Silvopastoral systems (SPS) are one of the most common livestock production systems in the Sahel. They are composed of a mix of trees, pastures, and livestock in the same area. Known for providing several beneficial services compared to traditional pastures, SPS can release or absorb greenhouse gases. So far, our understanding of the magnitude and spatial distribution of greenhouse gas emissions in Sahelian SPS is subject to many uncertainties. This is mainly due to a lack of experimental and modelling studies focused on the region.

We use a process-based model, STEP-GENDEC-N₂O, that couples vegetation growth, biogeochemistry, and gas emissions to investigate the spatial and temporal pattern of carbon dioxide (CO₂) and nitrous oxide (N₂O) emissions from soil and estimate their annual budget in the Sahelian SPS. After model validation using in-situ data collected at the Dahra site (north-western Senegal), simulations were performed on the entire Sahelian area (latitude: 13°N to 18°N; longitude: 18°W to 20°E) divided into 18271 grid cells of 0.1° x 0.1°, from 2010 to 2021. Input variables were extracted from different datasets available at global or regional scales.

We found that the spatial pattern of CO₂ and N₂O emissions from soils in Sahelian SPS can be mainly explained by the spatial distribution of soil properties (soil temperature, soil sand, and clay content), climate, and animal load. The overall estimated CO₂ and N₂O emissions from Sahelian SPS during the 2010-2021 period were 0.054 ± 0.005 Tg C yr^-1 (1 Tg = 10¹² g) and 0.046 ± 0.008 Tg N yr^-1, respectively. These values are relatively low compared to other estimates for grazing and cropping systems in other regions. Mapping CO₂ and N₂O emissions from soils in SPS at the Sahel-wide scale helps identify emission hotspots in order to establish more effective mitigation strategies and management policies for Sahelian SPS.

How to cite: Agbohessou, Y., Delon, C., Grippa, M., Mougin, E., Ba, S., Ngom, D., and Roupsard, O.: Soil CO2 and N2O emissions in Sahelian Silvopastoral systems: spatial distribution and annual budget estimation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7304, https://doi.org/10.5194/egusphere-egu23-7304, 2023.

Calcareous soils are characterized by containing a greater amount inorganic carbon (SIC) than organic carbon (SOC), and both contribute to CO₂ emissions to the atmosphere. SOC mineralization and SIC dissolution are related to soil moisture content, but their effect on CO2 emissions from calcareous soils is unclear. This investigation aimed to evaluate the effect of moisture content on CO₂ emission of a calcareous soil in the Comarca Lagunera, Mexico.

Calcareous soil samples were taken from a cropland and shrubland of Comarca Lagunera, Mexico and their physical and chemical properties were determined. For a 30-day period, 100g of soil were incubated in closed-jars and two moisture treatments, related to field capacity (FC) and permanent wilting point (PWP) values were applied. The CO₂ emission assessment was performed every two days using an infrared gas analyzer (IRGA, PP Systems, UK).

For cropland, the FC, PWP, SIC and SOC values were 27.2 %, 14.6 %, 7.3 % (140.4 Mg ha^-1) and 0.23 % (4.4 Mg ha^-1), while for shrubland, the values were 27 %, 11 %, 7.6 % (152.8 Mg ha^-1) and 0.08 % (1.6 Mg ha^-1), respectively. Average emission of CO₂, every two days, from cropland soil was 2.1 g CO₂ m^-2 h^-1 for moisture at FC, while to PWP was 1.7 g CO₂ m^-2 h^-1, and for shrubland soil was 1.8 g CO₂ m^-2 h^-1 for moisture at FC, while to PWP was 1.6 g CO₂ m^-2 h^-1.

In both cases, cumulative CO₂ emissions were significantly higher in FC compared to PWP. For cropland, cumulative CO₂ emissions were 23.4 g CO₂ m^-2 h^-1 and 29.4 g CO₂ m^-2 h^-1, but for shrubland were 21.7 g CO₂ m^-2 h^-1 and 25.3 g CO₂ m^-2 h^-1. Cumulative CO₂ emissions for moisture content at FC were equivalent to a soil carbon (C) loss of 1.9 Mg ha^-1 and 1.7 Mg ha^-1 for cropland and shrubland, respectively. This result implies the loss of 43.2% (1.9 Mg C ha^-1 / 4.4 Mg SOC ha^-1) of the SOC content in the cropland, but for the shrubland it suggests the total loss of the SOC (1.6 Mg C ha^-1 / 1.6 Mg SOC ha^-1) and a part of the SIC content (0.1 Mg C ha^-1 / 152.8 Mg SIC ha^-1).

