Displays

Throughout the Anthropocene, the conversion of land to agriculture and atmospheric deposition of nitrogen have resulted in significant changes to biogeochemical cycling, including soil carbon stocks. Quantifying these changes is complex due to a number of influential factors (including climate, land use management, soil type) and their interactions. As the largest terrestrial store of carbon, soils are a key component in climate regulation. In addition, soil carbon storage contributes to numerous ecosystem services including food provision. It is therefore imperative that we understand changes to soil carbon stocks, and provide effective strategies for their future management.

Modelling soil systems provides a means to estimate changes to soil carbon stocks. Due to linkages between the carbon cycle and other major nutrient cycles (notably nitrogen and phosphorus which often limit the productivity of ecosystems), models of integrated nutrient cycling are required to understand the response of the carbon cycle to global pressures. Simulating the impacts of land use changes requires capacity to model both semi-natural and intensive agricultural systems.

In this study, we have developed an integrated carbon-nitrogen-phosphorus model of semi-natural systems to include representation of both arable and grassland systems, and a range of agricultural management practices. The model is applicable to large spatial scales, as it uses readily available input data and does not require site-specific calibration.  After being validated both spatially and temporally using data from long-term experimental sites across Northern-Europe, the model was applied at a national scale throughout the United Kingdom to assess the impacts of land use change and management practices during the last two centuries. Results indicate a decrease in soil carbon in areas of agricultural expansion, yet in areas of semi-natural land use, atmospheric deposition of nitrogen has resulted in increased net primary productivity and subsequently soil carbon. The results demonstrate anthropogenic impacts on long-term nutrient cycling and soil carbon storage, and the importance of integrated nutrient cycling within models.

How to cite: Janes-Bassett, V., Davies, J., Bassett, R., Yumashev, D., Rowe, E., and Tipping, E.: Modelling soil carbon stocks in semi-natural and agro-ecosystems – quantifying national scale impacts of the Anthropocene, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18355, https://doi.org/10.5194/egusphere-egu2020-18355, 2020.

Soil organic carbon (SOC) is one of the most important indicators of soil quality and agricultural productivity. This paper presents the application of Regression Kriging (RK), Geographically Weighted Regression (GWR) and Geographically Weighted Regression Kriging (GWRK) for prediction of topsoil organic carbon stock in Tarialan. A total of 25 topsoil (0-30 cm) samples were collected from Tarialan soum of Khuvsgul aimag in Mongolia. In this study, seven independent variables were used including normalized difference vegetation index (NDVI), soil adjusted vegetation index (SAVI), normalized difference moisture index (NDMI), land surface temperature (LST) and terrain factors (DEM, Slope, Aspect). We used root mean square error (RMSE), mean error (ME) and determination coefficient (R²) to evaluate the performance of these methods. Validation results showed that performance of the GWRK, GWR, and RK approaches were good with not only low values of root-mean-square error (1.38 kg m^-2, 1.48 kg m^-2, 0.69 kg m^-2), mean error (0.28 kg m^-2, -0.22 kg m^-2, 0.17 kg m^-2) but also high values of R² (0.76, 0.72, 0.94). The estimated SOC stock values ranged from 0.28-16.26 kg m^-2, 0.72–15.24 kg m^-2, 0.16–15.83 kg m^-2 using GWRK, GWR, RK approaches in the study area. The highest average SOC stock value was in the wetland (6.47 kg m^-2, 6.08 kg m^-2, 6.44 kg m^-2) and the lowest was in cropland (1.63 kg m^-2, 1.48 kg m^-2, 1.80 kg m^-2) using these approaches. According to the validation, GWRK, GWR, and RK approaches produced satisfactory results for estimating and mapping SOC stock. However, Regression Kriging was the best model, followed by GWRK and GWR to predict topsoil organic carbon stock in Tarialan.

How to cite: Manaljav, S. and Tserengunsen, P.: Geospatial modeling approaches for mapping topsoil organic carbon stock in northern part of Mongolia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-600, https://doi.org/10.5194/egusphere-egu2020-600, 2020.

Soil organic carbon (SOC) is an important carbon pool sensitive to land use change (LUC). There are concerns that at the end of PECs cultivation cycle, the re-conversion of these crops back to arable land could negatively impact the SOC stock. However, a positive effect of reconversion on SOC is possible, due to the high amount of C added to the soil with the disruption of belowground biomass (BGB) during re-conversion process. In this study, C storage potential in SOC and BGB of six perennial energy crops (PECs) was measured in a 11 years old field trial in Italy before its reconversion to arable land. SOC dynamics and greenhouse gases (GHGs) emission were measured in the first two years after the reconversion. SOC and GHG measurements were compared to ECOSSE soil carbon model predictions (run for a LUC from arable land to PECs and re-conversion to arable land) to understand SOC dynamics. After 11 years of cultivation, PECs significantly increased SOC stock respect to arable land. In average, BGB accounted for the 68% of total carbon stocked by PECs. The ECOSSE soil carbon model successfully simulated the dynamics of SOC pool and the GHGs emissions from soil after the re-conversion of PECs.

How to cite: Martani, E., Pilla, M., Ferrarini, A., Amaducci, S., and Hastings, A.: Simulation of soil organic carbon stock and greenhouse gases emission from Perennial Energy Crops cultivation cycle in Italy with ECOSSE model: from establishment to removal, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10846, https://doi.org/10.5194/egusphere-egu2020-10846, 2020.

Our understanding of soil carbon (C) dynamics is limited; field measurements necessarily conflate fluxes from plant and soil sources and we therefore lack long-term field-scale data on soil C fluxes to use to test and improve soil C models. Furthermore, it is often unclear whether findings from lab-based studies, such as the presence of rhizosphere priming, apply to soil systems in the field. It is particularly important that we are able to understand the roles of soil temperature and moisture, and plant C inputs, as drivers of soil C dynamics in order to predict how changing climate and plant productivity may affect the net C balance of soils. We have developed a field laboratory with which to generate much-needed long-term C flux data under field conditions, giving near-continuous measurements of plant and soil C fluxes and their drivers.

The laboratory contains 24 0.8-m diameter, 1-m deep, naturally-structured soil monoliths of two contrasting C3 soils (a clay-loam and a sandy soil) in lysimeters. These are sown with a C4 grass (Bouteloua dactyloides), providing a large difference in C isotope signature between C4 plant respiration and C3-origin soil organic matter (SOM) decomposition, which enables clear partitioning of the net C flux. This species is used as a pasture grass in the United States, and regular trimming through the growing season simulates low-intensity grazing. The soil monoliths are fitted with gas flux chambers and connected via an automated sampling loop to a cavity ring-down spectrometer, which measures the concentration and ¹²C:¹³C isotopic ratio of CO₂ during flux chamber closure. Depth-resolved measurements of soil temperature and moisture in each monolith are made near-continuously, along with measurements of incoming solar radiation, rainfall, and air temperature a the field site. The gas flux chambers are fitted with removable reflective backout covers allowing flux measurements both incorporating, and in the absence of, photosynthesis.

