Books about hydroponics sound plausible. That is, until you actually _see_ the results. Plants grown in chemical nutrient solutions may be huge but look a little "off." Sickly and weak somehow. Without a living soil, plants can not be totally healthy or grow quite as well as they might.

By focusing on increasing and maximizing soil life instead of adding chemical fertility, organic farmers are able to grow excellent cereals and fodder. On richer soils they can even do this for generations, perhaps even for millennia without bringing in plant nutrients from elsewhere. If little or no product is sent away from the farm, this subsistence approach may be a permanent agricultural system. But even with a healthy ecology few soils are fertile enough by themselves to permit continuous export of their mineral resources by selling crops at market.

Take one step further. Cereals are mostly derived from hardy gra.s.ses while other field crops have similar abilities to thrive while being offered relatively low levels of nutrients. With good management, fertile soils are able to present these lower nutritional levels to growing plants without amendment or fortification with potent, concentrated nutrient sources. But most vegetables demand far higher levels of support. Few soils, even fertile soils that have never been farmed, will grow vegetables without improvement. Farmers and gardeners must increase fertility significantly if they want to grow great vegetables. The choices they make while doing this can have a strong effect, not only on their immediate success or failure, but on the actual nutritional quality of the food that they produce.

How Humus Benefits Soil

The roots of plants, soil animals, and most soil microorganisms need to breathe oxygen. Like other oxygen burners, they expel carbon dioxide. For all of them to grow well and be healthy, the earth must remain open, allowing air to enter and leave freely. Otherwise, carbon dioxide builds up to toxic levels. Imagine yourself being suffocated by a plastic bag tied around your neck. It would be about the same thing to a root trying to live in compacted soil.

A soil consisting only of rock particles tends to be airless. A scientist would say it had a high bulk density or lacked pore s.p.a.ce.

Only coa.r.s.e sandy soil remains light and open without organic matter. Few soils are formed only of coa.r.s.e sand, most are mixtures of sand, silt and clay. Sands are sharp-sided, relatively large rock particles similar to table salt or refined white sugar. Irregular edges keep sand particles separated, and allow the free movement of air and moisture.

Silt is formed from sand that has weathered to much smaller sizes, similar to powdered sugar or talc.u.m powder. Through a magnifying lens, the edges of silt particles appear rounded because weak soil acids have actually dissolved them away. A significant amount of the nutrient content of these decomposed rock particles has become plant food or clay. Silt particles can compact tightly, leaving little s.p.a.ce for air.

As soil acids break down silts, the less-soluble portions recombine into clay crystals. Clay particles are much smaller than silt grains. It takes an electron microscope to see the flat, layered structures of clay molecules. Shales and slates are rocks formed by heating and compressing clay. Their layered fracture planes mimic the molecules from which they were made. Pure clay is heavy, airless and a very poor medium for plant growth.

Humusless soils that are mixtures of sand, silt, and clay can become extremely compacted and airless because the smaller silt and clay particles sift between the larger sand bits and densely fill all the pore s.p.a.ces. These soils can also form very hard crusts that resist the infiltration of air, rain, or irrigation water and prevent the emergence of seedlings. Surface crusts form exactly the same way that concrete is finished.

Have you ever seen a finisher screed a concrete slab? First, smooth boards and then, large trowels are run back and forth over liquid concrete. The motion separates the tiny bits of fine sand and cement from denser bits of gravel. The "fines" rise to the surface where they are trowelled into a thin smooth skin. The same thing happens when humusless soil is rained on or irrigated with sprinklers emitting a coa.r.s.e, heavy spray. The droplets beat on the soil, mechanically separating the lighter "fines" (in this case silt and clay) from larger, denser particles. The sand particles sink, the fines rise and dry into a hard, impenetrable crust.

Organic matter decomposing in soil opens and loosens soil and makes the earth far more welcoming to plant growth. Its benefits are both direct and indirect. Decomposing organic matter mechanically acts like springy sponges that reduce compaction. However, rotting is rapid and soon this material and its effect is virtually gone. You can easily create this type of temporary result by tilling a thick dusting of peat moss into some poor soil.

A more significant and longer-lasting soil improvement is created by microorganisms and earthworms, whose activities makes particles of sand, silt, and clay cling strongly together and form large, irregularly-shaped grains called "aggregates" or "crumbs" that resist breaking apart. A well-developed crumb structure gives soil a set of qualities farmers and gardeners delightfully refer to as "good tilth." The difference between good and poor tilth is like night and day to someone working the land. For example, if you rotary till unaggregated soil into a fluffy seedbed, the first time it is irrigated, rained on, or stepped on it slumps back down into an airless ma.s.s and probably develops a hard crust as well. However, a soil with good tilth will permit multiple irrigations and a fair amount of foot traffic without compacting or crusting.

