Sustainable soil management and climate change mitigation

Abstract

Sustainable soil management renders multifaceted benefits to meeting the United Nations Sustainable Development Goals (FAO, 2018; Hou et al., 2020; Keesstra et al., 2016). Its implications for climate change mitigation has been drawing particular interest in recent years (FAO, 2017; Poulton et al., 2018). On the one hand, soil represents the largest carbon pool in the Earth's terrestrial system, accounting for nearly five times that of the atmospheric carbon pool (Jansson & Hofmockel, 2020; Le Quere et al., 2018); on the other hand, N2O, CH4 and CO2 emissions from soils all represent significant fluxes that affect greenhouse gas balance in the atmosphere (Lal, 2019; Tian et al., 2019; Zhu et al., 2018). Soil micro-organisms play a critical role in the cycling of soil organic carbon (SOC), but we still lack sufficient scientific knowledge to build quantitative predictive models in the context of soil use and management (Cavicchioli et al., 2019; Jansson & Hofmockel, 2020). There is an urgent need to better understand how soil use and management affect climate change, due to both carbon sequestration and greenhouse gas emissions. Climate change also has a significant effect on soil carbon balance (Davidson & Janssens, 2006). On a global scale, rising temperatures have resulted in the higher heterotrophic respiration of SOC and thus CO2 emissions; however, this is partly due to increased plant growth and autotrophic fixation (Jansson & Hofmockel, 2020). Due to the complex feedback loops involved in these processes, the effect of climate change on the net flux of greenhouse gas emissions still remains unknown (Bradford et al., 2016; Davidson & Janssens, 2006). To better understand these interactive dynamics, it is imperative to have more field monitoring data and an in-depth examination of data from different sources. Given the interest among soil scientists, as well as great potential societal impacts, our editorial team at the journal of Soil Use and Management is commissioning a virtual special issue (VSI) with the topic of 'Soil and Climate Change Mitigation' (https://onlinelibrary.wiley.com/doi/toc/10.1111/(ISSN)1475-2743.soil-and-climate-change-mitigation). So far we have collected 22 papers, covering topics including (a) soil and greenhouse gas (N2O, CH4, CO2) emissions, (b) soil and carbon sequestration and (c) monitoring strategies. We intend to keep updating this VSI and continually collect high-quality research papers pertaining to climate change mitigation with sustainable soil management. Nitrogen input is essential for maintaining soil fertility and increasing crop yield (Campbell, 1978). However, nitrogen not taken up by crop roots can be converted to nitrous oxide (N2O), a greenhouse gas emission that renders 298 times the warming potential of CO2 (Jansson & Hofmockel, 2020). Inorganic N fertilizer is of particular concern in comparison with organic fertilizers. A recent study showed that inorganic N fertilizer tends to render a higher N2O emission intensity even when applied at half the N application rate as organic N fertilizer (Chirinda et al., 2021). Nitrous oxide emission factors may be region specific and vary under different climate conditions. Prolonged wet weather can increase N2O emissions due to enhanced anaerobic soil conditions (Chirinda et al., 2021). Hydrological gradient renders similar influences, e.g. in a grazed subtropical grassland, the N2O emission rates for isolated island, transient edge and pasture upland were 0.368, 0.178 and 0.003 N2O-N kg−1 dry soil h−1 respectively, representing two orders of magnitude variation (Hu et al., 2020). The N2O dynamic is affected by labile carbon content, as it can enhance anaerobic environment and thus increase N2O emissions. A study in northern Germany found that, when there was no extreme rainfall or freeze–thaw cycles, return of straw residue did not induce high N2O emissions; however, when glucose was added as a labile carbon source, N2O emissions increased by up to 32 times (Wang et al., 2020). N2O emissions are also affected by other site characteristics, such as soil mineralization–immobilization turnover and nitrification (Song et al., 2020), and clay content (Miller et al., 2020). From a climate mitigation perspective, it is imperative to reduce N2O emissions by lowering N input to soil, or fine tuning the N cycling process to completely oxidize ammonia to nitrate without producing N2O as a by-product (Jansson & Hofmockel, 2020). Researchers are developing a variety of strategies, for example urease inhibiting and coating technologies have been tried to reduce soil N2O emission, with varying levels of success (Ribeiro et al., 2020). Methane and carbon dioxide emissions from soil are also significant (Le Mer & Roger, 2001; Paustian et al., 2000). Methane and carbon dioxide emissions are enhanced under anaerobic and aerobic conditions, respectively. For CO2 emissions, peatland is of particular concern. Peat only covers 3% of the E