More water

I have been thinking a lot about water recently. I think about it as it falls from the sky (most days); I think about it as it flows off the field behind us, through our garden and into our next-door-neighbour’s garden; I think about it as I slosh through the mud to round-up the very soggy chickens (I’m thinking of trading them in for some ducks); and I think about it whenever I do the washing and have to dry it indoors.

In the UK, flooding seems to have been something of a theme of 2012, and the year-end is no different. Travel has been severely disrupted in the past few days as a result of flooding and landslides and not helped by a couple of fires associated with railway lines! Earlier in the year I wrote about the severe flooding in Aberystwyth and surrounding areas and discussed the issues associated with this, including building on floodplains and the impact of upland land use.

The recent flooding is particularly acute because the ground, having been exposed to months of wet weather, is saturated. This means that any water which does fall doesn’t soak into the soil, but immediately flows over the surface, quickly reaching streams, rivers and drains, thus potentially causing flash floods. So we could reduce this problem in the long-term both by having more tress in the landscape – to intercept water and slow down the rate that it reaches the soil – and by having soils that have a greater capacity to hold water.

It is the latter that I have been pondering over the past couple of days. Because our garden receives so much run-off from the field behind, we have had to build raised beds to prevent our vegetables drowning and we’ve had to raise the level of the area where the chicken enclosure is to prevent the chickens dissolving! The latter we achieved by using recycled plastic boards to enclose an area of about 11m2 that used to be lawn and filling it with wood chip. The wood chip now needs topping up (a job for the new year) as it has started to settle and rot down. We noticed earlier in the week that it was starting to get puddles on the top of it – despite still being about 10 cm higher than the natural surface of the garden. So, yesterday I decided to loosen it with a fork to improve the drainage a bit. And what did I discover? That what we have now is soil! Despite the wet conditions, the area is teaming with earth worms. We have inadvertently created a brilliant composting system – carbon from the wood chip and nitrogen (plus lots of other nutrients) from the chicken poo. I’m really quite excited about how efficient it has been… and how much water it is holding. I’m seriously thinking of setting part of it aside to grow potatoes next year!

Soil

The soil is an important resource for managing water in the landscape

The ingredients for a good soil – that is fertile and acts like a sponge – are right there in my back garden, so why aren’t they right there in the surrounding countryside? Well, the problem seems to be this balance between carbon and nitrogen. Soil micro-organisms need both, and if we upset the balance, we cause problems. Gardening books warn us not to dig wood chips into the soil because they will ‘rob’ it of nitrogen. In fact, what happens is that wood chip contains loads of carbon but not much nitrogen. Micro-organisms need nitrogen if they are to make use of all this ‘feast’ or carbon and, being really efficient critters, they scavenge nutrients much quicker than plants and so they grab all the nitrogen they can, leaving the soil somewhat depleted. If we are gardening, we avoid this either by composting our wood chip along with things that are nitrogen rich (like chicken poo, or kitchen waste) or by simply using it as a mulch on the surface, where it breaks down much more slowly.

This sort of problem does not occur in modern agriculture… quite the reverse, in fact. Many farmers these days apply inorganic (chemical) fertilizer to their land. This is usually either just nitrogen (N), or a combination of nitrogen, phosphorus and potassium (NPK). So the thing that is missing in this case is carbon. In soils, the carbon is present in organic matter, so when nitrogen is boosted by fertiliser application, the micro-organisms start to break down the organic matter like mad. And here’s the rub… the organic matter is the stuff that makes the soil act like a sponge. So, our modern farming methods deplete the soil of organic matter (regularly because fertiliser is usually applied every year). Taking a crop off removes the plant material that would, in nature, mostly be returned to the soil thus boosting organic matter. So, with modern agriculture, we end up with soils that water flows through or washes away (thus exacerbating the situation).

Things are improving in some ways – for instance, we no longer burn stubble after cereal production, instead we plough it back into the soil, thus returning some carbon. And lots of organic farming techniques value incorporation of organic matter into the soil, but we need these practices to be much more widespread if we are to reduce the potential for flooding. According to Toby Hemenway, good quality soil can hold about a quarter of its volume of water, so if your soil is 30cm deep, it can soak up 7.5cm of rain…. isn’t that astonishing? OK, you are not going to be starting from a completely dry soil, but what if the soil in your garden could hold that amount of water: acting as a ‘water battery’ and storing that water for when you need it, whist slowing its movement through the land during periods of heavy rain? So, good soil is not just beneficial in wet places, it’s great for dry places too!

As climate change leads to there being more energy in our weather systems, we are likely to get more extreme weather – wetter and drier. By developing good soils, we can buffer the negative effects of these changes and make everyone’s lives more secure in terms of food security and safety from natural disasters… all through thinking enhancing the health of our soils.

Leave a comment

7 Comments

  1. Deano

     /  December 23, 2012

    Hi Jan
    I am using this principle in a deep litter chicken house, which seems to be working well so far.
    Deano

    Reply
  2. We have been using our chook poo impregnated sawdust as mulch on a particularly deprived garden bed, I am glad to hear that it is such an attractive place for the worms to hang out, we really need them here!

    Reply
  3. Hello, I’m a bit of a lurker, from Montreal. My garden is hiding under about three feet of snow right now, but I really loved this post because it explains something I’ve been trying to figure out: the wood chips. My husband and I bought a house this year (well, last year now, I suppose), and the previous gardener had put in about 4 inches of dyed red mulch. That mulch has been there so long it is decomposing and can support weeds and the occasional worm. Reading your post reassures me about composting it (I had seen advice on line about not digging in wood mulch because it would ‘rob the soil’… but it is becoming soil on its own. Too bad we don’t have any chickens to speed it along 🙂

    Reply
  4. Deano

     /  June 2, 2013

    Hi Jan
    I actually think that the advice normally given is wrong. Adding Nitrogen justreduces the amount of atmospheric Nitrogen that could be fixed. Leaving the wood chip as high carbon organic matter gives a competetive advantage to Nitrogen fixing bacteria, who will happily use that advantage for as long as it lasts. Conversely, adding Nitrogen already produced just moves it from one place to another.
    Just a thought, and one of many contrarian thoughts currently occupying my thoughts.
    All of the best
    Deano

    Reply
    • Interesting, Deano. I’ve talked to several people who are very surprised about the amount of carbon that I put into my beds in the garden, in the form of wood-chip (from the willow hedge), waste cardboard and shredded paper without apparent detrimental effect. So perhaps you are right… I’m just giving my nitrogen fixers the carbon resource that they need, although I do add lots of grass clippings provided by my neighbours in the summer. I suppose that, without some detailed soil analysis, it’s impossible to tell whether I am making a net gain of nitrogen.

      Reply

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