HERBICIDES AND NO-TILL FARMING

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Herbicides can be further divided into groups according to the route by which they attack. Contact herbicides kill a plant by destroying its surface cellular structure. Paraquat, for example, is a desiccant; that is, it robs moisture from the weed, killing it within a couple of days. Translocated herbicides actually enter a plant's vascular system — either through the foliage after direct spraying or through the roots after ground application — and disrupt one of its life processes. 2,4-D, an auxin-type herbicide, accelerates growth to the point that the plant dies. Atrazine, which is nearly as popular as 2,4-D, attacks chlorophyll production in a weed, limiting its ability to take nourishment from the sun. Dalapon, another widely used herbicide, interferes with the activity of a B vitamin called pantothenic acid which is essential to a plant's development. Others take such avenues of attack as halting the formation of amino acids, preventing the production of sugar and complex starches, and so on. There are nearly as many ways of killing weeds as there are herbicides.

WHAT SHOULD WE WORRY ABOUT?

Toxicity: Herbicides work because they're dangerous; almost without exception, a human could be killed by ingesting enough of a weed killer. Some herbicides, however, would have to be taken in pretty heavy doses to do the job. Paraquat is probably the most toxic weed killer in widespread use today. In laboratory tests, half of a population of rats will die if they're fed 150 milligrams of paraquat per kilogram of body weight. To put that in human terms, it takes about a teaspoon of paraquat to kill a person. People who handle herbicides — in both production and application — can be in great jeopardy if they don't exercise proper precautions.

How likely is it that we'll be poisoned by herbicide residues in our food? Not very likely. First of all, our nasty example chemical, paraquat, is only applied to fields at the rate of about a pound of active ingredient per acre, which means that its concentration would be pretty low op any given unit of food. And second, as you'll see in the paragraph on persistence, the concentrations of many herbicides drop off quickly. We do, however, consume some amount of herbicides on treated crops or via livestock that have eaten the crop or foraged on the ground. The long-term effects of even small dosages are very difficult to predict.

There is no question that wildlife is damaged or killed by certain herbicides. Birds can be injured if they get in the way of spraying (small amounts of paraquat can kill eggs), and the runoff from herbicide-treated fields can be injurious to a range of water-dwelling organisms. The herbicides paraquat, atrazine, and MSMA have been found to inhibit the growth and productivity of algae in streams, which can affect the overall bioproductivity of the water. (Of course, no-till farming goes a long way toward eliminating water runoff, so this new agricultural practice may limit that specific effect.)

Persistence: Herbicides remain active in the soil for anywhere up to about 30 months, but most of the commonly used chemicals have broken down by the end of the eighth week after their application. DDT, an insecticide, gained its notoriety because it remains active in the environment for a very long time, accumulating in the bodies of creatures (especially birds) exposed to it. Herbicides, as opposed to insecticides, are less likely to show such effects because they tend to break down as they work. For example, 2,4-D is degraded as it does its job of stimulating auxins in the plant. Paraquat may be the herbicide that presents the greatest persistence problem. Though it's held inactive in most soils, clay-heavy earth may enhance its cumulative qualities, eventually posing a hazard after a field has been sprayed for several years.

Ecological effects: There is widespread concern that herbicides may kill soil microorganisms, those bacteria and fungi that decompose organic matter and make the earth fertile. In fact, many herbicides may inhibit microorganism growth, and a few are very destructive. Others, such as 2,4-D, seem to have no effect at all.

There's also reason to worry about the development of strains of weeds that aren't affected by herbicides. This isn't a matter of the genetic development of strains resistant to herbicides, the way in which some insects have come to tolerate insecticides. Rather, weeds that are already resistant — Johnsongrass is a good example — often flourish in herbicide-treated fields. Because other weeds that may have competed with the resistant species have been wiped out, the tough weeds are free to run amok.

Problems such as the proliferation of resistant weeds emphasize one of the major criticisms that proponents of organic agriculture level against no-till/chemical farming. By attempting to dominate the soil (an essentially hubristic approach), farmers may leave themselves open to disastrous failures. Learning to work with and improve the soil is certain to be a far safer and more productive approach in the long run.

Are there means on the horizon for eliminating the need for synthetic organic herbicides? Certainly. The move away from monocropping is already reducing weed problems, and many of the facets of good husbandry (such as meticulous screening of seed for cleanliness) help. Then too, there are developments in natural weed control. Scientists at the University of North Carolina are using plants against plants. By incorporating allelopathic species (which release chemicals to fight off neighbors) as cover crops in conjunction with no-till plantings, they're having great success at controlling weeds. So, aspects of no-till may offer advantages over conventional tillage when coupled with natural controls.

In the near future, however, the necessity of having a successful crop every year just to keep the bank at bay is probably going to keep most no-till practitioners from trying any risky experiments. And in the meantime, no-till agriculture offers far more protection of our precious topsoil than the plow does. How soon the conversion to natural practices can be made is a difficult question. Chemical companies have a tremendous vested interest in seeing today's approach remain in place, and powerful vested interests seem to determine our nation's agricultural policies. If the conversion is to be made, it will probably have to develop from the soil upward.

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