Slash and burn agriculture has its merits. Chop down a piece of forest, set fire to the fallen trunks and limbs, and you will be left with a nutrient-rich ground. In our case, the trees were not the liana-laden buttressed hardwoods of Amazonia but grapevine-covered white pines. Crows, not macaws, perched in their crowns. All one winter we worked in the snow, carving a 150-by-I50-foot clearing in the woods. The bigger logs I rolled with a peavey to where I could later square them into beams to build a shed. The branches, oozing pitch from their cut ends, we piled in heaps and burned, warming our hands at the pyre.

The first summer the ground was still dotted with stumps. The corn and beans that we planted around them grew from soil that was thick with the accumulated duff of the forest floor, sweetened and fertilized with the ashes of our winter's work. Now, ten years later, only a couple of the largest stumps remain. The original leaf mold is long gone, as are the remains of those midwinter bonfires. We still harvest cartloads of vegetables from this ground each year, but only because we have continued to tend the soil.

The road we live on turns off the highway a mile from our house and climbs three hundred feet before it reaches us. We can hear the occasional big truck long before we see it, the labored downshifting as it grinds slowly up the last punishingly steep pitch. There is much to be said for living on a hill. Our growing season is a good six weeks longer than in the valley, where the cold air pools on frosty nights. And we are well out of reach of any floodwaters. But hill farms like ours have one great liability, and that is that over time the soil's fertility gradually slips away.

Part of the problem is gravity. The mineral elements that are essential for the growth of plants are water soluble, and percolating water washes them deeper into the ground or downslope. These nutrients may not leach as rapidly as they do in the case of newly cleared tropical rainforests, where the soil gets a hundred inches or more of rain a year, but the direction is the same. Furthermore, erosion carries away even those nutrients, such as phosphorus, that are comparatively tightly bound to individual soil particles. These are delivered to the alluvial floodplains downstream, in rich layers of silt left behind when the river overflows its banks.

A far greater cause of nutrient loss, however, is the very nature of gardening itself. We cut asparagus, shell peas, pick tomatoes, pull carrots, and dig potatoes. Not to mention the bouquets of flowers we gather or the herbs we dry. And every leaf, flower, stem, or root that we harvest from the garden takes nutrients with it. Each hundred-pound sack of potatoes takes away roughly ten ounces of nitrogen. And the farther away from the garden such nutrients travel, the less likely they are ever to come back. We have successfully trained our friends who leave with the back seats and trunks of their cars full of fresh produce to return the containers - the baskets, flats, and crates. But we have never quite been able to bring ourselves to say that we also need returned what's left after they have eaten the vegetables.

Seventeen different chemical elements have been identified as essential to plant growth. Not all of them are required in equal amounts. Carbon, hydrogen, and oxygen, for example, account for ninety-five percent of the dry weight of any plant and are abundantly provided by the atmosphere. At the other extreme are eight so-called micronutrients that are present in amounts of less than ten parts per million. These are chlorine, iron, boron, manganese, zinc, copper, molybdenum, and, most recently, nickel. If I grew tomatoes hydroponically I would need to add these trace elements, but anyone who plants in soil that contains organic matter usually has an ample supply.

The only elements that I, or most gardeners, need really be concerned about are six so-called macronutrients - nitrogen, phosphorus, potassium, calcium, sulfur, and magnesium. Of these I get to cross half off my shopping list. The form of ground limestone that I spread to keep the soil's pH at 6.5 (instead of its natural 5.0) is powdered dolomite, which contains magnesium in addition to calcium. I may someday need to add sulfur, but not so long as industrial smokestacks keep belching the sulfur dioxide that showers down on our soil as acid rain.

The bags of "complete" fertilizer stacked alongside the grass seed and dog chow at our local garden supply store actually contain only three nutrients - nitrogen, phosphorus, and potassium. These are the elements that plants are most likely to find lacking, and they are the ones that form the backbone of the United States chemical fertilizer industry.

The potassium (whose chemical symbol, K, comes from the Latin word kalium, meaning "alkali") is potassium chloride, also called muriate of potash. It has been recovered from the brine of Searles Lake, California, or mined near Carlsbad, New Mexico. The phosphorus (P) is a phosphate rock mined in Florida or one of half a dozen other states and treated with sulfuric acid to create superphosphate, which is more water soluble than rock phosphate.

