Soil Organic Carbon Evolution Research Articles

Soil temperature and local initial conditions drive carbon and nitrogen build-up in young proglacial soils in the Tropical Andes and European Alps

Climate warming has accelerated the retreat of mountain glaciers worldwide, exposing new areas to weathering, vegetation colonization, and soil formation. In light of probable climate changes such as warming and new extremes, understanding the factors that control soil organic carbon (SOC) and nitrogen build-up is crucial to comprehend proglacial soils and ecosystem formation. To this end, we examine the evolution of SOC, nitrogen (total N and NH4+), and phosphorus (available P) along nine 120-year chronosequences of deglacierization distributed between the European Alps and Tropical Andes. Our dataset includes geochemical analyses of 188 soil samples, in situ soil temperature data for the period 2019–2022, and hydrographic variables. Although time controls proglacial soil development at all sites, our study highlights distinct pedogenesis dynamics between proglacial landscapes depending on the micro and macro environmental context. Differences in soil development were strongly driven by growing degree days (GDD), maximum soil temperature, and parent material. Notably, we identified a positive effect of GDD on SOC and N (total N and NH4+), while our results indicate a negative effect of maximum soil temperature on SOC and NH4+, suggesting that overly high temperatures reduce microbial mineralization and organic matter input to the soil matrix. We reported the presence of higher initial SOC, total N, and NH4+ in the Andean sites than in the Alps sites, suggesting enhanced soil development at the Andean locations. This comparative study suggests the relative importance of maximum temperature and initial site conditions (e.g., parent materials, glacier biomes) during proglacial pedogenesis. Our findings highlight that soil temperature modulates pedogenesis in a complex way and suggest avoiding simply associating greater soil development with higher soil temperature in proglacial landscapes.

DYNAMICS OF SOIL ORGANIC CARBON AFTER MORE THAN 25 YEARS OF FARMING IN THE DANUBE DELTA

Soil organic carbon (SOC) is an important parameter in the context of global warming, and a special attention should be given to its dynamics. The purpose of this paper is to test the existence of SOC losses from the soils taken for farming for more than 25 years in some areas of the Danube Delta. Another objective is to quantify such SOC losses if they exist. The studied soils belong to two land reclamation areas, Carasuhat and Dunavat, from the Danube Delta. Data of present-day SOC stocks were compared to the SOC stocks calculated for the period until year 1996 for the same soil units in order to assess the dynamics of SOC losses for more than 25 years. We have found that a specific process was noted for the organic soils, Histosols, which were turned into histic soils after farming, meaning that there was a significant decrease in SOC pool. Thus, SOC losses due to farming were maximum for Histosols, and SOC stocks were highly significantly lower in 2022 versus 1996, due to increasing mineralization processes of organic matter and subsequent greenhouse gas emissions that occurred in cropland areas. Relationships have been found quantifying SOC losses versus the original 1996 stocks, confirming that Histosols, containing the maximum SOC stocks, present the highest risk of degradation. Lowering of the ground water and consequently the intensified oxidation of peat are very important factors in SOC losses beside the agricultural land use works. Policy makers, decision makers and stake holders should promote conservation of the natural landscape of the Danube Delta in order to increase SOC stocks and decrease CO2 and other greenhouse gas emissions into the atmosphere. Maintaining the former SOC stock at the present-day level and enhancing new organic C sequestration in the renatured parts of the less fertile Delta soils could contribute to global warming mitigation in the future and to supply agricultural products in the cropland already in use. Future research in characteristic stationary sites of the Danube Delta, especially in the farmland area, is recommended to improve our knowledge on SOC evolution.

