Changes In Soil Carbon Stocks Research Articles

Input database related uncertainty of Biome-BGCMuSo agro-environmental model outputs

ABSTRACT Gridded model assessments require at least one climatic and one soil database for carrying out the simulations. There are several parallel soil and climate database development projects that provide sufficient, albeit considerably different, observation based input data for crop model based impact studies. The input database related uncertainty of the Biome-BGCMuSo agro-environmental model outputs was investigated using three and four different gridded climatic and soil databases, respectively covering an area of nearly 100.000 km2 with 1104 grid cells. Spatial, temporal, climate and soil database selection related variances were calculated and compared for four model outputs obtained from 30-year-long simulations. The choice of the input database introduced model output variability that was comparable to the variability the year-to-year change of the weather or the spatial heterogeneity of the soil causes. Input database selection could be a decisive factor in carbon sequestration related studies as the soil carbon stock change estimates may either suggest that the simulated ecosystem is a carbon sink or to the contrary a carbon source on the long run. Careful evaluation of the input database quality seems to be an inevitable and highly relevant step towards more realistic plant production and carbon balance simulations.

Integrating beef cattle on cropland affects net global warming potential

Recent interest in integrated crop-livestock (ICL) systems has prompted numerous investigations to quantify ecosystem service tradeoffs associated with management. However, few investigations have quantified ICL management effects on net global warming potential (GWP), particularly in semiarid regions. Therefore, we determined net GWP for grazed and ungrazed cropland in a long-term ICL study near Mandan, ND USA. Factors evaluated for their contribution to net GWP included carbon dioxide (CO2) emissions associated with production inputs and field operations, methane (CH4) emissions from enteric fermentation by beef cattle, change in soil carbon stocks, and soil-atmosphere CH4 and nitrous oxide (N2O) fluxes. Net GWP was significantly greater for grazed cropland (946 kg CO2equiv. ha-1 yr-1) compared to ungrazed cropland (200 kg CO2equiv. ha-1 yr-1) (P=0.0331). The difference in net GWP between treatments was largely driven by emissions from enteric fermentation (602 kg CO2equiv. ha-1 yr-1). Among other contributing factors, CO2 emissions associated with seed production and field operations were lower under ungrazed cropland (P = 0.0015 and 0.0135, respectively), while soil CH4 uptake was greater under grazed cropland (P = 0.0102). Soil-atmosphere N2O flux from each system negated nearly all the CO2equiv. sink capacity accrued from soil carbon stock change. As both production systems resulted in net greenhouse gas (GHG) emissions to the atmosphere, novel practices that constrain GHG sources and boost GHG sinks under semiarid conditions are recommended.

Positive long-term impacts of restoration on soils in an experimental urban forest.

As urbanization increases worldwide, investments in nature-based solutions that aim to mitigate urban stressors and counter the impacts of global climate change are also on the rise. Tree planting on degraded urban lands-or afforestation-is one form of nature-based solution that has been increasingly implemented in cities around the world. The benefits of afforestation are, however, contingent on the capacity of soils to support the growth of planted trees, which poses a challenge in some urban settings where unfavorable soil conditions limit tree performance. Soil-focused site treatments could help urban areas overcome impediments to afforestation, yet few studies have examined the long-term (>5yr) effects of site treatments on soils and other management objectives. We analyzed the impacts of compost amendments, interplanting with shrubs, and tree species composition (six species vs. two species) on soil conditions and associated tree growth in 54 experimental afforestation plots in New York City, USA. We compared baseline soil conditions to conditions after 6 yr and examined changes in the treatment effects from 1 to 6 yr. Site treatments and tree planting increased soil microbial biomass, water holding capacity, and total carbon and nitrogen, and reduced soil pH and bulk density relative to baseline conditions. These changes were most pronounced in compost-amended plots, and the effects of the shrub and species composition treatments were minimal. In fact, compost was key to sustaining long-term changes in soil carbon stocks, which increased by 17% in compost-amended plots but declined in unamended plots. Plots amended with compost also had 59% more nitrogen than unamended plots, which was associated with a 20% increase in the basal area of planted trees. Improvements in soil conditions after 6 yr departed from the initial trends observed after 1 yr, highlighting the importance of longer-term studies to quantify restoration success. Altogether, our results show that site treatments and tree planting can have long-lasting impacts on soil conditions and that these changes can support multiple urban land management objectives.

