[permaculture] heavy clay and cover crops, more on shade

Dieter Brand diebrand at yahoo.com
Thu Mar 19 19:04:02 EDT 2009


Each soil and each climate poses its own challenges; and solutions may vary accordingly.  I deal with extremely severe conditions both in terms of soil and climate: my heavy clay soil has been ploughed by previous owners to the point where a mere 15 inches of pure clay and rubble devoid of any topsoil are left on top of the rock bed.  In addition, the semi-arid climate with a dry season of about 5 months doesn’t allow for much biomass production during the main growing season in the summer.

In the last 12 years, I have tried most scenarios:

On the garden-scale, I made huge amounts of compost (rows of 50 plus meters per year) for integrating into the garden soil.  However, this is only possible on a small scale.  Sometimes I didn’t manage more than 2 to 3 square meters a day because in addition to digging in the compost I had to remove large stones, crab grass etc.  After more than 10 years, I now have a quarter acre garden with good soil where I can grow most of our food (all of our vegetables, salads, legumes, etc.) without ploughing and without fertilizers.  I don’t even use compost anymore.

On the fields, I cut the grass/weeds at the onset of the dry season for use as mulch (I stopped making large amounts of compost).  On average, I use the biomass of 3 acres to mulch 1 acre.  I broadcast beans, squash, sunflowers, millet, corn and other seeds for dry lands before mulching.  Then I water once or twice (in April and May I still have enough water, during the summer, I need all the available water for the garden).  This usually keeps the crops alive for about 3 months without rain; longer on good soil.  On a strip of land where I have repeated this for 3 years, the grasses/weeds are now about 3 feet tall, while on the surrounding land the growth is a mere 3 inches.  This gives me nearly enough growth on this plot not to transfer anymore biomass from other fields.  And I can start on improving the next field.

On the hill-sides, I use native perennials which I cut/shred on-site after broadcasting seeds.  I’m also testing closely spaced fast growing acacias which grow without water during the summer to use as sacrificial trees.  But this is a long-term project.

I have experimented with all kinds of cover-crops for biomass production and for loosening the soil, but in the end it is usually the native grasses and weeds that proof to be best.  Basically, anything that grows well and produces a lot of biomass under your condition is good.

Clay soil is very good, but it needs to be covered by a layer of topsoil.  It doesn’t have to be a foot thick; already an inch of dark dirt rich in organic matter can make a huge difference.

Ploughing will loosen the soil temporarily, but it destroys soil structure and will result in even greater compaction before long.  The only way to improve a heavy clay soil is by organic matter, if possible, applied to the top without ploughing.  The soil needs to be covered at all times, preferably by a life mulch, and if that is not possible, by a dead mulch.

Depending on climate, a mixture of annuals and perennials (trees, bushes) works best.

Dieter Brand


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