Judging a crop by its cover

Transcription

1 Judging a crop by its cover Cover crops have attracted huge interest recently, with no end of open days and claims for the benefits they bring. CPM searches for the science to back these up. By Tom Allen-Stevens While there s a lot of AHDB funding that s concerned with developing practical applications on the farm for scientific developments, sometimes it happens the other way round. There are one or two practices that take off on farm, but before most growers feel they want to invest too heavily, they d like a little science wrapped around it. Cover cropping is a prime example. There s been a strong demand from growers for more information, according to Dr Paul Gosling of AHDB Cereals and Oilseeds. We re catching up with what s already happening on farm, he admits. There s already a lot of trials going on, both independent and commercial, and a number of growers trying various cover crops on farm for themselves. We ve focused our attention on finding out what s been learned from these activities and 52 bringing that knowledge together. That s not to say there isn t underlying research that can feed into the process. NIAB TAG has been doing a lot of work on rotational practice there s some good history there. Then there are elements of the research undertaken as part of the AHDB and industry-funded 2.6M Soils Platform that are relevant to cover crops. There s also an on-going project studying the added value cover crops bring to integrated grassweed management. Information Sheet Initially, AHDB-funded activity has worked towards summarising the research, along with findings from on-farm practice, into an Information Sheet that s just been published. Cover cropping is a topic that s been included in our research and KT strategy, as we know it s a priority for growers, assures Paul Gosling. But future work is unlikely to involve a lot of field trials and research we don t think there s much value in replicating research that s already underway. Instead, we ll focus on sharing best practice through the Monitor Farm network, for example, and farm-based KT activities aimed at developing ideas on how cover crops are best utilised. Alongside this, there s work undertaken by other AHDB divisions into cover crops, he points out. This includes trap-cropping and research into biofumigation for the control of They can improve the soil structure and make a big difference to nutrient retention, reducing nitrate leaching. potato cyst nematode and other soil-borne pests in the AHDB Potato and Horticulture divisions. For cereal growers, an important driver of the move into cover crops has been the rise of herbicide resistance. That s prompted a greater adoption of spring cropping, notes Dr Jonathan Storkey of Rothamsted Research, who s been working with NIAB Paul Gosling has focused his attention on finding out what s been learned from existing trials and on-farm activities and bringing that knowledge together.

