Probing our soils with GROW Observatory

Interpid soil testers – Kaska, Laura and Cathy.

As gardeners, we hardly have to be reminded about the importance of soils for growing. We know that without productive soil our gardens and crops fail. Understanding soils in our own growing patch and how to care for them is the first step to a productive garden. With this in mind, this month we have explored soils at the Community Garden with a free online course From Soil to Sky, offered by the GROW Observatory project. In the process we also contributed our data to the GROW Observatory project database, which will help build a picture of soils across Europe and monitor their health through remote satellite sensing.

Kaska was joined by Cathy, one of our bloggers and experienced Tayport gardender, to work through the 4 week online course, which finished last week. Cathy worked through the hands on activities in her own garden, and last Sunday, they both joined forces with another volunteer, Laura, to put our growing patch at the Tayport Community Garden through its paces.

The course covered a vast amount of material and we picked out some highlights for you below.

Soil is Earth’s living skin

The driest definition of soil describes it as 45% minerals, 25% water, 25% air and 5% organic matter. After exploring the course’s other materials we prefer to think about soil as Earth’s living skin instead:

“Most of the planet is not living. It’s mineral, it’s never known life, it’s just this rock and yet soil starts forming on it and it creates this very thin layer where life is possible.

Soil is the interface between biology and geology – it’s the living skin of the Earth.”

Those lines come from an inspiring documentary film Symphony of the Soil, produced in celebration of the Year of the Soil in 2015. Kaska wrote more about this and growing her own soils with worms in her post from last year.

Healthy soil protects us

Much is made of soil as provider of our food (up to 95% of our food is grown in soil) but it looks like healthy soils are equally important for keeping us safe from floods and climate change. We were stunned to learn that with careful management soils can store up to 75% of our carbon dioxide emissions and have a substantial impact on preventing climate change. In recorgnition of this, the French government has included management of soils for carbon storage as part of France’s climate change prevention strategy. If we follow in their footsteps we’d also end up with healthier, more productive soils as a bonus.

Our growing patch – climate, microclimate and topography

Cath and Laura examining land cover and canopy cover in a low raised bed area chosen as a representative site for our GROW Observatory analysis at Tayport Community Garden.

At a global scale, the interplay between rainfall and temperature is the major factor determining the type of vegetation which evolved to grow in a particular area (or its biome). This interplay influences how much moisture is available for plants – the more moisture available, the larger and more lush the plants in the local biome (this is all to do with balance between PET and AET but we will leave the technical terms aside here). In Tayport we have a reasonable, but not overwhelming, annual rainfall of 664mm, combined with relatively low average temperatures of 8.3°C (Source: climate-data.org). This means a reasonable amount of moisture allowing for development of a wet/dry temperate forest biome. Of course, our changing climate means that we are expecting our area to get wetter and warmer in the long run, which will influence not only the local biomes but also the types of crops we are able to grow (for the most up to date predictions see the RHS report on Gardening in a Changing Climate published in 2017).

The microclimate of each locality also has significant influence on growing conditions. At Tayport we are near the river and the sea and their influence causes our winter temperatures to be slightly higher than inland Fife, so we miss out on many snow and frost days. Since we started working at the Garden last year, we have realised that the site is also very windy, despite being surrounded by lots of trees. During April’s drought this meant that the soil had been drying out very quickly and we’ve had to protect it and the young seedlings by covering planted areas with fleece.

Topography also plays a role – our Garden site is fairly flat so at first sight you would not expect much variation in growing conditions. But when you look closely it actually does have a minor slope of 2-3° in several directions, and a few small dips. Last year’s winter flooding highlighted the impact of these minor topographical features on water content in the soil as the lower-lying areas became waterlogged and muddy. The dry winter and spring made those much less obvious this year but this may become more of a problem with the expected increase in longterm average local rainfall due to climate change. So far we have tried to adapt to the wetter areas of the Garden by using high raised beds and creating a living willow tunnel/wildflower meadow area.

Getting a closer look beneath our feet

Soil pit near curling pond showing ‘native’ soil horizons. Note the lack of stones in the topsoil.

Soil pit at the Garden showing the depth of the rubble layer.

Laura thought that exploring soil profile and texture was the best part of our hands on session on Sunday – she was surprised by the complexity of what’s beneath our feet. But the process was not without its frustrations!

If you were one of the unfortunates involved in our ground bed prep you will know that the major ‘feature’ of the soil in the Garden is a thick layer of building rubble lurking around 20-30cm under the soil surface. By talking with the local residents, we have learned that the site was filled with rubble by the council around 30 years ago, covered with a thin layer of soil and topped with the lawn. So when asked to find a site representing native soil of our growing patch we had to get a bit creative…

Thankfully, we remembered that earlier this year the council dug a couple of ditches to check for the historical drainage pipes used for flooding the curling pond area (and which propably contributed to flooding of the site last year). This allowed us to see the soil’s profile to a considerable depth. We thought we could see the thin, darkly coloured organic matter layer (O horizon), followed by at least 50cm of subsoil where organic and mineral components mix (A horizon), which gradually merged into around 50 cm of subsoil with mineral components (B horizon). Of course, as amateur soil scientists, we may not be 100% right on this!

Soil from the native pit

Soil prepared for texture testing – all stones removed and lumps crumbled up

We extracted soil for texture analysis from the lowest part of the mineral horizon and conducted a touch test and sediment test. The touch test was very quick and easy to interpret, but gave less precise results than the sediment test.

