Trends In Soil Organic Carbon Research Articles

The effect of stand characteristics on soil organic carbon content in spruce and deciduous stands

Aim of study: To determine the effects of stand characteristics, which closely relate to forest management practices, on the soil organic carbon (SOC) content in the organic (O) and surface mineral (A) soil horizons in spruce and deciduous stands, and to show SOC dynamics during the life of production stands. Area of study: Spruce and deciduous stands located throughout the Czech Republic. Material and methods: The effects of age, density of stocking and canopy of stand on SOC content in the O and A horizons, and the difference between categories of variables and the trends of SOC were evaluated in spruce and deciduous stands (401 plots) at lower and middle elevations. Main results: SOC content changed during the life of stands. In spruce stands, a decreasing trend of SOC with stand age was found in the A horizon. In deciduous stands, SOC content was higher overall in the A horizon, fluctuating slightly with stand age, but more balanced during the life of stands. Based on the results, in terms of management of dying spruce stands and carbon sequestration, felling should be carried out in the age group of 81-120 years in spruce stands, whereas in deciduous stands felling should take place in older stands (141 years and more). Density of stocking and canopy of stand had no substantial effect of SOC content. Research highlights: Deciduous stands have the potential to replace dying spruce stands at lower elevation in terms of carbon sequestration.

Topography modifies the effect of land‐use change on soil respiration: A meta‐analysis

AbstractSoil respiration is controlled by land‐use changes associated with cropland vegetation restoration, and this can vary with topography, although the magnitude of this effect and the underlying mechanisms are still unclear. We synthesized 69 recently published papers from China to explore the influence of topography‐related changes in land use on soil respiration where croplands were converted into orchards (abbreviated as C‐O), grasslands (abbreviated as C‐G), or woodlands (abbreviated as C‐W). Our results showed that not only did land‐use change have a significant influence on soil respiration, but this varied with topography. While C‐O resulted in a decrease in soil respiration by, on average, 3.1%, both the magnitude and sign of the change varied with topography, with an 8.2% increase for flat areas and a 14.7% decrease for slopes. For the C‐G conversions, soil respiration increased, on average, by 21.4%, with a 19.5% and a 24.3% increase for flat and slope topography, respectively. For C‐W, soil respiration increased, on average, by 28.0%, with only a 1.6% increase for flat areas, but a 39.9% increase for slopes. Soil temperature, soil moisture, root biomass, soil organic carbon (SOC), soil microbial biomass carbon (MBC), soil carbon‐to‐nitrogen ratio (C:N ratio), and soil density also varied with topography, with larger changes for slopes than for flat topography. Increases in soil respiration associated with different topography were closely related to changes in soil temperature, SOC, MBC, and root biomass (P < 0.05), but were not correlated with changes in soil moisture, C:N ratio, or soil density (P > 0.05). The contribution of different drivers to the change in soil respiration under different topographical conditions showed a trend of SOC > root biomass > MBC > soil temperature. Based on these results, topography‐related variations in soil respiration need to be accounted for when quantifying the impact of land‐use change on C budgets.

Integration of a process-based model into the digital soil mapping improves the space-time soil organic carbon modelling in intensively human-impacted area