The nitrogen (N) in these bags is the most expensive of the three components, and the one that is most valuable to the gardener. Nitrogen gas, although it makes up seventy-eight percent of the earth's atmosphere, cannot be used by plants until it is "fixed," or combined with oxygen or hydrogen to make compounds such as nitrates or ammonia, which plants can use to synthesize proteins. The principal industrial process for doing this is the Haber process, named for the German chemist who won a Nobel prize in 1918 for its discovery. This synthetic fixation requires energy, lots of it. Twenty-five thousand BTUs go into producing a single pound of nitrogen fertilizer, and nitrogen fertilizer production consumes two percent of the total natural gas used in this country. When you are calculating which of two formulations of fertilizer is the better buy, it is sufficient to determine the relative prices for the nitrogen. The phosphorus and the potassium each contribute less than ten percent of the cost.

I used to buy hundreds of pounds of chemical fertilizer every year. I was a teenager then, just beginning to grow vegetables, and I was gardening by the book, specifically a tattered paperback copy of The Pocket Book of Vegetable Gardening, by Charles H. Nissley, extension professor of vegetable gardening at the New Jersey Agricultural Experiment Station. This was the only popular book that I could find at the time, and its copyright was 1942. I bought fertilizer in eightypound bags of 10-10-10, secure that I was getting eight pounds of actual N, P, and K in every one. I spread it liberally. "An application of approximately fifty pounds to every 1,000 square feet of garden surface is usually satisfactory" Nissley counseled. I added more for good measure. It was only five dollars a bag, and it seemed better to be safe than sorry. Every time a plant looked a little yellow, I slopped on some more nitrogen. Everything was green, very green. The soil was awash in nutrients.

Yes, there were a few problems. On several occasions I scorched the edges of leaves by applying one drench too many of the soluble salts. And the overabundance of nitrogen kept the bell peppers making leaves when they should have been making flowers. But I went on fertilizing the same way for years before I had any real second thoughts. It was when the per-bag price of fertilizer shot up and never quite came down that I began to try to do things differently.

It wasn't just the talk of nitrates polluting groundwater, or worries that some of our fertilizer was contributing to the algal blooms downstream. It was the realization that the soil in the garden had become distinctly grittier and less friable than when I had first turned it over. It wasn't the garden we have now, southfacing and well drained, but rather a piece of low ground in back of the house. But even here the soil now held water less well and was more prone to crusting. In short, it displayed all the classic symptoms of insufficient organic matter. The realization wasn't an epiphany, mind you. Realizing that I, too, had become a victim of this commonest problem took a couple of years to sink in. But in the end it was no less embarrassing to have been so smitten by the power of a handful of chemicals that I'd neglected the obvious. And when we got around to moving the garden to the better location across the road, cutting down the pines and breaking fresh ground, I resolved to pay more attention to the soil itself.

New ground in this part of the country can contain as much as ten percent organic matter. But cultivation reduces that swiftly. Whether by hand or beast or gasoline tiller, the repeated stirrings of the soil mix in extra air; the result is the same as if you were blowing on a glowing coal. The organic content burns up. You can keep the fire stoked by adding fresh organic matter, but even diligent gardeners can rarely keep the organic content of cultivated ground at more than fifty percent of what it was before they first plunged a spading fork into it.

The organic matter is essential, though, because it is the fuel for the community of microorganisms that inhabits soil. A single teaspoonful of soil may contain five billion bacteria, twenty million filamentous fungi, and a million protozoa. These fix nitrogen from the air, produce organic acids that serve as a solvent for minerals, help roots take up nutrients from the soil, and prey on plant pathogens.

At the same time the organic matter attracts and holds nutrients, reduces leaching losses, binds soil particles into aggregates (producing a good tilth), and soaks up water. In short, organic matter and the microorganisms that live on it are better stewards of soil structure and fertility than any chemical company. Those who feed the soil and let the soil in turn feed their plants are engaged in what can best be called biological gardening.