Organic carbon contents of mineral grassland soils in Switzerland over the last 30 years

Long-term monitoring data on the evolution of soil organic carbon (SOC) content and soil stocks are crucial considering climate change and carbon sequestration. Due to the slow processes involved, it takes longer time spans until changes in SOC stocks become detectable. Thus, long-term monitoring is essential.Beside measurements, models are often used to report changes in SOC stocks for greenhouse gas (GHG) inventories. Consistent field data over extended periods are essential for validating such models whereby data from long-term monitoring is of great value. We present SOC measurements from the topsoil (uppermost 0.2 m) of 24 grassland sites of the Swiss Soil Monitoring Network (NABO) for six sampling campaigns from 1985 to 2014 and compare their evolution with predictions by the RothC model, which, for example, is used for the Swiss GHG Inventory. While there was no general temporal trend of the measured data over all sites, from a single site perspective, SOC stocks decreased/increased on 8% and 25% of the sites respectively. When comparing the measured data with the predictions from modelled values from RothC, a good fit was achieved in two thirds of the cases. However, at 5 out of the 24 sites (21%), the modelled SOC changes over time were lower than the measured ones. For 3 out of the 24 sites (12%) the model predicted higher SOC stock increases than were measured. Overall the modelled data fit well together with the measured ones. Most of the sites revealed stable values over time or increasing trends between 1985 and 2014, which might indicate that the SOC stocks potentially are in equilibrium and that the farming management used in Switzerland is suited to maintain these stocks in topsoils. There might not be a big potential for C sequestration, however, it is also very important to maintain SOC stocks over time. For future climate change scenarios accurate long-term SOC data and modelling are important for gathering the required information.

Plant and soil microbial responses to irrigation retirement in semiarid cropping systems

Water scarcity limits irrigated agriculture, and there is an increasing frequency of situations where farmers must transition from irrigated to dryland cropping systems. This transition poses several challenges, and it is necessary to understand the changes in crop productivity and soil health for the design of viable cropping systems. Our objective was to compare the impact of irrigation retirement on crop production and soil microbial dynamics under the two major crops of the semiarid High Plains. In a formerly irrigated field, we installed a transition experiment that consisted of two irrigation managements, irrigated and non-irrigated (retired), under two cropping systems: continuous maize and continuous winter wheat. Lower soil moisture after irrigation retirement decreased plant biomass production in both crops, with a higher effect on maize (2 to 6-fold decrease) than on wheat (20% less aboveground biomass production). In both crops, irrigation retirement affected crop development in the order grain yield > aboveground biomass > belowground biomass. Soil microbial communities were less affected by irrigation retirement than the evaluated crops and changes were concentrated in the maize agroecosystem. After three seasons, the high decrease in maize productivity and soil moisture resulted in 50% less extracellular enzyme activity in the dryland treatment, but without consistent effects on microbial biomass or community composition assessed by phospholipid fatty acids. Winter wheat appears as a viable option not only to sustain crop production but also to minimize the negative impacts of irrigation retirement on soil health. However, root production was lower in wheat than in maize, which may affect the long-term evolution of soil organic carbon.

Soil Organic Carbon and Geochemical Characteristics on Different Rocks and Their Significance for Carbon Cycles

Soil organic carbon (SOC) is significant for soil quality and global carbon cycles. SOC was observed to be related to soil geochemistry, and soils originating from different bedrocks have different geochemical properties, but the effect of bedrock on SOC is still undefined. Soils overlying different bedrocks in Zhenxiong County and Weixin County were sampled. Specifically, soils in the mineral horizon, which are less affected by the external environment than surface soils, are focused on to reveal the effect of bedrock on SOC. Al/Ti, Fe/Ti, and Al/Fe indicate a soil–rock successive relationship. SOC contents in the mineral horizon are 0.19–2.74% (1.24% on average), and those in the surface horizon are 1.26–4.01% (2.63% on average). SOC contents in the surface and mineral horizons of the same bedrock are significantly positively correlated, implying that the bedrock is an important factor affecting SOC. SOC in the mineral horizon is related to the first transition metal ions. Significantly, positive correlations of SOC (p < 0.01) with Co, Cu, Ti, V, and Zn, and a positive correlation (p < 0.05) with Ni were observed in the mineral horizon. Organic transition metal complexation seems to play an important role in governing SOC in the mineral horizon. That is, the complexation maintains organic carbon stability, slows down its decomposition rate, and accumulates organic carbon. The Ca–SOC positive correlation in the mineral horizon exits because Ca also can complex with organic carbon. Co, Cu, and V–SOC positive correlations (p < 0.05) were also observed, but there were no significant positive correlations (p < 0.01) in the surface horizon because surface SOC had diversified sources. An SOC evolution model influenced by the bedrock was forwarded. Thus, the different soil geochemistry originating from different bedrocks should be noticed when SOC and global carbon cycles are discussed.

