Guy’s news: I wish they wouldn’t call it ‘dirt’

A week of rain has restored soil water to ‘field capacity’, much to the relief of our crops and hard-pressed irrigation team. Field capacity is the maximum amount of water the soil can hold: what’s left clinging to the particles after gravity has drained away what it can, but before evaporation or root absorption remove any more. Imagine a wet sponge left to drain for a bit but not squeezed. The finer the particles and the larger the area, the more water can be held.

As a very general rule, well-established plants start to suffer when about half the water held at field capacity has been lost (the ‘wilting point’). The difference between the field capacity and the wilting point is the ‘available water capacity’ (AWC), and is hugely variable; it can be four times higher in a sticky, heavy clay than a coarse, light sand. As well as water, clays also hang onto nutrients better, making them potentially more productive than sands – but also more prone to waterlogging and structural damage, harder to create a fine seed bed, and
generally harder to manage. Clay-land farmers refer to sands as ‘boy’s land’. The sweet spot is a sandy clay loam which has a mixture of particle sizes (large sand, through silt, to very fine platelets), combining their best qualities.

Too much info? Actually, that is a gross simplification. You could spend a lifetime studying soil and still be ignorant. Though its physical makeup is important, farmers’ management of the soil also has a massive, long-lasting effect. Adding organic matter, particularly stable and mature compost, can, over years, increase sands’ ability to hold water, and make clays easier to manage by stabilising the structure. Increasing the organic matter in a sand from 0.5% (typical of an over-cultivated, chemically fed arable sand) to 3% (more typical of well-managed sand in an organic rotation) could double the AWC, allowing crops to thrive well after they would have wilted. The impact of good soil management is huge – not just in agricultural productivity, but also in reducing flooding, fighting climate change through sequestering carbon, controlling water pollution and increasing biodiversity. Organic farmers are well ahead, but conventional farmers are starting to get interested in proper soil management too. Perhaps, after half a century, we have finally managed to show them what is possible.

11 responses to “Guy’s news: I wish they wouldn’t call it ‘dirt’

  1. Tessa Hillman

    Very interesting and important. Thanks Guy

  2. Fascinating. Thanks Guy. Never too much info!

  3. There’s slways more to learn…
    Too much information? Here’s a load more!! 😉

    And thanks for your great talk at Business Forum Mid Devon last night.

  4. Yes, another thank you to Guy, from a thinking gardener.

  5. What an interesting read! Good to hear that other farmers are thinking your way, or beginning to.

  6. Vivien Cruickshank

    Very sad to think that the soil in conventional farms is dead, lifeless and contaminated with chemicals. These farmers are environmental criminals.

  7. Great info…I’m glad it’s finally raining too….just hope it doesn’t carry on like this all summer. Organic matter…and farming…rules! Still loving the veg box… thank you.

  8. Is there any sandy soil in the UK? I thought the lack of it explains the absence of white asparagus which is a very popular delicacy this time of year in Germany where it is grown in the sandy soil of the North German plain. It is thicker than green asparagus and not so woody. It is peeled before cooking, but if you want the full flavour you make a stock with the peels and cook the stems in that. Served with new potatoes, sauce Hollandaise and wafer-thin slices of smoked ham. Hmm!

  9. Tell us more about the soil biome, please.

  10. “I wish they wouldn’t call it ‘dirt'”
    Referring to ‘soil’ as ‘dirt’ seems more prevalent among those who have grown up in cities and without gardens, and it does come across as a lack of respect for the soil. But then, if you refer to a garment as ‘soiled’, how does that differ from ‘dirty’?

  11. I learned a lot from the blog. Thanks Guy. Wouldn’t it be nice if we grow organic plants without using harmful chemicals. The food that we eat from farmers are filled with harmful chemicals. The farmers also pollute the water because of irresponsible farming. I think there should be regulations with the use of this harmful chemicals. Animals are also affected with the use of harmful chemicals. Is phosphorous-free farming possible?

    Please check out my blog if you can:
    http://all-about-water-filters.com/save-our-water/

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