A summary of the 2nd Webinar in Hope Farm's 20th Anniversary series, by Sophie Mott, RSPB’s Conservation Advisor for Cambridgeshire
If you’ve read the previous blog, you’ll already know about Hope Farm’s 20th Anniversary Webinar Series, five webinars covering important nature focused farming topics being delivered by industry experts and farmers alike.
The second webinar of the series took place on the 24th November, exploring the topic of soil health and cover crops. Featuring some captivating talks from the RSPB, Agrii, and Oakbank Game and Conservation. If you missed out, never fear, the webinars are available online, or you can read about it here!
The webinar began with an introduction from Hope farm’s manager Georgie Bray. Georgie spoke briefly about the journey Hope farm has taken in the last 20 years. Until recently it’s focus has been on demonstrating the importance of providing habitats around the edges of fields for building resilience in populations that are reliant on farmland. Identifying marginal and less productive areas that could instead become productive for wildlife has been key to its success, whilst remaining a profitable business. Over the last 20 years Hope farm has changed its farming system from ploughing to min till, fallows to cover cropping and simple cropping to diverse rotations including spring crops and has shown how these changes have benefited the farm agronomically and in its ability to support the wider ecosystem. The use of cover crops, direct drilling, and organic matter is not new to farming, however the way these mechanisms are being refined and appreciated is growing and they are becoming ever more important in a sustainable farm business. At Hope farm we have been through a learning curve of using these techniques, particularly with cover crops on heavy land, where we have seen the good the bad and the ugly but we are learning all the time and are by no means at the end of that journey.
Cover Crops vs Cultivation trials at Stow Longa - Steve Corbett
Steve is a key member of staffing working at Agrii in the east of England. Steve and his team are investigating cover crops over a five-year trial at Stow Longa, an area of heavy clay soils. The trial is looking at cultivations and cover crop mixes and how they fit into the whole system including the bottom line, yields and blackgrass control.
Steve begins by warning that poorly established cover crops waste money. It is very important to have a goal before cover cropping a field and know what are you trying to achieve. This will affect the appropriate choice of plants to use.
If your goal is weed control, one element of this trial was looking at whether cover crops helped with blackgrass control or got in the way of managing it. In some plots in this trial, there are 700-1000 ears of blackgrass per square meter. For context 100 ears of blackgrass = 1 tonne wheat yield decrease. The trial used 24m plots under different management; plough, deep cultivation, direct drill, oil radish at 20kg/ha, black oat and radish at 25kg/ha, phacelia at 10kg/ha, white mustard at 10kg/ha and a phacelia and mustard mix both at 12kg/ha. The blackgrass levels were then monitored among other things. Steven noted that within as little as a year, there were visible improvements in the soil structure from the cover crop plots, particularly in those containing shallow rooting plants such as phacelia.
Like with any crop, establishment is key to successful cover cropping. At Stow Longa they used a culti-drill with a seeder on board, along with discs, tines, levelling and a packer unit. The right machinery is vital to ensuring seed to soil contact and good moisture context. Steve mentioned the importance of setting up the soil in order to drill later. This is particularly relevant to blackgrass management with the aim of minimal disturbance to the soil while planting the seed. Drilling in these plots for cover crops and crops are predominately by direct drills, to avoid bringing blackgrass into the germination zone.
Over the 5 years, Steve was able to compare yields, costs, and gross margins in the different treatments. Interestingly, the results from the best cultivated plots (Karat at different depths) averaged £547 a year and the results from the worst cover crop (fodder radish) plots averaged £350 a year. A reduction of 35% gross margin. However, this is a difficult scenario within in a blackgrass situation and whilst the absolute value of using cover crops to combat blackgrass is unclear, several other studies have shown that the changes in agronomy associated with cover cropping are able to manage blackgrass as part of a system of tools rather than the use of the cover crops directly. Additionally, some of the other cover crop species were getting close to the margins produced by the best cultivation plots with phacelia and mustard averaging only £40-60/ha less. Is this a cost worth paying for a more sustainable system? Well let’s have a look at what else is going on.