Soil organic carbon (SOC) in intensively human-impacted areas often presents extremely complicated patterns in space and time, which brought a new challenge to space–time SOC modelling. Here we attempt to create a space-for-time GWRK-RothC model by incorporating the predictions of the process-based RothC model into the geographically weighted regression kriging (GWRK) for improving the space–time modelling of SOC in intensively human-impacted area. We collected a total of 1219 topsoil samples (0–20 cm) from southern Jiangsu Province of China in 1980, 2000, and 2015, and modelled the spatiotemporal dynamics of SOC by using the modified RothC model (with a newly-added pH modifier for representing the impact of soil acidification on SOC decomposition), the space-for-time GWRK, and the proposed space-for-time GWRK-RothC model. Results showed that the change trends in SOC derived by the three methods were similar, with an overall trend of SOC increase during 1980–2000 and SOC decline in the subsequent 15 years (2000–2015). However, their performances for space–time SOC modelling were different. The proposed space-for-time GWRK-RothC model had the highest accuracy in representing the spatiotemporal evolution of SOC in the study area, with the lowest root mean square error (RMSE) (3.06 g kg−1), mean error (ME) (-0.19 g kg−1), and the highest coefficient of determination (R2) (0.61), compared to the accuracy of space-for-time GWRK (RMSE = 3.53 g kg−1, ME = -0.36 g kg−1, and R2 = 0.45) and RothC model (RMSE = 4.23 g kg−1, ME = 0.20 g kg−1, and R2 = 0.20). These results highlighted the importance of integrating process-model-derived SOC spatiotemporal dynamics information in space-for-time digital soil mapping (DSM) for improving the space–time SOC modelling. We believe that outputs from this study may offer valuable guidance for developing space–time DSM model to achieve better performance of SOC modelling in space and time, especially for areas affected by strong anthropogenic activities.

Changes in soil carbon sequestration and emission in different succession stages of biological soil crusts in a sand-binding area

BackgroundWe investigated the spatio-temporal dynamics of soil carbon dioxide (CO2)- and soil methane (CH4)-flux during biological soil crust (BSCs) deposition in a sand-binding area in the eastern Chinese Hobq Desert. The trends in soil organic carbon (C) content and density were analyzed during this process. The sampling sites comprised a mobile dune (control) and those with algal, lichen, and moss crust-fixed sands. The desert soil CO2- and CH4-flux, temperature, and water content were measured from May to October in 2017 and 2018. Simultaneously, organic C content and density were measured and analyzed by stratification.ResultsThe spatio-temporal variation in desert soil CO2-flux was apparent. The average CO2- fluxes in the control, algal, lichen, and moss sites were 1.67, 2.61, 5.83, and 6.84 mmol m−2 h−1, respectively, during the growing season, and the average CH4-fluxes in the four sites were − 1.13, − 1.67, − 3.66, and − 3.77 µmol m−2 h−1, respectively. Soil temperature was significantly positively correlated with CO2-flux but could not influence CH4 absorption, and C flux had minimal correlation with soil water content. The soil total organic C density at all sites was significantly different and decreased as follows: moss > lichen > algal > control; moreover, it decreased with soil depth at all sites. The accumulation of desert soil organic C could enhance soil C emissions.ConclusionIn a semi-arid desert, artificial planting could promote sand fixation and BSCs succession; therefore, increasing the C storage capacity of desert soils and decreasing soil C emissions could alter the C cycle pattern in desert ecosystems. Soil temperature is the major factor controlling desert soil CO2 flux and vegetation restoration, and BSCs development could alter the response patterns of C emissions to moisture conditions in desert soils. The results provide a scientific basis for studying the C cycle in desert ecosystems.

Applying CCB to predict management change affected long‐term SOM turnover of the Extended Static Fertilization Experiment in Bad Lauchstädt

AbstractLong‐term field experiments (LTEs) are invaluable in improving understanding of soil organic matter (SOM) turnover, as some of the involved processes have proceeded over centuries. Prediction of such slow carbon fluxes depends especially on the initialization of slow‐reacting model pools and requires monitoring for a very long time for evaluation. This study reports soil organic matter (SOM) modelling covering more than 100 years for a dataset of 36 treatments of the “Extended Static Experiment” that is based on the classical “Static Experiment Bad Lauchstädt.” The experimental scheme includes different fertilization treatments where the plots are arranged in two field stripes. A special feature of this experiment is the management change for each stripe after seven decades of continuous cultivation that includes a considerable alteration of organic amendments on different SOM levels. The Candy Carbon Balance (CCB) model was calibrated for soil organic carbon (SOC) dynamics regarding initial SOC content and one parameter describing the physical protection of SOM. Calibration was performed for each plot individually, for each stripe, and for the whole experiment, resulting in a relative root mean square error (rRMSE, (−)) of 0.050, 0.058 and 0.064, respectively. Model predictions for soil organic nitrogen (SON) dynamics were satisfactory using the calibration results for SOC and the average C/N ratio from all observations within this dataset (11.8) for model initialization. The model error for SON prediction reached from rRMSE = 0.09 (whole experiment) over rRMSE = 0.085 (each stripe) to rRMSE = 0.084 (each plot). Calibration results suggest some heterogeneity between the two field stripes. Restarting the model after the management change in 1978 using the plot‐specific calculated SOC value from previous simulations for the whole time period provided different results of predicted SOC trends and values, suggesting that the precondition of SOM in steady state was still not fulfilled after seven decades.Highlights SOC and SON were modelled for 36 treatments over more than one century. Model restarts after seven decades indicated that SOM pools were not in steady state. Modelling SON required only an additional input of the average C/N ratio of SOM Effect of serious fertilization changes can be well predicted by the tested model setup