Crumbs develop as a result of two similar, interrelated processes.

Earthworms and other soil animals make stable humus crumbs as soil, clay and decomposing organic matter pa.s.s through their digestive systems. The casts or scats that emerge _are crumbs._ Free-living soil microorganisms also form crumbs. As they eat organic matter they secrete slimes and gums that firmly cement fine soil particles together into long lasting aggregates.

I sadly observe what happens when farmers allow soil organic matter to run down every time I drive in the country. Soil color that should be dark changes to light because mineral particles themselves are usually light colored or reddish; the rich black or chestnut tone soil can get is organic matter. Puddles form when it rains hard on perfectly flat humusless fields and may stand for hours or days, driving out all soil air, drowning earthworms, and suffocating crop roots. On sloping fields the water runs off rather than percolating in. Evidence of this can be seen in muddy streams and in more severe cases, by little rills or mini-gullies across the field caused by fast moving water sweeping up soil particles from the crusted surface as it leaves the field.

Later, the farmers will complain of drought or infertility and seek to support their crops with irrigation and chemicals. Actually, if all the water that had fallen on the field had percolated into the earth, the crops probably would not have suffered at all even from extended spells without rain. These same humusless fields lose a lot more soil in the form of blowing dust clouds when tilled in a dryish state.

The greatest part of farm soil erosion is caused by failing to maintain necessary levels of humus. As a nation, America is losing its best cropland at a nonsustainable rate. No civilization in history has yet survived the loss of its prime farmland. Before industrial technology placed thousands of times more force into the hands of the farmer, humans still managed to make an impoverished semi-desert out of every civilized region within 1,000-1,500 years.

This sad story is told in Carter and Dale's fascinating, but disturbing, book called _Topsoil and Civilization _that I believe should be read by every thoughtful person. Unless we significantly alter our "improved" farming methods we will probably do the same to America in another century or two.

The Earthworm's Role in Soil Fertility

Soil fertility has been gauged by different measures. Howard repeatedly insisted that the only good yardstick was humus content.

Others are so impressed by the earthworm's essential functions that they count worms per acre and say that this number measures soil fertility. The two standards of evaluation are closely related.

When active, some species of earthworms daily eat a quant.i.ty of soil equal to their own body weight. After pa.s.sing through the worm's gut, this soil has been chemically altered. Minerals, especially phosphorus which tends to be locked up as insoluble calcium phosphate and consequently unavailable to plants, become soluble in the worm's gut, and thus available to nourish growing plants. And nitrogen, unavailably held in organic matter, is altered to soluble nitrate nitrogen. In fact, compared to the surrounding soil, worm casts are five times as rich in nitrate nitrogen; twice as rich in soluble calcium; contain two and one-half times as much available magnesium; are seven times as rich in available phosphorus, and offer plants eleven times as much pota.s.sium. Earthworms are equally capable of making trace minerals available.

Highly fertile earthworm casts can amount to a large proportion of the entire soil ma.s.s. When soil is damp and cool enough to encourage earthworm activity, an average of 700 pounds of worm casts per acre are produced each day. Over a year's time in the humid eastern United States, 100,000 pounds of highly fertile casts per acre may be generated. Imagine! That's like 50 tons of low-grade fertilizer per acre per year containing more readily available NPK, Ca, Mg and so forth, than farmers apply to grow cereal crops like wheat, corn, or soybeans. A level of fertility that will grow wheat is not enough nutrition to grow vegetables, but earthworms can make a major contribution to the garden.

At age 28, Charles Darwin presented "On the Formation of Mould" to the Geological Society of London. This lecture ill.u.s.trated the amazing churning effect of the earthworm on soil. Darwin observed some chunks of lime that had been left on the surface of a meadow. A few years later they were found several inches below the surface.

Darwin said this was the work of earthworms, depositing castings that "sooner or later spread out and cover any object left on the surface." In a later book, Darwin said,

"The plow is one of the most ancient and most valuable of man's inventions; but long before he existed the land was in fact regularly plowed and still continues to be thus plowed by earthworms. 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."

Earthworms also prevent runoff. They increase percolation of water into fine-textured soils by making a complex system of interconnected channels or tunnels throughout the topsoil. In one study, soil lacking worms had an absorption rate of 0.2 inches of rainfall per minute. Earthworms were added and allowed to work over that soil sample for one month. Then, infiltration rates increased to 0.9 inches of rainfall per minute. Much of what we know about earthworms is due to Dr. Henry Hopp who worked for the United States Department of Agriculture during the 1940s. Dr. Hopp's interesting booklet, _What Every Gardener Should Know About Earthworms._ is still in print. In one Hopp research project, some very run-down clay soil was placed in six large flowerpots. Nothing was done to a pair of control pots, fertilizer was blended in and gra.s.s sod grown on two others, while mulch was spread over two more. Then worms were added to one of each pair of pots. In short order all of the worms added to the unimproved pot were dead. There was nothing in that soil to feed them. The sod alone increased percolation but where the sod or mulch fed a worm population, infiltration of water was far better.

