"We have low commodity prices and rising input prices so we have to look at reducing inputs though better soil management," Soil Association farm business adviser Tim Bevan said at the event in Ormskirk, Lancashire, one of a series around the country in the AHDB-backed GREATsoils programme.
He explained that the physical, chemical and biological aspects to healthy soil "are all linked and overlap", adding: "It needs to be in aggregates or crumbs that the root hairs can grow between. If that breaks down, plants won't get air and water. It should also carry a negative charge that will hold onto nutrients like potash, and organic matter helps this. Good soil is also full of sugars from plant photosynthesis that leak out into the soil and help bind it and feed soil bacteria."
These "are not all bad" and release nitrogen when consumed by soil protozoa, he explained. "At each stage of the soil food web you get a release of nutrients, making what's locked up in the soil more available." But indices of soil health will vary greatly depending on soil type. "The soils of permanent pasture can be 15 per cent organic matter, but if you are growing carrots or asparagus on sand, getting even two per cent is difficult."
On soil testing, he said: "If you are taking land on, you need to know what you're getting," adding that a range of commercial laboratories now provide this service and will even test for soil microbial life. But growers can also roughly assess actinomycete bacteria content by whether soil smells healthy and can record numbers of earthworms, of which there are 26 native to the UK, performing different functions in the soil. Testing for organic matter "is also fairly easy and cheap", while a home BDH test kit allows growers to test their own soil pH, which is "fundamental", he said. "It that's wrong, you can put on all the nutrients you like and the plant can't take them up."
Measuring these on a three-year rotation "lets you know if these are going up or down", which makes business sense, he said, pointing out that this year's Soil Association Soil Farmer of the Year, Staffordshire arable grower Clive Bailye "has reduced inputs such as herbicides and seed treatments and is now taking on more land", he said. "These are the farmers who will be in business in 10 years' time."
Bailye has also taken part in the Soil Association's Innovative Farmers field labs programme, which Bevan urged attendees to consider, saying: "This is money in the pot for it, and scientists who are eager to help."
Cotswold Seeds owner and manager Ian Wilkinson said a loss of diversity in British farming has served to deplete soils. He suggested a range of ways to address this, including adding livestock to the rotation. "You can't overstate the importance of grazing for soils," he said. "Most of you don't have livestock and probably don't want to. But mixed farming doesn't require mixed farmers. A neighbour's sheep graze our farm."
Livestock farmers "love legumes" in leys for the liveweight gain they give and these are also known for their role in fixing nitrogen in the soil. "But this only happens above 8 degsC and the amount of nitrogen is highly variable", he said
Cover crops will be more effective both in biomass, which may be up to 50 per cent higher, and in their legacy in the soil, when made up of a range of plant types, for example by including the deeper-rooting chicory. But killing them off without glyphosate can be a challenge, requiring timely flailing or "crimping" (flattening) depending on the crop. "You can make expensive mistakes." Companion planting, such as intercropping brassicas with yellow trefoil, "will have an impact on the cash crop, but you may get more slugs - it's never black and white", he added.
Explaining the eight-year rotation for his own farm, he said: "You can't spend money doing this now and get the benefits in six months' time." But realising that farming his own land conventionally was failing to make money had necessitated a change in approach, he added.
Brassica grower Chris Molyneux demonstrated the impact on his land of a range of cover crop mixes, including oats, rye, vetch and berseem clover, calling the latter a "brilliant crop as it doesn't set viable seed and is killed off by the frost so you don't have to top it. It just sits there as a mulch in winter and then the nitrogen is available in spring." Such crops also add to the farm's biodiversity, for example by providing cover for partridges, he said.