Agricultural SOC Stocks
Pan-European SOC stock of agricultural soils
The future EU policy in agriculture will utilized SOC as indicator, both as a main parameter of soil quality and as a strategy to offset CO2 emission by C sequestration. However a consistent picture of agricultural SOC stock is missing as well as tools to orient the future policymaker decisions. To fill this gap, the JRC developed a comprehensive modelling platform with comparable and harmonised European geographical and numerical datasets.
We estimated a current top SOC stock of 17.63 Gt in EU agricultural soils, by an unprecedented model application running about 164,000 combination of climate, soil and land use/management.
A comprehensive model platform was established at a pan-European scale (EU + Serbia, Bosnia and Herzegovina, Croatia, Montenegro, Albania, Former Yugoslav Republic of Macedonia and Norway) using the agro-ecosystem SOC model CENTURY. The model was implemented with the main management practices (e.g. irrigation, mineral and organic fertilization, tillage, etc.) derived from official statistics. The model results were tested against inventories from the European Environment and Observation Network (EIONET) and approximately 20,000 soil samples from the 2009 LUCAS survey, a monitoring project aiming at producing the first coherent, comprehensive and harmonized top-soil dataset of the EU based on harmonized sampling and analytical methods.
CENTURY is a process-based model designed to simulate C, Nitrogen (N), Phosphorous (P) and Sulphur (S) dynamics in natural or cultivated systems, using a monthly time step (Parton et al., 1988; Shaffer et al., 2001). The soil organic matter submodel includes two fresh residue pools (litter) and three SOC pools. Litter is subdivided in two pools (metabolic and structural) and SOC into three pools (active, slow and passive). The metabolic litter pool represents easily decomposable constituents of plant residues, while the structural litter pool is composed of more recalcitrant, lignocellulose plant materials. The three SOC pools represent a gradient in decomposability. CENTURY was selected as the most suitable model for a pan-European SOC assessment since: (i) crop growth routines are integrated for both herbaceous and trees crops (e.g. orchard, vineyard), including the possibility to simulate mixed systems; (ii) the model has been tested successfully in several European countries (Lugato et al., 2006, 2007; Alvaro-Fuentes et al., 2012a); (iii) the effect of the main management practices in the agricultural fields are simulated (tillage, grazing, irrigation, fertilization, etc.); (iv) the monthly time step reduces the computational time when dealing with a large number of combinations.
For this study, the model was run with the coupled C-N sub-models.
A detailed explanation of the methodology and the platform of simulation developed could be found in: Lugato E., Panagos P., Bampa, F., Jones A., Montanarella L. (2014). A new baseline of organic carbon stock in European agricultural soils using a modelling approach. Global change biology. 20 (1), pp. 313-326.
This work is part of the CAPRESE project (CArbon PREservation and SEquestration in agricultural soils), an administrative arrangement between the JRC and the Commission - DG AGRI undertaken to develop policies addressing climate change soil-related aspects in European agriculture.
Using soils to mitigate carbon emissions
JRC scientists find that making alternative uses of arable land could potentially help capture significant amounts of carbon from the atmosphere. They investigated the potential carbon sequestration of six of the most representative agricultural management practices on arable soils, and finded that the conversion of arable land to grassland results in the highest potential soil organic carbon (SOC) sequestration rates, whereas the conversion of grassland to arable land has the effect of strongly increasing the amount of carbon losses to the atmosphere.
The scientists have used a recently developed high resolution pan-European simulation platform to assess the potential impact of six management practices on SOC stock levels of arable soil under two IPCC climate change scenarios to 2100: arable to grassland conversion (and vice versa), straw incorporation, reduced tillage, straw incorporation with reduced tillage, ley cropping and cover crops. According to the results of three policy simulations carried out by the scientists, the allocation of just 12% of arable land to different combinations of agricultural management practices would produce significant mitigation effects, which would be sufficient to reach the EU's target of cutting its emissions to 20% below of the 1990 levels by 2020.
Using the CENTURY agroecosystem model, six alternative management practices (AMP) scenarios were assessed as alternatives to the business as usual situation (BAU). These consisted of the conversion of arable land to grassland (and vice versa), straw incorporation, reduced tillage, straw incorporation combined with reduced tillage, ley cropping system and cover crops. The conversion into grassland showed the highest soil organic carbon (SOC) sequestration rates, ranging between 0.4 and 0.8 t C ha-1 yr-1, while the opposite extreme scenario (100% of grassland conversion into arable) gave cumulated losses of up to 2 Gt of C by 2100. Among the other practices, ley cropping systems and cover crops gave better performances than straw incorporation and reduced tillage. The allocation of 12 to 28% of the European arable land to different AMP combinations
resulted in a potential SOC sequestration of 101–336 Mt CO2 eq. by 2020 and 549-2141 Mt CO2 eq. by 2100. Modelled carbon sequestration rates compared with values from an ad hoc meta-analysis confirmed the robustness of these estimates.
A detailed explanation of the methodology and the scenarios could be found in: Lugato E., Bampa F., Panagos P., Montanarella L. and Jones A. (2014). Potential carbon sequestration of European arable soils estimated by modelling a comprehensive set of management practices. Global Change Biology (2014), 20, 3557–3567, doi: 10.1111/gcb.12551.
Data are also available for download.
Quantifying the erosion effect on current carbon budget
The idea of offsetting anthropogenic CO2 emissions by increasing global soil organic carbon (SOC), as recently proposed by French authorities ahead of COP21 in the ‘four per mil’ initiative, is notable. However, a high uncertainty still exits on land C balance components. In particular, the role of erosion in the global C cycle is not totally disentangled, leading to disagreement whether this process induces lands to be a source or sink of CO2. To investigate this issue, we coupled soil erosion into a biogeochemistry model, running at 1 km2 resolution across the agricultural soils of the European Union (EU). Based on data-driven assumptions, the simulation took into account also soil deposition within grid cells and the potential C export to riverine systems, in a way to be conservative in a mass balance. We estimated that 143 of 187 Mha have C erosion rates <0.05 Mg C ha−1 yr−1, although some hot-spot areas showed eroded SOC >0.45 Mg C ha−1 yr−1. In comparison with a baseline without erosion, the model suggested an erosion-induced sink of atmospheric C consistent with previous empirical-based studies. Integrating all C fluxes for the EU agricultural soils, we estimated a net C loss or gain of −2.28 and +0.79 Tg yr−1 of CO2eq, respectively, depending on the value for the short-term enhancement of soil C mineralization due to soil disruption and displacement/transport with erosion. We concluded that erosion fluxes were in the same order of current carbon gains from improved management. Even if erosion could potentially induce a sink for atmospheric CO2, strong agricultural policies are needed to prevent or reduce soil erosion, in order to maintain soil health and productivity.
A detailed explanation of the methodology and the scenarios could be found in: Lugato, E., Paustian, K., Panagos, P., Jones, A., Borrelli, P., 2016. Quantifying the erosion effect on current carbon budget of European agricultural soils at high spatial resolution. Global Change Biology. doi: 10.1111/gcb.13198, in press
Data are also available for download.
You can obtain access to the following data by filling in the online form; after which you will receive further instructions how to download the data:
a) Pan-European SOC stock of agricultural soils,
b) Potential carbon sequestration by modelling a comprehensive set of management practices,
c) Average Eroded SOC in agricultural soils
Important Note: Further improved versions will be released in the next years.