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'UK soils need protecting and restoring'—Prof. Steve McGrath comments on Parliament Soil Health Report

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Soils must be managed sustainably to avoid severe problems with food security and climate change

Professor Steve McGrath, Head of Sustainable Soils and Grassland Systems Department at Rothamsted Research responds to the Environmental Audit Committee's new report.

One of the benefits of the UN’s declaration of 2015 as the International Year of Soils was that the UK Parliament took notice of what is now called “Soil Health”. According to the just-released House of Commons Environmental Audit Committee first report, soil health is multi-faceted, depending on a range of biological, chemical and physical factors.  This is well known to soil scientists and to most of those who work in agriculture. However, public knowledge and government actions lags behind the science, although (soil) scientists must take some of the blame for this. This can be illustrated by looking at the areas the report focuses on:

  1. Contaminated land – since the economic downturn, the political focus and funding for assessing and remediating contaminated land has decreased. This means that some land may be affecting public health. Here we have a long-standing problem because the land owners who were responsible for the contamination are often not traceable to pay for the clean-up. There are (still) around contaminated 300,000 sites. Local councils do not have enough funding for clean-up and government support has been cut. The report calls for more government support, but I know personally from working on this that the real issue is that the evaluation and clean-up costs of contaminated land are enormous. Only newer cheaper methods for measurement and decontamination will help here.

  2. Soil organic matter loss – research has shown that some areas of the UK have lost a lot of soil organic matter, especially arable and peat soils.  Large amounts of carbon dioxide are emitted from soils, especially peats. If peats are not managed properly, they contribute to global warming and militate against our agreement in Paris to limit warming to 2 degrees. Peats need protecting and restoring by imposing the conditions that created the peat. The solution proposed for agriculture is that we sign up to the “4 per mil” initiative, which aims to increase soil carbon by 0.4 percent per year. But how will we do this sustainably? We know that grass leys and cover crops can help. At Rothamsted Research we have evidence that returning rather than removing straw in the long term can maintain, but does not increase soil carbon. As Keith Goulding said in a previous article, animal and human wastes can increase soil carbon, but there is not enough of these for all arable land. Alternatively, practices such as minimum tillage are proposed to increase soil organic carbon, but careful analysis by colleagues shows that this may increase the carbon only in the surface layer, and there is no strong evidence of a total increase. Another consideration is: 0.4 percent of what? If a soil has 1 percent carbon, a 0.4 percent increase is feasible, but if soils already have 2 or 3 percent soil organic carbon, then a 0.4 percent increase in this is a considerable amount and probably not achievable. We also know that there is an upper limit where soils reach an equilibrium no matter how much carbon is added; the carbon content remains the same.

  3. Soil management – avoiding poor soil management can prevent erosion of soils and nutrients and the rapid loss from land of large volumes of water that have contributed to flooding. The report highlights a well-known culprit – growing maize as an energy crop to feed anaerobic digesters. If this is done on sloping land and nothing is present to hold the soil between the rows, then erosion is likely. Soil that has been built up for thousands of years is lost. The solution seems to be either guidance or legislation to stop this practice. No-one likes new rules, but neither do they like flooding and loss of the soil, which is a non-renewable resource. Paying farmers through subsidies for controlling such practices and so increasing “soil health” seems to be a good idea.

  4. Monitoring trends in soil condition – occasional surveys have been done, but the report argues strongly for continued monitoring, especially as soils usually change slowly. Again, costs have to be contained, but with new methods, data could be available to not only see the direction of change, but also to demonstrate the usefulness (or not) of changes in land management by subsidies etc. Otherwise, to paraphrase what my colleague David Powlson said in the report – we only have anecdotal evidence.

At the end of the International Year of Soils, the International Union of Soil Science Societies declared the “Decade of Soils”. If we do not bring together the necessary knowledge and agree indicators and actions for the sustainable management of soils in the next decade, then this planet will have severe problems in food security, climate change, and public health. We await further reports from the EAC on other aspects of soil health with great interest.

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