Soil organic carbon storage, distribution, and influencing factors at different depths in the dryland farming regions of Northeast and North China

The knowledge of the spatial distribution of soil organic carbon (SOC) and of its influencing factors is crucial for understanding the global carbon cycle. Although the influence of climate, soil properties, and soil management on the SOC content has been extensively explored, their relative importance remains unclear, especially under dryland farming. Herein, we investigated the SOC density (SOCD) at different depths (0–10, 10–20, 20–30, and 30–40 cm) across an area of 37.79 × 104 km2 (420 sites) located in the dryland farming regions of Northeast and North China. The total SOC storage (SOCS) was estimated to be 1922.38 Tg, with a mean density of 5.78 kg C m−2 for the entire area. The three soil groups with the largest SOCS were Fluvo-aquic, Black, and Chernozem soils, accounting for 63.34% of the total SOCS in the study area. Overall, both the SOCD and SOCS increased from southwest to northeast at all investigated depths. A structural equation model was used to distinguish direct from indirect effects of different factors on SOCD. Soil properties (e.g., bulk density and pH) and natural conditions (e.g., mean annual temperature and mean annual precipitation) were found to be the main factors controlling the SOCD variation at depths of 10–20, 20–30, and 30–40 cm. However, the total (direct and indirect) effect of soil management on SOCD at a 0–10 cm depth was greater than that of natural conditions, and smaller than that of soil properties. With increasing soil depth, the total effect of natural conditions on SOCD changed from –0.33 to –0.58, whereas the indirect effect of soil management decreased from 0.47 to 0. These results indicate that compared with environmental factors, soil management practices such as tillage and fertilization had a greater influence on SOCD in the surface soil of dryland. Our study provides a valuable reference for future research on the long-term evolution of SOC in dryland farming regions.

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.

Soil organic carbon dynamics from agricultural management practices under climate change

Abstract. Sequestration of soil organic carbon (SOC) on cropland has been proposed as a climate change mitigation strategy to reduce global greenhouse gas (GHG) concentrations in the atmosphere, which in particular is needed to achieve the targets proposed in the Paris Agreement to limit the increase in atmospheric temperature to well below 2 ∘C. We analyze the historical evolution and future development of cropland SOC using the global process-based biophysical model LPJmL, which was recently extended by a detailed representation of tillage practices and residue management (version 5.0-tillage2). We find that model results for historical global estimates for SOC stocks are at the upper end of available literature, with ∼2650 Pg C of SOC stored globally in the year 2018, ∼170 Pg C of which is stored in cropland soils. In future projections, assuming no further changes in current cropland patterns and under four different management assumptions with two different climate forcings, RCP2.6 and RCP8.5, results suggest that agricultural SOC stocks decline in all scenarios, as the decomposition of SOC outweighs the increase in carbon inputs into the soil from altered management practices. Different climate change scenarios, as well as assumptions on tillage management, play a minor role in explaining differences in SOC stocks. The choice of tillage practice explains between 0.2 % and 1.3 % of total cropland SOC stock change in the year 2100. Future dynamics in cropland SOC are most strongly controlled by residue management: whether residues are left on the field or harvested. We find that on current cropland, global cropland SOC stocks decline until the end of the century by only 1.0 % to 1.4 % if residue retention management systems are generally applied and by 26.7 % to 27.3 % in the case of residue harvest. For different climatic regions, increases in cropland SOC can only be found for tropical dry, warm temperate moist, and warm temperate dry regions in management systems that retain residues.

