The latest by environment secretary Michael Gove warns parts of the UK are just 30-40 years away from the “fundamental eradication of soil fertility” and he says more should be done to protect future productivity and biodiversity.
What practical advice and government support this means for arable farmers remains to be seen. Soil health is clearly important for many reasons, not least its fundamental role in sustainable food production.
So how can you tell if improvements are required and where do you start putting things right?
Several indicators can be used to gauge soil health, says ADAS principal scientist John Williams.
“You can look at the chemical, physical and biological health of a soil. But it is very difficult to be prescriptive, because we have a huge range of soil types in this country.”
Standard soil analysis, which should be carried out every 3-5 years and costs £10-15/ha, helps check chemical fertility, which is important for nutrient availability, he explains.
“As well as looking at the P, K and Mg levels, you must pay attention to soil pH. If the pH is wrong it has a knock-on effect. When the chemistry is out of balance, so is the soil.”
In terms of physical soil health, there are various visual assessment tools available, but nothing beats digging a hole with a spade, Mr Williams says.
“Look for signs of compaction and check roots can grow down to exploit water and nutrients. If they can’t, consider changes to your cultivation strategy.”
Under-performing areas are obvious places to investigate, but they may be zones of poorer soil rather than being damaged, he adds.
Soil biological health is linked to organic matter, but there is no agreed definition of the optimum organic matter content or a target to aim for, Mr Williams says.
“A light, sandy soil will have less than 2% organic matter, while heavy clay will be more like 5%.
“Whatever your starting point, there are plenty of reasons to raise soil organic matter. Soils with good levels are more resilient, have better water-holding capacity and offer wider working windows.”
Organic matter can come from crop residues, bulky organic materials such as farmyard manure or composts and cover crops, he notes.
“The amount of organic matter in them varies. The most important thing to realise is that raising organic matter levels is a long-term process – don’t expect it to happen overnight.”
Good soil structure increases the window of opportunity to cultivate at the right time, explains Dr Elizabeth Stockdale, head of farming systems at NIAB TAG.
Digging up some un-trafficked soil beside a hedge is a good way of assessing physical condition, she says.
“It’s always worth looking at soil before and after field operations, so you can see if you’ve done any damage.”
Soil structure is governed by the interaction between mineral particles and soil organic matter, as they aggregate together to form crumbs and blocks.
“The gaps (pores) between aggregates are an important part of the structure. They control the balance of oxygen and water available to plant roots and soil organisms. That’s why travelling on a soil when it is too wet can cause significant structural damage.”
Plant roots and some soil organisms (such as earthworms) can change the soil’s structure, by moving through the soil, pushing particles around and extracting water. Along with drying and wetting processes, biological interactions have a central role in soil structure development.
“Supporting these biological processes helps create resilient soil structures, which will be very important in dealing with climate change,” notes Dr Stockdale.
Soil picture acknowledgement:Natural Resources Conservation Service Soil Health Campaign. CC BY