The effective ways of increasing agricultural productivity while minimising environmental impacts are debated, such as if biodiversity gains can be integrated into farming systems.
Overview of change
In 2020, the Natural Capital Committee stated that available data suggest the state of soils in the UK is declining and a national survey is needed on the extent and condition of soils.1 This would provide a baseline and data for the soil health target proposed under the Environment Bill 2020.2 Soil health has been described as “the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals, and humans”.3 Appropriate metrics and soil health measures continue to be debated due to the complexity of soils and their biodiversity.4,5 UK soils are estimated to currently store about 10 billion tonnes of carbon, with peatland soils containing the most. Soil carbon varies widely between soil types; an organic carbon value of 1.5% is considered a lower limit for arable soils with 40% clay, but would be considered high in soils that have less than 10% clay in England and Wales.6 Most arable soils have lost 40–60% of their organic carbon, 2 million hectares of soil are at risk of erosion and 4 million hectares at risk of compaction.7 Without national monitoring of soil organic carbon, structure and biodiversity, it will be difficult to assess the status of the range of benefits supporting human well-being provided by soil. These include growing food, carbon storage, water quality and reducing flood risk. Good stewardship of soils could increase the provision of these benefits.8,9 Increased frequency of climate extremes, such as droughts, represent a significant future threat to soils and the benefits they provide.10
Challenges and opportunities
Erosion is the process by which top-soil is carried away by wind and water, which is accelerated by activities such as removal of vegetative cover, ploughing down sloping fields and overgrazing. Erosion is directly linked to the loss of soil carbon, which may have been stable for millennia.11,12,13 A global survey found farmed soils to be losing more material to erosion than they are gaining.14,15 Modelling suggests there will be an increase in surface water run-off, from greater winter rainfall and more intense rainfall events from climate change, if soil conservation measures, such as cover crops and no till agriculture (not ploughing between crops), are not adopted.16 However, the effectiveness of no till agriculture depends on soil type and weather. No till agriculture may be beneficial for improving soil structure and some benefits that arise from the soil but it may reduce others,17 such as agricultural productivity.4,8,18 Not all farmers will adopt measures in the absence of incentives,19 such as payments for carbon storage.
Poor soil management can damage soil structure, which is not improved by shallow rooted crops that rely on fertilisers.20 Deep rooted crops and higher biodiversity grassland can increase fine roots, which bind soils and improve soil structure, as can crop diversification.21,22 Promoting a soil microbiome for higher plant productivity requires management of microbial and plant communities, and the processes they support.23,24 For example, adding nitrogen to soil over long time periods changes plant and microbe interactions decreasing diversity.25 Grassland plant communities shift towards fast-growing species with thinner larger leaves that rot faster.26 By contrast, relatively low nitrogen levels limit microbes’ ability to metabolise carbon compounds, so they excrete them as polymers that create an extensive network of pores for greater circulation of air, nutrients and retention of water.27 The ratio of carbon to nitrogen is also influenced by other additions to soil; for example, anaerobic digestion, an important source of carbon returned to land waste, is higher in nitrogen and lower in carbon raising concerns.28 Herbicides can also be used by soil microbes as carbon and/or nitrogen sources; their degradation can be enhanced through additions such as organic matter.29 Research on plant and soil microbe interactions also suggest additions, such as amino acids, may promote beneficial bacteria on plant roots.30
Soils and plant communities could be managed to maintain carbon storage and to be more resilient to climate change.31,32,33 For example, an assessment of 31 peatlands across England and Europe found that more peatlands became drier during the past 200 years than the previous 600 years and may become carbon emission sources without restoration and better management.34,35
With climate change, temperate soils are forecast to experience a high degree of variability in moisture conditions due to periods of drought, flood and intense rainfall events. Increased wetting and drying sequences will lead to higher turnover of soil carbon by microbes, increased greenhouse gas emissions, and changes in soil microbial communities and the processes they support.36,37,38 Similarly, tropical soils may release more greenhouse gases as they become warmer,39 and areas in Russia and Canada may become suitable for cultivation that releases carbon.40 But uncertainties remain in the global soil carbon response to climate change.41
Restoring lost carbon through conventional approaches may take decades; research suggests faster restoration approaches, such as applying biochar, result in very variable soil responses.42,43,44,45,46,47 Novel approaches have also been suggested for improving soils, such as super moisture-absorbent gels or gene-edited bacteria, could be used to improve the water content or fertility of dryland soils.48,49.