Amendment to clay soil Percolation rate in inches per minute Without worms With worms None 0.0 0.0 Gra.s.s and fertilizer 0.2 0.8 Mulch 0.0 1.5

Most people who honestly consider these facts conclude that the earthworm's activities are a major factor in soil productivity.

Study after scientific study has shown that the quality and yield of pastures is directly related to their earthworm count. So it seems only reasonable to evaluate soil management practices by their effect on earthworm counts.

Earthworm populations will vary enormously according to climate and native soil fertility. Earthworms need moisture; few if any will be found in deserts. Highly mineralized soils that produce a lot of bioma.s.s will naturally have more worms than infertile soils lacking humus. Dr. Hopp surveyed worm populations in various farm soils. The table below shows what a gardener might expect to find in their own garden by contrasting samples from rich and poor soils. The data also suggest a guideline for how high worm populations might be usefully increased by adding organic matter. The worms were counted at their seasonal population peak by carefully examining a section of soil exactly one foot square by seven inches deep. If you plan to take a census in your own garden, keep in mind that earthworm counts will be highest in spring.

Earthworms are inhibited by acid soils and/or soils deficient in calcium. Far larger populations of worms live in soils that weathered out of underlying limestone rocks. In one experiment, earthworm counts in a pasture went up from 51,000 per acre in acid soil to 441,000 per acre two years after lime and a non-acidifying chemical fertilizer was spread. Rodale and Howard loudly and repeatedly contended that chemical fertilizers decimate earthworm populations. Swept up in what I view as a self-righteous crusade against chemical agriculture, they included all fertilizers in this category for tactical reasons.

Location Worms per sq. ft. Worms per acre Marcellus, NY 38 1,600,000 Ithica, NY 4 190,000 Frederick, MD 50 2,200,000 Beltsville, MD 8 350,000 Zanesville, OH 37 1,600,000 Coshocton, OH 5 220,000 Mayaquez, P.R.* 6 260,000

*Because of the high rate of bacterial decomposition, few earthworms are found in tropical soils unless they are continuously ammended with substantial quant.i.ties of organic matter.

Howard especially denigrated sulfate of ammonia and single superphosphate as earthworm poisons. Both of these chemical fertilizers are made with sulfuric acid and have a powerful acidifying reaction when they dissolve in soil. Rodale correctly pointed out that golf course groundskeepers use repeated applications of ammonium sulfate to eliminate earthworms from putting greens. (Small mounds of worm casts made by nightcrawlers ruin the greens' perfectly smooth surface so these worms are the bane of greenskeepers.) However, ammonium sulfate does not eliminate or reduce worms when the soil contains large amounts of chalk or other forms of calcium that counteract acidity.

The truth of the matter is that worms eat decaying organic matter and any soil amendment that increases plant growth without acidifying soil will increase earthworm food supply and thus worm population. Using lime as an antidote to acid-based fertilizers prevents making the soil inhospitable to earthworms. And many chemical fertilizers do not provoke acid reactions. The organic movement loses this round-but not the battle. And certainly not the war.

Food supply primarily determines earthworm population. To increase their numbers it is merely necessary to bring in additional organic matter or add plant nutrients that cause more vegetation to be grown there. In one study, simply returning the manure resulting from hay taken off a pasture increased earthworms by one-third. Adding lime and superphosphate to that manure made an additional improvement of another 33 percent. Every time compost is added to a garden, the soil's ability to support earthworms increases.

Some overly enthusiastic worm fanciers believe it is useful to import large numbers of earthworms. I do not agree. These same self-interested individuals tend to breed and sell worms. If the variety being offered is _Eisenia foetida,_ the brandling, red wiggler, or manure worm used in vermicomposting, adding them to soil is a complete waste of money. This species does not survive well in ordinary soil and can breed in large numbers only in decomposing manure or other proteinaceous organic waste with a low C/N. All worm species breed prolifically. If there are _any_ desirable worms present in soil, their population will soon match the available food supply and soil conditions. The way to increase worm populations is to increase organic matter, up mineral fertility, and eliminate acidity.

Earthworms and their beneficial activities are easily overlooked and left out of our contemplations on proper gardening technique. But understanding their breeding cycle allows gardeners to easily a.s.sist the worms efforts to multiply. In temperate climates, young earthworms hatch out in the fall when soil is cooling and moisture levels are high. As long as the soil is not too cold they feed actively and grow. By early spring these young worms are busily laying eggs. With summer's heat the soil warms and dries out. Even if the gardener irrigates, earthworms naturally become less active.