We have collected net ecosystem respiration data, measurements of photosynthesis, and recorded potential drivers of respiration over two growing seasons through 2018 and 2019. Through partitioning fluxes between plant respiration and SOM mineralisation we have revealed clear diurnal trends in both plant and soil C fluxes, along with overarching seasonal trends which modify both the magnitude of fluxes and their diurnal patterns. Rates of photosynthesis have been interpolated between measurement periods using machine learning to generate a predictive model, which has allowed us to investigate the effect of plant productivity on SOM mineralisation and assess whether rhizosphere priming can be detected in our system. Through regression analyses and linear mixed effects modelling we have evaluated the roles of soil temperature, soil moisture, and soil N content as drivers of variation in plant and soil respiration in our two contrasting soils. This has shown soil temperature to be the most important control on SOM mineralisation, with soil moisture content playing only a minor role. We have also used our empirical models to suggest how the carbon balance of pasture and grassland soils may respond to warming temperatures.

How to cite: McCloskey, C., Kirk, G., Otten, W., and Paterson, E.: Empirical modelling of plant and soil carbon flux drivers under field conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11334, https://doi.org/10.5194/egusphere-egu2020-11334, 2020.

In the last years, soil organic carbon (SOC) dynamics have been explored for agronomic and environmental issues in different agro systems. Many soils of the world, especially in arid and semi-arid environments, contain large stocks of soil inorganic carbon (SIC) as carbonates. Yet, the SOC dynamics has been poorly investigated in these soils, due to the complexity of measurements and of the processes involved. Indeed, few previous studies have shown links between SIC and SOC dynamics. Theses interactions are initiated by biological activities, i.e. CO₂ production, are explained through equilibrium equations between soil carbonates and bicarbonates. However, few data were available on the specific impact of SIC on SOC mineralization especially at increasing soil depth.

Alley agroforestry systems increased SOC content in the tree rows without any change in the SIC content.  The heterogeneity in organic inputs and SOC contents induced by alley agroforestry allows the investigation of the interactions between SIC and SOC on CO₂ emissions.

To assess contributions of SIC to CO₂ emissions with depth, we incubated carbonaceous soil samples coming from an 18-year-old agroforestry system (both tree row and alley) and an adjacent agricultural plot. Soil samples were taken at four different depths: 0-10, 10-30, 70-100 and 160-180 cm. Total CO₂ emissions, the isotopic composition (δ¹³C, ‰) of the CO₂ and microbial biomass were measured. The SIC concentrations were from 48 to 63 g C kg^-1 soil and the SOC concentrations from 4 to 17 g C kg^-1 soil. The total amounts of CO₂ emissions from soil were correlated to C contents and decreased with depth (from 183-569 µgC g^-1 soil in top soil vs 21-25 µgC g^-1 soil in subsoil).

The contribution of SIC-derived CO₂ was not homogenous along the soil profile. It represented about 20% in the topsoil and 60% in the subsoil of the total soil CO₂ emissions. As the SOC content and the microbial biomass, the SOC-derived CO₂ emissions were larger in the topsoil especially in the tree row compared to the alley and the agricultural plot. The SIC-derived CO₂ emissions were also larger in topsoil and in tree rows at 0-10 cm than in alleys or agricultural plots (71 µg C g^-1 soil vs 45-48 µg C g^-1 soil) or in the subsoil (13-15 µg C g^-1 soil), whereas the amount of SIC was similar in top and subsoil and in tree rows, alleys or agricultural soils. This indicate that CO₂ emissions from SIC were linked to the SOC content and its mineralization.  In addition, our results suggest that the measurement of soil respiration in calcareous soils could be overestimated if the isotopic signature of the CO₂ is not taken into account. It also advocates more in-depth studies on carbonate dissolution-precipitation processes and their impact on CO₂ emissions.

Reference:

Cardinael, R., Chevallier, T., Guenet, B., Girardin, C., Cozzi, T., Pouteau, V., and Chenu, C. 2019 Organic carbon decomposition rates with depth and contribution of inorganic carbon to CO2 emissions under a Mediterranean agroforestry system, Eur J Soil Sci, https://doi.org/10.1111/ejss.12908.

How to cite: Chevallier, T., Cardinael, R., Guenet, B., Cozzi, T., Girardin, C., and Chenu, C.: Contribution of inorganic carbon to CO2 emissions under a Mediterranean agroforestry system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10139, https://doi.org/10.5194/egusphere-egu2020-10139, 2020.

Soil organic matter has generated international interest in carbon and nitrogen sequestration. In reality, small fluctuations of soil organic stock could have large impacts on global warming. Therefore, quantification of Soil Organic Carbon (SOCs) and Total Nitrogen (TNs) stocks in surface and deep horizons are important to control the release of greenhouse gases. The present research was undertaken in order to determine SOCs and TNs evolution over 50 years. For this aim, we selected two soils (P1 and P2) developed under contrasted pedogenetic conditions in North-West of Tunisia (Beja governorate). P1 is a Luvisol located in a forest region. However, P2 is a Cambisol situated in an agriculture zone. Soil samples were gathered from surface (0-30 cm) and deep (50-100 cm) horizons in 1971, 2005, 2012 and 2019. SOCs declined in surface and deep horizons during the experimental period in both studied soils. In the case of Luvisol, the values declined from 91.01 t/ha to 75.54 t/ha and from 53.00 t/ha to 24.51 t/ha, respectively in surface horizons and deep horizons. Likewise, the SOCs values decreased from 84.24 t/ha to 25.52 t/ha in surface horizons and from 24.45 t/ha to 14.20 t/ha in deep horizons of the Cambisol. The TNs recorded lower values than SOCs. Nevertheless, they showed the same behavior. Our results showed that the highest values of SOCs and TNs were recorded in the Luvisol. This soil exhibited the greatest amount of organic matter since it was developed under forest vegetation. In addition, the results showed an enrichment in SOCs and TNs of superficial horizons to the detriment of the deep horizons. Nevertheless, this decrease in organic stocks with depth occurred following different patterns according to soil type. In fact, the Cambisol reported an important depletion of soil organic stocks as compared to the Luvisol. The loss of SOCs and TNs were estimated to be 69.71% and 54.17% in surface horizon, and 41.94 % and 28.28 % in deep horizon, respectively. Indeed, the land-use change increases the decomposition of soil organic matter principal source of SOCs and TNs. Such a reduction has wider implications on global warming and soil fertility.  

How to cite: Tlili, A., Dridi, I., and Gueddari, M.: Organic Carbon and Nitrogen stocks in two soil types of Northwestern Tunisia: Temporal and spatial variation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-810, https://doi.org/10.5194/egusphere-egu2020-810, 2020.

Since 1993, analysing the soil of any cropped field at least every ten years is required to receive subsides associated with ecological services in Switzerland. After data quality control, we used 3’000 repeated analyses available from the cantons of Vaud and Geneva to quantify the deficit in Soil Organic Carbon (SOC), the SOC content change rate per year and its time evolution along the past 25 years. We then interviewed 120 farmers on a sample representative of the overall range of SOC change rates to analyse the relationships between their practices in the past ten years and the resulting rate.

The SOC deficit was quantified based on the soil vulnerability index, namely SOC to clay ratio (Fell et al., 2018; Johannes et al., 2017), with the 10% SOC:clay ratio as minimum desired SOC level. This yielded different deficits ranging from 20% to 70 % of the average SOC content in the Swiss cantons depending on the cropping systems and the soil types. 