Soil texture touch test indicated sand as the saill ball would crumble and not stay together.

Sediment test for soil texture – 80% sand, 29% silt and 1% clay (Sandy loam).

We were not surprised to find that both indicated that the subsoil was predominantly sandy, with little silt and almost no clay. Cath’s garden soil tests gave similar results and both are representative of soils in flat areas around Tayport. This sandy soil allows for good drainage but dries out very quickly and needs constant additions of organic matter to assure fertility and moisture retention. In contrast, a quick touch test of the top soil in one of our ground beds indicated a much heavier soil with significantly more silt and clay. This makes us think that the soil covering our growing area was brought in from elsewhere and has different properties to the soil native to the site. So it will require a different treatment to get the best out of it. Our high raised beds also contain imported soil from elsewhere in Fife (we have not tested those yet).

Of course, we also know that if you are based on the slopes of the hill in Tayport, your garden soil will have much higher clay component too!

If you’d like to have a go at soil testing in your own garden you can follow the instructions in the Permaculture soil testing handbook – PDF (this will not replace professional soil testing services but will give you a good understanding of your garden soil).

Growing our soils to grow our food

The last week of the course emphasised that the world’s soils are in trouble and that we can all make a difference by growing our soils using a range of regenerative growing techniques. We were also asked to summarise what we do in our own growing spaces.

Kaska, with help from Peter, our gardener, compiled the list of practices we have used in the Garden so far:

We’ve only been on the site for a over a year so we are still at the stage of establishing our growing space and it’s likely that our techniques will change over time. Shortly after we discovered our hidden soil feature, we gave up trying to dig our beds into the ground and build some low and high raised beds. Our massive potato patch was dug through using an excavator to break through the rubble. We’ve been removing a lot of stones from all those beds since! For the raised beds we imported top soil from elsewhere. To improve the soil we have been adding compost, rotted through animal manure, and rockdust to all the beds. Last year some beds were put under green manure which was dug through (the phacalia and clover mix also fed our pollinators). The newly imported soil is rather ‘lumpy’ and we hope that growing potatoes in it this year will help break it up.

We use rather conventional gardening techniques but trying to stick to a chemical-free credo as much as possible. All beds are dug through and weeded. We use some intercropping (e.g. sowing fast growing radish amongst the slow growing parsnip), double cropping and crop rotation. We have done some mulching around our fruiting hedge and use fleece to reduce water loss from the soil on the garden beds. With unpredicable weather, Peter does not want to risk putting too much mulch down amongst the vegetables even with such a dry start of the year in case it case the weather turns wet later in the season. We try to create feeding and nesting areas for pollinators – our annual wildflower mixes, wet meadow area, and sensory hedge all designed to contain pollinator-friendly plants. We have started a compost and a wormery which hopefull will help us feed the soil in the future. We don’t have a mains water and rely on a rainwater collection system (topped up by kind donations from our neighbours). At the moment we hand-water everything but will be installing watering systems throughout the garden and the polytunnel, to be powered by the solar panel-based pump.

Cath has compiled her own list, based on what she’s been doing at her sandy soil Tayport garden over the last 20 years or so:

General. I grow veg in raised beds with native soil enriched with home-make compost. I try to avoid digging my raised beds too deeply as the subsoil (sand) isn’t that far down. I grow plants in blocks and practice crop rotation up to a point. It’s all very well in theory but doesn’t work if you grow more of one family (in my case brassicas) than another (onion family). But I do what I can. I should do more mulching as it definitely conserves moisture. Paths are mulched. I water with a watering can only in dry weather. I used growmore fertiliser generally, and slug pellets but only in areas wild-life can’t get into.

Arranging your growing space. I use intercropping, eg radish between slow-growing parsnips. Double cropping within one season is a bit tricky in Scotland with the shorter growing season, although I will replace early maturing crops (broccoli) with an overwintering crop such as chard. I grow plants in smallish blocks so I suppose that’s multicropping, but all brassicas are grown together since they have to live under insect barriers.

Covering your soil to increase protection and fertility. I use bark mulch on paths and otherwise unused areas and was surprised how effective it was at keeping the moisture in as I dug down beneath it to plant some parsley plants and the soil was still moist even after a month of drought. The only problem is that the blackbirds like to turn it all over so it wouldn’t work that well for vegetables.
I sow phacelia whenever I have an empty area and it’s quite an effective green mulch although there’s not that much organic matter to dig in. Clover was more effective (grown in the past) but I don’t have enough garden to be able to give up an area to clover which needs more than one season to get going.

Compost. We compost everything in three large brick built compost bays, including all the stuff you’re not meant to. Chicken poo from our small flock of 3 chickens really gets it going and it gets incredibly hot in the summer, although not enough to kill all the weed seeds. It gets turned over regularly which is important, and is left to ‘mature’ for at least a year. The bays were faced with scaffolding planks which rotted but they’ve now been replaced with plastic wood (recycled plastic) which works well.

Of course, there is much else you can do with soil testing, and taking care of your soil. In fact, we already did professional lab tests last year to check for contamination and nutrient status – you can see the results here (PDF). We have plans for more hands on stuff you can get involved in too.

Watch this space for further reports on GROW Observatory experiments and more soil-related fun. We are particularly excited about looking at our soil life. In June and July we are planning a couple sessions on soil micobes, and we will be exploring our earthworms later in the autumn. I hope you can join us!

In the meantime, tell us what you know about your own soils and how you take care of them. Any interesting growing techniques and tips you can share?

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