Guest blog by Georgie Bray, Hope Farm Manager

Soil is the foundation that helps us to grow crops on the farm and look after so many of the species sitting at the base of the food chain in farmland ecosystems. Without healthy soils, crops suffer in our increasingly unpredictable climate, we leave land at higher risk of flooding, with reduced potential to sequester carbon, and of course a reduced potential to provide a diverse ecosystem below our feet as well. However, it is only in recent years that soil has been seen as more than just a growing medium for food by so many people. Even at Hope Farm, it is only in the last decade that we have focused more of our efforts to building biodiversity not just from around the field edges, but from the ground up – literally.a recent summer cover grown on farm August 2021

In recognising the importance of soils in farmland ecosystems, we have focused more and more of our research on soil at hope farm. More recently, there is our carbon farming project including an agroforestry trial, looking at the impact on soil carbon, economics and biodiversity. Cover crops and applying organic matter are two ways that we can improve our soils, and 6 years ago now we started to trial the implementation of these on our land, and the resulting impact on biodiversity. We wanted to look at cover crops and compost under the microscope, with an eye on crops, soil health and of course biodiversity, across three fields and 57 hectares on the farm. In 2018 we also moved out on to 7 other sites across the East of England, on clay-based soils, to see how cover cropped vs fallowed fields differed in terms of biodiversity.

Thanks to the help of donors’ money, to secure longer term management and analysis, and advice from Agrii, we have investigated the impact of cover crops and compost on worms, birds, above ground invertebrates, soil and crops for over five years now. This longer-term approach has been necessary as changes take time to realise in these kinds of systems. The support also helped to support this wider project about the impact on biodiversity in other farmed systems, which we are sharing the results of here. If you want to find out about the on farm results, have a read of our blog on the cover crops and soil health webinar from earlier last year, where Rob Field talked about the on farm trial.

What was the impact for biodiversity?
Thanks to this support, we have found that worms and above-ground invertebrates can benefit from cover crops, in our off-farm work. The insects above ground have moved in there to hibernate rather than live, including flies and aphids. We are yet to know if these aphids are arable pest or commensal species. Having more insects above ground could also mean more bird food availability in these habitats. We have also been able to reverse treatments of these plots with that continued support to add compost in the historic control plots in the fields, which will enable us to reduce risk of future carryover effects in future experiments on farm.

Interestingly, we have seen that as well as insectivorous birds like skylarks, pipits, and partridge, birds which typically feed on seeds overwinter are also using the cover crops. This unearths yet more questions about how these habitats may deliver for nature, and if these birds in-fact feed on insects if they are available overwinter.

We are asking yet more questions of granivorous birds. More granivorous birds were found than expected which may mean they're feeding on insects due to increased availability if they are able to feed both both insects and seeds - like yellowhammers for instance. We are not entirely sure what they are doing in these fields though. 

Learning along the way…
Something that was unforeseen at the beginning, and perhaps is one of the most obvious benefits, is the agronomic learning about how cover crops work on clay soils. We started the project with a simple two species mix of black oat and phacelia back in 2015. At the time this was deemed as a good mix to use, but in more recent years we’ve learnt a lot more about what mixes suit both our crops and benefit the soils, with the help of these extra sites we visited in 2018. We tend to go for much more diverse mixes now, that are broadleaved based to better suit the rotation that features more spring barley. The mixes are now varied depending on the crops they follow and go in front of to ensure a good compromise between delivery of soil benefits, cost, and time we have to establish a cover crop. Buckwheat for instance establishes so quickly but dies off within a few months and so is good as a catch crop ahead of a winter crop. The radishes take longer to get going but can deliver benefits with their deep fat roots for breaking through compaction. We still use phacelia as that establishes well, is useful for processing nutrients, and has lots of fine roots breaking through shallow soil compaction. Clovers, vetches, and other legumes are also handy if we have the time between crops and before the weather gets cold after drilling, as they can fix a bit of nitrogen to provide for following crops.

What’s next?
We have learnt a lot about how cover crops work, and potential impacts on biodiversity – but this has also predictably led to many more questions! Next, we want to find out more information about the impacts for different functional avian species groups, be that seed or insect eaters, and on invertebrates too. Yellowhammers have used the cover crops, but tend to feed on seed overwinter – so are they feeding on insects instead, and do some cover crop species serve better at providing this habitats than others? There are also indications that cultivations negatively impact the value of cover crops for birds, and this requires further investigation. The off-farm part of the cover and compost project has been really useful for us, and outlined the variability between different cover crops and benefits to different species – although with high variability and a small number of sites, it gets much trickier to unpick non-spurious results.
To help overcome these problems, we look forward to going back to our trial fields at the farm and work on different cover crops in more detail.