Abstract
Abstract. Sequestration of soil organic carbon (SOC) on cropland has been proposed as a climate change mitigation strategy to reduce global greenhouse gas (GHG) concentrations in the atmosphere, which in particular is needed to achieve the targets proposed in the Paris Agreement to limit the increase in atmospheric temperature to well below 2 ∘C. We analyze the historical evolution and future development of cropland SOC using the global process-based biophysical model LPJmL, which was recently extended by a detailed representation of tillage practices and residue management (version 5.0-tillage2). We find that model results for historical global estimates for SOC stocks are at the upper end of available literature, with ∼2650 Pg C of SOC stored globally in the year 2018, ∼170 Pg C of which is stored in cropland soils. In future projections, assuming no further changes in current cropland patterns and under four different management assumptions with two different climate forcings, RCP2.6 and RCP8.5, results suggest that agricultural SOC stocks decline in all scenarios, as the decomposition of SOC outweighs the increase in carbon inputs into the soil from altered management practices. Different climate change scenarios, as well as assumptions on tillage management, play a minor role in explaining differences in SOC stocks. The choice of tillage practice explains between 0.2 % and 1.3 % of total cropland SOC stock change in the year 2100. Future dynamics in cropland SOC are most strongly controlled by residue management: whether residues are left on the field or harvested. We find that on current cropland, global cropland SOC stocks decline until the end of the century by only 1.0 % to 1.4 % if residue retention management systems are generally applied and by 26.7 % to 27.3 % in the case of residue harvest. For different climatic regions, increases in cropland SOC can only be found for tropical dry, warm temperate moist, and warm temperate dry regions in management systems that retain residues.
Highlights
To meet the targets of the Paris Agreement of 2015 to keep the increase in global mean temperature well below 2 ◦C, and especially for the ambitious target of below 1.5 ◦C, several negative emission technologies which remove carbon dioxide (CO2) from the atmosphere have been proposed (Minx et al, 2018; Rogelj et al, 2018, 2016)
Sequestration of soil organic carbon (SOC) on cropland has been proposed as a climate change mitigation strategy to reduce global greenhouse gas (GHG) concentrations in the atmosphere, which in particular is needed to achieve the targets proposed in the Paris Agreement to limit the increase in atmospheric temperature to well below 2 ◦C
Cropland net primary production (NPP) increases in the dynamic LU simulation (h_dLU) from 0.7 Pg C a−1 in 1700 to 4.7 Pg C a−1 in 2018, while cropland SOC increases from 18 Pg C to a total of 171 Pg C (Fig. 2a and c) in the year 2018
Summary
To meet the targets of the Paris Agreement of 2015 to keep the increase in global mean temperature well below 2 ◦C, and especially for the ambitious target of below 1.5 ◦C, several negative emission technologies which remove carbon dioxide (CO2) from the atmosphere have been proposed (Minx et al, 2018; Rogelj et al, 2018, 2016). Different agricultural management practices have been proposed as carbon (C) sequestration strategies to mitigate climate change and increase the quality and health of the soil by increasing soil organic carbon (SOC) content of cropland soils (Lal, 2004), which decreases the risk of soil erosion and soil degradation (Lal, 2009). While irrigated systems generally tend to have higher SOC stocks due to positive feedbacks on plant productivity, the feedbacks and mechanisms on SOC development are still not well understood (Humphrey et al, 2021; Emde et al, 2021). The effectiveness of irrigation systems for SOC development is influenced by climate and initial SOC stock, and it tends to be higher in semiarid regions and less effective in humid regions (Trost et al, 2013)
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