Numerical model to simulate long-term soil organic carbon and ground ice budget with permafrost and ice sheets (SOC-ICE-v1.0)

Abstract. The degradation of permafrost is a large source of uncertainty in understanding the behaviour and projecting the future impacts of Earth's climate system. The spatial distributions of soil organic carbon (SOC) and ground ice (ICE) provide essential information for the assessment and projection of risks and impacts of permafrost degradation. However, uncertainties regarding the geographical distribution and estimated range of the total amount of stored carbon and ice are still substantial. A numerical soil organic carbon–ground ice budget model, SOC-ICE-v1.0, that considers essential aspects of carbon and hydrological processes in above-ground and subsurface environments and permanently frozen ground (permafrost) and land cover changes (ice sheets and coastlines) was developed to calculate the long-term evolution of local SOC and ICE. The model was integrated to cover the last 125 kyr – from the last interglacial to date for areas north of 50∘ N at 1∘ resolution – to simulate the balance between accumulation and dissipation of SOC and ICE. Model performance was compared with observation-based data and evaluated to assess allogenic (external) impacts on soil carbon dynamics in the circum-Arctic region on a glacial–interglacial timescale. Despite the limitation of forcing climate data being constructed on the basis of a single Greenland ice core dataset, the simulated results successfully reproduced temporal changes in northern SOC and ICE, consist with current knowledge. The simulation also captured regional differences in different geographical and climatic characteristics within the circum-Arctic region. The model quantitatively demonstrated allogenic controls on soil carbon evolution represented by a key parameter that reflects climatological and topo-geographical factors. The resulting circum-Arctic set of simulated time series can be compiled to produce snapshot maps of SOC and ICE distributions for past and present assessments or future projection simulations. Examples of 1∘ resolution maps for the Last Glacial Maximum and mid-Holocene periods were provided. Despite a simple modelling framework, SOC-ICE-v1.0 provided substantial information on the temporal evolution and spatial distribution of circum-Arctic SOC and ICE. Model improvements in terms of forcing climate data, improvement of SOC and ICE dynamics, and choice of initial values are, however, required for future research.

Soil carbon storage and mineralization rates are affected by carbon inputs rather than physical disturbance: Evidence from a 47-year tillage experiment

In spite of the large number of studies conducted on the drivers of soil organic carbon (SOC) stocks, there is still no consensus on the impact of tillage on the distribution and turnover rate of SOC in the soil profile. Few studies have characterized precisely the turnover of SOC using 13C natural tracing or simulated the SOC evolution per soil layer. In this study, we combined several approaches (diachronic analysis of SOC stocks, isotopic tracing and modelling) for characterizing the SOC evolution per soil layer in one of the oldest tillage experiments comparing no-till (NT), shallow till (ST) and full inversion tillage (FIT) combined with six crop managements. The new measurements made in 2017 reported in this paper confirm that i) tillage had no effect on SOC stocks integrated over the old ploughed layer (∼0−28 cm) or deeper (∼0−58 cm) and ii) reduced tillage affected the SOC distribution in the soil profile, with SOC storage in the upper layer (∼0−10 cm) offset by a SOC loss in the underlying layer (∼10−28 cm). The change in rotation (from C4 to C3 crops) in two crop management treatments allowed to quantify the decrease in C4 stocks during 19 years and calculate the specific mineralization rates relative to tillage treatments and soil layers. The mineralization rates did not vary significantly between tillage treatments in the whole (old) ploughed layer (∼0−28 cm) but varied according to depth and tillage. The highest rates were found in the layer 0−5 cm of NT or ST and the lowest rates in the layer 10−28 cm of the same tillage treatments. The rates were highly correlated with estimated C inputs and particulate organic matter contents in each layer, but not with tillage intensity. The evolution of total SOC and C4 stocks of each soil layer was simulated with AMG model during 47 years. The standard model (with a single mineralization rate) gave a good prediction of SOC evolution when applied to the whole profile (∼0−28 cm) but not for each individual layer. Including a relationship between C input and mineralization rate in the model allowed to well simulate the SOC evolution in all soil layers. This study shows that the main effect of a change in tillage on SOC storage is the change in the distribution of C input throughout the profile and the corresponding variation of the priming effect rather than the change in physical soil disturbance.

