbon (SOC) and soil total nitrogen (STN). In 2017–2018, a field micro-plot experiment was carried out in northeastern China to investigate the effects of different straw returning approaches on straw decomposition, C release, N release, SOC, STN, and the soil C–N ratio. Six straw returning treatments were applied: straw mixed with soil (SM) and straw buried in the soil (SB) at soil depths of 10 (O), 30 (T), and 50 cm (F). The results indicate that the straw decomposition proportion (SD), C release, and N release in SM + O were higher than that in SM + T and SM + F. Moreover, SOC and STN concentrations and the soil C–N ratio were significantly enhanced by SM/B + O in the 0–20 cm soil layers, SM/B + T in the 20–30 cm soil layer, and SM/B + F in the 40–60 cm soil layers. In the 0–50 cm soil profile, the highest SOC stocks were obtained using SB + T. The STN stocks were also significantly affected by the straw returning depth, but the effect was inconsistent between the two years. SD had a positive relationship with SOC and STN in the 0–20 cm soil layers; conversely, they were negatively related in the 30–60 cm soil layers. The results of this study suggest that straw buried in the soil to a depth not exceeding 30 cm might be an optimal straw returning approach in northeastern China.

Afforestation and agroforestry enhance soil nutrient status and carbon sequestration capacity in eastern China

AbstractAfforestation and agroforestry both sequester atmospheric carbon (C) and store C in the soil. However, the response of soil nutrients and soil organic carbon (SOC) to these practices has not been fully examined, especially in deep soil layers. We therefore investigated the effects of afforestation and agroforestry on the nutrient contents and organic carbon (OC) stocks within a 100‐cm depth in eastern China. The soil nutrient contents and stoichiometry as well as the SOC contents and stocks exhibited different vertical patterns and varied among the five planting systems. The total nitrogen (TN), total phosphorus (TP), and SOC contents decreased dramatically at a 20‐cm depth, and the total potassium (TK) content exhibited a different pattern. Compared with adjacent croplands and nurseries, the forest plantation and agroforestry systems had higher SOC stocks, ranging from 42.9 to 111.6 t·hm−2 in the whole soil profile. The SOC distribution among the depth gradient varied among planting systems, and the topsoil SOC stocks played crucial roles in total SOC storage within a depth of 100 cm in the cropland and nursery systems. The soil pH and bulk density (BD) were negatively correlated with the SOC content, and a significant positive linear relationship occurred between the TN and SOC contents and between the TP and SOC contents. We recommend that combinations of nitrogen (N) and phosphorus (P) fertilizers would benefit SOC storage and improve stabilization in agroforestry and plantation systems.

Soil organic carbon fractions and 14C ages through 70 years of cropland cultivation

Understanding the biogeochemistry of soil organic carbon (SOC) and SOC components is essential to assess soil quality and management practices in reclaimed croplands. Here we study the radiocarbon (14C) ages in profiles to a depth of 500 cm for five cultivation timespans: 5, 15, 35, 60, and at least 70 years from the Gutun watershed on the Chinese Loess Plateau. We isolated an acid-extractable SOC component (F1), three temperature stepped-combustion SOC components: F2 (400 °C), F3 (600 °C), and F4 (900 °C), and measured their 14C ages. Our results show that SOC stocks in reclaimed soils declined from cultivation times of 5 years (R5) to 15 years (R15), then increased with longer cultivation times, until 70 years (R70). The SOC content of the F2 and F3 fractions was higher than F1 and F4 over the past 60 years, while the F4 fraction in R70 had the highest value. Since the newly reclaimed croplands were heavily fertilized, R5 had high SOC and carbon management index (CMI) values, and 14C ages close to the other SOC fractions in the surface soil. The 14C ages of SOC fractions in deep soils were older than others, indicating a weak capacity to fix fresh C that infiltrated the deeper soils in R5. R70 contained the highest SOC stocks, but with a large proportion of old, non-labile SOC that contributed to relatively low SOC quality and CMI. Therefore, we predict that the R70 site would be unable to sustain optimal maize productivity. The SOC stocks under R35 were significantly lower than those from R5 and R70, but contained a high proportion of labile SOC, with relatively young 14C ages (compared to R60), even to a depth of 500 cm. This observation suggests that planting forest nurseries can improve SOC quality and promote SOC sequestration even in relatively deep soils. This study demonstrates the efficacy of labile SOC content and 14C ages as measures of SOC quality, and our findings offer useful guidance for the management of reclaimed croplands.

