The Evolution of Organic Carbon in Chinese Mollisol Under Different Farming Systems: Validation and Prediction by Using Century Model

Soil organic carbon （SOC） is an important indicator of soil degradation process. In this study, the long-term SOC evolution in Chinese mollisol farmland was simulated and predicted by validating, analyzing, processing and assorting concerning data, based on clarifying parameters of Century model need, combined with best use of recorded data of field management, observed data of long-term experiments, climate, soil, and biology, and achieved results from Hailun Agro-Ecological Experimental Station, Chinese Academy of Sciences. The results were showed as follows： Before reclamation, SOC content was around 58.00 g kg^-1, SOC content dropped quickly in early years, and then decreased slowly after reclamation. SOC content was around 34.00 g kg^-1 with a yearly average rate of 8.91‰ decrease before long-term experiments was established. After a long-term experiment, SOC would change under different farming systems. Shift farming system changed as follows： By 20-year model simulation, SOC content decreased from 34.03 to 30.19 g kg^-1, with a yearly average rate of 5.97‰; by 100-year model simulation, SOC content decreased to 24.31 g kg^-1, with a yearly average rate of 3.36‰. Organic farming system changed as follows： By 20-year model simulation, SOC content decreased slowly from 34.03 to 33.39 g kg^-1, with a yearly average rate of 0.95‰, 5‰ less than that of shift farming system; by 100-year model simulation, SOC content decreased to 32.21 g kg^-1, with a yearly average rate of 0.55‰. ＂Petroleum＂ farming system changed as follows： By 20-year model simulation, SOC content decreased from 34.03 to 32.88 g kg^-1, with a yearly average rate of 1.72‰, much more than that of organic farming system; by 100-year model simulation, SOC content decreased to 30.89 g kg^-1, with a yearly average rate of 0.96‰. Combined ＂petroleum＂-organic farming system changed as follows： By 20-year model simulation, SOC content was increased slightly; by 100-year model simulation, SOC content increased from 34.03 to 34.41g kg^-1, with a yearly average rate of 0.11‰. The above results provided an optimal way for maintaining SOC in Chinese mollisol farmland： To increase, as much as possible within agro-ecosystem, soil organic matter returns such as crop stubble, crop litter, crop straw or stalk, and manure, besides applying chemical nitrogen and phosphorous, which increased system productivity and maintained SOC content as well. Also, the results provided a valuable methodology both for a study of CO2 sequestration capacity and for a target fertility determination in Chinese mollisol.

Simulation of soil erosion dynamics in grassland ecosystem of semi-arid China using the CENTURY model

Soil erosion can cause considerable effect on global natural resources and eco-environment. In the paper, the CENTURY model has been used to simulate soil erosion in Xilin Gol Grassland of Inner Mongolia. The results showed before the 1960s, the soil erosion amount was over 2 kg /m2.a in grassland ecosystem in the study area because no trees had been planted. But after the 1960s the mean annual accumulator C lost from soil organic matter due to soil erosion was only 0.3 kg /m2.a in forest ecosystem. So afforestation has exerted notable effect on decreasing soil erosion amount in Xilin Gol Grassland.

Spatio-temporal Changes and Associated Uncertainties of CENTURYmodelled SOC for Chinese Upland Soils, 1980-2010