May conservation tillage enhance soil C and N accumulation without decreasing yield in intensive irrigated croplands? Results from an eight-year maize monoculture

Intensive management of agroecosystems has been widely indicated as major responsible for soil degradation, thus negatively impacting on relationships between agriculture and climate change. Conservation tillage (i.e. no-till and minimum tillage) has been recommended for enhancing soil organic carbon (SOC) and total nitrogen (STN) stocks while having a positive impact on food security, biodiversity, water quality and the environment. Nevertheless, positive responses were mainly reported in hot and semiarid climates, with rainfed crops and low N fertilization rates.Therefore, the main objective of this study was to test the adoption of conservation tillage in intensive maize cropping systems under temperate soil, with high N fertilization rate (> 200 kg N ha−1 yr−1) and organic matter input (i.e. manure distribution and high biomass return), and with permanent optimum water moisture due to irrigation. We conducted an 8-year field experiment on a maize (Zea mays L.) monoculture to assess: (i) the effect of no-till (NT) and minimum tillage (MT), on grain yield and biomass return as compared with conventional tillage (CT); (ii) how tillage systems affect the evolution of SOC and STN levels over time under these conditions; (iii) soil aggregation processes and mechanisms leading to SOC and STN changes in the long-term. Results showed that MT increased maize grain yield (+7 %) and total biomass (+10 %) compared with CT. Conversely, NT reduced maize grain and biomass production during the initial 5-year transition, but afterwards increased maize yield up to that of CT.At the end of the experiment, SOC sequestration was increased under NT and MT by 1.45 and 1.52 Mg C ha−1 yr−1 compared with CT, respectively. Also, STN accumulation was higher under NT and MT than under CT (+0.15 and +0.17 Mg N ha−1 yr−1, respectively). Most of such a SOC and STN increase was located into C- and N-rich macroaggregates. Within those macroaggregates (large macroaggregates, LM; small macroaggregates, sM), we found that C and N pools associated to mM accounted for between 41 and 65 % of total C and N content in NT and MT systems across the different soil layers, which is beneficial for long-term C and N stabilization in soils. Thus, introducing conservation tillage within intensive agricultural context devoted to maize monoculture as that of the Po Valley should be recommended to: (i) maintain (or even increase) maize yield, and (ii) enhance SOC and STN accumulation and stabilization.

Short and long-term impact of urban gardening on soil organic carbon fractions in Lixisols (Burkina Faso)

In sub-Saharan Africa, market gardening relies on the intensive use of organic amendments, but little is known about the impact of these practices on soil organic carbon (SOC) dynamics. Recent studies have demonstrated that a better understanding of carbon dynamics can be achieved by considering different carbon pools. Here we used a simple method of physical SOC fractionation to assess the impact of market gardening practices on the evolution of total SOC and its stable and labile sub-fractions over a period of several decades. The study was conducted at the Kuinima market gardening zone in Bobo-Dioulasso (Burkina Faso). Composite soil samples (0–15 cm depth) were collected from a chronosequence of 69 fields including control plots and plots farmed for more than 50 years. Samples were wet sieved at 20 µm after agitation or sonication to assess carbon content in the fine (i.e. stable) and coarse fractions. Our results show an asymptotic increase in total carbon content, from 9 g C kg−1 for uncultivated control plots to 28 g C kg−1 for plots cultivated for more than 50 years. This increase tends to stabilize after 30 years. A similar trend is observed for C content in the coarse fraction > 20 µm. In contrast, carbon content in the fraction < 20 µm increased linearly over time, and this increase was greater in sonicated than in agitated samples. Based on the comparison of the two fractionation methods, a strong contribution of micro-aggregation to the physical stabilization of SOC was hypothesized. This stabilization appears favored by short-range-order (SRO) iron and aluminum oxides and/or metal-humus complexes, as suggested by the strong correlation between stable C content and oxalate-extractable Fe and Al. Large and repeated additions of organic amendments in market gardening thus appear to lead to increased SOC content and promote SOC storage in the stable fraction, thereby contributing to soil quality improvement and the mitigation of climate change.