Simulating soil organic carbon in maize-based systems under improved agronomic management in Western Kenya

Improved management practices should be implemented in croplands in sub-Saharan Africa to enhance soil organic carbon (SOC) storage and/or reduce losses associated with land-use change, thereby addressing the challenge of ongoing soil degradation. DayCent, a process-based biogeochemical model, provides a useful tool for evaluating which management practices are most effective for SOC sequestration. Here, we used the DayCent model to simulate SOC using experimental data from two long-term field sites in western Kenya comprising of two widely promoted sustainable agricultural management practices: integrated nutrient management (i.e. mineral fertilizer and crop residues/farmyard manure incorporation) and conservation agriculture (i.e. minimum tillage and crop residue retention). At both sites, correlations between measured and simulated SOC were low to moderate (R2 of 0.25−0.55), and in most cases, the model produced fairly accurate prediction of the SOC trends with a low relative root mean squared error (RRMSE < 7%). Consistent with field measurements, simulated SOC declined under all improved management practices. The model projected annual SOC loss rates of between 0.32 to 0.35 Mg C ha-1 yr-1 in continuously tilled maize (Zea mays) systems without fertilizer or organic matter application over the period 2003–2050. The most effective practices in reducing the losses were the combined application of 4 Mg ha-1 of farmyard manure and 2 Mg ha-1 of maize residue retention (reducing losses up to 0.22 Mg C ha-1 yr-1), minimum tillage in combination with maize residue retention (0.21 Mg C ha-1 yr-1), and rotation of maize with soybean (Glycine max) under minimum tillage (0.17 Mg C ha-1 yr-1). Model results suggest that response of the passive SOC pool to the different management practices is a key driver of the long-term SOC trends at the two study sites. This study demonstrates the strength of the DayCent model in simulating SOC in maize systems under different agronomic management practices that are typical for western Kenya.

Assessment of Seasonal Variability in Soil Nutrients and Its Impact on Soil Quality under Different Land Use Systems of Lower Shiwalik Foothills of Himalaya, India

The present study was conducted to investigate the seasonal effects of five land use systems (LUSs), i.e., wheat–rice (Triticum aestivum—Oryza sativa) system, sugarcane (Saccharum officinarum), orange (Citrus sinensis) orchard, safeda (Eucalyptus globules) forest, and grassland, on soil quality and nutrient status in the lower Satluj basin of the Shiwalik foothills Himalaya, India. Samples were analyzed for assessment of physico-chemical properties at four soil depths, viz., 0–15, 15–30, 30–45, and 45–60 cm. A total of 120 soil samples were collected in both the seasons. Soil texture was found to be sandy loam and slightly alkaline in nature. The relative trend of soil organic carbon (SOC), macro- and micro-nutrient content for the five LUSs was forest &gt; orchard &gt; grassland &gt; wheat–rice &gt; sugarcane, in the pre- and post-monsoon seasons. SOC was highly correlated with macronutrients and micronutrients, whereas SOC was negatively correlated with soil pH (r = −0.818). The surface soil layer (0–15 cm) had a significantly higher content of SOC, and macro- and micro-nutrients compared to the sub-surface soil layers, due to the presence of more organic content in the soil surface layer. Tukey’s multiple comparison test was applied to assess significant difference (p &lt; 0.05) among the five LUSs at four soil depths in both the seasons. Principle component analysis (PCA) identified that SOC and electrical conductivity (EC) were the most contributing soil indicators among the different land use systems, and that the post-monsoon season had better soil quality compared to the pre-monsoon season. These indicators helped in the assessment of soil health and fertility, and to monitor degraded agroecosystems for future soil conservation.