2 Larger-seeded plants, such as oats, vetches and mustard that grow fast appeared to work well, especially in mixtures. TAG on added-value fallows an AHDB-funded project that looks at what cover crops can do for integrated grassweed management. The current project is an extension of a Defra LINK project led by Elm Farm assessing use of cover crops for organic growers, he explains. We wanted to see what elements of those systems we could develop for conventional growers if they re adopting over-winter fallows to get on top of blackgrass, could cover crops perform better than bare ground? Two trials were set up in autumn 2012, at Woburn, Beds, and Cambridge, testing a range of cover crops as possible entries to spring wheat. Poor weather that year hampered establishment and set back initial results, but subsequent trials have proved promising, reports Jonathan Storkey. Conventional growers are wrestling with a shorter window for cover crops most wouldn t want to take a field out of crop for an entire year as an organic grower would, and that limits the crops that would be suitable, he points out. We soon learnt that the clovers suited to organic systems only work if they re undersown in the crop or broadcast immediately after harvest. They didn t really demonstrate their value in fixing nitrogen in a cycle of just a few months. But larger-seeded plants, such as oats, vetches and mustard that grow fast appeared to work well, especially in mixtures. To assess the effect on blackgrass, weed seedling numbers have been counted in autumn, with head counts taken in summer, as well as seedlings counted in the following Farm trials provide prudent pointers While it s always good to trial one or two crops before adopting them across the farm, the AHDB Monitor Farm at Fawley, Herefordshire, has had the benefit of pitching no fewer than ten cover crop mixes side-by-side to see how they stack up. The approach was initially made by Natural England, recalls Andrew Goodinson of Hutchinsons, who s been monitoring the trials and supplies agronomy advice across the 1000ha of arable crops farmed by manager Mark Wood. They were keen to see what effect different crops had on aspects such as soil structure, over-winter run-off, earthworms and nutrient loss. The ten crops were established across the 10ha field in Aug 2014, with part of the field left fallow as a comparison. Half of each plot was drilled with a 4m Horsch drill, while the rest was broadcast. We also applied a top dressing of 30kgN/ha post emergence at right angles across half of each plot, notes Andrew Goodinson. The range of mixes are designed to fulfil a variety of different objectives there were leguminous mixes to capture atmospheric nitrogen in root nodules for the benefit of the following crop, while radish-based mixes have deep, strong Where the crops fail to establish well, more weeds take hold and the soil is more exposed to compaction caused by rainfall. roots to alleviate pans. Also included was a rye-based mix with fibrous, shallow roots, mustard mixes to grow fast and capture nutrients that would otherwise leach, and a mustard with biofumigation properties to address problems such as potato cyst nematode. One thing we noted early on was the importance of winter hardiness. Where the crops failed to establish well, more weeds took hold and the soil was more exposed to the surface compaction caused by over-winter rainfall. That comes down to getting the seed mix right, while the autumn N really helped establish the cover. Earthworm counts were noticeably greater in all plots, although it was hard to draw conclusions as to which mixes performed better, says Andrew Goodinson. Just by walking across and digging a few inspection pits you could tell the benefits the cover crop brings to the soil the rooting makes a clear difference to structure and drainage. Weeds, and blackgrass in particular, are not an issue on that field, he says. However, cover crops I ve seen elsewhere suggest tillage radish on its own is better at blackgrass suppression than seed mixes. There s a view that weed suppression is a bad idea, but while it s not germinating, the seed-bank will naturally degrade by 70% in the first year. Any that does come through produces a smaller seed head. However, his favoured mix, based on experience from the trials, would be white mustard, tillage radish and tame oats. The radish pushes a pan-busting root down, while the mustard soaks up N and slows down rain infiltration. The fibrous oats put a nice tilth in the top 50-75mm of topsoil. It s a good, flexible mix that spreads the risk. But more work is needed on seed rates, he says. In general, there s scope to reduce them, and it ll take time to learn how to fine-tune the mix Andrew Goodinson believes there s scope to reduce seed rates, but it ll take time to learn how to fine-tune the mix. and balance the economics with the benefits. But I don t think legumes have any value in over-winter cover crops they don t have enough time to sufficiently establish and are pointless if you re planting pulses as a spring crop. And we need to be careful with brassicas in an oilseed rape rotation, that could bring problems with clubroot and sclerotinia. Following the trials, the field was sprayed off 2-3 weeks before a pass with a Saxon cultivator in front of the 4m power-harrow drill combination that established the pea crop. Light cultivations or direct drilling is best you want to keep the crop debris in the surface. While there s no mix that fits all objectives, he s convinced cover crops should be an important part of a spring-cropping regime, and that these should be managed as a crop. There s a lot to learn, but equally every grower will need to figure out what works best for them. So it s important to see trials and find out what other growers are doing, although we should be wary of knee-jerk reactions to other people s experiences. 54

3 crop. What we ve found is that the biggest driver for blackgrass germination is not how much cover there is over winter, but the timing of the autumn cultivation. Just as much blackgrass germinates in a cover crop as on bare ground, and that can be taken out with glyphosate before the spring crop, in the same way as in an over-winter fallow, he reports. He accepts there may be opportunities with an over-winter fallow to sequentially cultivate or for multiple applications of glyphosate. Growers will balance this with the many other benefits we re finding for cover crops, such as soil structure, biodiversity and reducing nutrient loss. What s more, the ever present danger that overuse of glyphosate may lead to resistance always needs to be kept in mind. With one year of the project left to go, the main emphasis will be on collating reliable figures that growers will be able to use to assess how best to use cover crops. We need to analyse organic matter levels and bring together the data on weed control, notes Jonathan Storkey. What s needed now for growers is a trusted authority who can pull together the various strands of research and commercial practice and deliver concisely what the opportunities are, and that responsibility s fallen on Ron Stobart of NIAB TAG. We based the Information Sheet mainly on three sources, he explains. Firstly there s research work from the NIAB TAG New Farming Systems trials. In addition, we ve brought in information and practice guidance honed through field scale work with the Catchment Sensitive Farming (CSF) initiative, and this has been a particularly useful source of case studies. Split-field comparisons There s also additional information from other farm groups and on-farm experience. We ve been in touch with Kellogg s Origins growers, who have set up field strips and split-field comparisons and have developed collaborative cover-cropping research and best practice ideas on farm. Areas include improving soil structure, soil biology and nutrient retention, for example. The New Farming Systems study is a charitably funded initiative, delivered through NIAB TAG at Morley in Norfolk and supported by The Morley Agricultural Foundation and The JC Mann Trust. It s a long-term study that seeks to address energy usage and pollution risks in conventional rotation systems. Large scale, Jonathan Storkey found that just as much blackgrass germinates in a cover crop as on bare ground. replicated field trials focus on two main themes: cultivations across the rotation, exploring shallow tillage in particular, and fertility building, which is where the use of cover crops comes in. It s a useful study because these are large replicated trials with a range of different cropping rotations, including how cultivation systems interact, says Ron Stobart.