Our study shows that soil moisture content has a significant effect on CO₂ emissions from calcareous soils, such as Comarca Lagunera, where an increase in soil moisture corresponds to increases in CO₂ emissions into the atmosphere, where SIC and SOC reserves are involved.

How to cite: Martinez-Santiago, S., Benedicto-Valdés, G. S., López-Santos, A., Silva-Rojas, H. V., Ojeda-Trejo, E., Ramírez-López, E. M., and Delgadillo-Martínez, J.: Effect of moisture content on carbon dioxide emissions in calcareous soils of the Comarca Lagunera, Mexico, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10777, https://doi.org/10.5194/egusphere-egu23-10777, 2023.

The use of agroforestry systems and integrated production models have been considered as viable options for tropical regions. Several studies have reported that these sustainable production systems have decreased the GHG emissions into the atmosphere and increased soil carbon stocks. If successful, the integration of crops, forests, and livestock will account for around 23% of Brazil’s 112 million ha of pasture. Every ha of integrated agriculture and livestock farming (IALF) pasture has the potential to remove an average of 3.79 tCO2e from the atmosphere per year. However, given the dynamics and complexity of soil management required when integrating different production components, it is necessary to perform regionalized research about soil carbon storage capacity. According to the Fourth National Communication of Brazil to the United Nations Framework Convention on Climate Change (UNFCCC), greenhouse gas (GHG) emissions in Brazil totaled 1,467 teragrams (Tg) of CO2e in 2016. In the search for more sustainable agricultural systems that increase the productivity of cultivated areas and at the same time can mitigate GHG emissions, the National Plan for Low Carbon Emission in Agriculture (ABC Plan), now renamed ABC+, was created aiming to incorporate new practices to mitigate GHG emissions for the 2020–2030 period. The objective of ABC Plan is to expand the agricultural land using the technologies outlined in the plan by 72 million ha - the area is currently close to 50 million ha - and achieve an estimated mitigation capacity of 1.1 billion tCO2e by 2030. Areas that integrate agriculture, livestock and forests, known as agrosilvopastoral systems are projected to expand by over 10 million ha in the period, according to ABC+ Plan.  In order to make recommendations about the adoption of agrosilvopastoral systems, the objective of this study was to summarize the data from literature using the meta-analysis to evaluate the effect of integrated production systems introduction on soil carbon stocks, considering the different biomes in Brazil. When we compared the land use with low-productivity pastures and integrated production systems, we found an increase in soil C stocks under agropastoral, silvopastoral and agrosilvopastoral systems. Considering all the evaluated Brazilian biomes, higher soil C stocks were found for the integrated production systems when compared to low-productivity pastures. The Cerrado and Atlantic Forest biomes showed a higher sampling value, and this is due to the fact that  integrated production systems are more adopted in these two Brazilian biomes. Additionally, the agrosilvopastoral systems in the Cerrado biome showed the highest soil C stocks, but did not differ in relation to the Atlantic Forest and Pampa biomes. The agrosilvopastoral and silvopastoral systems were efficient on soil C inputs, and the values were 65.58 and 57.14%, respectively, higher than in low productivity pasture at 0-30 cm depth. These findings indicate that the land use with pastures and the introduction of trees in productive systems can reverse soil carbon losses. Additionaly, the introduction of trees can increase soil carbon stocks, supporting the potential of agroforestry systems to recover low-productivity areas in Brazil.

How to cite: Frazão, L. A., Ferreira, E. A., de Oliveira, W. R., de Freitas, I. C., Cerri, C. E., Vilela, J. M., Cherubin, M., Oliveira, D., and Franco, A.: Sustainable intensification of agriculture andlivestock production in Brazil: a meta-analysis of soil C changes in integrated systems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1998, https://doi.org/10.5194/egusphere-egu23-1998, 2023.

How to cite: Wang, S., Zhuang, Q., Zhou, M., Jin, X., Yu, N., and Yuan, T.: Temporal and spatial changes in soil organic carbon and soil inorganic carbon stocks in the semi-arid area of northeast China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1749, https://doi.org/10.5194/egusphere-egu23-1749, 2023.