Resolving to increase the organic matter of soil is easier than actually doing it. Many "organic" gardeners import their organic matter from great distances. But bringing organic matter from tens or hundreds or even thousands of miles away (in the case of peat moss) has always struck me as being scarcely different from trucking in chemical fertilizers from the same distance, as "chemical" gardeners do. A certain amount of moving things from one place to another is inevitable in gardening, but we want to reduce the consumption of fossil fuels that accompanies long-distance transport. We are aiming for a garden fertility as homegrown as the vegetables we harvest.

I won't claim that what I do is appropriate to commercial agriculture. But as a part-time farmer and amateur gardener, I belong to a great guild not bound by market economics. I measure our success in the declining amounts of chemical fertilizer that I add to the garden each year and the bushels of beans, cucumbers, and squash that we harvest nevertheless.

The number-one alternative to chemical fertilizer has always been animal manure. If we had a ready supply, I would happily add half a ton of horse or cow manure per thousand square feet every couple of years. But we don't keep animals. Nor do our nearest neighbors. The days when horsepower also generated horse manure are long gone. There are still riding stables and a few dairies, but none are close. And the manure we would be trucking up this hill would contain a lot of water. Horse manure is sixty percent water, cow manure eighty-five percent. If we were making an outing, we would probably go down to the beach instead and load up on seaweed, an equally old-fashioned source. Washed up on the high-tide line and sun-dried, it is nearly twice as good a source of nutrients per ton as horse manure (and the salt is not a problem).

Instead, we have been turning our attention to homegrown nutrients. The greatest nitrogen-fixing systems on earth are symbiotic bacteria. Chief among these are bacteria in the genus Rbizobium, which form nodules on the roots of leguminous plants from alfalfa to peas. Rotating crops with legumes is a practice that dates back millennia. The Greek Theophrastus, in the third century B.C., described how broad beans add fertility to the soil. Planted one year in three, they provide a significant amount of the nitrogen needed for the vegetable crops that follow. The trick is not to try to improve things by adding lots of soluble nitrogen to the soil, because it suppresses the growth of the nitrogen-fixing bacteria.

I also intend to start using legumes not just in rotation but also as an undercrop. Eliot Coleman, the author of The New Organic Grower, has been undersowing squash and cabbage with white clover by planting the clover seed four to five weeks after the crop plants are established. The great advantage of this technique is that in northern New England, where Coleman gardens, the plants have time to become established before cold weather sets in and to make a significant contribution as a nitrogen-fixing, overwintering cover crop. At present the only cover crop that we can sow is winter rye, because we wait until we have harvested the last carrots and cabbages. By then it's too cold to plant anything besides this nonlegume.

Cover crops are a source of both nutrients and organic matter, but by themselves they aren't enough to keep the organic content of our gardens as high as it should be. So I prowl our land for caches of ready-to-use organic matter. I scoop up the crumbled remains of a pile of rotted logs, dig black muck and leaf mold out of the channel that runs through the center of our cranberry bog, and salvage the sphagnum that the beavers gather up and use to dam the overflow of our pond. All of this is fair game.

We save the ashes from our wood stoves and spread them on the snow in the early spring to make it melt faster. A pound of wood ashes is the equivalent of two thirds of a pound of ground limestone in terms of raising the pH, so I have to watch that I don't raise the pH above the optimum 6.5. The fresh ashes also contain a certain amount of caustic lye, so I never spread them directly on growing plants.

The merits of using rock phosphate or the more soluble superphosphates are something that I will leave others to debate, noting only that phosphorus doesn't move very fast in the soil, so you have to put it where it's going to be needed. No matter how soluble a particular brand of fertilizer is advertised to be, in acid soils the phosphorus reacts with the first soil particles it encounters and is firmly bound up. This immobility has one advantage: leaching losses are only measurable over periods of fifty to one hundred years. Because phosphate water pollution is caused by surface runoff, I dig in any phosphate that I add.

I mulch everything heavily, in the belief that nature abhors bare ground and that this is how wild plants get their compost. Part of our garden gets pine needles, raked from beneath the pines. There is no need to worry about them lowering the pH of the soil. We have a friend who mulched with nothing but pine needles for twenty years and never changed her pH an iota. Besides, I'd be happy to have an excuse to add more potassium-rich wood ashes. We also mulch with shredded leaves, cartloads of which we rake up from under the apple trees each fall for the primary purpose of controlling apple scab. Anytime that I can do two good things for the labor of one I think I'm on to something.

