Source: Farming Futures, 3rd August 2016
Healthy soils comprise mineral material, organic matter, biological organisms, air and water, and are a vital asset for farmers and land managers. They take millennia to form, but are often taken for granted and sometimes neglected, resulting in degradation over decades. Soils underpin agricultural production by providing a rooting medium for crops and by storing and cycling nutrients and water. Healthy, fertile soils ensure more sustainable and resilient crop production by maintaining high yields and cycling water and nutrients efficiently. Improving soil quality can shift the fertiliser-response curve to the left, supporting higher outputs with lower inputs, and thus delivering “sustainable intensification”.
Delivering ecosystem services
As well as underpinning agricultural production, soils deliver many valuable ecosystem services for which farmers and land owners are not directly paid – although cross-compliance and agri-environmental scheme criteria linked to farm subsidies represent a crude form of “payment for ecosystem services”.
Soils across the globe store over 1500 Giga-tonnes of carbon, twice as much as is in the atmosphere. By keeping that carbon out of the atmosphere, soils play a vital role in regulating our climate, and some scientists argue that soil management to increase carbon sequestration could offset a large portion of greenhouse gas (GHG) emissions from animals and fossil fuels.
Soil management also strongly influences the release nitrous oxide (N2O), a GHG 298 times more potent than CO2 on a weight basis. Soils purify (or contaminate) water infiltrating through to groundwater and flowing into rivers, thus playing an important role in regulating water quality. Good soil structure can help soil to act as a sponge during storm events, ameliorating the peak flows in rivers that inflict expensive flood damage to land, infrastructure and properties.
Finally, among many other ecosystem services, soils also host and support diverse flora and fauna, supporting biodiversity.
Despite the strong links between soil health, economic returns and wider human wellbeing, soils can sometimes be neglected by farmers and land managers, for a variety of reasons. In grassland systems, soils remain hidden. Soil structure and problems such as compaction may be inferred from grass growth or infiltration measurements, but can most reliably be assessed by digging local test pits.
In arable systems, soil degradation via organic matter oxidation, erosion and compaction occurs at a steady but almost imperceptible rate. By the time soil degradation becomes obvious, full remediation may require a decade or more of adapted management.
For the large areas of tenanted farmland, long-term soil remediation and maintenance, e.g. building up organic matter through compost and manure additions, is a financially risky strategy – who will reap the long-term benefit?
Trends in livestock farming, such as the increasing use of maize silage as a cattle feed, can also change land use in a way that threatens soil quality and increases erosion risk. The extent of soil erosion and degradation across the UK and Europe is well documented, for example in EU scientific reports.
Soil organic matter content is a key indicator of soil health, and has been declining for decades across UK arable land, with implications for nutrient and water cycling, flood protection, resilience to climate change and delivery of multiple ecosystem services. Reversing these trends is essential to assure the sustainability and resilience of UK farming, and requires a long-term view to make the necessary investments in soil quality.
A portfolio of management practices exists to maintain and enhance soils. First off, know your soils! Regular soil testing for nutrient availability and structure is crucial to inform appropriate management. Matching stocking densities and cropping to soil types, soil condition and topography can significantly reduce the risk of compaction and erosion. Aeration and subsoiling can remedy compaction problems.
There are various decision support tools available to facilitate good nutrient management planning, such as the Fertiliser Manual RB209 and simple calculators such as MANNER-NPK available from the PLANET website.
Technology is constantly evolving to facilitate good soil management, including precision fertiliser application guided by yield-mapping and GPS-assisted steering. When it comes to delivery of ecosystem services, invaluable information is available via digitised soil databases such as LandIS and the European Soil Data Centre. Reliable sources of free advice on good practice include the Environment Agency’s Think Soils manual, Defra’s Guide to Cross Compliance in England, Natural England’s Catchment Sensitive Farming project and AHDB. But there are also many less reliable sources of “advice”, and it can be difficult to navigate through the mass of sometimes conflicting information pertaining to soil management.