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As the Worm TurnsFarm Practices are Key to Encouraging EarthwormsBy Matthew WernerEarthworms are one of the best soil conditioners available to farmers. Charles Darwin, a great student of worms, determined that earthworms annually create between 8 to 18 tons of rich castings per acre (figures since confirmed by modern scientist). All this worm manure does wonders for the soil and best of all, it's free. If conditions are favorable for them to "go under and multiply," these creatures will do more for your soil than just fertilize it. Healthy populations can improve a soilâs porosity and water infiltration rates, increase soil humus levers, decompose plant residues and generally improve soil health in innumerable ways. So what exactly do these "livestock of the soil" need to be happy and healthy? Like most animals, they require food, water and shelter. The most practical approach to increasing their numbers may be the Field of Dreams method: manage the habitat and they will come. This means developing an understanding of how different farm practices influence their numbers and using those practices that tend to encourage earthworms to proliferate. Before you begin changing your farm practices to accommodate worms, it is useful to know the different kinds of worms and how they work. Know Your Earthworms Endogeic earthworms are the workhorses of most California soils. They generally live and eat within the deeper mineral soil horizons, and are not as disturbed by the loss of surface organic matter or chemical application as other species. They are commonly found clustered around the root balls of plants; here they are busy feeding on the decaying portions of root systems and on the fungi, bacteria and nematodes that live there in great abundance. Epigeic earthworms live close to the surface, where organic matter is concentrated. These include the red worms that are readily purchased from commercial earthworm dealers. Itâs not practical to add this kind of earthworm directly too most farm soils and expect a big increase in the populations, because they need an abundant and regular supply of surface organic to thrive. However, they can be very useful for transforming organic wastes into high-quality fertilizer, a process call vericulture. The third type, the anecic species, are heroic creatures exemplified by the nightcrawler. These are large, muscular species that create deep, vertical burrows that become their permanent residence over a life span that may last one to ten years. Named for their habit of coming to the surface at night to feed on dead and decaying plant matter, these earthworms drag organic matter from the surface down to their burrows. They are capable of incorporating the entire leaf fall from a deciduous forest into the soil in a matter of months, and can play this same role in orchards. In the process, they mix surface and deeper soil horizons. This type of earthworm seems to be relatively rare in California but can be successfully introduced into orchards, vineyards and other no-till crop systems. Managing for Earthworms Cultivation: One of the practices that most affect earthworms is cultivation, especially deep plowing. Plowing physically disrupts earthworm habitat, kills some earthworms in the process, and exposes others to predication. It also buries surface organic matter, destroying earthworm habitat. Moldboard plows, which invert the topsoil layer where most worms feed and many live, are the most damaging. Chiseling or disking is less disruptive, especially if it is done minimally. Studies of no-till of minimum-till fields typically reveal that earthworms thrive when farmers cut back on deep cultivation. Chemicals: Not all farm chemicals are bad for earthworms, but many are sure to reduce their populations. Probable the worst group is fumigants, which are a fiasco for earthworm populations. Fungicides are also generally not toxic to earthworms, although they can decrease the amount of plant residue that ends up in the soil for earthworm consumption, thereby reducing their food supply. Toxicity varies in other groups of chemicals. Organochlorine compounds, which continue to persist in various forms in many farm soils, are generally highly toxic, especially chlordane, heptachlor, and toxaphene. Organophosphorous compounds such as malathion and chlorpyrifos are probably not toxic at normal field application rates, while others like phorate are very toxic to earthworms. The carbamates also vary, with many being highly toxic. At very high dose rates even Bt(Bacillus thurimgiensis) may kill earthworms, but it should pose no problem at normal application rates. Ammonium-based fertilizers can also discourage earthworms because they acidify the soil. On the other hand, earthworms benefit indirectly form the increased amount of vegetation caused by higher fertility. Lime can be added to counteract soil acidity. Generally, fertilizers composed of organic matter are much preferred. To maintain healthy earthworm populations, avoid using chemicals that are toxic to earthworms. Since many farm chemicals in use today have not been tested for their effects on earthworm's populations, all inputs should be used cautiously. The way a pesticide is applied may also have an effect. For example, a study showed that anecic species were most susceptible to surface applications of benomyl, and were less affected when the chemical was