Though the SOC deficit was different between the cantons, the distribution of SOC change rates was very similar, ranging from -50‰ to +50‰ with a median value close to 0. The average change rate, however, was significantly and linearly changing with time, from -4‰ in the 1995-2000 period to 9‰ in the present. This pattern was identical on both cantons and can be related to the introduction of different mandatory measures in 1993-1998 such as cover crops in fall, and a minimum of 4 crops in the rotation, and the development of conservation agriculture practices.

The detailed analysis of cropping practices and related SOC change rates allowed revealing the major options allowing for rapid sequestration and conversely. Moreover, exceptions to the general trends, allowing either to compensate SOC losses practices or jeopardizing sequestration efforts, were also highlighted. Two performing cropping systems were emerging: polyculture with breeding and conservation agriculture. Farmers’ income per ha of these systems were equal to or larger than the conventional models. Interestingly, the first factor for high sequestration performance was diversified rotation and intensive cover crops, regardless of the manuring level. These results were used to define the agricultural sections of the climate plan of the cantons.

Fell, V., Matter, A., Keller, T., Boivin, P., 2018. Patterns and Factors of Soil Structure Recovery as Revealed From a Tillage and Cover-Crop Experiment in a Compacted Orchard. Front. Environ. Sci. 6. https://doi.org/10.3389/fenvs.2018.00134

Johannes, A., Matter, A., Schulin, R., Weisskopf, P., Baveye, P.C., Boivin, P., 2017. Optimal organic carbon values for soil structure quality of arable soils. Does clay content matter? Geoderma 302, 14–21. https://doi.org/10.1016/j.geoderma.2017.04.021

How to cite: Boivin, P., Dupla, X., Sauzet, O., and Gondret, K.: Organic carbon sequestration potential, rate and associated practices, as observed in Swiss arable land, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19490, https://doi.org/10.5194/egusphere-egu2020-19490, 2020.

Widespread shrub encroachment in global drylands may increase plant biomass and change soil organic carbon stocks of grassland ecosystems. However, the response of soil inorganic carbon (SIC), which is a major component of dryland carbon pools, to this vegetation shift remains unknown. Here, we conducted a systematic field survey in 75 pairs of shrub-encroached grassland and control plots at 25 sites in the grasslands of the Inner Mongolia Plateau to evaluate how shrub encroachment affects SIC density (SICD) in these ecosystems. We found that shrub encroachment significantly reduced SICD in the upper 100 cm, especially in the subsurface soil (20-50 cm layer). The magnitude of SICD changes was related to the change in soil pH, shrub patch size, and initial SICD, reflecting that the reduction in SICD might be attributed to the shrub encroachment-related soil acidification. Our results also revealed that the lost SIC was mainly released into the atmosphere rather than redistributed into deeper soil layers. Overall, we provide the first evidence for the soil acidification-induced SIC loss caused by shrub encroachment. Our findings highlight the non-negligible role of SIC dynamics in the C budget of shrub-encroached grassland ecosystems and the need to consider these dynamics in terrestrial C cycle research.

How to cite: Liu, S., Zhou, L., Li, H., Zhao, X., Zhu, Y., Shen, H., and Fang, J.: Shrub encroachment decreases soil inorganic carbon stocks in Mongolian grasslands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5304, https://doi.org/10.5194/egusphere-egu2020-5304, 2020.

The agricultural European Innovation Partnership (EIP-AGRI) Focus Group on Soil Organic Matter (SOM) content in Mediterranean regions highlighted the poor organic carbon (OC) content in the investigated soils, with some areas, especially in Southern Europe, showing low (≤2%) or even very low (≤1%) OC values. For this reason Emilia-Romagna Region (Northeastern Italy) invested heavily in the Rural Development Programme (RDP), which financed projects addressed to the needs of specific geographical areas. Among these, SaveSOC2 project (Save Soil Organic Carbon) aims to evaluate the quantity and quality of SOM in both conventional and organic farms from distinct pedo-climatic setting of Emilia-Romagna Region and with possible critical issues, in order to identify the best agricultural practices which could contribute to i) carbon conservation and sequestration in soil and ii) mitigation of SOM mineralization responsible for the greenhouses emissions. Here we report the data of the “Tassinari” organic farm located at Bondeno, near Ferrara city in Padania Plain, an area characterized by soil with very low amount of OC. In the selected organic farm, topsoil samples (0-15 cm and 15-30 cm depth) were collected from strawberry fields and orchards converted from conventional to organic production since 1992. The soils have loam and silt loam texture, they are subalkaline (pH: 7.9-8.7) and nonsaline (EC: 0.1-0.2 dS m^-1). To characterize the soil inorganic (SIC) and organic (SOC) carbon, for each sample, elemental and isotopic analyses were performed using the Thermally Based Separation protocol tested by Natali et al. (2018) with an EA-IRMS. As expected, the vertical distribution of carbon along each site showed a negative correlation between SIC and SOC contents, as IC slightly increase over depth while OC show a clear decline. Moreover, irrespectively of the sampling depth, the OC values (0.90-1.14 wt.%) are always lower than those of IC (1.04-2.50 wt.%). The relatively low negative δ¹³C values of the total carbon (from -12.1‰ to -9.0‰) reflect the predominance of SIC in the investigated topsoils. The low storage of organic matter in this area is also confirmed by the OC stock value in the topsoils, which is on average 42.6 Mg/ha. A Soli TOC Cube® was also used to discriminate the labile organic carbon (TOC₄₀₀) and the residual oxidizable carbon (ROC) fractions, which are oxidized at temperature below and above 400°C, respectively. In all the investigated topsoils, the TOC₄₀₀ values (0.60-0.84 wt.%) are higher than those of ROC (0.21-0.28 wt.%), indicating large amount of “fresh” organic matter, and low amount of residual organic carbon. The high relative presence of labile OC pools, probably due to the soil fertilisation with easy available organic compounds, can be critical for SOM sequestration, preventing the accumulation of stabilised organic compounds.

Natali C., Bianchini G., Vittori Antisari L. 2018. Thermal separation coupled with elemental and isotopic analysis: A method for soil carbon characterisation. Catena 164, 150-157.

How to cite: Brombin, V., Bianchini, G., Natali, C., Vittori Antisari, L., Falsone, G., De Feudis, M., Salani, G. M., Mistri, E., and Malavasi, F.: Carbon speciation and carbon isotopic characterization of agricultural soils in Emilia-Romagna Region (Northeastern Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7325, https://doi.org/10.5194/egusphere-egu2020-7325, 2020.

