Posted by Herve | Posted in Sustainable agriculture | Posted on 18-07-2010
Tags: agricultural practices, food crisis, myth debunking, soil erosion, thinking differently
Throughout history, the richness and health of their soils has made the underlying power or utter downfall of nations and empires[1]. Over the past century mankind has witnessed an increasing trend towards top soil depletion[2], threatening the very basis of our complex societies[3].
“Soil erosion is second only to population growth as the biggest environmental problem the world faces,” said David Pimentel, professor of ecology at Cornell. “Yet, the problem, which is growing ever more critical, is being ignored”[4]. It has nowadays reached a point where, to save the world from agricultural collapse, an in-depth rethink of soil management in view of sustainably improving soil fertility is needed.
I have already exposed in previous posts how good agricultural practices, including natural farming and the preservation of untouched spaces could contribute to a more fertile land. Today I want to discuss weeds.
Weed control is a relatively new concern of mankind. Available literature indicates that relatively few agricultural leaders and farmers became interested in weeds as a problem before 1200 AD or even 1500 AD. Real emphasis, both on a legal and technical standpoint, only appeared in the late 19th century[5]. In actual facts, overlooked knowledge from the past use to consider some of the wild plants we call weed as companion crops, food or even medicine.
Professor Cocannouer has been teaching conservation and biology for close to fifty years, but has always thrived to go on the field (literally) to learn from nature, not only in his home state of Oklahoma where he has spent much time learning from the Indians, but also in other part of the world such as Europe, India and the Philippines.
From a lifetime of researches on weed, he concludes that overall, controlled weed are beneficial to the land by the following aspects:
1. Deep-rooted weeds feed in the lower soil and by doing so bring nutrients back to the surface and reduce the effects of leaching. This is particularly important for trace nutrients which are not added to most standard fertilisers, but could also have implication for the leaching of nitrates. Since weeds and crops do not feed in the same depth of the soil they do not excessively compete for nutrients and water.
2. The strength of weeds roots is able to break hard pans and restore the nutrients circulation between lower soil and the topsoil. This could have interesting applications in environmental restoration where hard layers effectively lock toxins and salts in the topsoil.
3. Weeds roots also help open the soil and increase its fibre content, which then make it easier for crops, the roots of which are generally weaker, to reach further into the ground and gain additional access to nutrients. Without those fibres the soil particle settle close together into a compact condition. Ultimately the lower soils becomes so agglutinated that the upward movement of capillary water is severely hampered, and the soil is then endangered of becoming thrown out of balance.
4. When they die, weeds roots increase the ground’s organic content, which then is being eaten by a multitude of micro-organisms, insects, worms and fungi, and processed into fertile dirt upon which the plants and crops can in turn feed.
5. Deep-feeding weeds will cause a capillarity movement of water along the outside of their roots, thus bringing back toward the surface some of the water which ran too far down to be available for the other crops. The upward moving moisture will become immediately available to the crop roots that are feeding in the surface soil, therefore a thin crop of weeds interspersed into conventional crop will help go through drier parts of the year.
6. Weeds are sources of food for many birds, whose dropping will in turn serve as natural fertilisers for the crops. Some of the birds attracted by the weeds will also prey on the insects and help to control their population.
7. Some weeds can provide a ground cover which will prevent direct exposition of the ground to the sun and help retain moisture.
However, anyone who expects to take a mediocre or poor piece of land and get a good crop of vegetable from it solely through mothering the vegetables with weeds is likely to be in for some disappointment: the weeds, if handled correctly, will do constructive work in the soil, but they won’t perform magic. The whole art of correct weed handling is to strike the right balance in weed control: neither left loose nor eradicated. If the weeds are growing too thickly, their roots will fail to develop into those useful deep-divers, and the weeds will choke the other plants. Also, in order to fulfil their potentials of bringing nutrients back to the surface, weeds need to be returned to the soil after they die (by turning them in for instance).
Now, in his work Joseph Cocannouer specifically refers to a number of weeds as specially worth investigating:
This non-exhaustive list goes on in the original book: Weeds, guardians of the soil
Obviously this approach is not even in its infancy. Professor Cocannouer was a pioneer, but no one really continued his work on weeds. If weeds deserve better consideration than what they had until now, a fair amount of careful experimentation is needed by anyone who would like to use them correctly.
Sources:
[1] Dirt: The Erosion of Civilizations, David R. Montgomery
[2] Global Survey of Human-Induced Soil Degradation http://www.fao.org/nr/land/information-resources/glasod/en/
[3] telegraph.co.uk: Britain facing food crisis as world’s soil ‘vanishes in 60 years’ http://goo.gl/Yx2O
[4] Cornell University: Slow, insidious soil erosion threatens human health and welfare http://www.news.cornell.edu/stories/march06/soil.erosion.threat.ssl.html
[5] F. L. Timmons, Weed Science Society of America, Volume 53, Issue 6 (November-December 2005) http://goo.gl/86Ip
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