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Soil Fertility from The New Organic Grower

By Eliot Coleman
From The New Organic Grower

The following excerpt is from Eliot Coleman’s book The New Organic Grower: 30th Anniversary Edition (Chelsea Green Publishing July 2018) and is reprinted with permission from the publisher.


I learned my first important lesson in soil fertility from the US Department of Agriculture, albeit by default on their part. It happened in 1966 when I began growing vegetables on rented land in New Hampshire. Since I had limited farming experience at that time, I eagerly read everything I could find on the subject. The USDA, in an article about fertilizer nutrients in agricultural production, stated unequivocally that nitrogen was nitrogen and phosphorus was phosphorus. They said that it did not make any difference to the plant where the nutrient came from. Nitrogen from manure and nitrogen from a bag of store-bought fertilizer were the same. To me, that was welcome news indeed.

Bring on the Free Manure

I was not aware at the time that the reason for these pronouncements was to discredit the organic farmers who claimed that manure or compost produced superior plants. In my naïveté, what I saw was a chance to save some money. I would not have to buy fertilizers! Just down the road was a horse farm with huge piles of rotted manure that the farmer was giving away, even delivering free to anyone who wanted some. Chicken manure, which the article said was high in phosphorus, was available from another neighbor. I figured that if the USDA experts said there was no difference between the elements in manure and those in store-bought fertilizer, that was good enough for me. I went with the manure and started a couple of acres of vegetables with what I assumed was the assurance of the USDA that everything would work out just fine.

shovel holds black dirt

And work out fine it did. During the three years I farmed that place, I had the best vegetables anywhere around. Not only that, but they got better every year. In fact, the old-timers were coming and asking the new kid how he did it rather than the other way around. Obviously, soil fertility was a function of a number of factors, and they did not have to be chemically processed or cost a lot of money to be successful.

When I did need to purchase nutrients, I continued to take the USDA at their word that elements were elements. I purchased unprocessed minerals such as rock phosphate. In the long run they were less expensive. Since they weren’t water-soluble or subject to leaching, I could apply enough at one time to last a number of years. The lesson: Food for plants does not need to be prearranged in a factory. Nutrient availability is a result of biological and chemical soil processes that are stimulated by the agricultural practices I learned to use and trust—crop rotations, green manures, and animal manures. This biological system comes full circle. Each practice aids another, and the result is synergistic.

Building the Soil

To build a fertile soil, I focused right from the start on five amendments that I supplied as raw materials:

Organic matter. Compost or manure applied at the rate of 20 tons per acre (18,145 kilograms/4,000 square meter) every other year as a general rule.

Rock phosphate. A finely ground, natural rock powder applied every four years (quadrennially).1 There are two forms—hard rock phosphate, containing 33 percent P2O5 and colloidal phosphate containing 22 percent P2O5. I prefer the colloidal form, but other growers will make an equal case for the hard rock.

Greensand marl (glauconite). An ancient seabed deposit containing some potassium, but principally included as a broad-spectrum source of micronutrients. Applied quadrennially. Dried seaweed is another popular (although more expensive) source of potassium and micronutrients. It breaks down more rapidly and has the additional benefit of stimulating biological activity in many soils.

Limestone rock. A ground rock containing calcium and magnesium that is used to raise the soil pH. Sufficient lime should be applied to keep the pH within the range of 6.2 to 6.8.

Specific micronutrients. Elements such as zinc, copper, cobalt, boron, and molybdenum are needed in very small quantities but are absolutely essential for a fertile soil. They will usually be adequately supplied if the grower has paid attention to pH and organic matter. The need for supplemental application of micronutrients is best gauged through careful soil testing and grower observation. In many cases boron is the one element to need amending. Obviously, if a soil test indicates that one of the micronutrients is already well supplied, that supplement will not be needed.

Two Ways to Fertilize

Although this is a chapter on soil fertility, I am first going to discuss philosophy. That may be unconventional, but it is crucial to an understanding of the supplements recommended above. There are two basic philosophical approaches to fertilization:

Feed the plant directly. This involves using soluble fertilizers so the nutrients are “predigested” for plant use without the need for the natural soil processes.

Feed the soil and let soil processes provide for the plant. This involves creating and maintaining the optimalconditions of a fertile soil, under which ahealthy soil-plant economy can exist.