Moisture regime influence on soil carbon stock and carbon sequestration rates in semi-arid forests of the National Capital Region, India

Understanding the dynamics of soil carbon is crucial for assessing the soil carbon storage and predicting the potential of mitigating carbon dioxide from the atmosphere to the biomass and soil. The present study evaluated variations of soil carbon stock in semi-arid forests in India under different moisture regimes. Soil organic carbon (SOC) and soil inorganic carbon (SIC) stocks were determined in different moisture regimes i.e. monsoon, post-monsoon, winter and pre-monsoon seasons at 0–10 and > 10–20 cm depths. SOC stock showed significant variations under different moisture regimes. The highest SOC stock was during winter (22.81 Mg C ha−1) and lowest during the monsoon season (2.34 Mg C ha−1) among all the ridge forests under study. SOC and SIC stock under different moisture regimes showed significant negative correlation with soil moisture (p < 0.05), as a sudden increase in soil moisture after rainfall results in an increase in carbon loss due to microbial decomposition of accumulated carbon during the dry period. There was an increase in annual SOC stock and a decrease (or no change in some cases), in SIC stock at both the depths during the study period. The SOC and SIC sequestration rates were estimated as any increase/decrease in the respective stock during each successive year. SOC sequestered ranged between 0.046 and 0.741 Mg C ha−1 y−1. Similarly, SIC sequestration ranged between 0.013 and 0.023 Mg C ha−1 y−1 over all ridge forests up to 20 cm depth. The Delhi ridge forests, which accounts to 0.007% of the semi-arid regions of India, contribute 0.25–0.32% of the national potential (semi-arid region) for SOC sequestration up to 20 cm depth. The estimates of the rate of C sequestration in this study provide a realistic image of carbon dynamics under present climatic conditions of semi-arid forests, and could be used in developing a database and formulating new strategies for carbon dioxide mitigation by enhancing soil C sequestration rates.

Comparative study on spatial variability of topsoil moisture content and carbon stocks as influenced by land use and soil and water conservation structures in the semi-arid Ethiopian highlands

ABSTRACT Land uses and soil and water conservation (SWC) structures affect topsoil moisture and carbon stocks, particularly in the water deficit semi-arid environment of the northern Ethiopian highlands. This study was undertaken to assess the effects of land use and SWC structures on topsoil moisture, biomass, and soil carbon. Soil moisture was measured manually using gravimetric methods and theta probes with data loggers. Vegetation was inventoried and soil samples collected to assess carbon stocks of biomass and soils of different land uses. Merebmiti catchment had higher average gravimetric soil moisture content (GSMC; 24%) in wetlands, with the lowest (13%) in exclosures, whereas Mayleba catchment had relatively higher GSMC (14%) in exclosures and the lowest (8%) in rangelands. In both catchments, GSMC was higher at sampling locations closer to SWC structures than farther away. Merebmiti had significantly more biomass carbon (28.9 Mg ha−1) than Mayleba (6.32 Mg C ha−1). Higher soil organic carbon stocks were found in exclosures (46.1 ± 2.20 Mg ha−1) and wetlands (62.1 ± 2.9 Mg ha−1) than in frequently cultivated croplands (24.3 ± 1.4 Mg ha−1). Effective management of land use and implementation of SWC structures remarkably improves topsoil moisture content and carbon stocks in these catchments.