Detailed information on the spatio-temporal changes of cropland soil organic carbon(SOC) can significantly contribute to the improvement of soil fertility and mitigate climate change. Nonetheless, information and knowledge on the national scale spatio-temporal changes and the corresponding uncertainties of SOC in Chinese upland soils remain limited. The CENTURY model was used to estimate the SOC storages and their changes in Chinese uplands from 1980 to 2010. With the Monte Carlo method, the uncertainties of CENTURY-modelled SOC dynamics associated with the spatial heterogeneous model inputs were quantified. Results revealed that the SOC storage in Chinese uplands increased from 3.03(1.59 to 4.78) Pg C in 1980 to 3.40(2.39 to 4.62) Pg C in 2010. Increment of SOC storage during this period was 370 Tg C, with an uncertainty interval of –440 to 1110 Tg C. The regional disparities of SOC changes reached a significant level, with considerable SOC accumulation in the Huang-Huai-Hai Plain of China and SOC loss in the northeastern China. The SOC lost from Meadow soils, Black soils and Chernozems was most severe, whilst SOC accumulation in Fluvo-aquic soils, Cinnamon soils and Purplish soils was most significant. In modelling large-scale SOC dynamics, the initial soil properties were major sources of uncertainty. Hence, more detailed information concerning the soil properties must be collected. The SOC stock of Chinese uplands in 2010 was still relatively low, manifesting that recommended agricultural management practices in conjunction with effectively economic and policy incentives to farmers for soil fertility improvement were indispensable for future carbon sequestration in these regions.

The potential for an old-growth forest to store carbon in the topsoil:A case study at Sasso Fratino,Italy

There is considerable interest devoted to oldgrowth forests and their capacity to store carbon(C)in biomass and soil.Inventories of C stocks in old-growth forests are carried out worldwide,although there is a lack of information on their actual potential for C sequestration.To further understand this,soil organic carbon(SOC)was measured in one of Italy's best-preserved old-growth forests,the Sasso Fratino Integral Nature Reserve.This reserve is on the World Heritage List along with other ancient beech forests of Europe,and it is virtually untouched due to the steepness of the terrain,even before legal constraints were imposed.Although the sandstone-derived soils are often shallow,they are rich in organic matter.However,no quantification had been carried out.By systematically sampling the topsoil across the forest,we accurately determined the average amount of SOC(62.0±16.9 Mg ha^(–1))and nitrogen(4.0±1.2 Mg ha^(–1))in the top 20 cm.Using the CENTURY model,future dynamics of SOC stocks were predicted to 2050 according to two climate scenarios,A1F1 and B2,the first of high concern and the second more optimistic.The model projected an increase of 0.2 and 0.3 Mg ha^(–1)a^(–1)by 2030 under the A1F1 and B2 scenarios,respectively,suggesting that the topsoil in old-growth forests does not reach equilibrium but continues accumulating SOC.However,from 2030 to 2050,a decline in SOC accumulation is predicted,indicating SOC net loss at high altitudes under the worst-case scenario.This study confirms that soils in oldgrowth forests play a significant role in carbon sequestration.It also suggests that climate change may affect the potential of these forests to store SOC not only in the long term but also in the coming years.

Scenario Analysis of Tillage, Residue and Fertilization Management Effects on Soil Organic Carbon Dynamics

Based on data from 10-year field experiments on residue/fertilizer management in the dryland farming region of northern China, Century model was used to simulate the site-specific ecosystem dynamics through adjustment of the model＇s parameters, and the applicability of the model to propose soil organic carbon （SOC） management temporally and spatially, in cases such as of tillage/residue/fertilization management options, was identified v/a scenario analysis.Results between simulations and actual measurements were in close agreement when appropriate applications of stover,manure and inorganic fertilizer were combined. Simulations of extreme C/N ratios with added organic materials tended to underestimate the measured effects. Scenarios of changed tillage methods, residue practices and fertilization options showed potential to maintain and enhance SOC in the long run, while increasing inorganic N slowed down the SOC turnover rate but did not create a net C sink without any organic C input. The Century model simulation showed a good relationship between annual C inputs to the soil and the rate of C sequestration in the top 20 cm layer and provided quantitative estimations of changes in parameters crucial for sustainable land use and management. Conservation tillage practices for sustainable land use should be integrated with residue management and appreciable organic and inorganic fertilizer application, adapted according to the local residue resource, soil fertility and production conditions. At least 50% residue return into the soil was needed annually for maintenance of SOC balance, and manure amendment was important for enhancement of SOC in small crop-livestock systems in which crop residue land application was limited.