Geospatial distribution of soil organic carbon and soil pH within the cocoa agroecological zones of Ghana

Geospatial distribution of soil organic carbon (SOC) and soil pH is an important component of soil fertility management in sustainable cocoa (Theobroma cacao L.) production. Spatial precision of cocoa soil fertility management in Ghana is rare due to paucity of spatially precise knowledge of farm soil properties. This study sought to provide spatially explicit knowledge of the underlying trends of SOC and pH in and across cocoa agroecological zones, covering 61 cocoa districts in Ghana. Soil samples collected at 20 cm depth from 739 newly established cocoa farms were analyzed using classical and geospatial statistical methods. We described the spatial pattern (clustering) of SOC and pH and predicted their spatial continuity from observed and unobserved locations. Results generally revealed unsuitably low SOC (0.39 ± 0.009 g/100 g) and strong acidity (5.35 ± 0.027). Univariately, SOC varied more continuously (58%) over a longer distance (1.424 km) than pH, which varied moderately around 55.7% over a shorter distance (0.598 km). Covariates improved the co-regionalized structure and homogeneity of the predictions. Thus, the spatial dependencies of SOC and pH were moderate but the risk of imprecision was higher for SOC than pH. This knowledge is crucial in our understanding of the geo-physicochemical phenomena controlling the spatial distribution of SOC and pH in the cocoa farms and districts across the agroecological zones. The findings underscored dwindling SOC and pH in line with historic boom-bust cycle of cocoa production hot and cold spots transitions. The findings are also indicative of the adverse implications of relying on current blanket fertilizer recommendations. Therefore, a change from the current agronomic practice of fertilizer use to one that recognizes the SOC and pH needs of specific areas, farms and cluster of districts is recommended.

Soil organic carbon pool under selected tree plantations in the Southern Western Ghats of Kerala, India

Soil organic carbon (SOC) is the most important indicator of soil quality and land-use sustainability. We evaluated the SOC pool and selected physico-chemical soil variables after conversion of native forest to monoculture tree plantations (teak, eucalypts and rubber) in the Southern Western Ghats region of Kollam district, Kerala, India. Soil samples were collected up to a depth of 50 cm in five depth increments from six locations each from the four selected land-use systems. Soil analyses were carried out as per standard methods. Average SOC concentration ranged from 41.89 to 54.09 g kg−1 (0–10 cm), and found decreased with depth up to 30.11 to 32.98 g kg −1 (40–50 cm). The highest SOC pool (0–50 cm) was observed under natural forest (225.34 t ha−1), followed by rubber (203.48 t ha−1), eucalypts (196.21 t ha−1) and teak plantation (194.61 t ha−1). Similarly, the SOC mitigation potential (carbon equivalent to CO2) decreased in the order natural forest > rubber > eucalypts > teak plantation. The SOC concentration showed significant variation between natural forest and tree plantations. Principal component analysis (PCA) was used to determine the major factors and trends to illustrate the variability in the data. PCA results suggest that higher SOC contents and its fractions were closely linked to the surface layers (0–20 cm) of soils under all treatments. Overall conclusion from this investigation is that SOC levels are strongly influenced by the prevailing land-use systems and found to decrease after conversion from natural vegetation to monoculture tree plantations. The information presented herein on the depth distribution of the SOC fractions and trends in aggregate carbon content may improve our knowledge and help in framing soil carbon prediction models in this region.