In the first case, the farmer provides plant food in a “predigested” form because the soil processes are considered inadequate. A symptom—poor plant growth—is treated by using a temporary solution— soluble plant food. In the second case the farmer makes sure that the soil processes have the raw materials needed to be not just adequate but exceptional. The cause of poor plant growth—lack of sufficient plant food in the soil—is corrected by providing the soil with the raw materials needed to produce that plant food.

Natural Processes

Although we are dealing with agricultural techniques, we can’t ignore the patterns of thinking that lead toward choosing one agricultural technology over another. These thought patterns stem from different points of view about the “natural system” that governs plant growth. Some questions:

  • Are natural processes so inefficient that we can do better by taking over their roles, even though the energy cost of such a choice is high? Or can natural processes provide all that we need if we work to enhance them?
  • Is it wise to rely on a crop-production system that is totally dependent on purchased materials involving great cost, supply networks, and safety considerations over which the farmer has no control? Or is it preferable to create a farm-generated system that relies on minimal quantities of off-farm products and maximum enhancement of the soil’s inherent fertility?
  • Is it acceptable to add only enough nutrients to get a crop? Or is it more worthwhile to try to provide all the known and unknown nutrients and growing conditions to allow the plants to grow at their optimum?

I have encountered many responses to these questions. There are always some growers who say, “Natural processes and growing optimum be damned. I just want to grow the crop with the least possible effort and deal with any problems later.” Unfortunately, later problems, when they occur, are not limited to low yields, but involve insects, diseases, and poor crop quality. Other purchased products—pesticides, fungicides—are then used to deal with the new problems. Since agricultural systems are interconnected, one action leads to another, and one problem begets a subsequent problem.

My own position on these issues is that I simply do not know enough to tamper with the natural system, and I have no desire to do so. I am an admirer of the intricate cyclical systems of the natural world, and I prefer to study them in order to make less work for myself, not more. Even if I thought I knew every- thing, I would rather let it be done for me by the real experts. The real experts in this case are all the processes that take place in a fertile soil—the interrelated activities of bacteria, fungi, dilute soil acids, chemical reactions, rhizosphere effects, and countless others we are unaware of.

My attitude toward the natural world is one of respect for a marvelously efficient system. If I attempt to feed the plant directly, I am in effect deciding that I can do a better job. On an infertile soil, where the system is working poorly, maybe I can. But on a fertile soil, the system can do a better job on its own. Therefore, my responsibility as a farmer is to add to the system the ingredients necessary to support a fertile soil. Those basic raw materials are organic matter and minerals in the form of powdered rock. So don’t buy finished products. Buy the few raw materials that cannot be farm-produced, and let the soil processes finish the job. Not only does that policy make good sense agronomically, it is also the most successful, most practical, and most economical approach.

How It All Works

Let’s say we start with an infertile soil. If we take the off-farm approach and add soluble fertilizers, a good crop can usually be grown. The soil serves merely as an anchor for plant roots, and the majority of the food for plant growth is provided by the fertilizer. The soil remains infertile, however, and the fertilizer application will have to be repeated for every crop. The situation is similar to helping a student by providing the answers to the test. The result may be a good grade, but the help will have to be given every time.

If, on the other hand, the second approach is chosen, we try to create a fertile soil by adding those ingredients that distinguish a fertile from an infertile soil. The fertile soil will then do what fertile soils do naturally—grow exceptional crops. To continue our student-and-teacher metaphor, this second process is like providing the student with the raw materials of knowledge (good books and study habits) so the student can develop the ability to excel on exams without help. I think most readers will agree that this second approach is the preferable choice in education. It is also the best choice for plant nutrition.

About the Author

Eliot Coleman has over 50 years experience in all aspects of organic farming, including field vegetables, greenhouse vegetables, rotational grazing of cattle and sheep, and range poultry. In addition to The New Organic Grower, he is the author of Four-Season Harvest, and The Winter Harvest Handbook, as well as the instructional workshop DVD Year-Round Vegetable Production with Eliot Coleman. Coleman and his wife, Barbara Damrosch, presently operate a commercial year-round market garden, in addition to horticultural research projects, at Four Season Farm in Harborside, Maine.