The exploitation of soils due to farming has produced a progressive loss of soil organic matter (SOM) over the years. At the same time, the degradation of SOM has led to a decline of several ecosystem services provided by soil, especially in mountain. Against this background, the partnership between Department of Physics and Earth Sciences of University of Ferrara and Department of Agricultural and Food Sciences of University of Bologna led to the creation of the SaveSOC2 project (Save Soil Organic Carbon), funded by Rural Development Programme of Emilia-Romagna Region. This project primarily seeks to investigate and promote carbon storage processes in agricultural soils of Emilia-Romagna Region (NE Italy). The present study outlines an overview about the SOM dynamics of “I Rodi” organic farm, located in the Modena Apennine. “I Rodi” produces and processes small organic fruits, especially raspberries. Three different sites (grassland -G, very low productive raspberries -LR, and good productive raspberries -GR) have been selected and the topsoils (0-15 cm and 15-30 cm) have been investigated. Elemental and isotopic analyses of soil C were performed using an EA-IRMS. In particular, the application of the Thermally Based Separation protocol [1] allowed the determination of both inorganic (IC) and organic (OC) carbon contents in each soil sample. OC accounted for 93.50% of the total carbon (1.72-4.84 wt.%). The negative δ¹³C values of the total carbon (from -27.8 to -19.7 ‰) confirmed the predominance of OC over IC in the investigated soils. The average values of OC isotopic C signature showed a decreasing trend among the three sites (-28.2, -27.2 and -25.8‰ for GR, G and LR, respectively), with the low productivity site having the highest δ¹³C value. The isotopic C signature of separated organic C fractions (0-15 cm topsoils) showed that humin (832-879 g/kg), which is the SOM fraction mostly interacting with the soil mineral phase and the largest pool, confirmed the observed trend (-27.5, -27.0, -26.4‰, GR, G and LR). The humic acids (6-17 g/kg) showed similar trend but lower δ¹³C values in all sites (-28.5, -28.0, -26.8 ‰, GR, G and LR). Finally, fulvic acids (5-10 g/kg) differed, having dissimilar trend and values of δ¹³C (-27.1, -26.8, -26.0 ‰ for G, GR and LR). Comparing to G, the GR data suggested that organic management i) did not decrease quantity and quality of organic matter, and ii) it was more efficient in OC stabilisation, increasing the amount of less transformed OC in both humin and humic acids (more negative δ¹³C values). In the LR site, instead, the observed trend can be due to low suitability of this soil to raspberries production, negatively affecting both crop yields and organic C dynamics. In our opinion, in order to combine agricultural productivity and its sustainability, more attention should be paid both to soil management and suitability in the area.

[1] Natali C., Bianchini G., Vittori Antisari L. 2018. Thermal separation coupled with elemental and isotopic analysis: A method for soil carbon characterisation. Catena 164, 150-157.

How to cite: Mistri, E., Bianchini, G., Natali, C., Vittori Antisari, L., Falsone, G., De Feudis, M., and Brombin, V.: Organic matter investigation in agricultural Apennine topsoils (Emilia-Romagna Region): carbon pools and isotopic C signature, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7646, https://doi.org/10.5194/egusphere-egu2020-7646, 2020.

Desertification is an important soil treat, affecting soil functions and ecosystem services   in arid and semiarid climate zones. Salinization is one of the principal processes which follows desertification and has a negative impact on soil properties and functions. Carbon sequestration is considered a principle soil function and the decline in soil carbon stocks in one of the main negative consequences of soil degradation. Soil salinization is caused by combination of natural factors (e.g. dry climate condition and high table of mineralized ground waters) and human activities such as improper water management. Globally, soils of the areas affected by salinization are considered to be poor in organic carbon due to low biomass and hampered microbiological activity. However, the contribution of inorganic carbon to the total carbon stocks in these areas can be comparable. Considering that soil inorganic carbon is more stable to mineralization compared to organic carbon, soil carbon stocks in saline landscape shall not be neglected.

Central Asian regions and especially the Aral Sea basin have been historically affected by desertification enhancing soil salinity. Hungry Steppe (Mirzachul) is an area of historical desertification and salinization, covering around 10000 km² at the territories of Uzbekistan, South Kazakhstan and Tajikistan. The region has a sharp continental climate with large seasonal fluctuations. Dry and semidesertic steppe vegetation dominates the natural areas (mainly coincided with high soil salinity), whereas most of the areas is managed to produce cotton, perennial grasses, melons and gourds. Soils are dominated by serozems corresponding to Calcisols in WRB soil classification. The research aimed to analyze the effect of salinization on carbon stocks in Hungry Steppe. To achieve this aim, soil carbon stocks were estimated at the four collective farms, referred as Water Consumer Assiociations (WCAs) or ‘shirkats’ in Syrdarya province: Khavast district in Yangier WCA, Mirzaobod district in Beruniy WCA  Oq Oltin district in Andijan WCA and Syrdarya district in Sobir  Rakhimov WCA. The selected sites belonged to different in land quality classes, based on the land evaluation survey carried out by the melioration expedition of the Ministry of Agriculture and Water Resources of Uzbekistan in 201,  from the lowest (Mirzaobod) to the highest (S. Rahimov). Soil pH, electroconductivity, chlorides, organic and inorganic carbon stocks and total nitrogen stocks were estimated for each of the areas. Although the internal variability in the analyzed parameters was high we clearly showed the highest stocks of soil inorganic carbon in the most salinized area, whereas the highest stocks of organic carbon were shown for the most fertile lands. However, we didn’t ding significant difference in the total carbon stocks between the sites. It can be concluded that desertification has more effect on the redistribution of organic and inorganic forms of carbon, rather than on the total carbon stocks.

Acknowledgements The experimental research was performed with the support of the Russian Foundation for Basic Research, Project # 18-54-41004 and Ministry of Innovation development of the Republic of Uzbekistan, Project # MRU-SQV 86/2017. Data analysis and mapping was supported by the RUDN project “5-100”.

How to cite: Demina, S., Vasenev, V., Ivashchenko, K., Brianskaia, I., Pulatov, B., and Pulatov, A.: Spatial variability of organic and inorganic carbon stocks in Hungry Steppe (Uzbekistan), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21454, https://doi.org/10.5194/egusphere-egu2020-21454, 2020.

In many semiarid Mediterranean soils, carbonates can constitute a significant proportion of the soil mass. Unlike other soil inorganic components, carbonates can react in the short term to changes in the soil water regime and the physical-chemical conditions of the soil solution. The introduction of irrigation can be associated to such changes, as it changes the water balance, the composition of the soil solution, and the concentration of CO₂ in the soil atmosphere.

To gain knowledge on the importance of the effect of irrigation on carbonates dynamics in the tilled layer of agricultural Mediterranean soils, we conducted a three-step study embracing field observations and numerical simulation.

In the first step, carbonates stocks and size-distribution were quantified for two different situations (irrigation and non-irrigation) in paired plots of three irrigation districts in Navarre (Spain). Our results, showed that although the net annual balance of total carbonates-C between irrigated and non-irrigated plots was neutral, carbonates concentration was lower with irrigation in the finest (< 50 μm) soil fractions (25.6 ± 2.6 carbonates 100 g⁻¹ without irrigation for 19.3 ± 2.1 with irrigation, on average).

In a second step, numerical simulations of the geochemical interactions between soil carbonates, the soil solution and irrigation water were run using actual soil characteristics and soil solution data from the tilled layer (0-30 cm) of two paired plots 9 years after irrigation started. A sensitivity analysis was also conducted to investigate the potential impact of water quality and crop types as sources of variability in the model outputs. The modelling results showed annual losses of carbonates-C in the range of 12.06-13.52 g m⁻² year⁻¹ in the studied depth under irrigation, depending on the quality of irrigation water, for 0.46 g m⁻² without irrigation.