Impact of plastic film mulching on global warming in entire chemical and organic cropping systems: Life cycle assessment

Plastic film mulching (PM) has been exploited as a beneficial cropping tool to control weeds and to improve soil conditions in temperate-monsoon climate regions. However, the impact of PM on global warming is not clearly understood because it can increase both net primary production (NPP) and soil organic matter decomposition. In particular, the additional greenhouse gas (GHG) emissions from the film manufacturing industry and from waste disposal processes have not been properly considered. To investigate the influence of PM on GHG fluxes in the entire cropping system, PM and no-mulching treatments were installed under organic and chemical fertilization treatments for maize cultivation. The net global warming potential (GWP) was determined by using two GHG (CH4 and N2O) fluxes and soil carbon (C) stock changes with CO2 equivalents within the entire cropping system. PM significantly increased the net GWP by 95 and 35% compared to no-mulching under the organic and chemical fertilization treatments, respectively, whereas most of the net GWP (88–91%) was affected by the GHG flux of the inner cropping boundary. In the cropping process, an average 83 and 91% of the net GWP was influenced by the decrease in the soil C stock in the organic and chemical fertilization treatments, respectively. In contrast, organic fertilization was effective in decreasing the net GWP under the same mulching system due to the reduced soil C stock. PM increased maize grain yield by an average of 52 and 70% compared to no-mulching in the organic and chemical fertilization treatments, respectively, and PM decreased the GHG intensity (GHGI), which implies a net GWP per grain yield of 20 and 30%, respectively, compared to no-mulching. In conclusion, PM can be an effective tool to reduce the GHGI compared to no-mulching; however, PM was more effective in the chemical fertilization treatment than in the organic amendment treatment.

Multilocation changes in soil carbon stocks from sugarcane straw removal for bioenergy production in Brazil

AbstractSugarcane (Saccharum spp.) straw has been identified as a valuable asset for bioenergy production, but it is also a primary carbon input for sustaining soil resources. Therefore, excessive removal of this crop residue can potentially decrease soil organic carbon (SOC) and have negative environmental consequences. Most crop residue management studies focus on site‐specific responses which are important, but do not provide comprehensive assessments across the multiple edaphoclimatic conditions needed by decision makers to guide sustainable sugarcane straw management. Temporal modifications in SOC stocks induced by straw removal were quantified in 10 field experiments located in south‐central of Brazil. Each field experiment was arranged in a randomized block design with four replications, including four straw removal rates: total (TR), high (HR), low (LR) and no removal (NR). Soil sampling was performed to a 30 cm depth at the trial establishment (baseline) and after 2 and 4 consecutive years of straw removal. The data indicate that about 19% and 25% of the C added via straw were retained in areas of sandy and clay soils, respectively, and show that excessive removal rates depleted SOC stocks across the evaluated sites. Furthermore, regardless of removal rate, maintenance of straw on sandy soils was not sufficient to sustain SOC stocks, which were depleted by 2.3, 1.9, 1.5, and 1.4 Mg ha−1 year−1 for the TR, HR, LR, and NR. Our measured data provide scientific information to support policy and management decisions for straw‐derived bioenergy in Brazil. They also suggest straw removal from clay soils will be less deleterious to SOC stocks than from sandy soils, where removal should be avoided.

Simulating changes in soil carbon stocks for Quercus forests and upland rice fields under climate change scenarios in Manipur (India)

Assessing soil organic carbon (SOC) stocks under different land uses and future climate change (CC) conditions is important to provide better land use planning strategies. In South and Southeast Asia, Quercus forests are widely distributed but are exploited as a source of raw materials and shifting cultivation. Rice is a major staple food grain crop, often cultivated with terracing as upland rice. However, few studies on SOC stocks and simulated SOC dynamics under climate change conditions are available in these regions for these important land uses. Here, we present a case study related to Manipur state in North East region (NER) of India. We used the RothC model to evaluate the short-term changes of SOC stocks in Quercus forests and nearby upland rice fields and the effects of CC on SOC stocks, based on two General Circulation Models (GCMs) and two CO2 Representative Concentration Pathways (RCPs) during three 20-year time periods. Under CC conditions (2019–2078), results differed among land uses, GCMs, RCPs, and time periods, and Quercus forests were more sensitive to climate change than upland rice. For Quercus forests, as average of all GCMs and RCPs, SOC decreased by 0.42 t C ha−1 year−1 in the first time period and by 0.17 t C ha−1 year−1 as sixty years average. In upland rice, SOC decreased by 0.20 t C ha−1 year−1 in the first time period and by 0.12 t C ha−1 year−1 as sixty years average. Results indicated that management strategies for Quercus forests and upland rice are needed for CC mitigation and adaptation particularly in very close CC scenarios.

