From danamex@mail.internet.com.mx Tue Oct 12 14:42:27 1999 Date: Tue, 12 Oct 1999 07:26:39 -0500 From: Ronald Nigh To: sanet-mg@ces.ncsu.edu Subject: Re: organic and nutrition [ The following text is in the "iso-8859-1" character set. ] [ Your display is set for the "US-ASCII" character set. ] [ Some characters may be displayed incorrectly. ] Dennis wrote >Granted that some sub-soils in some places (not just in a region of the >country but, where geology is complex, maybe in different parts of the one >farm) may have chronic deficiencies, or difficult pH, does not the >availability of nutrients to plants depend on soil management, particularly >the development of colloidal humus? > It is true that our first and foremost concern is to improve and maintain soil structure. Soil structure is dependent entirely on biological activity, the conversion of organic matter into energy (for soil microorganisms to grow and reproduce) and "colliods", "humus" and such, in other words secondary substances that bind together soil particles into 'crumbs' that produce a loose soil in with roots and grow freely and where water and air can penetrate freely (roots need water *and* air to metablolize properly). Achieving a good soil structure will solve most of your problems. If their are regional deficiencies, or more likely, imbalances among nutrient elements then this process of creating soil structure may run into difficulties. Plants may show any of a number problems including pests or diseases. The mineral status of a soil--and we're talking about maybe 22 elements here, not just two or three or six--is part of creating an optimum soil. (Unfortunately the idea of optimum soil isn't really addressed in soil and plant nutrition studies.) So, the answer to your question is "yes, but..." >Put it another way: if the growing of a crop removes something from the >soil, does that mean that something from a bag or a truck has to be added, >or does it mean that the management of the soil and plant and animal >production needs to be such as to maintain or improve soil quality, rather >than see it go downhill? Is not this point - the enhancement of soil >quality - the key factor in organic or sustainable farming, rather than >measuring deficiencies and making choices between additives? > If harvesting a crop removes an essential element from the topsoil, then this element becomes less available. If it was optimum at one point then it becomes less than optimum after being removed. It has to be replaced, it's as simple as that. If you take it out you have to put it back. There's no magic in "soil management"-- its physics and biology. How can you replace it? The most common way for many mineral elements to be restored is for deep rooted plants to bring them up again from the subsoil and deposit them in the top soil in leaf litter and other residues. If that element is scarce in the subsoil then it will be scarce in the topsoil--it will be quickly depleted in the harvest (perhaps, or by erosion) and will have to be supplied from other sources--"a bag or a truck" or from another part of the farm. Most descriptions of soil mineral content are misleading. They are talking about average amounts or minimum amounts necesary to prevent noticeable deficiency symptoms. But the level of Ca or B or Cu necessary to prevent obvious deficiency is usually quite different from the *optimumal* level of these nutrients for soil and plant health and productivity. What is more the optimal level isn't a fixed amount but varies according to the proportion of other elements. "Deficiencies" can be caused by high levels of an antagonistic element rather than by absolute absences of the deficient one. Higher N levels in the soil require higher Mo and Fe, for example. This is because these elements are used in enzyme systems the plant needs to metabolize N. These same principles apply to animal nutrition. How do you balance a soil optimally and know what elements to supply and when you are wasting your money? This is the art. Things are more likely to happen naturally on a diverse organic farm where the network of flows is more complex. A lot depends on the daily attention of the farm family, just noticing what is going on. But then questions arise and sometimes its not easy to find answers. It seems like the technical people and scientists are usually asking different questions. The behavior of our animals can give us clue. The freer they are to move around the more they can tell us about our soils etc. Sometimes animals have natural licks where they like go. These may just be salt, but natural licks probably have other mineral too. Getting these analyzed can give us a clue as to what is missing in the animals diet, and therefore in the soil (Geologically if there is a concentrated deposit in an area of some mineral itspossible that this mineral is deficient in the surrounding soils). Also watching what a cow eats after calving or when they are sick can be instructive. I have talked to graziers who use free choice mineral feeding. This is a system where minerals are given in separate trays and the cattle (or llamas or whatever) can choose their own mix. Observing what the animals do here can reveal worlds about the soil and the seasonal availability of minerals in the forage. Some graziers claim that this method allows very precise adjustment of the mineral levels in the soil, as the cattle carry these minerals and deposit them in their manure as they graze. I know one grazier who believes that cattle will go and deliberately drop in patch of soil that is deficient! Talk about sophisticated soil management, this beats precision farming! Anyway, talking to these people has convinced me we still have lot to learn about soil fertility. The point is optimal mineral balance should translate into healthy soil and plants and optimum quality foods. Ronald Nigh Dana, A.C. Mexico, D.F. & San Cristóbal de Las Casas, Chiapas Tel. y FAX 525-666-73-66 (DF) 529-678-72-15 (Chiapas) danamex@mail.internet.com.mx To Unsubscribe: Email majordomo@ces.ncsu.edu with the command "unsubscribe sanet-mg". If you receive the digest format, use the command "unsubscribe sanet-mg-digest". To Subscribe to Digest: Email majordomo@ces.ncsu.edu with the command "subscribe sanet-mg-digest". 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