Lastly, and because the acceleration of carbonate dissolution/precipitation cycles, together with the addition of calcium in fertilizers and irrigation water, can cause an increase in the formation of pedogenic carbonates, their proportion was estimated in paired plots from carbonates-C isotopic signatures: a preferential accumulation of pedogenic carbonates in the finest size fractions (87-92%) was observed with irrigation (61-74% without irrigation).

Future investigations

New field observations and numerical simulations will be done in an experimental plot in  which corn (Zea mays L.) has been grown since 2010 with and without irrigation. A numerical model will be developed to study the expected changes in the carbonate dissolution/precipitation cycles in semi-arid Mediterranean areas and these results will be compared with the concentration and characteristics of carbonates (size distribution and isotopic signature as an indicator of their geological or pedogenic origin) in the experimental plot.

Finally, the model will be validated at a regional scale, using a network of real representative agricultural plots in which there has been a change in land use from unirrigated to irrigated land in Navarre.

How to cite: De Soto, I. S., Virto, I., Enrique, A., Antón, R., and Barré, P.: Anthropogenic impact on inorganic soil C: Impact of Irrigated Agriculture on Carbonates Dynamics in Semiarid Land, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2775, https://doi.org/10.5194/egusphere-egu2020-2775, 2020.

The decline in organic carbon (OC) stocks after conversion from grassland to cropland under conventional soil tillage practices was 24-32% for American prairie soils. The respective decreases in OC stocks ranged from 27% to more than 40% for steppe soils of the European part of Russia and was about 31% in semi-arid steppe soils of South Siberia. Here, we present results on the soil OC stocks in steppe soils of Northern Kazakhstan, which partly were converted to arable land over the last 60 to 90 years. We sampled soils by genetic horizons along a north-south transect, where precipitation increased towards north but negligible variation in temperature. Soil samples were analyzed for organic and inorganic carbon as well as bulk density.

Surprisingly, we found along the transect on average only 3.5% smaller OC stocks at 0-10 cm depth in arable than in natural soils. Even more astonishing, all arable soils tested had larger OC stocks in the layers beneath 10 cm depth than the natural steppe soils. On average, the OC stocks in 10-100 cm depth were 34% larger in soils under arable management than in natural steppe soils. We credit the enhanced deep soil accumulation of OC in arable soils of Northern Kazakhstan to colloidal translocation of OC-rich particles along vertical pores. The cause of the increased in colloidal transport under arable management is still under evaluation but appears connected to the clayey soil texture and the large abundance of expandable clay minerals. We conclude that despite of the intense land use and severe climatic conditions accumulation of subsoil carbon is possible even after many decades of cultivation history. Our findings stress the importance of considering whole soil profiles for analyzing the consequences of land use change on the net carbon balance of soils.

How to cite: Prays, A., Banze, S., Jalowy, F., Kaiser, K., and Mikutta, R.: Deep soil accumulation of organic carbon under cultivated Kazakh Steppe soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1514, https://doi.org/10.5194/egusphere-egu2020-1514, 2020.

Mid-Infrared Reflectance Spectroscopy (MIRS, 4000–400 cm^-1) is being considered to provide accurate estimations of soil properties, including soil organic carbon (SOC) and soil inorganic carbon (SIC) contents. This has mainly been demonstrated when datasets used to build, validate and test the prediction model originate from the same area A, with similar geopedological conditions. The objective of this study was to analyze how MIRS performed when used to predict SOC and SIC contents, from a calibration database collected over a region A, to predict over a region B, where A and B have no common area and different soil and climate conditions. This study used a French MIRS soil dataset including 2178 soil samples to calibrate SIC and SOC prediction models with partial least squares regression (PLSR), and a Tunisian MIRS soil dataset including 96 soil samples to test them. Our results showed that using the French MIRS soil database i) SOC and SIC of French samples were successfully predicted, ii) SIC of Tunisian samples was also predicted successfully, iii) local calibration significantly improved SOC prediction of Tunisian samples and iv) prediction models seemed more robust for SIC than for SOC. So in future, MIRS might replace, or at least be considered as, a conventional physico-chemical analysis technique, especially when as exhaustive as possible calibration database will become available.

How to cite: Chevallier, T., Gomez, C., Moulin, P., Bouferra, I., Hmaidi, K., Arrouays, D., Jolivet, C., and Barthès, B.: Prediction of soil organic and inorganic carbon concentrations in Tunisian samples by mid-infrared reflectance spectroscopy using a French national library, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13092, https://doi.org/10.5194/egusphere-egu2020-13092, 2020.

Studies on soil organic carbon (SOC) stocks mostly focus on topsoils (< 30 cm). However, 30 to 63% of the SOC are stored in the subsoils (30 to 100 cm), and the factors controlling SOC storage in subsoils may be substantially different than in topsoils. The low mean SOC content in subsoils makes its quantification and characterization challenging. Thus, new approaches are required to depict the SOC stocks distribution in full soil profile. Hyperspectral imaging of soil core samples can provide high spatial resolution of the vertical distribution of SOC in a soil profile. The main objective of the ongoing study, within the Horizon 2020 European Project Circular Agronomics, is to apply laboratory hyperspectral imaging with a variety of machine learning approaches for the mapping of OC distribution in undisturbed soil cores. Soil cores were collected down to a depth of one meter in grasslands of 15 organic farms located in the Lungau Valley, in Austria. Some samples were divided into five depths in the field for classical bulk soil measurements (total carbon and nitrogen, texture, pH, EC and bulk density) on disturbed samples. Undisturbed soil cores were sliced vertically for laboratory hyperspectral imaging in the range of Vis-NIR (400-1000 nm). We were able to reveal the hotspots of OC and map the OC distribution in soil profile by applying a variety of machine learning approaches (i.e. partial least square and random forest regression) as a function of spectral responses. A digital elevation model was further exploited to investigate the effects of topographical factors such as elevation, aspect and slope on SOC profile distribution. Landsat 8 data were also used to depict the spatial variability of land insensitive cover/vegetation in study area.

How to cite: Ostovari, Y., Köppendörfer, B., Guigue, J., Van Groenigen, J. W., Creamer, R., Guggenberger, T., Grassauer, F., Hobley, E., Ferron, L., Martens, H., Kögel-Knabner, I., and Vidal, A.: Hyperspectral imaging for high-resolution mapping of soil profile organic carbon distribution in an Austrian Alpine landscape , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1006, https://doi.org/10.5194/egusphere-egu2020-1006, 2020.

