A blog on soil health by Georgie Bray - RSPB's Hope Farm Manager

Playing the waiting game!

Sitting in the farmhouse office, looking at another day with grey skies and puddles on the patio, you can’t help but wonder how much more rain can fall from the sky. It has been one of the wettest winters in our memory at Hope Farm, and although my memory is short, many other farmers have been saying how abnormally difficult this season has been. With Hope Farm sitting on heavy clay land, we are sitting tight for most of our drilling.

It is the year to be grateful of improved drainage in recent years, where water has been able to get off most of the fields. Alas, it is still frustrating to know that if our soils were that bit more resilient, we could make the more use of the few and far between dry windows. With soils under such pressure, it seems appropriate to reflect on how we are working to improve soil’s and so farm business’ resilience, and how we could further improve should these freakishly wet (or even dry) seasons reoccur.

So, what does soil health mean and why do we need it?

Every farmer has a pretty good grasp of good and bad soil but trying to describe it can be quite difficult. AHDB have done a good job of summarising soil health by breaking it down into three factors: physical, chemical and biological soil health. All factors are interlinked but breaking it down like this helps us to have a better idea of what we need to do to improve soil.

Physically, you want to have a good structure, with air and water pockets – that way, the biological components can breathe, roots have space to work and find nutrients, and it forms a kind of sponge. Chemically, you want soil to sit close to a neutral pH (although chalky soils are slightly alkaline). You also need the right balance of nutrients for crops to grow. Soil organic matter is also a fundamental component that we’re always looking to improve on. Biologically healthy soil means having a healthy and functional biodiversity that helps to process all the nutrients, make it available to plants, and maintain/create an optimal soil structure.

These benefits are sold largely for their agronomic benefit, but we are also interested in another reason. Having healthy soil allows for a diverse underground community that provides the building block for a diverse farmland ecosystem, reducing agricultural inputs whilst increasing the farm’s sustainability.

How do we monitor our soils on the farm?

At Hope Farm, we monitor our soils as part of both our long-term research projects and across the farm.

We are researching the impact cover crops and green (food) compost can have on the soil health, wider biodiversity, crops, and the farmers’ profit margin. Firstly, we’re monitoring soil biodiversity using monoliths and pitfall traps for larger soil invertebrates including worms, extraction methods for the smaller biodiversity, and DNA analysis for even smaller. Physical structure is assessed using bulk density analysis and (very technical!) spade digging. Chemical changes are assessed by looking at macro nutrients including soil organic matter and labile nitrogen. Crop yield performance is analysed using spatial combine data. All this together should give us a great indication of soil health, that we can look at in conjunction with the impact of these inputs on bird diversity. Although a thorough way of assessing cover crop and compost’s impact on soil health, this regime isn’t really what we can replicate across the whole farm. For the other fields, we take a slightly more pragmatic approach.

Worms are a good means for indicating soil health. These guys are good at improving soil drainage and cycling nutrients in the soil. If the soil is particularly disturbed, or there isn’t enough of the good stuff for them to feed on, you won’t find many worms. A good biologically active agricultural soil is meant to have at least 8 worms per spade-full if you go digging in autumn. When you start to look at the 3 groups of worms though (anecic, epigeic, and endogeic), you can get an even better idea of what’s going on. Where we have been using compost, there were lots of the green endogeic worms that are top soil feeders – as there is plenty of organic matter in the soil for them to feed on. Anecic and epigeic worms are litter feeders. We’re additionally interested in the diversity of worms and other larger critters in the soil as they provide a good source of bird food.

Although a bit subjective, you can get a good idea of what’s going on in the soil with a spade. By digging out three sides of a square, and lifting a monolith out the ground, you can see where the soil cracks (horizontal pans or to form crumbly aggregates), where the roots are penetrating, how it smells and how easily the soil breaks up in your hands. This has been useful for us on the farm where we’ve underlined areas that need subsoiling, to lift the compacted structure deeper in the ground, whilst leaving the top relatively intact.

There are lots of tools, apps, and scorecards out there to benchmark your soil health, returning to the same points year on year to monitor changes and hopefully monitor improvement. These are all things that we are starting up on the farm, to try and improve our knowledge of what the soil is doing further afield than our trials.

What are we doing to promote good soil health?

Historically, we have had to fit field operations in to a larger contractor’s busy schedule, and although sometimes necessary, that wasn’t always for the greater good long term. We do have a few core principles implemented now though that are improving the farm’s resilience for future years, enabling us to reduce cultivations on the farm, to grow high yielding crops with lower inputs and with high biodiversity (above and below ground).

Dealing with compaction in a timely way

Currently, we are dealing with historic compaction issues as a must but maintaining the long-term and patient view for management. Last autumn, we prioritised the most compacted fields to be cultivated. With the heavy rains through winter, we are pleased at least that the aerated soil is draining reasonably well, but at the same time have the downside of bare soil potentially leaching nutrients. It is always a balancing act, but other principles we’re working on for future years should help to remedy this catch-22.  

Keeping green cover on the land

Cover crops are a key to us reducing our cultivations, holding on to nutrients, and drawing water above the ground – the basic principle that we’re advocating and practising more, though, is to keep green cover on the soil. This year, we have extended the use of cover crops to beyond our trial fields, and before autumn sown crops as well as a spring sown crop.

We’re leaving volunteers for as long as possible before drilling. This winter, I am pleased that volunteer beans and spring barley were left up to the line that we knew we could drill. Those fields are sitting green now, not with a crop, but with volunteers that are at least keeping nutrients in the ground and drawing moisture out.

Where we’ve used cover crops for nearly 5 years, the cash crops in general look better, and where we have cover crops in the ground this winter, we don’t end up with half the field on the bottom of our wellies after a field walk (compared to some other parts of the farm!).

Adding organic matter

Until autumn 2019, we only used green (food) compost alone, as part of our field trials. It is rich in phosphorus and organic matter, although very low in nitrogen content. This year, we have been working more with neighbouring farms and local stables to get chicken muck and horse manure onto the farm. This way, we can not only increase the organic matter but also start to replace some of the inorganic nitrogen use on the farm with manures. To date, we’ve found an improvement in both worm numbers and crop growth where we’ve been using compost. Going forward, we hope that soil conditions will improve further on trial fields and on more of the farm with wider applications, on a rotational basis.

left (without compost): grey and dead looking with few worms and being hard to break apart. Right (with compost) spread over 4 years: crumbly darker soil with better aggregates, lots of worms and roots penetrating further through the soil profile.

Although across the farm, and the county, it’s a sorry story of either losing time to get winter crops in or struggling to manage a winter crop that is already drilled, it’s still worth noting everything we can do to stay resilient as a farm business in a bad weather year. It’s tempting to go ahead and get more in the ground, but we’ve stuck to our principles of keeping the green cover where we can and leaving the soil structure as intact as practical with timely operations. It may come in a few weeks that we bite the bullet with our remaining fields, and drill in reasonable rather than optimum conditions. Until that time comes, though, we maintain a long term view of the business’ resilience, looking after the soil so that we can grow profitable crops for the long term.