Natural and managed soil structure: On the fragile scaffolding for soil functioning

Soil structure in natural systems is a product of complex interactions between biological activity, climate and soil minerals that promote aggregation and accumulation of biopores. In arable lands, the management of soil structure often requires the mechanical fragmentation of hardened soil to improve seedbed, control weeds and bury plant residue. Despite difficulties in defining and quantifying soil structure, its critical role is evidenced by loss of productivity when natural structure is perturbed (e.g. compaction) and the long history of tillage in agriculture. To overcome persistent ambiguities among scientific disciplines regarding definition and function of soil structure, we propose a framework for distinguishing managed and natural soil structure based on their different formation processes and functions. Natural soil structure preserves ecological order and legacy that promotes biopore reuse, stabilizes foodwebs and protects soil organic carbon (SOC). The contribution of net primary productivity of natural lands to soil structure forming processes makes it a useful (surrogate) metric of soil structure. The benefits of managed soil structure for crops are quantified indirectly via comparisons with no-till farming under similar conditions. The levels and trends of SOC are useful metrics for the status of natural and managed soil structure. The systematic consideration of soil structure state in natural and arable lands using suitable metrics is a prerequisite for rational decisions related to land management and ensuring sustainable functioning of a fragile and central resource such as soil.

Revealing the scale- and location-specific controlling factors of soil organic carbon in Tibet

Soil organic carbon (SOC) leads to a significant impact on global carbon (C) cycling and soil quality. Variations in SOC are controlled by vegetation, geomorphic, geological and climatic factors, but the dominant environmental differs. In the Qinghai -Tibet Plateau, which contains large amount of low-latitude permafrost, the impact of environmental factors for the variations of SOC may be different due to the unique and complicated geographical condition. In this study, the two-dimension empirical mode decomposition (2D-EMD) is applied to examine the variations of SOC at different scales and locations, and the correlations between SOC and environmental factors are explained. The spatial distribution of SOC in Tibet was decomposed into three intrinsic mode functions (IMFs) under different scales, with spatial variation scales of approximately 7 km, 109 km and 338 km, which represented the small, medium and large scale, respectively. The remaining residual represented the variation trend of SOC across Tibet. The correlations between SOC and environmental factors (elevation, radiation, evapotranspiration and temperature) are distinguished by the physiographic zone at small and medium scales. Temperature is weekly or nonsignificantly correlated to SOC in cold-dry western Tibet at large scale. Normalized difference vegetation index (NDVI) and precipitation influenced SOC mainly at small scales, while the effects of precipitation and evapotranspiration on the distribution of SOC were due to geomorphology and type of permafrost. The combined effect of climate on SOC was larger than other factors at large scale while factors refer to DEM, evapotranspiration, water erosion and NDVI accounted for more contribution at small scale. The results indicated that the environmental factors influence SOC under a combination of scale and location effect. These findings are of great significance for future studies in SOC dynamic modelling under the influence of natural changes and human activities.

Is Soil Contributing to Climate Change Mitigation during Woody Encroachment? A Case Study on the Italian Alps

Background and Objectives: Over the last few decades, the European mountain environment has been characterized by the progressive abandonment of agro-pastoral activities and consequent forest expansion due to secondary succession. While woody encroachment is commonly considered as a climate change mitigation measure, studies suggest a still uncertain role of the soil organic carbon (SOC) pool in contributing to climate change mitigation during this process. Therefore, the objective of the study is to investigate the possible SOC variations occurring as a consequence of the secondary succession process at the provincial level in an Alpine area in Italy. Materials and Methods: A chronosequence approach was applied to identify, in five different study areas of the Belluno province, the land use/land cover change over four different stages of natural succession, from managed grazing land to secondary forest developed on abandoned grazing land. In each chronosequence stage, soil samples were collected down to the bedrock (0–60 cm depth) to determine the changes in the SOC stock due to the woody encroachment process. Results: In all areas, small or no significant (p &lt; 0.05) SOC stock changes were observed during the secondary succession in the upper 30 cm of mineral soil, while significant changes were evident in the 30–60 cm compartment, with the SOC stock significantly decreasing from 30% to 60% in the final stage of the succession. This fact indicates the great importance of considering also the subsoil when dealing with land use/land cover change dynamics. Conclusions: The recorded trend in SOC has been proved to be the opposite in other Italian regions, so our results indicate the importance of local observation and data collection to correctly evaluate the soil contribution to climate change mitigation during woody encroachment.