Impact of rainfed and irrigated agriculture systems on soil carbon stock under different climate scenarios in the semi-arid region of Brazil

Understanding the dynamics of soil organic carbon(SOC) is of fundamental importance in land use and management, whether in the current researches or in future scenarios of agriculture systems considering climate change. In order to evaluate SOC stock of the three districts(Delmiro Gouveia, Pariconha, and Inhapi districts) in the semi-arid region of Brazil in rainfed and irrigated agriculture systems under different climate scenarios using the Century model, we obtained RCP4.5 and RCP8.5 climate scenarios derived from the Eta Regional Climate Model(Eta-Had GEM2-ES and Eta-MIROC5) from the National Institute for Space Research, and then input the data of bulk density, p H, soil texture, maximum temperature, minimum temperature, and rainfall into the soil and climate files of the Century model. The results of this study showed that the Eta-Had GEM2-ES model was effective in estimating air temperature in the future period. In rainfed agriculture system, SOC stock under the baseline scenario was lower than that under RCP4.5 and RCP8.5 climate scenarios, while in irrigated agriculture system, SOC stock in the almost all climate scenarios(RCP4.5 and RCP8.5) and models(Eta-Had GEM2-ES and Eta-MIROC5) will increase by 2100. The results of this study will help producers in the semi-arid region of Brazil adopt specific agriculture systems aimed at mitigating greenhouse gas emissions.

Comparing predictions of long-term soil carbon dynamics under various cropping management systems using K-model and CENTURY

There is a strong demand for accurate estimates of long-term changes in soil organic carbon(SOC)with different agricultural practices under different soil and climate conditions.A process and analytic model,K-model,including a non-compartmental algorithm of soil carbon decomposition,was developed to simulate the changes of SOC under different cropping and soil management practices.This study evaluates the performance of K-model by comparing its predictions on SOC with measurements and predictions of CENTURY model,which is widely used for the similar purposes.Both K-model and CENTURY can predict the dynamics of SOC when site-specific soil and climate data are used to initialize simulations.Very similar annual carbon decomposition rates were simulated by the single carbon pool K-model and the 3-carbon pool CENTURY model.However,compared with experimental measurements of SOC,K-model produces relative smaller errors than CENTURY(<0.1 kg C m-2 vs.0.08-0.48 kg C m-2,and within±5%vs.±5%-45%),mainly resulting from smaller biases of predicted crop production.When detailed site-specific soil and climate data are not available for initialization and feeding the running of model,K-model can still reasonably predict the dynamics of SOC with its auto-correction function,but CENTURY produces poor results.In comparison with measurements,K-model has improved capacities to predict the effects of chemical fertilizer,manure application,residue management and fallow on SOC dynamics.

Effects of Aluminum Toxicity Induced by Acid Deposition on Pine Forest Ecosystem in Longli of Guizhou Province, Southwestern China

The effects of acid deposition on pine forest ecosystems in Longli of Guizhou Province, southwestern China are studied using indoor experiments and model simulations. Indoor experiments are designed to explore the aluminum toxicity on pine seedlings, and the long-term soil acidification model （LTSAM） and a terrestrial biogeochemistry model （CENTURY） are used to simulate the influences of acid deposition on pine forest ecosystems. The indoor experiment results of aluminum toxicishow that aluminum ions in solution limit plant growth and acid deposition enhances this effect by facilitating the release of aluminum ions from the soil. Pine seedling bio- mass and root elongation decrease as the aluminum concentration increases. The results of model simulations show that the soil chemis- try varies significantly with different changes in acid deposition. When the acid deposition increases, the pH value in the soil solution decreases and the soil A13＋ concentration increases. The increased acid deposition also has negative impacts on the forest ecosystem, i.e., decreases plant biomass, net primary productivity （NPP） and net C02 uptake. As a result, the soil organic carbon （SOC） decreases be- cause of the limited supply of decomposition material. Thus acid deposition need be reduced to help protect the forest ecosystems.