mixed into the soil. This is because they do not move beyond their permanent burrows, and therefore do not come into contact with subsurface soil beyond their burrows. However, endogeic species -- which constantly extend their burrows -- were most affected when the chemical was mixed into the soil. Cover: Earthworms prefer to live under cover. Sunlight is toxic and even lethal to earthworms. That is one reason why earthworms wiggle and squirm when dug out of the ground -- they have an instant response to light exposure designed to get them back below ground as quickly as possible. Some of the paler, deep -- dwelling species have no defense against sunlight and quickly die when exposed. To encourage earthworms, keep the ground covered with organic matter year-round if possible. Mulches and perennial cover crops are particularly valuable. Not only will mulch keep them cool, but it provides food as well -- both from the organic material itself and from the fungi, bacteria and other small creatures it supports. Organic mulch also keeps moisture in the soil, and reduces daily fluctuations in aboveground temperature. With annual crops, try to time plantings when there's vegetative cover from Jan.-March, when worms do most of their work. Monitoring Success A simple way is to turn over a shovel full of soil and count the worms present. Dig down eight inches to a foot, and count every earthworm you find in the shovel-full. DO this in half a dozen or more spots in each soil type on your land and come up with an average for each. If you find 5 to 10 worms per shovel, that represents a fairly healthy earthworm community. Do this at about the same time each year to determine how your management practices are affecting earthworm populations. If counts are low, you might consider introducing worms. The best time to introduce worms is on a cloudy day. Fall or early winter is a good time. The soil should be moist. Anecic earthworms, can be introduced by direct inoculation, but transferring blocks of soil (minimum size: one cubic foot each) from an area with large earthworm populations into farm soils might work better. Nightcrawlers can be purchased from bait dealers, who generally get them from nightcrawler harvesters in the Pacific Northwest. Another idea is to set aside a small portion as needed to bring it near pH-7, irrigate it regularly, establish a cover crop and cut it periodically to provide an organic mulch as food and cover. Introduce a population of an anecic species, which you can "farm" as needed. From this reservoir blocks could periodically be taken and introduced into the field. This might be done each year in the fall when earthworm activity is increasing. The rate of spread varies with species and condition in the field. Lumbricus terrestis, the nightcrawler, is capable of traveling at least 60 feet on the soil surface in the course of one evening foray. I first experimented with inoculative release of anecic earthworms in a Watsonville apple orchard that had only endogeic worms. I purchased 500 nightcrawlers from a bait deader (cost was approximately $55 for 1,000 worms), and introduced them in clumps of 40 earthworms per one square meter in eight spots in the organically managed section of the orchard. Soil was loosened at the release spots with a fork, and covered with soil and litter. I placed a measured amount of apple litter over each inoculation spot, held in place by a chicken wire screen. Two months later, only 20% of the litter remained at the inoculation spots, while areas without nightcrawlers add, 80% remained. I surveyed the orchard in the following winter and found that nightcrawlers were still present, and they had traveled outwards from the inoculation spot. I also found some juveniles, indicating that the nightcrawlers were reproducing. Some Central Valley orchardists are beginning to experiment with inoculative release of anecic earthworms. A survey conducted by the BIOS project in seven Merced County orchards found endogeic earthworm species present, but no anecic species. At Ratzlaff Orchards in Winston, nightcrawlers have been added to a dozen spots in a block of almond trees. With a mowed cover crop and 2.25 inches of water every 8 days up until min-August, this orchard should provide ideal habitat for nightcrawlers. After allowing time for pesticide residual to break down, Chick Segers of Hopeton Farms plans to release nightcrawlers in a transitional block of almonds soon after the rainy season starts this fall Ray Eck of Hilmar is excited about the potential of introducing anecic earthworms into his orchards and about earthworms in general. "Earthworms play in important role, especially in non-tilled orchards," he said. "They help aerate the soil and get the oxygen down there. This is especially good in systems where you are trying to encourage the activity of microorganisms. Charles Darwin was more effusive. "It may be doubted whether there are many other animals which have played so important a part in the history of the world as have these lowly organized creatures," he wrote in his groundbreaking text, The Formation of Vegetable Mould Through the Action of Worm. You may not feel quite so strongly about earthworms, but if you can entice them to set up housekeeping on your farm, they may just change the history of your soil. -------------------------------------------------------------------------- |
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