The impact of different grazing intensity and management measures on soil organic carbon density in Zhangye grassland.

Studying the spatial and temporal changes of grassland soil organic carbon (SOC) is helpful in promote the management of regional ecosystem carbon sinks. Grazing is one of the main ways of rational utilization of grassland. Different grazing intensities will affect the change of SOC density. Under different grazing intensity and management measures in Zhangye grassland, this study uses the parameter localized CENTURY model to simulate the temporal and spatial variations of SOC density from 1970 to 2022. The results showed that long-term light grazing reduced the average SOC by 195.114 g·m-2 and 1.91%. Moderate and severe grazing, respectively, for a long time made the total SOC density loss of 5.21% and 17.69%. In a short period, mild and moderate grazing reduced total SOC first and then increased it. Under light grazing, total SOC density appeared higher relative changes in the southeast, and lower in the northwest and central. There was no significant difference in the relative changes of total SOC between steppe and desert grasslands under light grazing. The decrease range of steppe was gradually greater than that in desert grassland. Since different management measures were implemented in some sampling sites in 2017, we divided the study period into two periods, 1970-2016 and 2017-2022. The implementation of degraded grassland improvement, fallow grazing, and rotational grazing would increase the total SOC density and mild SOC density, rotational grazing > degraded grassland improvement > rest grazing. Rotational grazing and the improvement of degraded grassland increased the density of active and inert SOC, while resting grazing decreased the density of SOC.

[Spatiotemporal Simulation and Prediction of Soil Organic Carbon Density in Gannan Grassland Under Future Climate Scenarios].

To study the temporal and spatial distribution characteristics of soil organic carbon density in grassland and explore the relationship between organic carbon density and influencing factors is of great significance to the management and maintenance of grassland ecosystems in Gannan Autonomous Prefecture, which is conducive to realizing the goal of "double carbon," promoting carbon sink, and mitigating climate change. Taking Gannan Tibetan Autonomous Prefecture of Gansu Province as the research object, based on data from two CMIP6 future climate scenarios (SSP126 and SSP585), the CENTURY model was used to simulate and predict the temporal and spatial changes in soil organic carbon density in grassland of Gannan during 2023-2100. The main conclusions were as follows:① From 2023 to 2100, total organic carbon density, slow organic carbon density, and inert organic carbon density all showed a downward trend, whereas active organic carbon density fluctuated first and then increased. Meanwhile, the total organic carbon density, active organic carbon density, slow organic carbon density, and inert organic carbon density under the SSP585 scenario were higher than those under the SSP126 scenario. ② Mann-Kendall mutation analysis showed that the abrupt change in the difference of soil total organic carbon density (Δsomtc) occurred in 2030. The abrupt change in the difference of soil active carbon density (Δsom1c) occurred in 2027. ③ During the study period, the average soil organic carbon density of Gannan grassland was 7 505.69 g·m-2 under the SSP126 scenario and 7 551.87 g·m-2 under the SSP585 scenario. Gannan grassland soil organic carbon density was higher in the west and lower in the east, and the coefficient of variation was relatively stable. ④ The results of partial correlation analysis showed that precipitation was positively correlated with soil organic carbon density, whereas temperature was significantly negatively correlated with soil organic carbon density under future climate scenarios. ⑤ The results of the Theil-Sen Median trend analysis and Mann-Kendall test showed that under the two climate scenarios, the soil organic carbon density in Gannan showed an overall downward trend, in which Luqu County showed the fastest downward trend and Dibe County showed the slowest.

Comparative analyses of different biogenic CO2 emission accounting systems in life cycle assessment.

The biomass-derived CO2 emission is usually treated as neutral to climate change. However, due to the stay of biomass-derived CO2 in the atmosphere, many researchers believe that biomass-derived CO2 also has climate change benefit. Therefore, many methods to account the global warming potential of biomass-derived CO2 (GWPbio) were proposed. Based on those new methods, we developed an accounting system for climate change impact of biomass utilization in this study, and compared it with the conventional accounting system which follows the carbon neutral assumption. A case study of caragana-to-pellet bioenergy production system was simulated to test the performance of the GWPbio accounting system. The CENTURY model was used to simulate carbon dynamics of caragana plantation in the Loess Plateau in China, and life cycle assessment (LCA) model was developed to estimate the life cycle emissions of the caragana-to-pellet system. Attributed to short rotation of caragana plantation and fast biomass accumulation after harvest, the GWPbio values around 0.044 were obtained. When the GWPbio was applied to LCA, significant high life cycle CO2 emission was found in comparison to the conventional method. However, the GWPbio accounting system has lower positive climate change impact than the conventional accounting system in assessing the overall impact of biomass utilization. This indicated that the application of GWPbio accounting system would encourage the utilization of biomass and allow a fair comparison with fossil fuels. In the sensitivity analysis, we found the accounting system was sensitive to biomass accumulation and all the corresponding factor affecting biomass accumulation.