Adaptation in U.S. Corn Belt increases resistance to soil carbon loss with climate change

Increasing the amount of soil organic carbon (SOC) has agronomic benefits and the potential to mitigate climate change. Previous regional predictions of SOC trends under climate change often ignore or do not explicitly consider the effect of crop adaptation (i.e., changing planting dates and varieties). We used the DayCent biogeochemical model to examine the effect of adaptation on SOC for corn and soybean production in the U.S. Corn Belt using climate data from three models. Without adaptation, yields of both corn and soybean tended to decrease and the decomposition of SOC tended to increase leading to a loss of SOC with climate change compared to a baseline scenario with no climate change. With adaptation, the model predicted a substantially higher crop yield. The increase in yields and associated carbon input to the SOC pool counteracted the increased decomposition in the adaptation scenarios, leading to similar SOC stocks under different climate change scenarios. Consequently, we found that crop management adaptation to changing climatic conditions strengthen agroecosystem resistance to SOC loss. However, there are differences spatially in SOC trends. The northern part of the region is likely to gain SOC while the southern part of the region is predicted to lose SOC.

Assessment of Soil Organic Carbon Stock under Different Density Classes of Oak (Quercus leucotricophora) Forests in Uttarakhand, India

Soil organic carbon (SOC) is one of the most important and essential constituents of soil. It is the largest reservoir of terrestrial carbon. Here, an investigation was carried for the assessment of Soil Organic Carbon in three different density classes of Oak forest of Chakrata (Distt. Dehradun), Itarna (Distt. Tehri Garhwal) and Lansdowne (Distt. Pauri Garhwal) forest divisions of Uttarakhand. Three soil samples from each forest system at 0-30 cm depth were collected from each density to assess soil organic carbon stock. A total of 81 soil sample were collected in three seasons. In summer season among all three division maximum Soil Organic Carbon was assessed in Chakrata dense forest division (81.65 t ha-1), followed by moderate forest (47.66 t ha-1) and open forest (37.68 t ha-1) of Chakrata forest division. In Lansdowne forest division maximum SOC was found in dense forest (79.82 t ha-1) followed by moderate (48.53 t ha-1) and open forest (35.37 t ha-1) respectively. A similar trend was reported in case of Itarna forest division. Where (78.47 t ha-1) come up to maximum reservoir of SOC followed by moderate forest (46.50 t ha-1) and open forest (34.52 t ha-1) respectively. In rainy season among all three division maximum Soil Organic Carbon was assessed in Chakrata dense forest division (66.24 t ha-1), followed by moderate forest(45.62 t ha-1) and open forest (29.53 t ha-1) of Chakrata forest division. In Lansdowne forest division maximum SOC was found in dense forest (75.48 t ha-1) followed by moderate 48.65 t ha-1) and open forest (22.36 t ha-1) respectively. Similar trend was reported in case of Itarna forest division.In winter season among all three divisions maximum Soil Organic Carbon was assessed in Chakrata dense forest division (81.89 t ha-1), followed by moderate forest (56.62 t ha-1) and open forest (32.32 t ha-1) of Chakrata forest division. In Lansdowne forest division maximum SOC was found in dense forest (81.90 t ha-1) followed by moderate (57.43 t ha-1) and open forest (35.99 t ha-1) respectively. A similar trend was reported in case of Itarna forest division. This study reveals that in the Soil Organic Carbon is maximum in the dense forest followed by moderate and open forest which could be possibly due the more flora and fauna in the dense forest followed by moderate and open forest. Possibly the activities of flora and fauna lead to the addition of more carbon content in the soil. The study demonstrated similar trends of SOC in three different dense, moderate and open density classes of Oak forest. These outcomes of the study may explore the possibility to improve the scientific basis of forest management and land use in the near future.