Changes in soil organic carbon and total nitrogen stocks along a chronosequence of Caragana intermedia plantations in alpine sandy land

Accurate assessment of soil organic carbon (SOC) and total nitrogen (TN) stocks and analyzing the main influencing factors after revegetation for restoration of sandy soils in alpine regions are important for formulating sustainable management measures and understanding the role of revegetation in mitigating climate change. This study compared SOC and TN stocks and their vertical distributions among 6-, 11-, 17- and 31-year-old Caragana intermedia plantations and shifting sand dunes. The results showed that SOC and TN stocks significantly increased as plantation age increased, with the 31-year-old stands having the highest SOC stocks (26.73 Mg ha−1) and TN stocks (2.64 Mg ha−1), which were 97.4% and 149.56% higher, respectively, than those of the shifting sand dunes. Compared to the total soil depth, SOC and TN stocks at all stand ages were higher in surface soil (0–20 cm). SOC stocks in the surface soil of the 6-, 11-, 17- and 31-year-old stands were 38.03%, 71.32%, 103.67% and 253.30% higher, respectively, than those in the surface soil of the shifting sand dunes, and TN stocks in the surface soil were 17.03%, 117.96%, 148.93% and 232.06% higher, respectively, than those in the surface soil of the shifting sand dunes. The percentage of the SOC and TN stock in the 0–20 cm soil depth increased significantly as plantation age increased, with the 31-year-old plantation reaching 43.66% and 33.39%, respectively. Redundancy analysis and correlation analysis showed that at 0–20 cm soil depth, above-ground biomass was the main influencing factor for SOC and TN stocks. At 20–80 cm soil depth, fine root biomass and medium root biomass were the main influencing factors for SOC stocks, and medium root biomass was the main influencing factor for TN stocks.

Distribution of carbon and nitrogen along hillslopes in three valleys on Herschel Island, Yukon Territory, Canada

Thermokarst results from the thawing of ice-rich permafrost and alters the biogeochemical cycling in the Arctic by reworking soil material and redistributing soil organic carbon (SOC) and total nitrogen (TN) along uplands, hillslopes, and lowlands. Understanding the impact of this redistribution is key to better estimating the storage of SOC in permafrost terrains. However, there are insufficient studies quantifying long-term impacts of thaw processes on the distribution of SOC and TN along hillslopes. We address this issue by providing estimates of SOC and TN stocks along the hillslopes of three valleys located on Herschel Island (Yukon, Canada), and by discussing the impact of hillslope thermokarst on the variability of SOC and TN stocks. We found that the average SOC and TN 0–100 cm stocks in the valleys were 26.4 ± 8.9 kg C m-2 and 2.1 ± 0.6 kg N m-2. We highlight the strong variability in the soils physical and geochemical properties within hillslope positions. High SOC stocks were found at the summits, essentially due to burial of organic matter by cryoturbation, and at the toeslopes due to impeded drainage which favored peat formation and SOC accumulation. The average carbon-to‑nitrogen ratio in the valleys was 12.9, ranging from 9.7 to 18.9, and was significantly higher at the summits compared to the backslopes and footslopes (p < 0.05), suggesting a degradation of SOC downhill. Carbon and nitrogen contents and stocks were significantly lower on 16% of the sites that were previously affected by hillslope thermokarst (p < 0.05). Our results showed that lateral redistribution of SOC and TN due to hillslope thermokarst has a strong impact on the SOC storage in ice-rich permafrost terrains.

