[permaculture] arid soil building
diebrand at yahoo.com
Mon Dec 14 14:27:23 EST 2009
The typical weather pattern of a Mediterranean climate is dry and hot summers and wet and mild winters; having said that, there are huge differences from one place to another. Even in recent discussions, we have heard of annual rain falls varying in a rang from 300 to 800 mm per annum, and the actual range is probably even larger. And if you add different types of soil, it is very difficult to generalize.
As I mentioned before, in our hillside property of depleted heavy clay, almost every square foot of land performs differently. And, when I go 5 miles further to the Ocean, there is flat land with deep sandy soil on top of a layer of clay that practically never dries out. Many plants will grow there even without irrigation that wouldn’t survive on our land at a distance of only 5 miles. Portugal is a small country, but there are considerable differences in climate; in the North and Center it has been raining for months now, while we hardly get any rain in the South. Parts of the North look as green as Ireland all year round, while in the South the climate is more like North Africa.
>Med climates don't lack water, they lack fertility!!
I don’t believe that is true, at least not in our place. Even though our heavy clay looks a light shade of yellow when dry, it does produce good growth with sufficient humidity. For example, once in a while we get a very wet year with 800 mm or more of rain. In many places the clay gets as soft as butter and my foot sinks in an inch or more. In other years, the soil stays dry for most of the year, especially in higher laying parts. In a wet year, weeds and grasses will be as much as three times taller and denser than in a dry year. The limiting factor here is water.
>/manage your soil cover/.
Personally, I don’t like bare soil dry land farming. Too hard on the back and too hard on the soil! But from those of my neighbors, who still practice dry land farming with dirt mulch and manure, I do know that results are much better then what can be achieved with organic mulches. Also, while it is possible to do mulched gardening with irrigation on a small scale; there is no way this can be done on a larger farming scale and without irrigation in this region. Anyway, whether we collect mulching material from the surrounding land for feeding the garden or whether we use manure from goats that feed on the surrounding land, the effect is the same. In both cases we need to import fertility into the garden from the surrounding land, which is too dry to produce food crops. There may even be a case in favor of manure over mulch in that manure does stay in the soil for a long time, while with mulch (or compost) some fertility may be gassed off into the
atmosphere, especially during the dry season. But here too, it is difficult to generalize; the answer to the question of which involves the fewest losses: manure, compost or mulch, will very much depend on local conditions.
>And any strategy that increases fertility will increase water.
That is true. Soil I have improved with compost, mulch, cover cropping etc. for the last 10 years has much better tilth and can hold much more water than soil that has not been improved. Comparing improved and not-improved soil side by side, I can detect a difference in growth of a factor of about 10. However, while this type of soil improvement is possible on the garden scale, it is not feasible on the farming scale.
Well, I hope this provides another point of view.
PS: Part of our property is densely covered by perennials such as cork oaks and madrone. Some of the cork oaks are huge and must be several centuries old. When one of these giants tumbles over, its roots rip open the soil and expose a section through the soil with only a couple of inches of loose forest soil covering the heavy clay. In other words, even after constant forest coverage for several centuries without any cultivation whatsoever, there is still hardly any dark topsoil. So, yes tilling is bad, but it doesn’t explain everything. This climate just does not produce the type of humus-rich dark soil typical of temperate or cold climates. It does take the labor of the farmer to grow food crops. And I think it’s best to keep an open mind as to which method or combination of methods works best under local conditions without excluding any method from consideration.
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