Soil carbon stock estimations: methods and a case study of the Maranhão State, Brazil

Soils feature significant variations in soil carbon stocks through land-use changes, management practices, and intrinsic characteristics. The aim of this study was to estimate the changes in soil carbon stock under different scenarios of land use and agricultural management in the Maranhao State, Brazil, considering the conversion from the conventional agriculture into conservationist management systems. Changes in soil carbon stocks were estimated from the scenario t0 to the current scenario (2010), followed by the adoption of a conservationist scenario by the year 2030. Soils under pasturelands presented the highest average of carbon stocks (62.19 Mg ha−1), followed by forestry lands (61.60 Mg ha−1) and agricultural lands (38.28 Mg ha−1). The conversion of native vegetation into an intensive agricultural use contributed to soil carbon losses of 1.57 Mt C, with pasturelands accounting for 1.36 Mt C and agricultural lands for 0.21 Mt C by 2010. The replacement of intensive agricultural systems into conservationist systems in the current areas has a technical potential for soil carbon sequestration of 0.6 Mt by 2030, with livestock and agricultural lands accounting for 0.54 and 0.03 Mt C, respectively.

Soil carbon stock changes due to afforestation in Japan by the paired sampling method on an equivalent mass basis

To identify the soil carbon stock changes from croplands/grasslands to forestlands in Japan, we compared the soil carbon stock of a cropland/grassland with that of an adjacent forestland at 22 different sites. With respect to a 0–30-cm depth basis, the soil carbon stock in the cropland/grassland was the same as that in the forestland; however, it was less than that in the forestland when an equivalent mass approach was used. The ratio of the soil carbon stock in the forestland to that in the cropland/grassland was 1.11 on average, which is comparable with previous mass-corrected paired sampling studies. The ratio was affected by two factors: tree age and current vegetation. Mean annual temperature, mean annual precipitation, phosphate absorption coefficient, litter quantity, and former land use did not affect the ratio. According to a comparison with the results of a paired study for deforestation, the application of the reciprocal of the soil carbon stock ratio of deforestation to the ratio of afforestation was slightly overestimated. Further studies are necessary to establish a general conclusion. Some previous studies, including those involving non-mass-corrected data, are possibly biased, and more studies using the paired sampling method with equivalent mass basis must be conducted to provide the general factor for soil carbon stock change in the future.

Effects of rising CO2 levels on carbon sequestration are coordinated above and below ground

An analysis of experiments in which the air around terrestrial plants or plant communities was enriched with carbon dioxide reveals a coordination between the resulting changes in soil carbon stocks and above-ground plant biomass. A meta-analysis of terrestrial CO2-elevation experiments.

Changes in soil carbon stocks under plantation systems and natural forests in Northeast India