Post – Mining soil as carbon storehouse under polish conditions

The main aim of these studies was to determine the potential for carbon sequestration in brown coal open-cast mine by phytoremediation using scots pine (Pinus sylvestris L.) and giant miscanthus (Miscanthus x giganteus) plants. This paper presents relationships between soil organic carbon (SOC) sequestration and carbon phytosequestration in waste dump associated with open-cast lignite mine in Central Poland. The research is the continuation of previously carried out experiments, but was conducted in field conditions. In reclamation of post-mining landscapes, during field experiment, an effect of sewage sludge, compost and lake chalk amendments and in combination of plants was investigated. The impact of soil amendments on carbon stock, CO2 emission reduction, plant biomass production and carbon content in shoots and roots was studied. The highest SOC stock was found in soil treated with sewage sludge (33 Mg*ha−1) and compost (45 Mg*ha−1) stabilized by lake chalk. These fertilizer combinations also contributed the most in relation to CO2 emission reduction through SOC stock (83 Mg*ha−1 and 127 Mg*ha−1 respectively). In addition, greater amounts (60–100%) of soil organic matter was converted into humic acids fraction. This phenomenon could be the initial stage of the progressive process of organic matter deposition and carbon sequestration in post-mining area. Carbon phytosequestration was determined through carbon bound in plant tissues. The highest carbon content (60%) in both plant species was recorded in treatments with sewage sludge and compost with lake chalk. Stabilization of compost by lake chalk application was good method to improve the efficiency of carbon sequestration in soil and carbon phytosequestration. Improving the efficiency of these two processes, through skillfully selected soil additives and plant species, may be used on a larger scale in the future as an alternative to the storage of carbon dioxide, especially in degraded areas.

Soil Organic Carbon Stock Assessment in a Grassland and a Polyculture Tree Plantation

Polyculture tree plantations are generally characterized by the sustainability to resist disturbance, potential for higher yield and better ecological services. A study was conducted in a polyculture tree plantation and a grassland site inside the main campus of Visayas State University, Baybay City, Leyte to (1) estimate and compare the soil organic carbon (SOC) stocks between the two land uses, and (2) find relationships between soil physicochemical properties, and SOC in the polyculture tree plantation and grassland. In each land use, soil samples were collected at depth intervals of 0-10 cm, 10-30 cm, and 30-50 cm. Higher SOC stocks in the 10 – 30 cm and 30 – 50 cm depths and the whole profile of the polyculture tree plantation (23.02, 43.28, 45.18, 111.47 Mg C ha-1 , respectively) compared to the grassland site (27.53, 35.70, 28.93, 82.14 Mg C ha-1 ) were observed. Thus, this polyculture tree plantation significantly improved some soil physicochemical characteristics and increased SOC stock after conversion from grassland.

Predicting the Potential Impact of Climate Change on Carbon Stock in Semi-Arid West African Savannas

West African savannas are experiencing rapid land cover change that threatens biodiversity and affects ecosystem productivity through the loss of habitat and biomass, and carbon emissions into the atmosphere exacerbating climate change effects. Therefore, reducing carbon emissions from deforestation and forest degradation in these areas is critical in the efforts to combat climate change. For such restorative actions to be successful, they must be grounded on a clear knowledge of the extent to which climate change affects carbon storage in soil and biomass according to different land uses. The current study was undertaken in semi-arid savannas in Dano, southwestern Burkina Faso, with the threefold objective of: (i) identifying the main land use and land cover categories (LULCc) in a watershed; (ii) assessing the carbon stocks (biomass and soil) in the selected LULCc; and (iii) predicting the effects of climate change on the spatial distribution of the carbon stock. Dendrometric data (Diameter at Breast Height (DBH) and height) of woody species and soil samples were measured and collected, respectively, in 43 plots, each measuring 50 × 20 m. Tree biomass carbon stocks were calculated using allometric equations while soil organic carbon (SOC) stocks were measured at two depths (0–20 and 20–50 cm). To assess the impact of climate change on carbon stocks, geographical location records of carbon stocks, remote sensing spectral bands, topographic data, and bioclimatic variables were used. For projections of future climatic conditions, predictions from two climate models (MPI-ESM-MR and HadGEM2-ES) of CMIP5 were used under Representative Concentration Pathway (RCP) 8.5 and modeling was performed using random forest regression. Results showed that the most dominant LULCc are cropland (37.2%) and tree savannas (35.51%). Carbon stocks in woody biomass were higher in woodland (10.2 ± 6.4 Mg·ha−1) and gallery forests (7.75 ± 4.05 Mg·ha−1), while the lowest values were recorded in shrub savannas (0.9 ± 1.2 Mg·ha−1) and tree savannas (1.6 ± 0.6 Mg·ha−1). The highest SOC stock was recorded in gallery forests (30.2 ± 15.6 Mg·ha−1) and the lowest in the cropland (14.9 ± 5.7 Mg·ha−1). Based on modeling results, it appears clearly that climate change might have an impact on carbon stock at horizon 2070 by decreasing the storage capacity of various land units which are currently suitable. The decrease was more important under HadGEM2-ES (90.0%) and less under MPI-ESM-MR (89.4%). These findings call for smart and sustainable land use management practices in the study area to unlock the potential of these landscapes to sequestering carbon.

