[permaculture] arid soil building
diebrand at yahoo.com
Fri Dec 4 06:37:25 EST 2009
I live in a severely dry type of Mediterranean climate with between 12 to 25 inches of rain per annum usually between October and April. However, this year we didn’t get any real rain from February to November, and with temperatures in the 80 to 90 F range from March through October, the soil has been dry for about 9 months. We have a badly eroded hillside property with heavy clay and hardly any top soil. In some places there is not more than a foot of clay and rubble on top of the solid rock.
Traditional farmers here, like in most arid regions of the World, use tilling and manure for Dryland Faming with a Dirt Mulch. The dirt mulch is extremely efficient in cutting soil evaporation to zero. If it does rain or if irrigation is used, the soil needs to be hoed immediately afterwards to prevent soil humidity evaporating through the capillaries forming in the soil crust. Irrigation is performed by flooding channels between the rows. Plants are widely spaced. With zero evaporation, no transpiration through weeds and wide spacing it is possible to grow crops from May to August with _zero rain_ because all remaining soil humidity can go to the food crops. Wheat is grown from November to June. This season, farmers will loose the cool season crop, because it only started to rain in December, which is too late for sowing so as to get a harvest before the next dry season.
This type of _bare-soil cultivation_ has permitted generations of farmers to make a living under very difficult circumstances. On the downside, it is extremely hard labor to hoe a field in the scorching sun from morning till night. There are a few old farmers who continue the tradition even today, but for young people who leave the land for the city it is far too hard. The constant soil disturbance due to tilling and hoeing which is often performed during high temperature is also very bad for the soil. As long as the soil was fed with manure, soil organic matter and fertility were maintained, but with the increasing use of synthetic fertilizers, the soil is bound to suffer even more.
I have therefore experimented with _covered-soil cultivation_ typical of Natural Farming from rain-rich Japan. My experience is that an _organic mulch_ can never be as efficient as a _dirt mulch_ in preserving soil humidity. After years of tests I found that, in my unimproved clay soil, dry land crops like beans etc. will at most survive for 2 months under an organic mulch without water (no rain, no irrigation). In a soil that has been improved by compost, mulch and cover cropping for 5 to 10 years, the same crop may survive for 3 or more months and even produce a meager harvest, but it is hardly worth the labor.
When irrigation is used with a covered soil, much water is lost because it evaporates in the soil surface or the mulch layer. Once the soil is dry, most irrigation water will run off the surface, vole tunnels or ant hills, without penetrating the soil. Here again, the flooding used in traditional farming is a lot more effective since no water is lost; it all goes directly to the plant roots in the subsoil.
After about 10 years of soil building in which I put a new humus-rich layer of topsoil onto the clay, I can grow most of our food without plowing, without fertilizers or any external input whatsoever, simply by returning organic matter to the soil. But if I wanted to make a living by farming, I would have to use manure and tilling as in traditional farming.
I think organic matter ought to be returned to the soil as _a living substance_ to feed the soil organisms and not as _a biologically dead_ charcoal substance. Biochar advocates claim that it improves water retention. This may sometime be the case for sandy soil, I have no opinion on that. But I believe charcoal may even reduce water retention in clay soil or make it water repellent when it dries out completely as it does in the dry season. I have made very good experiences with organic matter in different forms (mulch, compost, humanure and even entire wood logs). It is the best way of improving depleted heavy clay. I do sprinkle the ashes from our wood stove on the fields, but I would never add charcoal. Nor would I add lime, rock dust or a million other soil amendments offered by the shopping malls of alternative farming.
--- On Thu, 12/3/09, Rain Tenaqiya <raincascadia at yahoo.com> wrote:
From: Rain Tenaqiya <raincascadia at yahoo.com>
Subject: [permaculture] arid soil building
To: permaculture at lists.ibiblio.org
Date: Thursday, December 3, 2009, 9:21 PM
We live in a classic Mediterranean climate, with about 35 inches of rain that comes in intense bursts that usually start from the middle of October and start petering out in April. I feel there must be a lot of knowledge about this climate given its long history in Europe.
I have started to compost in pits because it takes so long above ground. I have even used tarps, as was recommended. They help, but I really need to irrigate the piles to see reasonable results. We have all sorts of fungi from the forest nearby, so I don't think inoculants are necessary.
Part of my problem could be that aside from the first year, when we had record floods, we have been in a drought. Maybe this is the new normal, however.
We collect and use all of our humunure and urine, and I bring in a ton of leaves and straw from around our site. I also have several long-term wood compost piles. I finally broke down and got some rock dust, zinc sulfate, and gypsum, for specific areas. I've also brought in forest soil from nearby for the main food forest and kitchen garden, which also got a layer of horse manure from a neighbor. I'm thinking about spraying seeweed on trees that are doing the worse. In general, however, I really want to minimize off-site inputs.
As far as biochar goes, the soil actually has a fair amount of charcoal from past fires. I couldn't justify putting all that carbon in the air by burning all the wood around our site. If I wait long enough, a wildfire might do it for me, however. Hmm, interesting.
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