Understanding the impact of land use conversion from forests to plantations on soil organic carbon (SOC) stocks is critical for sustainable land and forest management in Northeast India (NEI). The present study was conducted in West Garo hills district of Meghalaya state in NEI, to evaluate the impact of plantations (rubber, tea, areca nut, cashew nut and pineapple) on SOC stocks in comparison with a natural forest. Soil samples were collected from plantations of different age classes (0–5, 5–10, 10–15, 15–20, 20–25, 25–30, and 30–40 years old) to assess their potential for C storage. RothC model was run at equilibrium on forest land-use, and thereafter was calibrated and validated to model SOC stocks in the plantations over the 40 years chrono-sequence using the baseline average climate data. Results showed that with increase in age of plantations (at 40 years), SOC stocks decreased to 57.4, 50.3 and 44.4 Mg C ha−1 in rubber, areca nut and pineapple plantations at the average rate of 0.41, 0.58 and 0.73 Mg C ha−1 yr−1, respectively. This corresponded to a SOC stock loss of about 22, 32 and 40% compared to the initial SOC stock under forest (73.6 Mg C ha−1). Conversely, SOC stocks in tea and cashew nut plantations increased to 83.4 and 75.4 Mg C ha−1 (at the average rate of 0.24 and 0.05 Mg C ha−1 yr−1), corresponding to a SOC gain of about 13 and 2.5% compared to that under forest over 40 years. The data on abrupt climate change (ACC) scenario by RothC simulations showed that rubber, areca nut, pineapple and forest land uses would lose carbon at the rate of 0.65, 0.65, 1.42 and 0.13 Mg C ha−1 yr−1, respectively. Conversely, tea and cashew nut plantations might gain C at the rate of 0.35 and 0.23 Mg C ha−1 yr−1, respectively, representing a valuableoption for storing C and mitigating and adapting to climate change. Further, protecting and restoring natural forests and/or mixed stands of native tree species might reduce the risks of the loss of biodiversity and be a viable option for sustainable land management in NEI.

Energy, water and carbon exchanges in managed forest ecosystems: description, sensitivity analysis and evaluation of the INRAE GO+ model, version 3.0

Abstract. The mechanistic model GO+ describes the functioning and growth of managed forests based upon biophysical and biogeochemical processes. The biophysical and biogeochemical processes included are modelled using standard formulations of radiative transfer, convective heat exchange, evapotranspiration, photosynthesis, respiration, plant phenology, growth and mortality, biomass nutrient content, and soil carbon dynamics. The forest ecosystem is modelled as three layers, namely the tree overstorey, understorey and soil. The vegetation layers include stems, branches and foliage and are partitioned dynamically between sunlit and shaded fractions. The soil carbon submodel is an adaption of the Roth-C model to simulate the impact of forest operations. The model runs at an hourly time step. It represents a forest stand covering typically 1 ha and can be straightforwardly upscaled across gridded data at regional, country or continental levels. GO+ accounts for both the immediate and long-term impacts of forest operations on energy, water and carbon exchanges within the soil–vegetation–atmosphere continuum. It includes exhaustive and versatile descriptions of management operations (soil preparation, regeneration, vegetation control, selective thinning, clear-cutting, coppicing, etc.), thus permitting the effects of a wide variety of forest management strategies to be estimated: from close to nature to intensive. This paper examines the sensitivity of the model to its main parameters and estimates how errors in parameter values are propagated into the predicted values of its main output variables.The sensitivity analysis demonstrates an interaction between the sensitivity of variables, with the climate and soil hydraulic properties being dominant under dry conditions but the leaf biochemical properties being most influential with wet soil. The sensitivity profile of the model changes from short to long timescales due to the cumulative effects of the fluxes of carbon, energy and water on the stand growth and canopy structure. Apart from a few specific cases, the model simulations are close to the values of the observations of atmospheric exchanges, tree growth, and soil carbon and water stock changes monitored over Douglas fir, European beech and pine forests of different ages. We also illustrate the capacity of the GO+ model to simulate the provision of key ecosystem services, such as the long-term storage of carbon in biomass and soil under various management and climate scenarios.

Advanced Bayesian approaches for state-space models with a case study on soil carbon sequestration

Sequestering carbon into the soil can mitigate the atmospheric concentration of greenhouse gases, improving crop productivity and yield financial gains for farmers through the sale of carbon credits. In this work, we develop and evaluate advanced Bayesian methods for modelling soil carbon sequestration and quantifying uncertainty around predictions that are needed to fit more complex soil carbon models, such as multiple-pool soil carbon dynamic models. This paper demonstrates efficient computational methods using a one-pool model of the soil carbon dynamics previously used to predict soil carbon stock change under different agricultural practices applied at Tarlee, South Australia. We focus on methods that can improve the speed of computation when estimating parameters and model state variables in a statistically defensible way. This paper also serves as a tutorial on advanced Bayesian methods for fitting complex state-space models, which will be of interest to soil scientists and other environmental scientists more generally.