In summary, the experiment drilled and harvested 602 plots over 5 years. In these plots we can see noticeable differences in soil structure, health and biology between the cultivated and cover cropped plots. Blackgrass control is possible but as part of a system of techniques, cover crops alone cannot solve the issue. Averaged over the five years, cover crops did not produce better yields or gross margins but can get close with the right species for the soil type and system. Additionally, they have shown very good indications of providing long term improved soil health.
What can cover crops do for you and where to start? - Ian Gould
Ian is the director of Oakbank Game and Conservation ltd. He has worked with seeds for over 30 years having started his career at the planting and breeding institute in Cambridge. He started with Oakbank in 1994 who supply seeds and advice for Countryside stewardship and other environmental projects, alongside a woodland management division.
Ian began by stating that cover crops are an investment where the return is not always quickly clear to see. Repairing soil biology takes time, but Ian sees cover crops as doing this by working with nature. As stated in the previous talk, Ian agreed that determining a goal before cover cropping will help dictate the right mix for that goal. There is no perfect cover crop mix, you need to know what you wish to achieve in order to choose the right mix. These goals can be things like;
How do cover crops help soil structure? Plant roots give out a range of exudates that exchange nutrients and other products. One crucial product is glomalin, a sugar-like substance that helps to create soil aggregates. The pore spaces between aggregates have a large surface area to store nutrients and allow water and air infiltration. These spaces are vital to a healthy functioning soil. Other exudates play a key role in feeding the soil microbiology. A diverse (6+ species) cover crop mix helps to feed these processes as different roots produce different amounts of certain exudates, so the more variation you have, the greater support you offer the soil community.
How do cover crops help with climate change? At a farm level, climate change is providing increasingly erratic weather conditions. In order to continue our farming operations we must build as much resilience into the soil as possible. Carbon is the key ingredient for this. There is a vast amount of research happening about how to sequester carbon in soil. Two key messages from this research, firstly up to 50% of soil organic carbon is dead biology, necromass. Necromass is all the soil biology; fungi, bacteria, etc that die in the soil. The matter bonds to soil particles and forms a very stable form of carbon so the more biology you have in soil, the more necromass you will accrue over time. Secondly, roots are more important than shoots. Different plants have different rooting structures, mustard, for example, grows large above ground biomass but little root mass, whereas, vetch has a very large root mass. These roots are feeding biology deep in the soil and bringing nutrition up to the surface where it can be more easily reached by the next crop. This is just one reason why multispecies cover crop mixes are important. A mix that contains; pulses, legumes, radishes, cereals, among other things, can support soil, provide nitrogen (legumes), and feed biodiversity both above and below ground including large animals such as birds and mammals.
In order to get a successful cover crop Ian suggested drilling immediately behind the combine or as soon as you can, or even establishing it before harvest as he showed in a picture of an oilseed rape crop with an established clover mix growing up underneath. The harvested rape did not damage the clover and the field had no period of bare ground.
Ian finished his presentation by recapping a few points to consider as crucial first steps to cover cropping;
Cover crop and compost trials at Hope farm and in East Anglia - Rob field
Rob is a senior conservation scientist for the RSPB, joining in 2000. He has studied farmland and steppe birds, the influences of land management and land use change, the relationships into land use and climate change mitigation and biodiversity conservation. He lives on a family farm in a self-built 0 carbon house. So really, there is nobody better to walk us through the cover crop, soil health and biodiversity research taking place at Hope farm and other farms in the area.
The Hope farm project was a two-way field scale trial across three fields looking at how the use of cover crops and / or compost affect the soil and plant communities, soil organic matter and yield of the cash crop. The cover crop used in the trial was a simple black oat and phacelia mix, the compost used was green compost from green bin collection processed by high temperature composting. The two-way trial was looking at the singular and combined effect of these two components (figure 1).
