May 4, 2020
Deeper Thinking For The Best Wet Winter Recovery
How well we recover from last winter is far more about what we grow and how we grow it after the crops we have in ground this season than it is about how we manage land that has been too damaged to crop.
Correcting soil damage within the profile that may not be obvious by the time we get to the autumn will be crucial here. And in doing this rotation will be every bit as important as cultivation.
This is the firm view of Agrii regional technical adviser and Cambridgeshire farmer, David Felce who knows more about soil management than most from extensive investigations on his own farm near St Neots and trial work across the country as part of the Agrii R&D team.
“Uncropped land is, arguably, the least of our problems this year,” he argues. “It gives us the greatest opportunity for remedial work with the fewest constraints on what we do and when.
“Far more problematic is the vast majority of land that has undoubtedly been damaged but is currently being cropped. We have so much less opportunity to deal with damage at depth here ahead of the 2021 crop we’re depending on to make-up for this season’s lost margins. A lot of our soils are shocking underneath, and we fail to repair them at our peril.”
To illustrate his point, Mr Felce urges growers to think back to the ‘recovery’ harvest following the very wet winter of 2012.
Anxious not to be caught out again the following autumn, many people drilled as much of their wheat as they could early. To be fair, it established reasonably well. However, in far too many cases, the dry spring and early summer of 2014 exposed serious structural problems in the soils below, resulting in very poor performance.
Just how poor was brutally clear in the long-term cultivations trial on heavy clay at Agrii’s Stow Longa technology centre near Huntingdon. Crusoe wheat sown in late September with shallow tillage and no soil working at depth averaged just 4.54 t/ha. This was in marked contrast to the 12.77 t/ha delivered by the same variety sown alongside it a month later following deep cultivation.
While the black-grass burden in the early-sown crop was noticeably higher at 41 ears/m2 against just 2 ears/m2, this difference was calculated to be sufficient for a yield deficit of around 0.5 t/ha rather than the 8t/ha-plus actually recorded.
“This underlines how vital it is to sort out the structural issues rather than ignoring what lies beneath,” Mr Felce stresses. “Especially so, as the last thing we can afford is two years of poor performance in a row.”
So where are the main problems likely to be in our soils this season? And how best should we deal with them and when?
While heavy clay soils clearly suffered worst over the winter, David Felce’s greatest concerns are for those with a significant silt content like the Hanslope clays he farms. This is because silt runs down the profile to accumulate in impermeable layers wherever it encounters resistance. Which means minor damage that may naturally be overcome by self-structuring in other clays become serious issues.
“Relatively high silt soils over clay are always the most problematic in my experience,” he explains. “What’s more, the problems can occur at any depth in the profile and unevenly across the field depending on specific conditions and where the initial damage occurs. So, we can only find out what we need to deal with by getting out with a spade.
“Once we get into the summer it can be easy to forget exactly where those wet holes were. But a crop in the ground can actually be valuable here. Areas of differential growth and ripening are really good at highlighting where structural problems lie, allowing us to target our digging. And Rhiza satellite imagery provides a very useful addition, indicating differences that may not be obvious from the ground but could be every bit as important
“I don’t believe we should necessarily confine ourselves to merely pinpointing problems in our cropped areas this summer, though,” says Mr Felce. “Checking drain outflows, jetting drains and clearing ditches (within agri-environment scheme rules, of course) are all things we can usefully be doing to get ahead.
“Nor do I feel we should shy away from working areas of fields to deal with soil damage wherever crop growth is particularly poor. We have little to lose in current production from these areas and so much to gain in the performance of our next crop.”
Strategic mole draining within the crop can be valuable in dealing with some issues, while subsoiling may be more appropriate for others. Whatever working is done, however, Mr Felce insists it needs to be well planned and managed.
“We should only attempt to mole soils that have a clay content of 30-40% and a sand content of less than 30%,” he advises. “And only then when the soil above the mole is dry enough to avoid damage and that within the area to be moled sufficiently plastic to hold a channel. Otherwise we will do more harm than good.
“We need to make sure the mole goes into a gravelled drain too. Alternatively, if we’re going into a ditch, we should be careful the mole doesn’t rise up at the outfall, as it naturally tends to do. I always make a plastic pipe connection here to avoid this.
“Whenever we do it – whether in areas of a poor standing crop or between harvest and our next crop – we can also do far more harm than good with a subsoiler. Again, the soil needs to be in the right state for good vertical fissuring without smearing. We have to get the leg spacing and wing size and angle right to ensure we fissure across the whole working width without too much disturbance.
“In addition, we have to target our low disturbance leg carefully to work within the band of disrupted drainage, not below it,” adds Mr Felce. “We will always achieve some loosening immediately beneath the leg. But, working too deep risks driving the problem deeper.”
The need to correct any soil damage ahead of the following crop and the importance of working in the right conditions to do so makes the choice of what to sow after crops currently in the ground every bit as crucial to a successful 2021 recovery as metal at depth.
Given the need to get it in before mid-September, the best position for oilseed rape will clearly be after any uncropped ground. Where soils are in good condition, David Felce has few concerns about going into OSR after spring barley as well as winter cereals. He is, however, extremely nervous about the idea of the crop wherever there is any doubt about soil condition.
“Oilseed rape and poor soil condition are a recipe for disaster,” he observes. “Not least with the flea beetle pressures we are facing these days. In most cases, there isn’t enough time to reliably deal with soil damage ahead of sowing after anything other than winter barley. So, I simply wouldn’t want to take the risk.
“Providing it’s not down to crops as late to harvest as linseed or beans, there may be time to get damaged ground in the right place for mid-October wheat drilling, but that all depends on the weather. So, we should look hard at what needs doing; be honest with ourselves about what we can do in the time available; and only drill wheat once we’ve sorted out our soils sufficiently well.”
Wherever this is in doubt, Mr Felce urges growers to serious consider either late hybrid winter barley with aggressive rooting better able to cope with compromised soils or spring barley to give more time to correct them.
“Recent Stow Longa trials have shown what a good option hybrid barley can be on heavy ground in difficult conditions,” he reports. “A crop of Belfry direct drilled at the end of September, for instance, average 9.92t/ha compared with KWS Zyatt direct drilled three weeks later averaging just 7.53t/ha. And it did so with 100kg/ha less nitrogen and far less black-grass seed return.
“Our long-term Stow Longa rotations work has also shown spring barleys can generate consistently higher margins and result in lower black-grass populations than winter wheats under challenging conditions, regardless of cultivations regimes.
“If we want the best recovery from last winter, we simply have to appreciate there are no quick fixes in soil management,” concludes David Felce.
“Summer fallowing may be a solution for the minority of ground nationally that remains uncropped, although metal will be essential here as their challenge is far too great for cover crop roots alone. But what the vast majority of our soils need, above all, is care, patience and flexibility to bring them back to where we need them to be with the right rotation as well as correct cultivation.”