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;

Effect of Long-Term Nutrient Management on Soil Organic Carbon Sequestration in Rice–Rice–Fallow Rotation

A study was conducted on long-term (for 31 years) rice–rice–fallow cropping sequence to determine the effect of balanced chemical fertilizer and integrated nutrient management (INM; chemical fertilizer + poultry manure 2 tonne ha –1 ) on soil organic carbon (SOC) sequestration. C mineralization rate (k), microbial population, SOC and C content in the mean water stable soil aggregate (MWDw) were measured from field soil. The C dynamics was described using DSSAT crop and DNDC models. INM increased soil bacteria and improved SOC stock by 27.98%, although C loss was higher with this treatment. A decreasing trend of bacterial population and SOC was observed in the balanced chemical fertilizer (15%) and fertilizer control (46%) treatments compared to initial soil. A positive correlation (r = 0.94) was found between C content of MWDw and soil bacteria population, which provided evidence of vital contribution of soil bacteria for SOC sequestration. In INM treatment, k (incubation study) was 0.011 tonne year –1 , and it was less than DNDC- and DSSAT-generated data. However, k value (0.010 tonne year –1 ) obtained in the incubation study of the balanced chemical fertilizer was similar to DNDC model data. An increasing trend of paddy yield (10 years) was observed in INM compared to balanced chemical fertilizer. In conclusion, microbial population, SOC sequestration and crop yield were high with INM. For sustainable rice production and C sequestration, INM is superior to balanced chemical fertilizer. Between two models used, DNDC is better for prediction of SOC balance.

Soil microbial community responses to labile organic carbon fractions in relation to soil type and land use along a climate gradient

There has been a growing interest in studying the labile C pool in order to promote the sequestration and stabilization of soil organic carbon (SOC). Although labile SOC fractions have emerged as standardized indicators because of their potential to detect early SOC trends over time, the relationships between microbial attributes and labile SOC remains poorly understood. In this study, we explored the influence of labile SOC fractions on the topsoil bacteria-archaea community across 28 sites with different land use, climate aridity, and soil types across a wide range of SOC content (0.6–12%) in central Chile. We applied Illumina sequencing to the 16S rRNA to examine shifts in the diversity and composition of these soil microbial communities. Additionally, labile SOC fractions such as the permanganate oxidizable carbon (POXC) and light fraction organic matter (LFOM), along with the soil physicochemical properties were analyzed. The results demonstrated that among all of the environmental factors tested, the pH, POXC/SOC ratio and LFOM were key drivers of microbial community structure (β-diversity). The α-diversity metrics exhibited a decreasing trend when aridity increased, and community structure was found to vary, with high POXC/SOC in sites associated with drier conditions. In addition, POXC/SOC ratios and LFOM were clearly related to shifts in the relative abundances of specific taxonomic groups at genera level. When there was high POXC/SOC and low LFOM content, members of Bacteroidetes (Adhaeribacter, Flavisolibacter, and Niastella), Proteobacteria (Skermanella, Ramlibacter, and Sphingomonas), and Archaea (Thaumarchaeota) were found to be the most dominant groups; however, the microbial taxa responded differently to both labile C fraction types. These results have implications for understanding how labile C content can potentially be used to predict shifts in the microbial community, thus facilitating the development of predictive ecosystem models, as well as early warning indicators for soil degradation.

Inter‐annual simulation of global carbon cycle variations in a terrestrial–aquatic continuum

