Soil organic carbon dynamics from agricultural management practices under climate change

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.

Soil organic carbon and its' stock potential in different land-use types along slope position in Coka watershed, Southern Ethiopia

“…The finding is confirmed by [50]; SOCS observed in the topsoil (0-10 cm) was 60% of the total. As reported by [9] soils converted to cropland lost 13-18% of their SOC for the top layer of 20 cm. Similarly, the amount of SOC is approximately double (2x) the amount of C in atmospheric carbon dioxide (CO 2 ) and threefold that in aboveground vegetation globally in the 30 cm surface layer [51].…”

“…SOC improves soil properties by retaining a vital soil nutrient for the growth of plants and providing energy to the microbial community. It could be affected by various factors such as vegetation [7], altitude and climate [8], land-use-cover changes (LULC) [9], topographic factor [10], and loss of topsoil by erosion [11,12,13], and fire [14].…”

Management-induced changes in soil organic carbon on global croplands

“…Similarly, agricultural management data are held constant at the level of 1965 until 1965. We acknowledge that this introduces a bias, as agricultural management changed prior to 1965, but this approach follows others studies on the effects of land use change and management (e.g., Schaphoff et al, 2018a;Herzfeld et al, 2021) and is limited by the data availability on harvest statistics (and other management effects).…”

“…The effects of agricultural productivity on cropland SOC dynamics, including historical yield trends and associated increases in residue inputs, can be directly accounted for in our modeling approach. In contrast, process-based studies (Pugh et al, 2015;Herzfeld et al, 2021) often lack data on relevant management aspects that drive production increases. Herzfeld et al (2021) also consider historical management trends for fertilizer and manure inputs and on residue removal rates and tillage systems but cannot reproduce the substantial increase in agricultural productivity over the last few decades.…”

“…In global-scale carbon cycle assessments, management systems are typically represented as spatially explicit patterns that are static in time (e.g., for growing seasons in Portmann et al, 2010, multiple cropping systems in Waha et al, 2020, andirrigation systems in Jägermeyr et al, 2015) or as stylized (in the sense of uniform management assumptions) scenarios (e.g., Pugh et al, 2015;Lutz et al, 2019). Herzfeld et al (2021) account for historical changes in fertilizer and manure inputs, residue removal rates, and tillage systems and report SOC losses from cropland expansion over the period from 1700-2018 of 215 GtC. Within their stylized future management scenarios under future climate change, they find that none of the management aspects considered (residue management and no tillage) can create a positive SOC stock change on current cropland areas that counteracts the still-continuing legacy flux from the initial land use change.…”