Management of Grazed Landscapes to Increase Soil Carbon Stocks in Temperate, Dryland Grasslands

Management of the temperate, grazed grasslands in New Zealand for more than a century has led to swards dominated by ryegrass/clover, which, with inputs of inorganic fertilisers, are highly productive for grazing animals. In the last 20 years the widespread introduction of irrigation to dryland areas on flat land has increased productivity further. However, these intensive practices decrease soil carbon stocks. In contrast, there is limited evidence that improved management of dryland, grazed, hill country grasslands can lead to increases in soil carbon stocks. To address global needs for food security and climate change mitigation, priority actions to increase soil carbon stocks need to focus on improved management practices to increase carbon inputs and retention in soils identified as having high potential for increasing carbon storage. While there are limited data from New Zealand studies, international observations suggest that soil carbon stocks can be increased by enhancing below-ground carbon inputs from plants with deep roots, using swards with diverse species, and moderate grazing rather than harvesting biomass. However, there is less certainty about the processes regulating the formation and decomposition of soil organic matter and their dependence on soil physical properties and microbial accessibility. Scaling findings from plot studies to forecast long-term changes in soil carbon stocks at the landscape scale can be done using models but new approaches are required to integrate the impacts of multiple concurrent practices associated with grazing management.

Changes in soil carbon and nitrogen stocks following degradation of alpine grasslands on the Qinghai‐Tibetan Plateau: A meta‐analysis

AbstractUntil now, nearly 90% of alpine grasslands on the Qinghai‐Tibetan Plateau (QTP) have been degraded. However, there is currently no consensus on how soil organic carbon (SOC) and soil total nitrogen (STN) stocks vary with the degradation succession of alpine grasslands in this region. Here, a meta‐analysis was conducted to quantify the dynamics of SOC and STN stocks in topsoil (0–30 cm) at different degradation stages of alpine grasslands on the QTP. The results showed that grassland degradation led to average losses of 48 and 39% for SOC and STN stocks, respectively. The changes in SOC and STN stocks following grassland degradation did not differ significantly between grassland types, but were significantly affected by grassland degradation stage. The reductions in both SOC and STN stocks increased with the degradation stage, and the highest reductions were all found at extreme degradation stage. The results indicated that the depletion of SOC and STN pools were aggravated with the degradation succession of grassland. The tightly coupled SOC and STN implied that the depletion of SOC stock was closely related to that of STN stock during the process of grassland degradation. Positive relationships were detected between the dynamics of vegetation coverage and that of SOC or STN stock, indicating that vegetation coverage could not only reflect grassland degradation, but might also be a potential indicator of SOC and STN status. The findings suggest that preventing the degradation succession of alpine grasslands is vital to maintain or promote SOC and STN levels on the QTP.

Assessing changes in soil carbon stocks after land use conversion from forest land to agricultural land in Japan

In the context of their role in global climate change, changes in soil carbon stocks resulting from land use conversions from forest to agricultural lands (cropland and grassland) and subsequent agricultural activities were investigated with data from a total of 46 soil sampling sites across Japan (28 cropland and 18 grassland sites). Collection of soil sample pairs from forest land and adjacent agricultural land converted from forest land allowed derivation of the soil carbon change factor (SCCF; ratio of soil carbon stock in the agricultural land to that in the forest land at the time of soil sampling). Depth-based SCCFs for a fixed depth of 0–30 cm were 23% greater than mass-based SCCFs determined by the equivalent soil mass approach, in which soil carbon stocks in all replicated samples from forest land and agricultural land were calculated for different depths but equal masses of the soil mineral fraction. The overestimation of SCCFs by the depth-based approach was more pronounced in Andosols, particularly in croplands on Andosols, because soil bulk densities in forest lands were much lower than those in croplands on Andosols. The mass-based SCCFs for croplands (upland fields and orchards) and grasslands (pasture land and grazing land) after deforestation were 0.741 ± 0.259 (a 25.9 ± 25.9% decrease in soil carbon stocks after an elapsed time of 2–85 years) and 0.858 ± 0.212 (a 14.2 ± 21.2% decrease after an elapsed time of 26–81 years), respectively. Therefore, conversions from forest land to cropland or grassland resulted in a significant carbon loss from most soils in Japan. Soil carbon stocks in cropland converted from forest land declined as the elapsed time after deforestation increased although the uncertainty was large. Of the environmental variables, soil type (Andosols versus non-Andosols) and tillage frequency during cultivation had little impact on mass-based SCCFs; however, the SCCFs decreased with higher mean annual air temperature at the sites.