Evolution of soil organic carbon in a carbonaceous glacial till as an effect of crop and fertility management over 50 years in a field experiment

Changes in soil organic carbon (SOC) content depending on different factors are extensively investigated when the soil is in steady-state equilibrium between formation and decomposition of soil organic matter. However, studies of SOC formation and dynamics in initally organic matter free soil are rare. Evolution of soil organic carbon was studied in a field experiment established in 1964 on a carbonaceous glacial till soil with very low initial SOC content (1.28 g kg−1). The effects on SOC content changes of bare fallow, barley and different perennial fodder crops such as grasses, clover-grass mixture, galega, hybrid lucerne and a turfgrass mixture, with or without mineral N and PK fertilisation and manure, were studied. There were 19 treatments in total and most had unchanged plant cover composition throughout the experiment. During 1964–2014, SOC stock increased in all treatments, by 0.11 Mg ha−1 y−1 in bare fallow and by at most 0.50 Mg ha−1 y−1 in the treatment with hybrid lucerne and manure. Average SOC sequestration rate was 0.35 ± 0.11 Mg ha−1 y−1. SOC changes were highly correlated with estimated C inputs and were therefore higher in treatments with perennials than with an annual barley crop. C retention efficiency for total crop-derived C inputs and for organic amendments was 6.1% and 22%, respectively. Water-soluble C measured in 2014 increased linearly with SOC, indicating that the quality of recently formed SOC was not strongly affected by the treatments. However, water-soluble C as a fraction of SOC was significantly lower in treatments with legumes than in treatments with bare fallow or a barley or grass crop. These results demonstrate that the quantity and quality of C inputs were both main drivers for observed changes in SOC. However, C retention efficiency of C inputs was relatively low. This may be related to soil texture with high sand proportion, suggesting that SOC sequestration rates in light-textured soils may be lower than expected even in case of low initial SOC content.

Modeling soil organic carbon evolution in long-term arable experiments with AMG model

Reliable models predicting soil organic carbon (SOC) evolution are required to better manage cropping systems with the objectives of mitigating climate change and improving soil quality. In this study, data from 60 selected long-term field trials conducted in arable systems in France were used to evaluate a revised version of AMG model integrating a new mineralization submodel. The drivers of SOC evolution identified using Random Forest analysis were consistent with those considered in AMG. The model with its default parameterization simulated accurately the changes in SOC stocks over time, the relative model error (RRMSE = 5.3%) being comparable to the measurement error (CV = 4.3%). Model performance was little affected by the choice of plant C input estimation method, but was improved by a site specific optimization of SOC pool partitioning. AMG shows a good potential for predicting SOC evolution in scenarios varying in climate, soil properties and crop management.

Twenty-five years of observations of soil organic carbon in Swiss croplands showing stability overall but with some divergent trends