Sustainable intensification practices, such as integrated soil fertility management (ISFM), form a strategy to close yield gaps while maintaining soil fertility and, typically, are locally tested in field trials. However, to estimate the potential impact of ISFM on a regional scale, field trials are insufficient and biogeochemical models are required. These models need to be calibrated and evaluated when applied to new environments. Here, we present a robust calibration of the DayCent agroecosystem model to simulate the impact of ISFM practices on maize productivity in Kenya, using a probabilistic Bayesian calibration technique with data from long-term field trials at four sites in central and western Kenya. We assessed the efficiency of DayCent in simulating: 1) maize grain yield, 2) changes in soil organic carbon (SOC), and 3) nutrient use efficiency of applied nitrogen (N) fertilizer under different ISFM treatments, which consisted of different organic resources combined with the addition or absence of mineral N fertilizer. After model calibration, both the simulations of maize yield (Nash Sutcliffe Efficiency, NSE 0.51) and change in SOC (NSE 0.54) improved significantly compared to runs using the standard DayCent parameters (NSE of 0.33 and -1.3 for yield and SOC change, respectively). A leave-one-site-out cross evaluation indicated the robustness of the approach for spatial extrapolation, i.e., the significant improvement of model simulations was achieved by calibrating the model with data from three sites and then evaluating it with data from the remaining site. The values of model parameters related to SOC decomposition were most altered  by the calibration, i.e., they were an order of magnitude higher compared to the default parameter values (derived for temperate climates). This suggests that the DayCent temperature function is not suitable to capture SOC decomposition across climates with a single set of parameter values. Further, similar maize yields were simulated for all treatments that received mineral N fertilizer and DayCent underestimated the yield increase observed in the field trials of the combined application of organic resources and mineral N compared sole mineral N application. In contrast, at low levels of nutrient inputs DayCent proved sufficiently sensitive to capture differences in maize yield levels. Finally, while mean yields by treatment were simulated well, year-to-year yield variation was not captured well by DayCent. In summary, our results indicate that DayCent is capable to estimate the mean impact that ISFM practices at typical rates of mineral fertilizer and organic resource applications have on yield and SOC, but may not be capable to estimate the differences in yield potential at very high inputs. While the cross evaluation indicated a robustness for upscaling, the suboptimal representation of year-to-year yield variabilities shows that future projections under a changing climate may be biased by the DayCent model. Consequently, improved model structures, such as improved soil moisture representation, are needed to reduce uncertainty.

How to cite: Laub, M., Necpalova, M., Van de Broek, M., Corbeels, M., Mathu Ndungu, S., Mucheru-Muna, M. W., Mugendi, D., Waswa, W., Vanlauwe, B., and Six, J.: A robust DayCent model calibration to represent the impact of integrated soil fertility management on maize yields and soil carbon stocks in Kenya, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1489, https://doi.org/10.5194/egusphere-egu23-1489, 2023.

Greenhouse gas emission can be partly compensated by enhancing soil organic carbon (SOC) levels in soils, e.g. in croplands, which have the highest potential due to their losses in SOC by intensive management. This can be achieved by adopting SOC enhancing soil management practices, such as the cultivation of cover crops (CC). So far, only few long-term experimental studies have investigated the effects of CC on a SOC pool level. There are still uncertainties how CC affect SOC fractions and the stability of the sequestered carbon.

By conducting a meta-analysis, we aim to quantitatively summarize studies related to CC effects on SOC pools throughout soil depths (up to 100 cm) in cropland soils relevant for Europe, as such an analysis is not available so far. We included global studies located in the dry, temperate, and boreal climatic zones, as these are present Europe. The pools chosen for this analysis are the microbial biomass carbon (MBC), the particulate organic matter (POM) and the mineral associated organic matter (MAOM) pool, as well as total SOC. Alongside, we study the effects of a broad range of moderators, such as pedo-climatic factors (e.g., climatic zones, soil texture), other agricultural management practices (e.g., effects of tillage, irrigation, liming, fertilization) and CC characteristics and their management (e.g., CC types, species number, frost resistance, residue management).

By searching several scientific and grey literature databases, we identified 64 studies, of which the majority was conducted in North and South America, whereas only five are available for Europe. The MBC, POM and MAOM pool are studied in 24, 44 and 19 of these studies, respectively. The mean experimental duration is eight years, with a maximum of 39 years. 54% of studies were conducted in a warm temperate climatic zone, 32% in a boreal and 14% in an arid zone. Means values for SOC pools, standard deviations and sample sizes for treatments with CC and controls without CC will be extracted from tables and figures. In order to perform a meta-analysis, logarithm response ratio as an index of effect size will be calculated for each study, which will then be summarized across studies by using weighing procedure. This meta-analysis will provide valuable information on the state of knowledge on SOC pool specific sequestration rates influenced by CC, corresponding quantitative summary results and the source of heterogeneity across studies. These results will offer guidance for future research and assist decision-making processes regarding climate friendly management of agricultural soils.