Relationship Between the Composition of Soil Aggregates and the Distribution of Organic Carbon Under Long-Term Abandoned Restoration

Soil aggregates are important carriers of soil organic carbon (SOC) accumulation, and play an important role in the evaluation of soil structure and quality. Natural recovery can promote change in soil aggregate structure and quantity via the redistribution of SOC in the aggregates. Natural restoration from farmland is an important vegetation restoration model on the Loess Plateau. The changes in soil aggregate structure and soil carbon stock after natural restoration have received extensive attention. However, little is known about the continuous study of soil changes on the abandoned grassland during the recovery process. Therefore, to understand how SOC accumulates in the process of natural recovery and quantitatively analyze the contribution of aggregates to the total soil carbon pool, we selected four abandoned grasslands of different restoration ages on the Loess Plateau, China, and studied the changes in soil structure, soil total organic carbon (TOC), soil C:N, soil aggregate distribution, soil aggregate stable index (mean weight diameter, MWD; geometric mean diameter, GMD), and aggregate-associated SOC changes as well as their correlations from 0-20 cm and 20-40 cm soil layers in abandoned grasslands. In addition, we calculated the contribution of aggregates with different sizes to soil TOC stock. The results showed that:① natural restoration increased the macroaggregate amount, MWD, and GMD, but decreased the amount of microaggregate and silt-and clay-sized fractions. There are significant differences in the distribution and stability of aggregates between different soil layers; the promotion effect of the surface was higher than that of the subsurface soils. ② In the 42 years after abandoning recovery, soil TOC stock, macaggregate-and mesaggregate-associated SOC stock increased significantly, and varied with soil depth and years of abandonment (1.92 times, 10.2 times, and 3.61 times). In contrast, micaggregate-associated SOC stock decreased significantly, and silt-and clay-sized fractions-associated SOC stock showed no distinct change. In addition, natural restoration promoted the ratio of C:N; nevertheless, the ratio of C:N under the surface showed a reduced phenomenon after 42 years of abandonment. ③ The improvement in soil TOC stock depends primarily on changes in the macaggregate-associated organic carbon stocks, which account for 80% of macaggregate, and the significant increase in the amount of macaggregate is the main reason for the high contribution.The results of our study suggest that natural restoration is conducive to the accumulation of soil organic carbon, and improvement in soil structure and stability. Macroaggregate is the key factor in soil organic carbon accumulation and soil structure improvement in the process of natural restoration.

Changes in Carbon Stocks and Chemical Attributes of an Oxisol as a Result of Adoption Period of No-tillage System in the Brazilian Eastern Amazon

The conversion of forest areas to grain cropping has promoted a decrease in soil organic matter stocks in the Amazon. This process is most striking when the conventional cultivation system is used. In order to evaluate the changes in soil carbon and nutrient stocks resulting from the time of adoption of the no tillage system in a dystrophic Yellow Oxisol of the Brazilian Amazon biome, a study was conducted in a grain producing area in the northeastern of Pará, Brazil. The treatments corresponded to the following systems: CT6- conventional tillage system with six years of implementation; No-tillage system with 3 (NT3), 4 (NT4) and 7 (NT7) years of implementation. All systems were always cultivated in corn / soybean rotation. Deformed and non-deformed soil samples were collected on a the 2013 crop year at 0-10, 10-20 and 20-40 cm depths. Stocks of carbon (SC) and phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) were calculated by using the equivalent soil mass methodology. Regardless of depth, the NT showed higher SC values than the CT. The adoption of NT showed a tendency of increasing SC of the soil over time. Such increases were up to 36% of the NT7 compared to the CT6. In NT7, the stocks of K, Ca and Mg were higher in relation to PC6. The EC correlated positively with the stocks of K, Ca and Mg in the areas under NT, regardless of the time of system adoption, up to 40 cm deep, indicating improvements in the soil fertility.