Soil hydraulic properties determine the fraction of rainfall that infiltrates versus runs off and have been assumed to remain constant, but research shows increased precipitation may reduce infiltration rates.50 Climate change may also indirectly impact soil erosion through the use of different crops.51
Key questions for Parliament
- What are the appropriate baselines and data needed for assessing the state of soil health nationally;1,4 such as a suite of soil ecological indicators based on essential biodiversity variables linked to targets?5
- What are the appropriate frameworks and incentives for increasing stable carbon in soils, such as peatland restoration,52 and managing microbial communities and cropping systems for soil health?53
- How to manage soils for mitigating and adapting to climate change and to sustain other benefits.54
Likelihood and impact
Continuing degradation of soil is likely globally with high impact,55 but managing soil carbon could also form part of net zero plans.
- Natural Capital Committee. (2020). Final Response to the 25 Year Environment Plan Progress Report
- UK Government. (2020). Environment Bill – environmental targets. Part B: an overview of the scope of targets
- United States Department of Agriculture, Natural Resources Conservation Service. Soils, Soil Health
- Lehmann, J, et al. (2020). The concept and future prospects of soil health. Nature Reviews Earth & Environment vol 1, pgs 544–553
- Guerra, C, et al. (2021). Tracking, targeting, and conserving soil biodiversity. Science, vol. 371, Issue 6526, pgs 239-241
- Verheijen, F, et al. (2006). Organic carbon ranges in arable soils of England and Wales. Soil Use Manage, vol 21, pgs 2–9
- Environment Agency. (2019). The state of the environment: soil
- The Royal Society. (2020). Soil structure and its benefits. An evidence synthesis
- Keith, A, et al. (2016). Soil stewardship as a nexus between Ecosystem Services and One Health. Ecosystem Services, vol 17, pgs 40-42
- Bardgett, R, and Van Wensum, J. (2021). Soil as Natural Capital, KVAB Thinkers’ report
- FAO. (2019). Soil erosion: the greatest challenge to sustainable soil management.
- FAO. (2019). Outcome document of the Global Symposium on Soil Erosion
- Olson, K. (2016). Impact of soil erosion on soil organic carbon stocks. Journal of Soil and Water Conservation, vol 71 (3) 61A-67A
- Evans, D, et al. (2020). Soil lifespans and how they can be extended by land use and management change. Environmental Research Letters, vol 15, 9
- Ritchie, H, 2021. Do we only have 60 harvests left? Our world in data
- Borelli, P, et al. (2020). Land use and climate change impacts on global soil erosion by water (2015-2070). PNAS, vol 117 (36) 21994-22001
- Acree, A, et al. (2020). Soil biochemical and microbial response to wheat and corn stubble residue management in Louisiana. Agrosystems, Geosciences and Environment, vol 3 (1), e20004
- Pittlekow, C, et al. (2014). Productivity limits and potentials of the principles of conservation agriculture. Nature, vol 517, pgs 365–368
- Wang, T, et al. (2019). Soil Conservation Practice Adoption in the Northern Great Plains: Economic versus Stewardship Motivations. Journal of Agricultural and Resource Economics, vol 44 (2), pgs 404 – 421
- Norris, C, and Congreves, K. (2018). Alternative Management Practices Improve Soil Health Indices in Intensive Vegetable Cropping Systems: A Review. Front. Environ. Sci.
- Gould, I, et al. (2016). Plant diversity and root traits benefit physical properties key to soil function in grasslands. Ecology Letters, vol 19 (9), pgs 1140-1149
- Tamburini, G, et al. (2020). Agricultural diversification promotes multiple ecosystem services without compromising yield. Science Advances, vol 6 (45), eaba1715
- Chaparro, J, et al, (2012). Manipulating the soil microbiome to increase soil health and plant fertility. Biology and Fertility of Soils, vol 48, pgs 489–499
- Bonanomi, G, et al. (2018). Organic Amendments, Beneficial Microbes, and Soil Microbiota: Toward a Unified Framework for Disease Suppression. Annual Review of Phytopathology, vol 56, pgs 1-20
- Huang, R et al. (2019). Plant–microbe networks in soil are weakened by century‐long use of inorganic fertilizers. Microbial Biotechnology, 12 (6), pgs 1464-1475
- Pichon, N, et al. (2020). Decomposition disentangled: A test of the multiple mechanisms by which nitrogen enrichment alters litter decomposition. Functional Ecology, vol 34 (7), pgs 1485-1496