They still lay a few eggs but many mature worms die. During high summer the few earthworms found will be small and young. Unhatched eggs are plentiful but not readily noticed by casual inspection so gardeners may mistakenly think they have few worms and may worry about how to increase their populations. With autumn the population cycle begins anew.

Soil management can greatly alter worm populations. But, how the field is handled during summer has only a slight effect. Spring and summer tillage does kill a few worms but does not damage eggs. By mulching, the soil can be kept cooler and more favorable to worm activities during summer while surface layers are kept moister.

Irrigation helps similarly. Doing these things will allow a gardener the dubious satisfaction of seeing a few more worms during the main gardening season. However, soil is supposed to become inhospitably hot and dry during summer (worm's eye view) and there's not much point in struggling to maintain large earthworm populations during that part of the year. Unfortunately, summer is when gardeners pay the closest attention to the soil.

Worms maintain their year-round population by overwintering and then laying eggs that hatch late in the growing season. The most harm to worm multiplication happens by exposing bare soil during winter.

Worm activity should be at a peak during cool weather. Though worms inadvertently pa.s.s a lot of soil through their bodies as they tunnel, soil is not their food. Garden worms and nightcrawlers intentionally rise to the surface to feed. They consume decaying vegetation lying on the surface. Without this food supply they die off. And in northern winters worms must be protected from suddenly experiencing freezing temperatures while they "harden off" and adapt themselves to surviving in almost frozen soil. Under sod or where protected by insulating mulch or a layer of organic debris, soil temperature drops gradually as winter comes on. But the first day or two of cold winter weather may freeze bare soil solid and kill off an entire field full of worms before they've had a chance to adapt.

Almost any kind of ground cover will enhance winter survival. A layer of compost, manure, straw, or a well-grown cover crop of ryegra.s.s, even a thin mulch of gra.s.s clippings or weeds can serve as the food source worms need. Dr. Hopp says that soil tilth can be improved a great deal merely by a.s.sisting worms over a single winter.

Gardeners can effectively support the common earthworm without making great alterations in the way we handle our soil. From a worm's viewpoint, perhaps the best way to recycle autumn leaves is to till them in very _shallowly_ over the garden so they serve as insulation yet are mixed with enough soil so that decomposition is accelerated. Perhaps a thorough garden clean-up is best postponed until spring, leaving a significant amount of decaying vegetation on top of the soil. (Of course, you'll want to remove and compost any diseased plant material or species that may harbor overwintering pests.) The best time to apply compost to tilled soil may also be during the autumn and the very best way is as a dressing atop a leaf mulch because the compost will also accelerate leaf decomposition.

This is called "sheet composting" and will be discussed in detail shortly.

Certain pesticides approved for general use can severely damage earthworms. Carbaryl (Sevin), one of the most commonly used home garden chemical pesticides, is deadly to earthworms even at low levels. Malathion is moderately toxic to worms. Diazinon has not been shown to be at all harmful to earthworms when used at normal rates.

Just because a pesticide is derived from a natural source and is approved for use on crops labeled "organically grown" is no guarantee that it is not poisonous to mammals or highly toxic to earthworms. For example, rotenone, an insecticide derived from a tropical root called derris, is as poisonous to humans as organophosphate chemical pesticides. Even in very dilute amounts, rotenone is highly toxic to fish and other aquatic life. Great care must be taken to prevent it from getting into waterways. In the tropics, people traditionally harvest great quant.i.ties of fish by tossing a handful of powdered derris (a root containing rotenone) into the water, waiting a few minutes, and then scooping up stunned, dead, and dying fish by the ton. Rotenone is also deadly to earthworms. However, rotenone rarely kills worms because it is so rapidly biodegradable. Sprayed on plants to control beetles and other plant predators, its powerful effect lasts only a day or so before sun and moisture break it down to harmless substances. But once I dusted an entire raised bed of beetle-threatened bush bean seedlings with powdered rotenone late in the afternoon. The spotted beetles making hash of their leaves were immediately killed.

Unexpectedly, it rained rather hard that evening and still-active rotenone was washed off the leaves and deeply into the soil. The next morning the surface of the bed was thickly littered with dead earthworms. I've learned to treat rotenone with great caution.

Microbes and Soil Fertility

There are still other holistic standards to measure soil productivity. With more than adequate justification the great Russian soil microbiologist N.S. Krasilnikov judged fertility by counting the numbers of microbes present. He said,

". . soil fertility is determined by biological factors, mainly by microorganisms. The development of life in soil endows it with the property of fertility. The notion of soil is inseparable from the notion of the development of living organisms in it. Soil is created by microorganisms. Were this life dead or stopped, the former soil would become an object of geology [not biology]."