Organische Kohlenstoffvorräte von Bodentypen in den Hauptnaturräumen Schleswig-Holsteins (Norddeutschland)

Zusammenfassung Die Verbesserung der Humusspeicherung in Böden im Hinblick auf eine nachhaltige Landbewirtschaftung erfordert genaue Kenntnisse über den organischen Kohlenstoff(Corg)-Vorrat in Böden, wobei auch die Wechselwirkungen zwischen Bodentyp, geologischem Ausgangsgestein sowie Landnutzung berücksichtigt werden müssen. Auf der Grundlage von insgesamt 925 Bodenprofilen in den vier Hauptnaturräumen (Östliches Hügelland, Vorgeest, Hohe Geest und Marsch) Schleswig-Holsteins (Norddeutschland) wurde der Corg-Vorrat bis in eine Tiefe von 90 cm quantifiziert. Die horizontspezifischen Parameter (u. a. auch Trockenrohdichte und Korngrößenverteilung) wurden im Rahmen der seit ca. 1970 durchgeführten bodenkundlichen Leitprofilaufnahmen vom Landesamt für Landwirtschaft, Umwelt und ländliche Räume Schleswig-Holstein (LLUR) und deren Vorgängerbehörden erhoben. Die vier Hauptnaturräume enthalten unterschiedliche Corg-Vorräte in den Bodentiefen 0–30, 30–60 und 60–90 cm. Insgesamt werden in Schleswig-Holstein mindestens 244 Mt Corg (0–90 cm Tiefe) gespeichert, wobei je nach Landnutzung, Bodentyp und geologischem Ausgangsgestein deutliche Unterschiede auftreten. Im Oberboden variieren die Corg-Vorräte von ca. 60 t/ha (Ackerböden der Marsch/des Östlichen Hügellands) bis ca. 130 t/ha (Grünlandböden der Geest). Im Unterboden verfügen neben den Mooren die humusreichen Marschböden, die Kolluvisole (Alt- und Jungmoränengebiet) und Gley-Podsole (Hohe Geest und Vorgeest) über die höchsten Corg-Vorräte bis 90 cm Tiefe. Das Speicher- und Verlustpotenzial von Humusmengen durch einen Landnutzungswechsel ist daher auch bodentypspezifisch zu bewerten.

Effects of fertilizer regimes on greenhouse gas emissions in a Gray Luvisol from central Alberta, Canada

This study investigated how different fertilizer regimes with a long-term repeated N application experiment affected on the soil Greenhouse gases (GHGs) emissions in a Gray Luvisolic from central Alberta, Canada. The results showed fertilizer regimes significantly influenced on GHGs emissions. The higher emissions of N2O and CH4 induced by NPKS soils were due to the superior utilization rate of mineral N and organic N. The CO2 emission rates indicated that soil organic carbon (SOC) was upper after Manure application than that after NPKS and Lime applications. The lowest Global Warming Potential (GWP) and highest pH of Lime soils suggested that liming application cause a significant decrease of GHGs by changing soil properties, such as pH. As for CH4 emissions during the incubation period, NPKS soil acted as sources, whereas the Lime and Manure soils acted as CH4 sinks. In addition, the fertilization history with higher SOC stocks in the Manure soils did not affect higher N2O emissions. In conclusion, this research showed liming application could be a better policy for improving soil properties in the acid Gray Luvisol from central Alberta, but liming may result in lower emissions of N2O and CO2 than the treatment of mineral fertilizer or farmyard manure.