Effects of land use change on turnover and storage of soil organic matter in a tropical forest

Land-use change of tropical forests causes loss of soil organic matter and plant productivity. Effects of fallow or plantation vegetation on soil organic matter storage need to be clarified to optimize land-use that maximizes soil organic matter storage and plant productivity. We compared 30-year changes in soil carbon stocks and litter decomposition under different land-uses (primary dipterocarp forest, Macaranga forest, Imperata grassland, transition of Imperata grassland to Acacia plantation, transition of Imperata grassland to oil palm plantation) in Indonesia. The Imperata grassland maximizes soil carbon stocks for up to 10 years due to considerable root litter inputs, but additional organic matter storage is limited over the following 20 years, due to high grass litter decomposability in the less acidified soil. The conversion of Imperata grassland to oil palm plantation causes greatest loss of soil organic matter, whereas Acacia plantation on Imperata grassland or the Macaranga forest maximizes soil carbon stocks due to input of recalcitrant forest litters and reduced microbial activities in the acidified soils. Farmers could adopt short-term ( 10 years) fallow under Acacia plantation on Imperata grassland or Macaranga regeneration forest to maximize soil organic matter storage. The optimum and feasible land-use strategies should be selected based on the length of fallow period and the original acidity of soil.

Integrated production systems: An alternative to soil chemical quality restoration in the Cerrado-Amazon ecotone

Soil organic carbon (SOC) is the main terrestrial carbon reservoir. The spatial distribution of SOC is mainly regulated by environmental factors and anthropogenic activity. Historically, land-use change has been responsible for much of the world’s greenhouse gas emissions. However, carbon storage can be improved through agricultural management, either by increasing carbon inputs through higher crop yields or by delaying the release of carbon into the atmosphere. Therefore, it is essential to correctly choose which cover crops to use and how long these crops will remain in the crop rotation system. In order to clarify these issues, the objective of this work was to evaluate the chemical quality and changes in soil carbon stock between no-tillage and soybean/corn crop succession systems and integrated crop-livestock systems. The study was carried out in Querência (MT), Brazil, located in the Cerrado/Amazon ecotone. The integrated systems were studied between 2007 and 2014. These systems followed annual crop rotation and forage rotation, and were laid out as a consortium or were isolated, with the aim of producing grain and meat. In order to determine soil chemical properties, 170 sampling plots were randomized among the treatments. The highest carbon values were observed in the integrated crop-livestock systems (ICL), probably due to higher inputs of organic residues. Crop rotation with plants of different families allowed better land use and soil exploration. However, integrated production systems comprising longer pasture periods, no-tillage, and soybean/corn crop succession decreased soil carbon. When comparing carbon stocks from 2010 to 2014, only integrated production systems ICL2 and ICL3 were able to increase carbon stocks. Our results highlight the importance of length of growing and correct choice of cover crops in maintaining SOC stocks, and thus provide insights to improve SOC stocks in agricultural land in Brazil's main producing region.

Deep soil C and N pools in long-term fenced and overgrazed temperate grasslands in northwest China

Fencing for grazing exclusion has been widely found to have an impact on grassland soil organic carbon (SOC) and total nitrogen (TN), but little is known about the impact of fenced grassland on the changes in deep soil carbon (C) and nitrogen (N) stocks in temperate grasslands. We studied the influence of 30 years fencing on vegetation and deep soil characteristics (0–500 cm) in the semi-arid grasslands of northern China. The results showed that fencing significantly increased the aboveground biomass (AGB), litter biomass (LB), total biomass, vegetation coverage and height, and soil water content and the SOC and TN in the deep soil. The belowground biomass (BGB) did not significantly differ between the fenced and grazed grassland. However, fencing significantly decreased the root/shoot ratio, forbs biomass, pH, and soil bulk density. Meanwhile, fencing has significantly increased the C and N stocks in the AGB and LB but not in the BGB. After 30 years of fencing, the C and N stocks significantly increased in the 0–500 cm soil layer. The accumulation of SOC mainly occurred in the deep layers (30–180 cm), and the accumulation of TN occurred in the soil layers of 0 to 60 cm and 160 to 500 cm. Our results indicate that fencing is an effective way to improve deep soil C and N stocks in temperate grassland of northwest China. There were large C and N stocks in the soil layers of 100 to 500 cm in the fenced grasslands, and their dynamics should not be ignored.