Weed management is leading soil husbandry specialist, Steve Townsend’s Soil First Farming focus
Weed management is leading soil husbandry specialist, Steve Townsend’s Soil First Farming focus in the latest of our special articles exploring the benefits and practicalities of a modern no-till approach to arable improvement.Article by Steve TownsendContrary to ‘old science’, ploughing is not the answer to black-grass problems. Full inversion tillage can certainly put annual weed seeds out of harm’s way. But even the most diligent ploughing will only do so temporarily. Repeated deep cultivation merely brings large numbers of viable seeds back to the surface to cause problems the following year.Nor is minimum tillage necessarily the ultimate solution. It can be extremely valuable. But only where conditions allow at least one, if not two, good stale seedbed glyphosate kills ahead of planting, and for those willing and able to delay drilling long enough to achieve them.In my experience and that of a growing number of my no-till colleagues, the best and most sustained solution to black-grass and other annual arable weeds lies in a far more integrated approach based on an understanding of weed biology and three core principles – the least soil disturbance, the best residue cover and a well-planned rotation.First the biology. Managing annual weeds is, more than anything else, a numbers’ game. Fewer weed seeds germinating mean fewer weeds setting seed and lower weed seed burdens the following year. Add to this the fact that most annual weed seeds are genetically programmed to germinate at the earliest opportunity and need to be stimulated to do so by soil movement and the first essential in reducing the weed burden has to be minimum disturbance.
An informed modern no-till approach leaves the majority of weed seeds soundly asleep by only moving the soil where the crop actually is. That way too the weeds only emerge where they face the most intense crop competition.This is aided by effective residue cover to suppress the germination and early growth of small-seeded weeds both by shading and through the wonderful force of allelopathy we explored last month. Aided, of course, by a timely dose of pre-planting Roundup (glyphosate) wherever conditions allow. Growing our own residue in the form of cover crops can be extremely valuable too – either as a short term bridge between harvest and autumn drilling or for winter cover through to spring planting. In both cases, we can take advantage of their competitiveness while growing and allelopathic chemicals once destroyed and left to decay on the surface – not to mention their soil structural and organic matter-building benefits.We’re only really beginning to appreciate the extent to which cover crops can help here. But already it’s clear that the decay of different crops produces different weed-inhibiting chemicals. Not many broad-leaved weeds grow after rye, for example, making it an ideal cover ahead of spring broad-leaf crops and maize.
While we’re on the subject, let’s not forget the crucial importance of rotation either. Spring cropping hasn’t really figured highly on most intensive arable radars – until this year, at least.As many of those with the most intractable black-grass problems are discovering, a single well-planned spring crop in the rotation can make all the difference in breaking the downward weed infestation spiral. Especially so when combined with minimum soil disturbance and effective residue cover as part of a determined conservation agriculture approach.The fact that this approach will be addressing the poor soil structure and drainage that is the root cause of most problems rather than merely the symptom that is bad black-grass, of course, makes it all the more valuable and sustainable.Steve Townsend is more than happy to discuss any tillage or soil management issues, interests or concerns with Farmers Guide readers by e-mail on [email protected]or by phone on 01452 862696.