After heavy rain, it’s common to see rivulets of water, stained red with soil, running down our roads. What we are witnessing is soil erosion. The Environment Agency has warned that soil erosion is accelerating in Devon and Cornwall under climate change.

Winter rainfall in the Southwest is becoming more prolonged and intense, washing soil off farm fields into roads and rivers. The Environment Agency warns that methods that used to prevent soil erosion are no longer effective. To protect future food security, we need to look at new ways to protect the land from heavy rains and flash floods.

Topsoil holds the organic matter and nutrients that create the fertility to grow our food crops. We are losing it at an alarming rate – 10 to 40 times faster than it is formed according to the Soil Association. While the Rothamsted agricultural research institution reports that 84% of fertile topsoil has been lost in the UK since 1850.

It cites the causes of soil erosion as intensive farming methods that cause the soil to lose its structure through soil compaction, overgrazing, the cultivation of crops that are not suited to the conditions and the application of artificial fertilisers and pesticides that destroy the microorganisms that naturally live in the soil and maintain its structure.

Winter cereals have been linked to the greatest levels of soil erosion in Devon. Wetter weather in the autumn slows the growth of autumn-drilled cereals leaving bare soil vulnerable to run-off throughout the winter. Keeping the soil covered with the previous year’s crops and delaying the sowing of cereals until the spring reduces soil loss.

Crops like maize, fodder beet and potatoes that are harvested late in the year increase soil compaction. A survey of 3,000 maize growing sites in the Southwest found that 75% of fields don’t let rainwater in deeper than the uppermost soil layer, so heavy rainfall washes the soil away.

Healthy populations of soil microorganisms are essential to maintain the soil’s structure and make nutrients available to plants. Research by the Rothamsted institute showed that artificial fertilisers applied to wheat crops reduced the population of good bacteria in the soil from 91% to only 19%.

Pesticides also destroy the natural fungi that exchange nutrients with plants, and they reduce worm populations that are vital to healthy soils – soils without earthworms are 90% less effective at holding onto water.

Replacing chemical fertilisers with methods that incorporate more organic matter in the soil, through the application of manure, plant wastes and compost, improves the health and diversity of soil organisms and makes the soil more resilient to erosion. Changing how we grow our food to protect our soils is critical to our future food security.

The Environment Agency gives advice on effective measures to prevent soil erosion and is asking residents who see discoloured water running off farm fields to report it to their incident hotline on 0800 807060.