4 Use seed mixtures to spread risk and deliver a range of rooting, but watch for seeds of different sizes that can settle when you drill. The key finding is that not all cover crops are the same if you re considering growing one, think carefully about your objectives for doing so first, then choose the crop that fits those objectives as well as your field equipment and farm practice. Adventurous roots Brassicas put down strong, adventurous roots that can help open up soils well beneath the surface, but there are potential rotational conflicts, such as a greater risk of diseases such as clubroot in oilseed rape. Cereals such as oats improve the surface tilth and draw out excess moisture, but can act as a green bridge for pests and diseases. Legumes such as clovers can fix nitrogen, but are slow to grow and really benefit from early sowing. There s one aspect that isn t disputed, however: cover crops are definitely beneficial overall, he says. They can improve the soil structure and make a big difference to nutrient retention, reducing nitrate leaching. They can minimise erosion risks, reducing diffuse pollution and phosphate losses in particular. Brassicas put down strong, adventurous roots that can help open up soils well beneath the surface. This has knock-on benefits for improving soil and water quality. But what does the grower get out of it? This is one of the questions I m always asked. New Farming Systems research suggests improvements can equate to a 60-70/ha benefit. This comes from raised yield, improved utilisation of N inputs and a better structured soil, he says. But the results are seen across the rotation, he stresses. Don t expect to see all the yield response in your spring barley, for example there s a knock-on benefit for the wheat crop that follows. What s more, this is a gross return there s the cost of the seed and managing the cover crop to consider, and that can vary substantially depending on what you grow and how it s managed. It s also early days with cover crops, he notes. We re all still very much learning as we go. If you want to maximise the benefits, find out as much as you can about cover crops, and then apply that knowledge in the context of your own farm how will it work on your soil type? Does it marry with the equipment you have? There are some unanswered questions and known issues some heavy-land farmers have found the crop cover can keep the soil surface wetter for longer in spring, for instance, hampering cultivations and delaying drilling. Some cover crops that produce a lot of biomass may lead to a lot of residue that s difficult to cope with. The type of residue produced and establishment 56

5 Research round-up AHDB Information Sheet 41, Opportunities for cover crops in conventional arable rotations, has just been published and is available to download at AHDB project , Added value fallows: The use of customised cover cropping approaches within integrated grass weed management, runs from Aug 2012 to April Its aim is to add value to fallows by incorporating cover crops that can enhance weed suppression, as well as delivering the additional benefits of improved soil structure, fertility and biodiversity. The project is led by NIAB TAG, with partners Rothamsted Research. Its total cost is 154,529, funded by AHDB. AHDB Soils Platform: This four-year programme runs from and comprises three projects investigating a range of practical and sustainable soil management practices. The work includes managing on-farm soil variability by using data from yield maps. Other parts of the programme are looking at how different types and quantities of organic matter influence soil structure and the effect of different cultivation techniques on the soil. The total cost is 2,616,736 with 1,620,753 funded by AHDB. AHDB-funded activity will focus on sharing best practice through the Monitor Farm network and farm-based KT activities. practice also interact here. Then there s the nebulous issue of allelopathy, whereby root exudates are thought to suppress plant growth and seed germination. In theory there s a balance between suppressing weeds and impact on your following crops; this may be a problem, but I haven t seen any clear evidence of it in Ron Stobart reckons there s a 60-70/ha benefit, but the results are seen across the rotation. the field. The difficulty is there s very little good UK field research that addresses it. He recognises there are still gaps in the understanding of cover crops. We have a lot of pieces of a jigsaw and need to learn more how they fit together on any particular farm. But that s no reason not to try cover crops. One piece of advice I d give is to use mixtures. Firstly that spreads your risk, and it also gives you a range of rooting that helps soil structure. There is a downside, though you get seeds of different sizes that can settle when you drill or spread and it may be tricky to calibrate your drill. 57