How to cite: Fohrafellner, J., Zechmeister-Boltenstern, S., Murugan, R., Keiblinger, K., Spiegel, H., and Valkama, E.: Cover Crops Affecting Pool Specific Soil Organic Carbon Sequestration in Cropland – A Meta-Analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2269, https://doi.org/10.5194/egusphere-egu23-2269, 2023.

Increasing pressures on agriculture related to climate change, as well as recent policy frameworks, have generated widespread attention towards research on soil organic carbon (SOC) sequestration. Promoting SOC accrual is of immediate interest for maintaining and restoring soil health in order to ensure continuous soil fertility and functioning. However, despite extensive research regarding soil health promoting farming practices, studies reflecting realistic management outcomes from farms are still scarce. We therefore conducted an on-farm study comprising 21 sites in North-Eastern Austria to compare two farming systems (an innovative ‘pioneer’ and a standard system) and undisturbed field margins as a reference. Pioneer soils have been managed according to soil health-oriented principles with e.g., minimal tillage, high-diversity cover crops and organic amendments to improve soil biology for many years, whereas neighbouring fields under ‘standard’ cultivation represent the current state-of-the-art conventional practices. Based on recent findings suggesting a predominant role of microbial-derived compounds in the long-term accumulation of organic C, the study focused on available nutrients, microbial biomass C, nitrogen (N) and phosphorus (P), ergosterol, potential activities of C-, N- and P-liberating enzymes as proxies for microbial functioning, and amino sugar contents as proxies for microbial necromass. In addition to management effects, we also investigated whether differences in texture composition across the study sites and soil depth (0-5, 5-20, 20-35 cm) affect microbial biomarkers. Our results indicate that microbial parameters, especially microbial biomass and necromass C, are significantly enhanced in soils of pioneer farming systems. Yet, pioneer cultivation did not reach the levels prevailing in the undisturbed reference system. Moreover, differences between systems were strongly pronounced in the topsoil and declined in deeper soil layers. Soil texture had a profound leverage on management effects. In addition, we could identify significant management predictors for dissolved C contents, which is an important pathway for microbial-mediated SOC sequestration. Our on-farm approach provides meaningful information on how farming systems can be changed towards more sustainability and higher C sequestration.

How to cite: Huber, S., Rosinger, C., Sae-Tun, O., Bodner, G., and Keiblinger, K.: On-farm research on innovative pioneer farms in North-Eastern Austria: microbial indicators affecting soil organic carbon (SOC) sequestration, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8716, https://doi.org/10.5194/egusphere-egu23-8716, 2023.

To partially compensate for CO₂ emissions, the 4 per 1000 initiative proposed an annual 4‰ soil organic carbon (SOC) stock increase. Yet, the feasibility of such an ambitious target is still under debate. The most efficient way to increase the SOC stocks is to increase the C input to the soil. Yet, knowing how much of an increase of SOC should be an objective is subjected to how much carbon is already stored within soils, and the prediction of the change of carbon pool with time. The objective of this work is to predict the carbon trends in forest soils to be able to better assess the target carbon sequestration. To this end, we use the AMG SOC model to simulate the carbon increase in French forests. AMG is a simple, two-pools model that consider the influence of environmental conditions and litter inputs to simulate the dynamics of SOC. AMG has been designed for agricultural soils, and has proved able to simulate SOC dynamics in croplands but has never been tested on forest soils. The model was run over the French RENECOFOR sites network where SOC measurements have been realized 17 years apart (1994-1996 and 2008-2012) on 95 sites and over which an average increase of +0.35 tC ha^-1 yr^-1 has been evidenced. We have applied the RockEval method, which mixes machine learning with thermal analysis techniques, in order to initialize AMG, separating the passive from the active carbon pool. We calibrated the model with the aim of simulating the SOC dynamics observed in the RENECOFOR. The results show that even if the model can be successful in predicting the carbon trends locally, there is no general parameterization allowing to reproduce SOC stock evolution trends at the scale of the 95 sites. Our findings suggests that even with a good performance in the case of agricultural soils, there is a need to better represent the litter inputting within the AMG model in the case of forests.

How to cite: Houballah, M., Le Noé, J., Ferchaud, F., Clivot, H., Barré, P., Guenet, B., and Delpierre, N.: Applying the AMG Soil Organic Carbon model to assess the carbon trends within French forests, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8046, https://doi.org/10.5194/egusphere-egu23-8046, 2023.