In his inimitable call-a-spade-a-spade way, soil husbandry specialist, Steve Townsend of Soil First Farming is on a quest to sort out the soil management wheat from the chaff in our new myth-busting series.
‘Cover cropping will solve your soil problems’ Compaction; low organic matter; nitrate leaching; less-than-ideal seedbeds; difficult grass weeds. Is there no end to the problems that can’t be solved with cover crops? There certainly seems to be if you believe the many experts who’ve jumped on this particular bandwagon. That’s not to say cover crops can’t be useful. They can be very valuable indeed. But it’s vital that the right materials are used for the right reasons and in the right ways. Otherwise they can add considerable extra expense for little, if any, return. Too often, for instance, I see ground lying far too wet in the spring even after well-established winter covers. Or fancy mixtures of up to 12–14 different species giving covers dominated by just 2 or 3 that could have been sown for a fraction the cost. Or poorly established, thin covers little better than weedy stubbles. If we want cover crops to repay our investment rather than merely supporting the seed trade, we have to sort out exactly what we want them to do and manage them to actually do it. We all know that soils under a crop keep in far better condition than they do when left bare. They’re less exposed to the elements and less vulnerable to capping, erosion and nutrient leaching. Equally, a good winter cover can be valuable in improving soil structure as well as helping to control weeds.
Biology Having said that, improving soil biology as much as structure is what we really should be using them for. In particular, producing the sugary exudates that feed the massive population of bugs in the rooting zone responsible for the mobilisation and supply of soil nutrients. That way we’re providing the healthiest soil conditions for our next crop from the
start rather than having to rebuild them every year after serious autumn and winter depletion. So how do we achieve this? Well, the solution is in the name. We need the best possible cover. And to get this we have to treat it like a crop. Roots/m2 are what really count. Specifically, we want a wealth of fine, narrow, well-lignified roots penetrating throughout the ground and leaving a network of channels as they slowly decay. The sort of rooting we get with mustard, linseed and oil radish rather than some of the many other species so often touted about. The more diverse the species mix the better for both soil biology and structure, it’s true. But only if we have the sort of soil conditions that allow us to establish them all reliably. Initially, we’re far better getting our roots/m2 as cheaply and dependably as possible from higher seed rates of fewer species. And sticking to those with similar-sized seeds we know will establish well alongside one another from the same sowing depth and timing; either small- seeded brassicas with linseed and phacelia on the one hand or larger-seeded cereals like oats and winter barley on the other. Paying much more than £20/ha for seed at this stage is a waste. Once we’ve improved the quality of our soil enough to allow a variety of different seeds to be reliably established from a single sowing, however, we can up the ante in cover crop complexity and cost. That way we take full advantage of the benefits of diversity – including much higher biomass – at the least risk.
Destruction Destroying our cover crops correctly is almost as important as getting them established consistently. Or more particularly, timing destruction to match their biology and the needs of the following crop. Drilling-on-the-green seems to
A good winter cover can be valuable in improving soil structure as well as helping to control weeds.
be the ultimate goal for many. Again, though, it’s horses for courses. It can be perfect for short term covers like linseed after oilseed rape that are still making a positive contribution to ground conditions, right up to the time the winter crops go in. However, once active growth stops in the early winter and before it restarts in the spring, most covers are actually doing virtually nothing. Other than preventing any soil drying, that is. So if it’s the best seedbed for drilling before April we want, we need to kill our covers off as early as we can in the New Year and let the weather do its job; bearing in mind that many species take a long time to die back after glyphosate spraying at this time of the year. Let’s be clear then, however valuable they can be, cover crops are not the answer to
every maiden’s prayer. They’re unlikely to do much to build organic matter in the short term, although they can help stop it declining and make useful improvements to soil biology over time. They won’t be a cost-effective way of improving soil structure either unless combined with other essential conservation tillage techniques. They will make no contribution at all if they aren’t carefully planned and managed. And, above all, they should never be seen as a quick fix. Over the coming months Steve Townsend will be exploring more of what he sees as the most damaging soil management myths exclusively with us. He is more than happy to discuss any tillage or soil management issues, interests or concerns with Farmers Guide readers by e-mail on steve. email@example.com or by phone on 01452 862696. ■
Cover crops can be very useful but it’s vital that the right materials are used for the right reasons and in the right ways.
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Contact Office: 01684 311811 Nigel Bullock: 07850 825980 • Ross Pushman: 07815 110529 email: firstname.lastname@example.org • www.bullocktillage.co.uk Bullock Tillage • Danemoor Farm • Malvern • Worcestershire WR13 6NL
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Farmers Guide Magazine April 2018 Issue