Changes in soil carbon stocks across the Forest-Agroforest-Agriculture/Pasture continuum in various agroecological regions: A meta-analysis

The contribution of agroforestry systems (AFS) to enhance soil organic carbon (SOC) storage in soil layers due to the presence of deep tree roots are of interest in the context of promoting carbon sinks and greenhouse gas mitigation. To quantify the relative soil C contribution from trees in agroforestry systems (AFS), this study assessed the reported differences in SOC stocks under agroforestry systems in comparison with other land-use systems (Agriculture, Forestry, Pasture, or Uncultivated Land) in various soil-depth classes in four agroecological regions (arid and semiarid, ASA; lowland humid tropics, LHT; Mediterranean, MED; and temperate, TEM) around the world. Using mixed-effect models and a meta-analytical approach, we synthesized data from 78 peer-reviewed studies that generated 858 data points (sites) on SOC stock under various AFS practiced globally. Comparing Agroforest vs. Agriculture or Agroforest vs. Pasture, SOC stocks under AFS were higher by +27% in the ASA region, +26% in LHT, and +5.8% in TEM, but –5.3% in the TEM in the 0–100 cm soil depth. The Agroforest aged between 10–20 years had higher SOC stock than newly established, as well as <10-year-old systems across all soil-depth classes and agroecological regions. Overall, Agroforest vs. Agriculture land management practices resulted in positive SOC stock changes within AFS up to 100 cm soil depth, whereas SOC stock under AFS was lower than under Forest. The results suggest that a general pattern of Forest – Agroforest – Agriculture – Pasture continuum could be expected in SOC stock decline during land-use changes. Improvement of SOC stocks under AFS varied across agroecological regions, the highest being under arid and semiarid region, closely followed by the low humid tropics. The important outcome of this meta-analysis is worthy of emphasizing of the role of AFS in climate change adaptation and greenhouse gas mitigation strategies by promoting carbon sinks.

Soil organic carbon stocks controlled by lithology and soil depth in a Peruvian alpine grassland of the Andes

The soil is the largest carbon (C) pool in the terrestrial ecosystem, and soil organic carbon (SOC) stocks play an important role in global C dynamics. Alpine grasslands of the Andes are characterized by high SOC stocks. Quantifying SOC stocks and unraveling key factors controlling SOC stocks, is necessary to obtain a better understanding of the dynamics of the large C stocks in this environment. However, most studies on C dynamics of the Andes focus on volcanic-ash soils, whereas information about non-volcanic ash soils in this region is scarce. Our objectives were: (i) to estimate SOC stocks in an alpine grassland of the Peruvian Andes (7° 11′S, 78° 35′W) with parent materials other than volcanic ash, and (ii) to identify the underlying soil formation and environmental (SFE) factors and soil properties explaining observed patterns of SOC stocks. We sampled 69 plots up to the parent material to measure soil properties and to calculate SOC stocks, in relation to lithology, land use, grazing intensity, slope angle, slope position and altitude. We applied linear models to identify key factors controlling SOC stocks. Our results showed that total SOC stocks had a mean value of 215 ± 21 T ha−1, whereas SOC stocks of the upper 10 cm and 40 cm comprised 29.3% and 80.0% of total SOC stocks respectively. The variation of the total SOC stocks was mainly explained by soil depth and soil moisture. When soil depth and soil moisture were controlled as conditional variables, lithology became the key factor controlling the total SOC stocks. For the SOC stocks of the upper 10 cm, soil moisture explained a large part of the variation, whereas lithology, grazing intensity and altitude were also significant predictors. Our results also show that when soils are sampled with limited depths instead of the entire soil profile, SOC stocks can be underestimated, and the effects of the SFE factors on SOC stocks can be overestimated.