Figure 1. Map showing the three fields in the Hope farm trial, split into four quarters, each with a treatment of either; no cover, no compost, or compost added, or cover crops added, or both cover crops and compost added
Unsurprisingly, the addition of compost to field quarters had a positive effect on soil organic matter, with a notable increase that was not found in the quarters that received only a cover crop or no treatment. After a couple of years, the soil structure of the no treatment quarters was compacted, with very little root penetration. However, the quarters receiving compost more organic matter in the surface zone, more friable aggregates and less compaction. The cover crop and compost quarters also showed this with the addition of the compost being dragged much further down into the soil profile. The quarters receiving both treatments had the most improved soil structure. The cover crop only quarters had improved soil structure in the form of aggregate size and friability, but it lacked the organic matter addition seen in the composted treatments (figure 2).
Figure 2. Visual soil assessment of the four treatments as labelled.
As well as the soil structure, the trial also looked at the invertebrates, including earthworms and foliar invertebrates. Earthworms are a good indicator species and are important to the soil ecosystem, by moving things around the soil and beginning the breakdown process of leaf litter. In the summer they are often forced into aestivation, a type of hibernation where they move down the soil profile, due to dry conditions as they need moisture to continue their work. This trial found that in the summer earthworm abundance in the rooting zones were significantly increased by the addition of compost due to the increase water retention the additional organic matter provides, allowing the earthworms to keep working even though it was hot above ground. There was an increase, though less so, by the use of cover crops, and an intermediate increase in the dual treatment, perhaps as the extra plant matter will have absorbed a little of the extra moisture.
The summer foliar invertebrate counts were more abundant in the cover crop plots, even though, by this time the field now contained the cash crop. This effect was seen still seen in the field of winter wheat, demonstrating a legacy effect of cover cropping the previous year (figure 4).
Figure 4. Foliar invertebrate numbers, showing the affect of cover cropping. The field quarters receiving cover crops have a might larger box than their nil cover crop counter parts
Additionally, the trial has been examining the yields of the cash crops following these treatments. The yields are very variable partially due to the initial learning curve involved in establishing cover crops. However, there is no significant yield drop between the conventional quarter and the treatment quarters, and yield seemed higher in quarters with any treatment compared to no treatment in oilseed rape. So worst case scenario is that cover crop wasn’t making matters worse with the crop yield but were making things better in other respects, i.e. the soil and biology.
Finally, the trial also looked at birds using the trial fields. The winter green cover provided by cover crops increases both bird abundance and number of species using a field compared to a winter cereal. Oilseed rape also had high numbers of birds using the field, presumably because it also provides a large green biomass quickly into the winter. However, the OSR did not have as great a species diversity as the cover crops (figure 6).
Figure 6. Chart on the left showing numbers of birds counted in each crop type and chart on the right showing the number of species counted in each crop type. For both abundance and species richness of birds, cover cropped fields held the largest amount closely followed by OSR, then winter beans, then fallow field, then winter wheat with the lowest.
Rob then moved on to talk about some work that was conducted other farms in the South East of England. A survey of seven farms comparing fields of disced stubble to fields containing cover crops. The survey looked at the vegetation, the above ground invertebrates, soil invertebrates and birds. The cover cropped fields had denser vegetation of many different plant species, causing a varied structure and providing a good covering of leaf litter. This translated into having more arthropods, particularly beetles, and also invertebrates that feature of the diet of birds. Earthworms also had larger populations in the cover cropped fields. Unsurprisingly following this, there was an increased in the number of insectivore birds also in the cover cropped fields.
In summary, compost increases soil organic matter and is good for earthworms, particularly in the summer as it helps the soil to retain water, allowing the earthworms to remain active nearer the surface. The cover crops influenced summer and winter foliar invertebrate numbers even after that cover crop is gone, with some lasting legacy effects. This then influenced winter bird use, particularly for insectivores. Soils under cover crops had more soil invertebrates of types more indicative of soil health, particularly worms. We are currently unclear as to the impact of invertebrate numbers on crops (pests, neutral or beneficial). There is more work to be done here but at the very least this seems to indicate that cover crops are neural, i.e. they do not damage your farming system or business, and quite possibly are likely to be beneficial in some respects.
If you’d like to watch this webinar it can be found on youtube here
If you’d like to tune into the rest of the series the following webinars are;
27th January 2021 6.30pm - Insecticide-free farming
Register to the event here
24th February 2021 6.30pm - Future Funding for Wildlife Friendly Farming
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