Soil carbon inventory to quantify the impact of land use change to mitigate greenhouse gas emissions and ecosystem services.

Currently the land use and land use change (LULUC) emits 1.3 ±â€¯0.5 Pg carbon (C) year-1, equivalent to 8% of the global annual emissions. The objectives of this study were to quantify (1) the impact of LULUC on greenhouse gas (GHG) emissions in a subtropical region and (2) the role of conservation agriculture to mitigate GHG emissions promoting ecosystem services. We developed a detailed IPCC Tier 2 GHG inventory for the Campos Gerais region of southern Brazil that has large cropland area under long-term conservation agriculture with high crop yields. The inventory accounted for historical and current emissions from fossil fuel combustion, LULUC and other minor sources. We used Century model to simulate the adoption of conservation best management practices, to all croplands in the region from 2017 to 2117. Our results showed historical (1930-2017) GHG emissions of 412 Tg C, in which LULUC contributes 91% (376 ±â€¯130 Tg C), the uncertainties ranged between 13 and 36%. Between 1930 and 1985 LULUC was a major source of GHG emission, however from 1985 to 2015 fossil fuel combustion became the primary source of GHG emission. Forestry sequestered 52 ±â€¯24 Tg C in 0.6 Mha in a period of 47 years (1.8 Tg C Mha-1 year-1) and no-till sequestered 30.4 ±â€¯24 Tg C in 2 Mha in a period of 32 years (0.5 Tg C Mha-1 year-1) being the principal GHG mitigating activities in the study area. The model predictions showed that best management practices have the potential to mitigate 13 years of regional emissions (330 Tg C in 100 years) or 105 years of agriculture, forestry and livestock emissions (40 Tg C in 100 years) making the agriculture sector a net carbon (C) sink and promoting ecosystem services.

Vinasse application and cessation of burning in sugarcane management can have positive impact on soil carbon stocks.

Bioenergy crops, such as sugarcane, have the potential to mitigate greenhouse gas emissions through fossil fuel substitution. However, increased sugarcane propagation and recent management changes have raised concerns that these practices may deplete soil carbon (C) stocks, thereby limiting the net greenhouse gas benefit. In this study, we use both a measured and modelled approach to evaluate the impacts of two common sugarcane management practices on soil C sequestration potential in Brazil. We explore how transitions from conventional (mineral fertiliser/burning) to improved (vinasse application/unburned) practices influence soil C stocks in total and in physically fractionated soil down to one metre. Results suggest that vinasse application leads to an accumulation of soil C of 0.55 Mg ha-1yr-1 at 0-30 cm depth and applying unburned management led to gains of ∼0.7 Mg ha-1yr-1 at 30-60 cm depth. Soil C concentration in the Silt+Clay fraction of topsoil (0-20 cm) showed higher C content in unburned management but it did not differ under vinasse application. The CENTURY model was used to simulate the consequences of management changes beyond the temporal extent of the measurements. Simulations indicated that vinasse was not the key factor driving increases in soil C stocks but its application may be the most readily available practice to prevent the soil C losses under burned management. Furthermore, cessation of burning may increase topsoil C by 40% after ∼50 years. These are the first data comparing different sugarcane management transitions within a single area. Our findings indicate that both vinasse application and the cessation of burning can play an important role in reducing the time required for sugarcane ethanol production to reach a net C benefit (payback time).

Drivers of soil and tree carbon dynamics in urban residential lawns: a modeling approach.