In field homogenous application of fertilizers can be considered as a non-environment friendly agricultural practice as it ignores site specific variations of soil and plant properties. Conventional fertilizing management usually results in overfertilization guiding to burdens of the environment in terms of chemical pollution in soil-water system and Greenhouse Gas (GHG) emissions in the atmosphere. The effects are expected to be more severe in Mediterranean region under the evolving climate change. Site-specific fertilizing management on the other hand, poses a practice that is adapted to high precision spatial soil, climatic and plant conditions. In this sense, the agricultural practices are properly adjusted to the needs of the crops. The research is focused on the assessment of the impacts of conventional and site-specific management of nitrogen fertilization to carbon and water footprint at cotton cultivation in field level. The study area concerns two cotton fields in Central Greece that were monitored with the use of classical soil analytical methods and remote sensing sensors throughout a cultivation period. The monitoring process led to the delineation of the fields in different management zones needing variable fertilizing doses. Further, all conventionally applied practices were annotated concerning the last 4-year period in order to collect historical fertilizing data. In both cases (conventional and site-specific) the carbon and water (blue, green, grey) footprints of the two fields were calculated. Carbon footprint was calculated by assessing IPCC 2006 guidelines (updated in 2019) as regards direct and LULUCF emissions. For this, Tier 2 emission factors were used for the main emission categories, as these were defined by the Greek State, while for the other categories, emission factors of Tier 1 of IPCC guidelines were used. For the determination of water footprint, local meteorological data and cotton development stages concerning Greek conditions were used. The determination of the footprints was realized with the use of a software tool developed by the BalkanROAD project in the framework of INTERREG Balkan-Mediterranean 2014-2020 programme, which addresses territorial competitiveness and environment. Preliminary results show encouraging prospective for the improvement of carbon and water footprint when shifting from conventional to site-specific management.

How to cite: Papadopoulos, A., Troyanos, G., Kalivas, D., Doula, M., Kavasilis, S., Zagklis, G., and Kolovos, C.: Impact of site-specific fertilizing management in carbon and water footprint. The case of cotton under Mediterranean conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13668, https://doi.org/10.5194/egusphere-egu2020-13668, 2020.

Post agricultural development of traditionally intensively cultivated high fertility soils is a relevant question in surroundings of towns affected by urban sprawl, where extent areas of former cultivated soils are converted into residential, industrial or infrastructural surfaces. Part of these areas will covered by artificially sealed soils, but always extent areas remain for green areas, managed with different intensity, which allows recharge of soil organic carbon stocks and soil regeneration processes. In our study agricultural and post agricultural soils were sampled in a Chernozemic landscape affected by urbanization processes. Besides of other regeneration processes, concerning to the improvement of soil structure, we found that soil organic carbon stocks in the 0-30 cm soil layer are significantly higher in post agricultural soils (9.4±0.5 kg·m^-2) as in ploughed (6.4±0.8 kg·m^-2) or in ploughed plus irrigated (5.6±0.7 kg·m^-2) profiles. The difference was found to be significant not only until the depth of the cultivated layer (30 cm), but until the sampled 70 cm depth throughout (17.8±0.9; 10.8±3.3 and 10.6±2.7 kg·m^-2 respectively). Our results point on the high carbon recovery potential of suburban areas converted from fertile cultivated soils.

How to cite: Novák, T. J., Márta, L., and Balogh, S.: Soil organic carbon stock development in chernozemic soils following agricultural abandonment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15424, https://doi.org/10.5194/egusphere-egu2020-15424, 2020.

The decline in soil organic carbon (SOC) is generally perceived as a major threat to the sustainability of the soil due to its key role in many productive and non - productive soil functions. The aim of this research is to assess the intensity of changes and the spatial variability of SOC and soil depth in the last 60 years. Estimation of spatial variability of soil properties was performed by using digital soil mapping. A study area is located in the chernozems area in south Moravia (Czechia). This region is traditionally intensively cultivated with the strong impact of water and tillage erosion. The study is based on the analysis of historical data that comes from the Large-scale mapping of Agricultural Soils in Czechoslovakia soil database. Our dataset contained data from 120 soil profiles. A new field investigation shows significant SOC losses on steep slopes and slope shoulders with a decrease of depth of the humic horizon. As a result, there is a gradual transformation of soil units from the former Calcic Chernosems into the Haplic Calcisols. These findings are the result of ongoing environmental changes with the strong impact of historical agricultural policy and inappropriate interference in the landscape.

How to cite: Juřicová, A., Chuman, T., and Žížala, D.: Changes in soil properties on agricultural land with the impact of water and tillage erosion in the last 60 years, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16855, https://doi.org/10.5194/egusphere-egu2020-16855, 2020.

Mediterranean areas are vulnerable and at high risk of desertification, although harboring high fractions of the global biodiversity. Resilience of these (agro)ecosystem strongly relies on soil preservation, and thus the reduction of both the sediment and soil organic carbon (SOC) losses. However, SOC dynamic is understudied in the Mediterranean areas, especially in the arid and semiarid regions [1].

Here we are summarizing the known and unknown of the SOC modelling in a highly variable Mediterranean area, namely Sicily (southern Italy). In addition, we highlight main research needs to increase the reliability of the estimation of the SOC change in time.

A total of 6674 soil samples were taken in various sampling campaigns from the 1993 to the 2008 from various depths (of which only 20% with soil bulk density [SBD] information) from both agricultural and forest lands on a 25,711-km² area [2]. Such database was used for SOC modelling through various procedures including classification and regression trees (CARTs) and Least Absolute Shrinkage and Selection Operator (LASSO) [3-5].

Modelling SOC stock estimated with an already developed pedotransfer (R² = 0,3) function for SBD consisted in a high uncertainty, with a ratio between the model mean absolute error and the modelled 90^th percentile higher than 26.9%, suggesting that SBD information or its reliable prediction is a prerequisite for SOC stock modelling in these areas, especially in agricultural land. In addition, taking into account the sampling campaign almost doubled the r squared of the CART models, which on average outcompeted the kriging and LASSO methods for the prediction certainty.

When modelling the time-variation of the SOC concentration through the use of non-paired samples [5], the closer of which was few km apart, a mean SOC variation was highlighted, and the model yielded high pseudo-R² (0.63–0.69) and low uncertainty (s.d. < 0.76 g C kg⁻¹). However, these s.d. can be used only to highlight strong variations at a relatively low resolution (i.e. 1-km), especially if data are not collected with the same sampling scheme. The variation found in the aforementioned work [5] likely depended on a change of both the sampling scheme and land use rather than an accumulation or loss of SOC in a given land use.

Thus, measuring SOC concentration and SBD in time-paired sites appears as a prerequisite to detect a SOC change in a given land use, especially if taking into account that the most important SOC predictors throughout the experiments were rainfall and temperatures and climate change is likely to differentially affect each site. To overcome such a lack, a time paired-sampling was performed in 2017 in 30 sites in the arable land, providing evidence that the increases estimated from the 1993 to 2008 were not evident when resampling the 10% of the 1993’s sites in field with continuous arable land use.

Reference: [1] Schillaci et al. DOI: 10.3301/ROL.2018.68; [2] Schillaci et al. DOI: 10.1016/j.catena.2018.12.015; [3] Veronesi and Schillaci DOI: 10.1016/j.ecolind.2019.02.026; [4] Lombardo et al. DOI: 10.1016/j.geoderma.2017.12.011; [5] Schillaci et al. DOI: 10.1016/j.scitotenv.2017.05.239

How to cite: Saia, S., Schillaci, C., Lipani, A., Perego, A., and Acutis, M.: Achievements and challenges of the modelling of soil organic carbon in a highly variable Mediterranean area, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18914, https://doi.org/10.5194/egusphere-egu2020-18914, 2020.