The temporal evolution of soil organic carbon (SOC) is of major importance given its status as a key parameter in many soil functions. Furthermore, soils constitute an important reservoir of carbon in our environment. In light of climate change, consistent SOC data over extended periods in combination with information on agricultural management are much required, but still scarce. We report SOC changes in the topsoil (0–20 cm) of Swiss cropland measured at well-defined monitoring sites resampled every 5 years from 1990 to 2014 by the Swiss Soil Monitoring Network NABO using consistent sampling protocols and quality assurance. Data on agricultural management practices were retrieved from farmers. Overall, SOC remained stable for the ensemble of monitoring sites, although increasing and decreasing trends were observed for individual sites, ranging from − 11 to + 16% relative change per decade. Changes in the agricultural management of cropland triggered substantial changes in SOC contents for some sites. Moreover, sites with a low ratio of SOC/clay (< 0.1) generally showed more positive trends than sites with higher ratios. We presume that SOC was either at or near steady state, given the consistency of management practices over the last few decades. Finally, our study provides insights into the uncertainties related to (real-world) SOC monitoring and underlines the relevance of short-term SOC variations that could hamper the detection of long-term trends. The minimum detectable change (MDC) by the applied monitoring scheme is estimated at 0.35% per year, in relative terms.

Introduction of a natural resource balance indicator to assess soil organic carbon management: Agricultural Biomass Productivity Benefit

The rising demand for feed and food has put an increasing pressure on agriculture, with agricultural intensification as a direct response. Notwithstanding the higher crop productivity, intensive agriculture management entails many adverse environmental impacts. Worldwide, soil organic carbon (SOC) decline is hereby considered as a main danger which affects soil fertility and productivity. The life cycle perspective helps to get a holistic overview when evaluating the environmental sustainability of agricultural systems, though the impact of farm management on soil quality aspects is often not integrated. In this paper, we introduce an indicator called Agricultural Biomass Productivity Benefit of SOC management (ABB_SOC), which, relying on natural resource consumption, enables to estimate the net effect of the efforts made to attain a better soil quality. Hereby the focus is put on SOC. First, we introduce a framework to describe the SOC trend due to farm management decisions. The extent to which remediation measures are required are used as a measure for the induced SOC losses. Next, ABB_SOC values are calculated as the balance between the natural resource consumption of the inputs (including remediation efforts) and the desired output of arable crop production systems. The models RothC and EU-Rotate_N are used to simulate the SOC evolution due to farm management and the response of the biomass productivity, respectively. The developed indicator is applied on several rotation systems in Flanders, comparing different remediation strategies. The indicator could be used as a base for a method to account for soil quality in life cycle analysis.

A proposal for using process-based soil models for land use Life cycle impact assessment: Application to Alentejo, Portugal

Abstract Human occupation and transformation of land are a root cause of ecosystem services degradation. For example, land use (LU) and land use change (LUC) are drivers of soil organic carbon (SOC) change, decreasing the biotic production potential of soils. In Life Cycle Assessment (LCA) there is a growing trend towards accurate and regionalized impact assessment of LU∖LUC. Available impact assessment models apply statistical procedures to a simplified static characterization framework, including a limited set of aggregated LU classes. In this paper we propose process-based modelling as the basis for LU/LUC Life Cycle Impact Assessment (LCIA) and calculate midpoint process-based characterization factors (CFs) using SOC depletion as the impact indicator. This forecast or scenario-based approach included climate change scenarios for the study region. Temperature and precipitation changes are likely to affect the role of LU in SOC accumulation, which should influence LUC choices today. As proof of concept we used the region of Alentejo, Portugal, which was divided in more than 1500 unique homogeneous territorial units (UHTU). We used the process-based model RothC to establish the likely dynamic SOC evolution after LUC in each UHTU. Our work suggests that process-based models are necessary to move beyond the calculation of CFs for generic LU classes. We provide CFs for individual crops and discriminated LU classes and management practices. We additionally provide insights and indication for future work leading up to the production of global CFs using similar soil models and an updated procedure for CF calculation.