Soils constitute the largest sink of terrestrial carbon (C), and urban soils have the potential to provide significant soil C storage. Soils in urbanized landscapes experience a multitude of human alterations, such as compaction and management subsidies, that impact soil C dynamics. While field studies may provide data on urban soil C storage, modeling soil C dynamics under various human impact scenarios will provide a basis for identifying drivers of urban soil C dynamics and for predicting the potential for these highly altered soils to store C over time intervals not typically amenable to empirical validation. The goal of this study was to model soil C dynamics in residential lawns using CENTURY, a dynamic mechanistic model, to determine whether drivers of soil C dynamics in natural systems (e.g., soil texture) were equally useful for estimating soil C content of highly modified soils in urban residential areas. Without incorporating human impacts, we found no relationship between initial CENTURY model simulations and observed soil C (P > 0.05). Factors that best explained soil C accumulation for the observed soil C (bulk density, r2  = 0.30; home age, r2  = 0.37; P < 0.01) differed from those found important for the CENTURY model simulations (percent sand, r2  = 0.72, P < 0.001). Therefore, we conducted a modeling exercise to test whether simulating potential construction disturbance and lawn management practices would improve modeled soil and tree C. We found that incorporating these factors did improve CENTURY's ability to model soil and tree C (P < 0.001). The results from this analysis suggest that incorporating various human disturbances and management practices that occur in urban landscapes into CENTURY model runs will improve its ability to predict urban soil C dynamics, at least within a 100-yr time frame. Thus, enhancing our ability to provide recommendations for management and development practices that result in increasing urban soil C storage.

Simulation of use and management effects on the soil organic matter pools of the atlantic forest biome, Brazil / Simulação dos efeitos do uso e manejo sobre os compartimentos da matéria orgânica no solo no bioma da florestal atlântica, Brasil

Soil organic matter simulation in areas under long term use provides an important tool to test future scenarios, enabling the adoption of less impressive management to environment. The purposes of the present study were: a) to simulate, with the Century model, the impacts on soil organic matter, according to the adoption of different crop management, with forage purposes, in two different soils and; b) to validate the Century model for these managements and soils by comparing the simulated values with those measured in the field. The following treatments were evaluated: in the Oxisol area ­ brachiaria pasture with fertilizer (BPw) and without fertilizer (BPwo), the Incept area ­ corn for silage (CS), Coast Cross pasture (CC) and sugar cane field (SC). The microbial biomass represented the active compartment of carbon and nitrogen, the particle free light fraction represented the slow compartment of carbon and nitrogen and the passive pools were determined by the difference of the total minus the active and the slow pools (passive = total ­ (active + slow)). The Century model showed great potential to simulate the dynamics of the total C and N stocks for tropical soils, which was confirmed by similarity between the simulated values and those measured in the field.

Simulação da matéria orgânica no solo em longo prazo é uma ferramenta importante para testar cenários futuros, permitindo a adoção de uma gestão menos impactante ao meio ambiente. Os objetivos do presente estudo foram: (a) simular o modelo do CENTURY, com os impactos sobre a matéria orgânica do solo em função do manejo diferente em culturas com fins de forragem em dois solos diferentes e, (b) comparar o estoque simulado com os reais de matéria orgânica, medidos no campo. Foram avaliados os seguintes tratamentos: na área de Latossolo Vermelho em uso de pastagem com fertilizantes (BPW) e sem fertilizante (BPwo), no Cambissolo - testou os usos com milho para silagem (CS), e pastagem com coast cross (CC) e um plantio de cana-de-açúcar (SC). A biomassa microbiana ativa representa compartimento de carbono e do nitrogênio, a fração leve livre de partículas representada o compartimento lento do carbono e de nitrogênio e os compartimentos passivos foram determinadas pela diferença do total menos o ativo e os compartimentos lentos (Passivo Total = - Ativo + Lento). O modelo Century demonstrou grande potencial para simular a dinâmica do C total e estoques de N para solos tropicais, o que foi comprovado por semelhança entre os valores simulados e medidos no campo.