Soils in the dry tropical croplands of south India are inherently low in soil carbon (C) stock, and it is essential to accumulate the soil C for sustainable soil management. Biochar is generally considered to be a useful material that enhance the soil C stock, though its real effect on soil C dynamics is still unclear especially in the dry tropical croplands such as south India. Thus, our objective was to evaluate the effect of biochar application on soil C dynamics for optimal soil management in south India. Field experiment was conducted in Tamil Nadu state (Inceptisols) from Sep. 2017 to Apr. 2019 (1.5 years), which include two times sorghum cultivation (each 4 months) with six treatment plots (control (C), biochar (B) (8.2 Mg C ha^-1), farmyard manure (FYM) (F) (1.1 Mg C ha^-1), chemical fertilizer (CF) (100 kg N; 40 kg P ha^-1), biochar and FYM (B+F), and biochar and chemical fertilizer (B+CF)). We applied biochar once at the beginning of the experiment to evaluate the effective duration of biochar in soil after application, while we applied FYM every year before crop cultivation. We periodically measured the CO₂ efflux rate (29 times totally) with continuous environmental data including soil moisture (0-15 cm) and soil temperature (5 cm), and estimated the total CO₂ flux as C output, based on the relationship between the CO₂ efflux rate and environmental data. We found that the CO₂ efflux rate in the B+F plot tended to be lower than the F plot throughout the experimental period, though the significant difference between the B+F plot and F plot was only in the cultivation period of the 1^st year, in case of using the analysis of variance for each cultivation period separately. We found that cumulative CO₂ flux in the B+F plot (2.2 Mg C ha^-1 1.5 year^-1) was also lower than the F plot (2.5 Mg C ha^-1 1.5 year^-1), and that biochar and FYM application decreased ca. 0.3 Mg C ha^-1 1.5 year^-1 decomposition compared to the application of FYM alone. This might be because combined application of biochar and FYM decreased the soil microbial activity, resulting in the lower FYM decomposition in the B+F plot. Our results indicate that biochar combined with FYM application would effective for soil C sequestration, and hence for sustainable soil management in the dry tropical cropland.

How to cite: Seki, M., Sugihara, S., Miyazaki, H., Jegadeesan, M., Kannan, P., and Tanaka, H.: Biochar combined with manure application can decrease organic matter decomposition compared to manure alone in the dry tropical cropland of south India, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17848, https://doi.org/10.5194/egusphere-egu2020-17848, 2020.

Conservation agriculture (CA) involves complex and interactive processes that ultimately determine soil C storage, making it difficult to identify clear patterns, particularly, when the results originate from many experimental studies. To solve these problems, we used the ARMOSA process-based crop model to simulate the contribution of different CA components (minimum soil disturbance, permanent soil cover with crop residues and/or cover crops, and diversification of plant species) to soil organic carbon (SOC) sequestration at 0-30 cm soil depth and to compare it with SOC evolution under conventional agricultural practices. We simulated SOC changes in two sites located in Central Asia (Almalybak, Kazakhstan) and Southern Europe (Lombriasco, Italy), which have contrasting soils, organic carbon contents, climates, crops and management intensity.  Simulations were carried out for the current (1998-2017) and future climatic scenarios (period 2020-2040, scenario Representative Concentration Pathway 6.0).

Five cropping systems were simulated: conventional systems under ploughing at 25-30 cm with monoculture and  residues removed (Conv–R) or residues retained (Conv+R); no-tillage (NT) with residue retained and crop monocultures; CA and CA with a cover crop, Italian ryegrass (CA+CC). In Conv–R, Conv+R and NT, the simulated monocultures were spring barley in Almalybak and maize in Lombriasco. In CA and CA+CC, crop rotations were winter wheat - winter wheat - spring barley - chickpea in Almalybak; maize - winter wheat - soybean in Lombriasco, together with Italian ryegrass in the +CC options.

In Lombriasco, conventional systems led to SOC decline of 170-350 kg ha^-1 yr^-1, whereas, NT and CA prevented the decline and kept it on the slightly positive level under both climate scenarios. A low rate of SOC increase most likely stems from, in addition to climates, the low silt-clay fraction (34%), and thus, more vulnerable to mineralization and decay.

In Almalybak, SOC loss in conventional systems was 480-560 kg ha^-1 yr^-1 under current climate, and NT prevented the loss only under current climate, but not under the future climate scenario. In contrast, CA allowed for the annual C sequestration of 300 kg ha^-1 and up to 620 kg ha^-1 with cover crops. Under the future climate scenario, the model predicted somewhat less C sequestration under CA, probably, due to the reduction of residue biomass. Particularly, in Southern Kazakhstan, CA has the largest potential for C sequestration under both climate scenarios, twice exceeding the objectives of the “4 per 1000” initiative. This initiative claims that an annual growth rate of 0.4% in the soil carbon stocks, or 4‰ per year, in the first 30-40 cm of soil, would significantly reduce the CO₂ concentration in the atmosphere related to human activities.

How to cite: Acutis, M., Valkama, E., Kunypiyaeva, G., Karabayev, M., Zhapayev, R., Zhusupbekov, E., Perego, A., Schillaci, C., Sacco, D., Moretti, B., and Grignani, C.: SOC modelling and cropping system managements in contrasting climatic conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9404, https://doi.org/10.5194/egusphere-egu2020-9404, 2020.

We explored the effects of conversion from vineyard to tree plantation on humus forms, soil organic carbon (SOC) stocks and other soil properties by sampling paired plots in a hilly area of Monferrato (Piedmont, Italy).

The study area is located at Rosignano Monferrato (AL) and includes a vineyard (VY) and a nearby 30-years-old tree plantation (TP) for wood production that replaced an existing vineyard, where eight poplar clones were consociated with other timber species (wild cherry, European ash, manna ash, deodar cedar). The area under study covers 3 ha and extends along a slighty-wavy slope with an average gradient of 15%; according to the WRB classification, soils are Calcaric Cambisols (Loamic).

The impact of land use change on soil properties was evaluated considering the spatial variability of soil characteristics, testing for autocorrelation among the model residuals. Soil sampling was performed from 3 layers (0-10 cm, 10-40 cm and 40-70 cm) at 61 and 69 points in the VY and the TP respectively, to characterize soil pH in water, organic carbon content and SOC stock, C:N ratio, soil texture and total carbonates. The common pedological origin of soils within the study area was verified and confirmed by comparability of soil texture and carbonates content of the deeper layer.

At TP the humus forms were described and classified; the organic horizons were sampled and analyzed for OC content determination.

Statistical analyses showed significant (p-value < 0.05) differences for all the investigated layers between the considered land uses with regard to pH, SOC stock and C:N ratio.

Our study provided evidence that: (1) the conversion from vineyard to tree plantation resulted in the appearance of organic horizons: the main humus forms in TP were Mull and Amphi; (2) 30 years of tree plantation strongly modified SOC stock, resulting in an increase of 26% in the first 70 cm, which became 42% if the organic layers were included; (2) soil acidification (pH difference of 0.4) and change in SOC type (C:N increase of 1) were also observed in TP compared to VY; and (3) the spatial distribution of soil properties in the VY were affected by erosive and depositional dynamics unlike the TP where vegetation counterbalance erosion.

