Soil management for water resources – a can of worms?

Earthworms are probably not the first iconic species you think of in the context of river health. It’s easy to laugh at the notion that the wriggly pink strings that hide underneath your compost bin are a key part of a functioning hydrological system – and yet they, and the soil they live in, are.

Soil stores, purifies, retains and drains water – regulating its flow to groundwater bodies and rivers alike, and playing a key role in water quality by taking up nutrients or releasing sediment. Like any ecosystem, soil relies on a complex network of interactions between organisms of all sizes, as well as physical and chemical processes, and much more, but earthworms in particular tell us a lot about how our soil is functioning and in turn influence how it behaves.

Underground beavers building drainage channels

In their daily burrowing-about, the so-called ‘anecic’ (deep burrowing) worms create drainage channels that allow rainwater to infiltrate into deeper layers of the ground.

Think of them as underground beavers, regulating and adapting the ecosystem around them!

At the same time, they help build up organic matter, a component of soil that can hold 10 times its weight in water and so increases the ability of soil to retain water.

They are sensitive to harsh farming practices, and so make a good indicator species for soil health. Overall, healthy earthworm populations equate to healthy soils – and healthy soils are a prerequisite for a healthy water cycle.

A worm burrows

Knee-deep in mud?

Soils, however, are mostly not in a good condition. Total costs of soil degradation across England and Wales come to £1.2 billion every year – mainly because of compaction and loss of organic matter (you can read more in the EA’s State of the Environment: Soil).

Among other impacts, degradation reduces soils’ ability to infiltrate, store and filter water, in turn meaning that more water runs off the surface. In heavy rain, this can mean increased flood risk, and in low rainfall periods, it can reduce recharge to streams and groundwater.

Additionally, less water is available for crops, reducing drought resilience. Degraded soil is worse at filtering pollutants from water and can even become a pollution source when sediments and nutrients are washed into watercourses or leach into the groundwater. Focusing on water quantity alone, studies have estimated that improving soil health on a catchment scale from poor to good could reduce runoff by half in small storms (Hess et al 2010).

Annual cost of soil degradation in England and Wales

Ask not what your soil can do for you...

A range of nature-based solutions are available to improve soil health that can be implemented both in arable as well as livestock farming.

In our PROWATER project (funded by the European Regional Development Fund), we are looking at how these measures could be implemented on a catchment scale to protect water resources.

Grazed pastures cover the majority of our pilot catchments (the Little Stour and the River Beult), especially in the Beult where the heavy soils are less suited to intense arable cultivations.

To improve soil health on pastures, apart from reducing the stocking density (the number of animals per area, which has a huge impact on compaction), the use of more diverse species mixes is a measure that is increasingly popular.

Different plant rooting depths can have a big impact on drainage and drought resilience © Cotswold Seeds.

Getting to the root of the problem

The pastures that our cattle and sheep graze on are often dominated by few grass species, made productive by applications of fertiliser. These species-poor pastures may look green and pleasant, but their short root systems, limited offerings for pollinators and need for nutrient input have some drawbacks. Inclusion of more diverse plant species (a ‘diverse sward’ or ‘herbal ley’) is one of the many measures that are increasingly implemented to offer more benefits to environment and economy alike. On field scales, tests have shown improved drainage and infiltration on fields that include more diverse species mixes with deep rooting herbs such as chicory and plantain, as well as improvements in water quality as less nitrogen is applied and more is taken up. More diverse mixes can penetrate into deeper layers of the soil, breaking up dense structures and increasing organic matter levels. They provide welcome forage for pollinators – and importantly, they also benefit livestock health and productivity (and earthworms like living with them!). (You can find out more details about herbal leys here for example:

Cultivating a field

Experts in our fields

On two PROWATER demonstration sites, we have implemented these measures in partnership with the land managers of a livestock and an equestrian farm, to see the impact they could have on how water moves through the catchment. There is one key difference:

  • one site is in the Little Stour, on the chalk aquifer where we are mainly interested in recharge to the chalk groundwater feeding both chalk streams and public water supply,
  • and the other is in the Beult catchment, on clay soils where water retention in the landscape slows the flow to reduce flood risk and allow a more reliable abstraction downstream in the Medway.
Healthy soils look like sponge cakes

Protecting and restoring landscapes for water

We see this as one of the key opportunities to work with farmers to improve the resilience of our environment and the health of our catchments, to safeguard our water resources and much more. More diverse pastures and herbal leys are just one way to reduce input of fertilizers and pesticides, to provide a resource for pollinators and to create a more resilient farming system. There are many other similar measures – reducing or stopping tillage, for example, where farmers stop ploughing fields and instead drill seed directly into the soil – being trialled and implemented by progressive farmers across this country and beyond.

Alongside that, there must be space for the other assets we, and the creatures we share our landscape with, rely on – the grasslands and fens, wet woodlands and streams. Many of these ambitions are being pushed forward in “Environmental Land Management Scheme” tests and trials across the country, debated in parliament in various bills, and hotly contested on virtual pub evenings (is that just us?).

There is still a long way to go to embed this approach in our day-to-day decision making, but PROWATER allows us to put forward some evidence and suggestion as to how we can build a system that is truly resilient. Maybe let’s take a life lesson from our inspirational cold-blooded friends: like an earthworm, we are not only able to respond to the environment we find ourselves in – we have the power to improve it.

Visit our PROWATER project page

Cultivating land