Importance of cover crops in alleviating negative effects of reduced soil tillage and promoting soil fertility in a winter wheat cropping system

Reduction of soil tillage is of paramount importance for agricultural soil preservation. However, it is often accompanied by yield reduction and weed management problems. In this perspective, cover crops could play an important role to alleviate weed infestation and sustain yield. In this study, the results from a three-year experiment of cover crop cultivation in different soil tillage treatments is presented, together with results from DayCent simulations on the long term evolution of soil organic carbon and total nitrogen. Eight cover crop treatments were set up as subtreatments in a long term experiment in Switzerland. Cover crops were cultivated for a short two-month period between two winter wheats. Substantial differences in cover crop growth were observed depending on cover crop species. In all tillage treatments, high cover crop biomass production allowed to supress weed biomass compared to the no cover crop control. Wheat grain yield was higher in the minimum tillage than in the plough treatment. In the no till treatment, wheat yield was notably low, except in the field pea treatments, where wheat yield reached values similar to that observed in the plough and minimum tillage treatments. In addition, these differences in biomass production translated into important differences in nutrient inputs, and even in soil nutrient concentration in some cases. Long term simulations showed that cover crop cultivation could increase drastically soil organic carbon and total nitrogen, especially in reduced tillage treatments. Altogether, these results demonstrated that the presence of a well-developed cover crop, even for only two months, allows to sustain wheat yield in a no till treatment. It impacts also soil fertility and nutrient cycling. This study shows that an accurate use and management of cover crops, in interaction with tillage reduction, could maintain yield and improve soil fertility in the long term.

Evolution of soil organic carbon during a chronosequence of transformation from cacao (Theobroma cacao l.) plantation to grassland

The aim of this research was to evaluate the impact of the soil use change of the Cocoa Agroforestry System (CAS) on soil organic carbon (SOC) levels and other indicating soil chemical fertility properties (apparent density ρb, cation exchange capacity CEC, total soil N TSN), when a soil use change occurs from CAS to grassland (GL). For this, in order to be selected was recorded, considering different time intervals (1-5, 6-10 y 11-20 years). However, a CAS of 20-35 years was considered as a reference. In addition, soil samples were taken at -30 cm depth to determine the contents of SOC, TSN, CEC, ρb, soil organic matter (SOM) and the soil C/N relationship. Consequently, an in situ resistance to soil penetration was evaluated. The results indicated the change in soil use from CAS to GL, did not cause a significant decrease in the amount of stored SOC (0-30 cm) during the considered time with respect to CAS. However, if only the first -10 cm of soil is sampled, a significant soil compaction is observed throughout a decrease in the CEC value in the long term (20 years).

Long‐term development of organic carbon contents in arable soil of North Rhine–Westphalia, Germany, 1979–2015

Europe currently faces a decline in soil organic carbon (SOC) content under arable cropping irrespective of improved management practices. In this study we used more than 32 000 SOC data from the entire North Rhine–Westphalia (NRW) area to elucidate the temporal development and current state of SOC content in arable soil from 1979 to 2015 and, in addition, to identify potential causal factors of changes in SOC content. The dataset comprised 7401 data points for 1979–2003 from FIS StoBo, the branched information system on soil contamination in NRW, and 24 930 data points for 2007–2015 from the Agricultural Investigation and Research Institute NRW (LUFA NRW); all data considered refer to soil sampled at 0–30 cm. We found that topsoil carbon contents in arable soil increased over the entire NRW area during the 1980s (from 1.87% in 1979 to 2.82% in 1987), and that this increase was followed by an exponential decrease from 1988 to 2015 (1.42% SOC in 2015) without a new equilibrium being reached. Livestock‐poor regions showed a more rapid gain and a more rapid loss of SOC contents than regions with large livestock densities. The data correlated with changes in grassland area, which was reduced in NRW by about 360 000 ha mainly between 1970 and 1990; that is, recently ploughed grassland probably contributed to increasing averages of SOC contents in arable land during this period, but not thereafter. We conclude that past changes in land use controlled the evolution in SOC from 1979 to 2015, and there is little opportunity for changed management practices to prevent ongoing loss of SOC from the topsoil.HighlightsThe SOC contents in arable soil in North Rhine–Westphalia (NRW) show temporal trend. The SOC contents increased during the 1980s, but decreased thereafter. Data from the entire NRW area indicate that new SOC equilibria have not yet been reached. Past changes in land use still control current SOC evolution.