- Neal, A, et al. (2020). Soil as an extended composite phenotype of the microbial metagenome. Scientific Reports, vol 10, Article number: 10649
- Johnson, K, et al. (2018). Heat and soil vie for waste to cut emissions. Nature vol 563, pg 626
- Kanissery, R, et al. (2019). Herbicide Bioavailability Determinant Processes in the Soil. J Bioremediat Biodegrad 10:458, vol 10(1)
- Ichihashi, Y, et al. (2020). Multi-omics analysis on an agroecosystem reveals the significant role of organic nitrogen to increase agricultural crop yield. PNAS, vol 117 (25), pgs 14552-14560
- Paustian, K, et al. (2016). Climate-smart soils. Nature, vol 532, pgs 49–57
- Terrer, C, et al. (2021). A trade-off between plant and soil carbon storage under elevated CO2. Nature, vol 591, pgs 599–603
- de Vries, F, et al. (2012). Land use alters the resistance and resilience of soil food webs to drought. Nature Climate Change, vol 2, pgs 276–280
- Swindles, G, et al. (2019). Widespread drying of European peatlands in recent centuries. Nature Geoscience, vol 12, pgs 922–928
- Brown, L, and Holden, J. (2020). Contextualizing UK moorland burning studies with geographical variables and sponsor identity. Journal of Applied Ecology, vol 57 (11), pgs 2121-2131
- Pronk, G, et al (2020). Carbon turnover and microbial activity in an artificial soil under imposed cyclic drainage and imbibition. Vadose Zone Journal, vol 19 (1),e20021
- Najera, F, et al. (2020). Effects of drying/rewetting on soil aggregate dynamics and implications for organic matter turnover. Biology and Fertility of Soils, vol 56, pgs 893–905
- de Vries, F, et al. (2018). Soil bacterial networks are less stable under drought than fungal networks. Nature Communications, vol 9, Article number: 3033
- Nottingham, A, et al (2020). Soil carbon loss by experimental warming in a tropical forest. Nature, vol 584, pgs 234–237
- Hannah, L, et al. (2020). The environmental consequences of climate-driven agricultural frontiers. PLoS ONE, vol 15(2): e0228305
- Xu, W, et al, (2020). Reducing Uncertainties of Future Global Soil Carbon Responses to Climate and Land Use Change With Emergent Constraints. Global Biogeochemical Cycles, vol 34 (10), e2020GB006589
- Majumder, S, et al. (2019). The impact of biochar on soil carbon sequestration: Meta-analytical approach to evaluating environmental and economic advantages. Journal of Environmental Management, vol 250, 109466
- Amoah-Antwi, C, et al. (2020). Restoration of soil quality using biochar and brown coal waste: A review. Science of The Total Environment, vol 722, 137852
- Rubin, R, et al. (2020). Biochar Simultaneously Reduces Nutrient Leaching and Greenhouse Gas Emissions in Restored Wetland Soils. Wetlands, vol 40, pgs 1981–1991
- Bednik, M, et al. (2020). Wheat Straw Biochar and NPK Fertilization Efficiency in Sandy Soil Reclamation. Agronomy, vol 10(4), 496
- Pranagal, J, and Kraska, P. (2020). 10-Years Studies of the Soil Physical Condition after One-Time Biochar Application. Agronomy, vol 10(10), 1589
- Sykes, A, et al. (2019). Characterising the biophysical, economic and social impacts of soil carbon sequestration as a greenhouse gas removal technology. Global Change Biology, vol 26 (3), pgs 1085-1108
- Zhou, X, et al. (2020). Super Moisture Absorbent Gels for Sustainable Agriculture via Atmospheric Water Irrigation. ACS Materials Lett., vol 2 (11), pgs 1419–1422
- Vidiella, B, et al. (2020). Synthetic soil crusts against green-desert transitions: a spatial model. Royal Society Open Society, vol 7, (8)
- Caplan, J, et al. (2020). Decadal-scale shifts in soil hydraulic properties as induced by altered precipitation. Science Advances, vol 5 (9), eaau6635
- Mullan, D. (2013). Soil erosion under the impacts of future climate change: Assessing the statistical significance of future changes and the potential on-site and off-site problems. Catena, vol 109, pgs 234-246
- Climate Change Committee. (2020). The Sixth Carbon Budget, Agriculture and land use, land use change and forestry
- Kopittke, P, et al. (2020). Soil organic matter is stabilized by organo-mineral associations through two key processes: The role of the carbon to nitrogen ratio. Geoderma, vol 357, 113974
- Veermann, C, et al (2020). Caring for soil is caring for life – Ensure 75% of soils are healthy by 2030 for food, people, nature and climate. European Commission Directorate-General for Research and Innovation
- FAO, ITPS, GSBI, SCBD, and EC. (2020). State of knowledge of soil biodiversity – Status, challenges and potentialities, summary for policymakers.
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