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

Proposed European policy in the agricultural sector will place higher emphasis on soil organic carbon (SOC), both as an indicator of soil quality and as a means to offset CO2 emissions through soil carbon (C) sequestration. Despite detailed national SOC data sets in several European Union (EU) Member States, a consistent C stock estimation at EU scale remains problematic. Data are often not directly comparable, different methods have been used to obtain values (e.g. sampling, laboratory analysis) and access may be restricted. Therefore, any evolution of EU policies on C accounting and sequestration may be constrained by a lack of an accurate SOC estimation and the availability of tools to carry out scenario analysis, especially for agricultural soils. In this context, a comprehensive model platform was established at a pan-European scale (EU + Serbia, Bosnia and Herzegovina, Croatia, Montenegro, Albania, Former Yugoslav Republic of Macedonia and Norway) using the agro-ecosystem SOC model CENTURY. Almost 164 000 combinations of soil-climate-land use were computed, including the main arable crops, orchards and pasture. The model was implemented with the main management practices (e.g. irrigation, mineral and organic fertilization, tillage) derived from official statistics. The model results were tested against inventories from the European Environment and Observation Network (EIONET) and approximately 20 000 soil samples from the 2009 LUCAS survey, a monitoring project aiming at producing the first coherent, comprehensive and harmonized top-soil data set of the EU based on harmonized sampling and analytical methods. The CENTURY model estimation of the current 0-30 cm SOC stock of agricultural soils was 17.63 Gt; the model uncertainty estimation was below 36% in half of the NUTS2 regions considered. The model predicted an overall increase of this pool according to different climate-emission scenarios up to 2100, with C loss in the south and east of the area (involving 30% of the whole simulated agricultural land) compensated by a gain in central and northern regions. Generally, higher soil respiration was offset by higher C input as a consequence of increased CO2 atmospheric concentration and favourable crop growing conditions, especially in northern Europe. Considering the importance of SOC in future EU policies, this platform of simulation appears to be a very promising tool to orient future policymaking decisions.

Simulações espacialmente explícitas dos estoques de carbono orgânico de um LATOSSOLO BRUNO por meio da integração do modelo century com GIS / Spatially explicit simulations of soil carbon stocks in Humic Hapludox, using Century model and GIS

Os modelos de simulação, uma vez calibrados localmente, são ferramentas úteis para a avaliação dos impactos da agricultura sobre a dinâmica do carbono orgânico do solo (COS) e planejamento de sistemas agrícolas sustentáveis em escala regional. O presente trabalho teve como objetivo estudar a dinâmica do COS em um LATOSSOLO BRUNO Aluminoférrico típico muito argiloso, localizado em uma região de clima subtropical, por meio de simulações com o modelo Century - versão 4.0, apoiado em levantamentos históricos e técnicas de geoprocessamento e sensoriamento remoto. Verificou-se que, para o período atual, a mudança de uso do solo, representada pela conversão da vegetação nativa em agricultura, causou uma redução no conteúdo de carbono ao longo dos anos, sendo que as lavouras com maior tempo de exploração e submetidas ao preparo convencional apresentaram os menores estoques. Por outro lado, nas simulações futuras (ano 2058), verifica-se que as lavouras, quando sob manejos conservacionistas, podem recuperar, e até superar, os estoques de COS encontrados no solo sob vegetação nativa de campo.

Simulation models are useful tools for assessment of the impacts of agriculture on nutrient and soil organic C (SOC) dynamics. Results of simulation studies can be applied to develop sustainable agricultural systems. This study simulated SOC in clayey Humic Hapludox with Century model (version 4.0) in a subtropical climate, with support from historical soil and land-use surveys; GIS and remote sensing techniques. Major reductions in SOC stocks were observed after land under native vegetation was converted to agricultural use, especially under annual crops managed under conventional tillage. Simulations of these soils under current management to the year 2058 showed that soils under conservation systems (especially no tillage) can recover and in some cases even exceed the original SOC stocks under native vegetation.

Long-Term Response of Nutrient-Limited Forests to CO"2 Enrichment; Equilibrium Behavior of Plant-Soil Models.

Established process-based models of forest biomass production in relation to atmospheric CO"2 concentration (McMurtrie 1991) and soil carbon/nutrient dynamics (Parton et al. 1987) are integrated to derive the @'Generic Decomposition and Yield@' model (G'DAY). The model is used to describe how photosynthesis and nutritional factors interact to determine the productivity of forests growing under nitrogen-limited conditions. A simulated instantaneous doubling of atmospheric CO"2 concentration leads to a growth response that is initially large (27% above productivity at current CO"2) but declines to <10% elevation within 5 yr. The decline occurs because increases in photosynthetic carbon gain at elevated CO"2 are not matched by increases in nutrient supply. Lower foliar N concentrations at elevated CO"2 have two countervailing effects on forest production: decreased rates of N cycling between vegetation and soils (with negative consequences for productivity), and reduced rates of N loss through gaseous emission, fire, and leaching. Theoretical analysis reveals that there is an enduring response to CO"2 enrichment, but that the magnitude of the long-term equilibrium response is extremely sensitive to the assumed rate of gaseous emission resulting from mineralization of nitrogen. Theory developed to analyze G'DAY is applicable to other published production-decomposition models describing the partitioning of soil carbon among compartments with widely differing decay-time constants.