Soil organic carbon stock variation with climate and land use in shale derived soils

Anthropogenic activities, urbanization and industrialization cause an increase in the atmospheric carbon dioxide. Current focus of the soil scientists and the environmentalists is to quantify the carbon stocks and its flow in the agroecological system which is one of the main causes of global warming and climate change. The information on the distribution of soil organic carbon (SOC) stocks in the soil profiles in relation with changing climate is barely sufficient. Objective of this study was to quantify the effect of climate and land on the equilibrium of SOC stocks in soil profiles with development. Murree soil series (Typic Hapludolls) in humid climate and under coniferous forest, and Tirnul soil series (Typic Haplustepts) in semiarid climate under cultivation, were selected. Triplicate soil profiles were selected for each of the soils and sampled at genetic horizons level. Cumulative SOC stocks in Typic Hapludolls soil profiles (95 Mg ha-1) were significantly greater than Typic Haplustepts (30 Mg ha-1). The Typic Hapludolls had significantly greater SOC stock at each horizon level under humid climate. This research concludes that soils under forest and humid climate had higher SOC stocks as compared to the soils under semiarid climate and cultivation.

Crop rotation, tillage system, and precipitation regime effects on soil carbon stocks over 1 to 30 years in Saskatchewan, Canada

For both agronomic and environmental purposes, it is relevant to assess the effect of various land management practices on soil organic carbon (SOC). In the North American Great Plains, fallowing was used to increase soil water storage and production of succeeding crops. In addition, tillage was done to prepare seed beds and to control weeds. But these management practices led to important SOC losses, mainly due to increased mineralization with tillage and reduced plant C inputs with fallowing. In recent years, reduction of fallowing, use of minimum and no-tillage management practices and diversification of crop rotations with the inclusion of pulse crops have been studied. But the results are variable according to soil and climatic situations. In addition, long-term data are not always available. In this context, the objective of the present work was to assess over time the effects of cropping systems involving the use of various tillage management, the presence or absence of fallowing (1981–2011), and the presence or absence of pulse crops (1997–2011) on plant C inputs and SOC stocks along a 0–30 cm silt loam soil profile at Swift Current, SK. First changes between SOC stocks were apparent five years after the start of the experiment involving changed crop systems and mainly in the surface 0–7.5 cm soil layer instead of 0–15 cm or 0–30 cm soil profiles. This study confirmed the accumulation of SOC under continuous wheat systems in comparison to fallow-wheat rotations, probably related to larger C inputs in the continuous wheat systems. Although the effect of tillage was quite scattered in time, it seemed to be more pronounced in the fallow-wheat rotations than in the continuous wheat systems, with higher SOC stocks with no tillage. Then, the replacement of fallow phase by pulse crops offered promising potential to rebuild SOC stock after fallow-wheat rotations, even if its efficacy might depend on the initial SOC content and/or its combination with a tillage reduction. Finally, even if a kind of equilibrium could set after changes from a traditional fallow wheat rotation, the SOC dynamics might be highly influenced by precipitation regime and all the carbon accumulated for decades could be lost in few years (less than five in this study). Indeed, in this semi-arid prairie, the increase of the apparent decomposition with precipitation exceeded that of the plant biomass C inputs.

Soil organic carbon increases under intensive agriculture in the Central Sands, Wisconsin, USA

Soil organic carbon (SOC) plays a crucial role in maintaining fertility and productivity in sandy soils. This study mapped the spatial variability of SOC concentration, A-horizon thickness, and SOC stocks from the Central Sands in Wisconsin. Soil samples were collected from three different areas (area A, B, and C) that were sampled through grid sampling (GS, n=100), conditioned latin hypercube sampling (cLHS, n=100), and random sampling (RS, n=150) schemes. Average SOC concentration of the A-horizon from soil sampling area A, B, and C were 6.1, 7.1, 8.3gkg−1, respectively. The mean A-horizon thickness for agricultural soils was 28cm compared to 15cm under adjacent grassland. Regression kriging was selected as prediction model where ECa and local topographic information (i.e., slope gradient, slope aspect, elevation, wetness index, altitude above channel network etc.) were used as predictors. We observed an increased SOC content, SOC stock, and A-horizon thickness with ECa and wetness index. SOC from area B had the strongest spatial dependency (NSR=0.64) followed by area A (NSR=0.72), whereas that from area C was the weakest (NSR=0.78). Compared to SOC content and A-horizon thickness prediction, SOC stocks prediction had the maximum uncertainty. Predicted SOC stock (tha−1) ranged from 28 for sampling area A to 40 for B, and 59 for area C. These high SOC stocks are the result of decade long intensive agriculture with high amount of nitrogen input and irrigation. It has resulted in deep A-horizon and high SOC stocks. This study found that SOC stocks in the Central Sands could be estimated from A-horizon thickness (R2 ~0.5).