AbstractThe advanced process‐based model, National Integrated Catchment‐based Eco‐hydrology (NICE)‐BGC, which incorporates the whole process of carbon cycling in land, was modified to include the feedback between soil organic content and overland carbon fluxes. It is a crucial and difficult task to evaluate the balance of the terrestrial carbon budget including the effect of inland water robustly. To accomplish this purpose, NICE‐BGC was applied to quantify the global biogeochemical carbon cycle closely associated with the complex hydrological cycle during the 36 years between 1980 and 2015. The model demonstrated that the inter‐annual variations of carbon cycle have been greatly affected by the extreme weather patterns. In particular, spatial distribution of temporal trends in riverine carbon fluxes and their relation to soil organic carbon (SOC) were analysed between different biomes and major river basins. Although there was a positive relationship between SOC and riverine flux of dissolved organic carbon and particulate organic carbon in the northern boreal region, it is difficult to see this relation in other regions. Further, the evaluation of potential controlling factors of temporal trends in SOC and fluvial carbon exports was also helpful to quantify the inter‐annual variation or temporal trend caused by the various effects. SOC was more influenced by temperature variations, whereas riverine carbon exports were mainly determined by precipitation variations. Finally, net land flux including inland water (−1.49 ± 0.50 PgC/year) showed a slight decrease in the carbon sink in comparison with previous values (−2.33 ± 0.50 PgC/year). These results help to distinguish the carbon cycle in different river basins and to re‐evaluate carbon cycle change explicitly including the effect of inland water because this effect has been so far implicitly included within the range of uncertainty in the Earth's global carbon cycle comprising land, oceans, and atmosphere.

Intensive long-term monitoring of soil organic carbon and nutrients in Northern Germany

Since 2003, the regional long-term soil monitoring network (SMN) Schleswig–Holstein (SH) includes an intensive monitoring program (I-BDF) with (sub-)annual measurements at four sites. This is the first study investigating the benefits of this SMN where study sites are no experiments but managed by independent farmers. The main objective of this study was to investigate whether, and under which circumstances, annual soil carbon and nutrient measurements are more beneficial within a soil monitoring network than common five- to ten-year measurements using modeling and nutrient balances. Soil measurements (stocks of soil organic carbon (SOC), Ntot, P and Mg), weekly leachate-NO3–N and management data were used for comparison. C and N changes were modeled with DNDC (DeNitrification–DeComposition); P and Mg were calculated as full nutrient balances and compared to the observations using performance metrics. The results show that DNDC could reproduce the long-term trend of SOC and Ntot well, but this could also be by coincidence as the type of trendline depended on the starting year. The model results could not depict measured short-term variations in soil which were due to field heterogeneities caused by farm management. NO3-N leaching was strongly overestimated when organic fertilization and stronger rainfall occurred. Comparing stock changes with nutrient balances revealed that, in several cases, long-term trends could be shown to a limited extent and reproduced only very few short-term changes and variations. The results suggest that only annual soil property measurements can depict the soil’s variability and contribute to the identification of the true long-term trend.

Estimating the contribution of crop residues to soil organic carbon conservation

Crop residues contribute to the maintenance of soil organic carbon (SOC) stores, a key component of soil fertility and soil-based climate change mitigation strategies, such as the ‘4 per 1000’ initiative. Residues are also in demand in sectors coupled to crop production, such as the supply chain of livestock and bioenergy production. Ongoing debate revolves around balancing these competing uses, but science-based assessments of the long-term sustainability of residue exploitation are rare. This work uses biophysical simulation modelling to explore the likely response of SOC to different management strategies, using the land area of North Rhine-Westphalia (Germany) as a case study. Four strategies are tested: zero, one third and 100% removal of cereal residues, plus an approach proposed by the State farm advisory service. Simulations are carried out for the period 1971–2050 and 19 crop rotations coincident with land use throughout the study area. Uncertainty associated with the modelled SOC changes is explored by sampling values of relevant parameters for SOC turnover and running an ensemble of model configurations. Simulated SOC is used to trace time-dependent response functions following a change in residue management under different soil textures, initial SOC levels and crop rotations. Results highlight a general exponential decrease in SOC, with relative changes in 2050 distributed between +10% and −40% with respect to a reference period. SOC loss can be buffered or offset by returning all crop residues to the soil. Under such management, an SOC increase can be achieved on clayey soils characterized by a low initial SOC. Under moderate crop residue removal, positive SOC trends are limited to a few crop rotations. In this context, 4 per 1000 increase rate in SOC appears largely out of reach through residue management, calling for additional measures to meet the targets of land-based mitigation of anthropogenic emissions.