Our principal mulch is hay. Bales of mulch hay, once a waste product, have by now become nearly as expensive as new bales. And they are considerably heavier and moldier. So we make our own. We don't bale our hay, we just cut it. We have a small gasoline-powered sickle-bar mower, but we use a scythe when it won't start. We let the cut hay dry in the sun for a while to lighten the load, or just rake it right away if we are in a hurry. We pitch the loose stems into a hand cart, tucking the corners in the way that people did when this was the only way to move hay. In order to end up with the equivalent of an inch of baled hay covering a one-thousand-square-foot garden surface, you need three to five thousand square feet of hayfield. If it's average hay, you are getting twenty-five, ten, and forty pounds of NPK per ton. If it's good legume hay, you are getting fifty pounds of actual nitrogen. Some of this becomes available to soil organisms immediately, the rest in the year that the mulch takes to break down. By spring, what's left of the preceding year's mulch is easy to incorporate into the upper top few inches. I dig it in chiefly to encourage the soil to warm up in the spring, but other gardeners just leave the mulch where it is, knowing full well that nature feeds from the top down.

As for our compost heaps, those piles of garden waste, we no longer locate them off to one side of the garden. Why risk letting nutrients leach into nongarden soil, or having tree rots invade their heart? We build our compost piles right where we garden. That way, too, we don't have far to carry either the ingredients or the finished product. These aren't scientifically prepared piles. We've never been in a rush to make fast compost, the kind that heats up and pasteurizes itself, so we have never paid much attention to carbon-nitrogen ratios. But we are very good about adding everything to them. From the first rhubarb leaves to the last frosted tomato vines cut off their poles, we pile any and all scraps of loose vegetation into a heap. We add rotten apples, sods, ashes, even meat scraps, lobster shells, and the occasional dead woodchuck (what better place to assure that what has been feeding on the garden will in turn feed it?). It takes a year for such a pile to become compost. Whenever we tear one apart, we reserve any undecayed remains to start the next piles. The rest we eagerly add to the garden beds. Both the nature of composting itself - incredible shrinking heaps - and the enormous value of the resulting partially decayed organic matter means that no one ever has too much, or even enough.

I don't suppose we will ever return to the time when lilacs were planted around every outhouse and hogs rooted beneath the wooden seats, their more efficient digestion enabling them to use as food half of what humans excreted and convert the remainder to pig manure. But we are proud of the Clivus Multrum, a Swedish composting toilet, that we use. From its enormous white tank in our cellar we periodically retrieve five-gallon pails of a rich organic brew that would make any Chinese gardener envious. The problems of heavy metal contamination in sewage sludge vanish when you don't mix your sewage with the effluents of industry.

Our friends in the city say that they envy us our freedom here, our opportunities to try new ways to shorten and tighten the nutrient loop. The city does force

This book is nearly out of print (sadly). Several copies are probably available from: amazon.com barnesandnoble.com booksnow.com

people to garden in tighter quarters. But we can't help noticing that some of the people who envy us our hayfield and pine grove are still raking up their leaves every fall, bagging them in plastic, and putting them out on the curb for the city to collect. Six months later they are buying back plastic bags filled with organic matter in the form of peat moss. Concerns over municipalities' refusal to collect "yard waste" vanish if you recognize that there really isn't any such thing. Municipal composting programs, as admirable an alternative to landfills as they may be, would all be rendered unnecessary if homeowners could be persuaded not to throw away their organic matter in the first place.

The proper place for organic matter to end its days is at home, not in the outskirts of some distant dump, no matter how well managed it is. I like to think of piles of leaves or brush or compost heaps as horning rooms. There was a time when every New England home had one, a small room next to the chimney where babies were delivered and the dying spent their last days. Childbirth and death were properly considered home matters, and those lying close by the kitchen could be easily cared for. These stores of organic matter don't have to be right in view, but they should be kept close to hand. They represent a central principle in the quest for sustained fertility. There is no need to welcome back nutrients when you haven't said goodbye.

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Posted by Anthony Benoit abenoit@trcc.commnet.edu
Environmental Engineering Technology at Three Rivers