How to cite: Ferré, C., Facciotto, G., Bergante, S., and Comolli, R.: Effects of conversion from vineyard to tree plantation on humus forms, soil organic carbon stock and other soil properties, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4644, https://doi.org/10.5194/egusphere-egu2020-4644, 2020.

Planting trees is suggested as a cheap measure to capture CO₂, but might conflict with agricultural land use. Changing pasture and cropland into agroforestry systems like nut orchards might increase carbon (C) sequestration, without encroaching on agricultural land use. C-sequestration can act as a climate engineering measure to mitigate increasing CO₂ emissions to the atmosphere. The general discourse is that agroforestry systems can sequester more carbon than cropland or pastures. Data on the impact of land use change from agriculture to agroforestry systems like nut orchards in the temperate climate zone are scarce.

In this study we analysed C-sequestration dynamics in above and below soil stocks and fluxes, from the perspective of global climate mitigation. Field measurements and lab results on chronosequences from pasture and cropland to stands of Corylus and Juglans trees have been combined with modelling future pathways at the level of parcels. The object of study was a temperate nut orchard located on sandy soils in the Netherlands (Province Gelderland).

Data on C stocks and fluxes have been collected in four methods: (1) field sampling analysed in a laboratory, (2) field survey, (3) collecting historic agricultural management data by interviewing and document analysis, and (4) analysing data by literature review. Focus was on C-stock data analysis and additional analysis of the C-budget change over years (chronosequence).

Results show different patterns (all data related to sequestration in reference plots):

C-sequestration in soil organic carbon (based on field samples, 0-60cm depth) ranges from -0.1 to 2.2 Mg C ha^-1yr^-1.

C-sequestration in Corylus trees (based on field data and allometric equations) ranges from 0.5 to 1.2 Mg C ha^-1yr^-1.

C-sequestration in Juglans trees (based on field data and allometric equations) ranges from 0.3 to 0.7 Mg C ha^-1yr^-1.

C-sequestration in below ground biomass (based on allometric equations) ranges from 0.06 to 0.4 Mg C ha^-1yr^-1.

The parameterized allometric equations show a large increase in C-sequestration, ranging from 0.9 to 3.5 Mg ha^-1yr^-1. Compared to grassland and cropland estimates this is 10 times higher, meaning a potential useful contribution to the mitigation of CO₂ emissions. Further we observed an increase in quality of soil organic carbon, due to a shift to higher C/OM and C/N levels, lower annual OM breakdown and larger amounts of observed earthworms.

How to cite: Roest, E., Lansu, A., Baltissen, T., and Dekker, S. C.: From Pasture and Cropland to Nut Orchards: Modelling the Dynamics of Carbon Sequestration by Agroforestry Systems in the Temperate Climate Zone., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11195, https://doi.org/10.5194/egusphere-egu2020-11195, 2020.

Reducing carbon footprint has increasingly become an important topic regarding the management of industries and universities from different fields. Newcastle University promised to achieve the goal of net-zero carbon dioxide emissions by 2040, and the first process from this ambitious target is to produce a 43% reduction by July 2020, against a 2005/06 baseline. According to the report from Carbon Management Plan 2019 of Newcastle University, there are still 1,720 tons of carbon that should be reduced or offset during this year.

Two farms were investigated in this project: Nafferton Farm (NF) and Cockle Park Farm (CP) . Soil sampling was conducted within each field at three depth increment (0-30 cm, 30-60 cm and 30-90 cm) separately. Except for soil analysis, this study also chooses some plots in the woodlands around two farms to estimate the carbon storage by various vegetation species, and these two sections will offer comprehensive information about the quality and quantity of carbon in two farms.

On average, the percentage of total carbon (TC) from all soil profiles was higher under woodland than crop fields in CP. Because the hectare of crop fields is greater than woodland, the sum of total carbon in individual soil layers from the areas is comparatively larger in crop lands, where C stock is 14,122 tons, 6,017 tons, 5,437 tons for the 0-30 cm layers, 30-60 cm layers and 60-90 cm layers, respectively. Meanwhile, the data is 1, 905 tons, 822 tons, and 648 tons for three soil depth layers in the woodland of CP. In Nafferton Farm, the value of TC from the corresponding soil layers is 17,841 tons, 6,844 tons, 6,177 tons separately.

The results attained so far represent that TC and soil organic carbon (SOC)  in each farm are all statistically significantly different (p< 0.001) with respect to soil depth, but differences were not significant with respect to crop and tree species grown in a single area. Moreover, TC in surface soil of NF is statistically higher (p< 0.01) than that in CP. In Cockle Park Farm, C contents from woodland were considerably higher than those in crop fields (p< 0.001) and the difference of TC and SOC at individual depth layer cannot be ignored. Gross carbon sequestration of plants in woodland is 150.64 tons’ annually, which was calculated by i-Tree Ecosystem Analysis. Simultaneously, the total carbon of trees, including leaf biomass and tree trunks, is in a range of 3,198- 4,096 tons in the woodland of CP. Consequently, the current quality of carbon in topsoil from the whole fields of two farms and the woodland of CP is 35,610 tons which is over four times as high as the estimated carbon emission produced by University in 2019/20 ( 8, 181 tons).

Overall, it is recommended that the management team of university should attach importance to the operation of two farms. The expectation of mitigating 1,720 ton’s carbon in the short term can be fulfilled if the management department considers converting 58.79 ha crop fields to mixed-species woodland.

How to cite: Wang, J., Werner, D., and Manning, D.: Investigation of the carbon sequestration potential of soils and woodlands at university farms, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19866, https://doi.org/10.5194/egusphere-egu2020-19866, 2020.

Grasslands are one of the major sinks of terrestrial soil organic carbon (SOC). Understanding how environmental and management factors drive SOC is challenging because there are scale-dependent effects, and large scale drivers affecting SOC both directly and through drivers working at fine spatial scales. Here we address how regional and landscape factors, and grazing management, soil properties and nutrients, and herbage quality factors affect SOC in mountain grasslands in the Pyrenees. Taking advantage of the high variety of environmental heterogeneity in the Pyrenees, we fitted a set of models with explicative purposes including variables that comprise a wide range of environmental and management conditions. We found that temperature seasonality (MMT) was the most important abiotic driver of SOC in our study. MMT was positively related to SOC but only under certain conditions: exposed hillsides, steep slopes and relatively highly grazed areas. High MMT conditions probably are more favourable for plant biomass production, but landscape and grazing management factors buffer the conversion of this biomass into SOC. Concerning biochemical SOC predictors, we obtained some unexpected interaction effects between grazer type, soil nutrients and herbage quality. Soil N was a crucial factor modulated by effects of livestock species and neutral-detergent fibre content of vegetation. Herbage recalcitrance effects varied depending on grazer species. These results highlight the need to expand knowledge about grassland SOC drivers under different environmental and management conditions.

How to cite: Rodríguez, A., Canals, R. M., Plaixats, J., Albanell, E., Debouk, H., García-Pausas, J., San Emeterio, L., Jiménez, J. J., and Sebastià, M.-T.: Interacting abiotic, biochemical and management factors explain soil organic carbon in Pyrenean grasslands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19993, https://doi.org/10.5194/egusphere-egu2020-19993, 2020.