Crop Biomass, Soil Carbon, and Nitrous Oxide as Affected by Management and Climate: A DayCent Application in Brazil

A current national research priority in Brazil is the assessment of potential climate change impacts in agriculture. In this study, the DayCent model was used to predict changes in crop biomass, soil C stocks, and N₂O fluxes of a major agricultural area in Brazil. The model was calibrated and validated using datasets from 30-yr-old experiments. Simulations of current and alternative management practices to 2100 using IPCC climate scenarios A2 and B1 were conducted. Predicted crop biomass increases ranged from 5% (sorghum [B1]) to 65% (soybean [A2]). DayCent simulated higher soil organic carbon stocks in the wheat–soybean system (VAL1) than in the wheat–soybean–vetch–sorghum system (VAL2) in both climate scenarios. Soil organic carbon accumulation by 2100 (±16 Mg C ha⁻¹ above current 46 Mg C ha⁻¹) was forecast in cropping systems with pastures (Cynodon sp.), regardless of the climate scenario. Daily N₂O fluxes were underestimated by ±41% (0.85 g N–N₂O ha⁻¹ d⁻¹) in VAL1 and overestimated by 17.5% (0.28 g N–N₂O ha⁻¹ d⁻¹) in VAL2. Cumulative N₂O fluxes produced mixed results, which were 29% lower than observed in VAL1 and 5% higher in VAL2 but within the range of values reported in other greenhouse gas studies in southern Brazil. Simulations of N₂O fluxes to 2100 with IPCC climate change scenarios B1 and A2 in southern Brazilian indicated higher annual fluxes across the alternative treatments tested in comparison to current fluxes. According to model predictions, climate change would lead to larger relative increases in N₂O emissions from no-tillage (27% in B1 to 41% in A2), but these enhanced fluxes would still be lower than those from tillage by approximately 25%.

Effect of the different types of land-use on the distribution of soil organic carbon in north Nile Delta, Egypt

In Egypt, the need for accurate information on soil organic carbon (SOC) content has increased due to the importance of SOC stocks for sustainable use of natural resources and to meet the requirements of the Kyoto Protocol. Thus, the objectives of the present study are: (1) to quantify the vertical distribution of the soil bulk density (SBD) and SOC content in the soil of north Nile Delta, Egypt under different types of land-use; (2) to provide estimates of the carbon sequestration rate (CSR) of those soils under different types of land-use; and (3) to establish a baseline data on SOC stocks for future studies on SOC dynamics. Ten sampling stations were selected to represent the north Nile Delta during May 2014. In each of the sampling station, 4 sampling sites were selected to represent the virgin lands, 4 to represent fish farms and 12 to represent crop lands (four cultivation histories: 5, 15, 30 and 50 years × three crop types: clover, Trifolium alexandrinum L., sugar beet, Beta vulgaris L., and rice, Oryza sativa L.). Effect of crop type was significant in relation to SBD, SOC content, and SOC stock. In general, SOC stock increases as the number of years of cultivation increases. The SOC stock under crop land and fish farm were 1.6 and 1.5 times as that of virgin land. Rice was the crop with lowest SBD and highest SOC stock. The average CSR of crop land was 352, 134, 88 and 62 g C m−2 year−1 for 5, 15, 30 and 50 years of cultivation, respectively. The highest CSR (545 g C m−2 year−1) was observed in crop land cultivated for 5 years by rice, while the lowest (21 g C m−2 year−1) was observed in crop land cultivated for 50 years by sugar beet. On the other hand, the average CSR of fish farm was 143 g C m−2 year−1. In conclusion, the conversion of virgin land into crop land or fish farm contributed to SOC sequestration.