Soil Ecology: The Basics of Fertility
Table of Contents
Living SoilSoil Food WebSoil Nurture
Soil Nurture
Soil Testing
Most of us have grown up thinking that soil fertility revolves around the question of what we need to buy and add to soil to bring it into balance and heightened productivity. We look to soil tests to guide us in making the proper purchased applications. Certainly when we begin working with a piece of ground, especially if it has been badly abused, there may be additions we need to make. Be cautious about soil tests, however. There is no unified approach to soil testing. Different laboratories use different procedures, such as different solutions to extract soil nutrients; report results differently; and adopt different approaches to interpreting the results. For example, I remember how confused I was by test results I used to get from the Extension Service: They always noted that both phosphorus and potassium were “very high”—and then routinely went on to recommend application of chemical fertilizers containing 10 percent of each. Later, I worked with a soil consultant (a student of William Albrecht), who also noted the high levels of phosphorus and potassium, but who recommended “no fertilizer needed”—and indeed pointed out that it would be easy for my soil to rise to dangerously excessive levels of phosphorus, if I weren’t careful with certain organic matter applications such as manures. Since most soil analyses focus so much on crop needs for nitrogen, imagine my surprise when he also recommended no added nitrogen. When I asked about that, he replied dismissively, “Oh, with organic matter at the level you have, you don’t need any added nitrogen, except maybe a little for really heavy feeders like corn.”
Soil Nurturing Strategies
By all means, find and work with a competent soil consultant if you feel your soil has serious deficiencies or special needs. But I urge that your main focus be not on what you need to add to your soil, as purchased inputs, but on strategies to maximize the diversity, health, and population densities of your friends in the soil.
It is unfortunate but true that the key to doing so is largely to choose strategies directly opposite to almost all current agricultural practice, which are injurious to soil life in three ways:
- Monoculture The growing of a single species on vast tracts reduces diversity of soil life.
- Use of harsh chemicals There is no synthetic chemical—whether used to fertilize crops, kill insects or weeds, or suppress disease—which has been demonstrated not to be destructive of soil populations.
- Excessive tillage Frequent tillage of soil is disruptive of soil life and robs it of its carbon (organic matter) reserves.
The alternative to such destructive practices is to imitate natural soil ecologies in order to:
- Maximize diversity and population densities of soil organisms While homesteaders are unlikely to practice monoculture in the conventional agricultural sense—to grow nothing but carrots, for example, on all their available ground—we should constantly find ways to “mix it up” in how we manage our soil. Crops of different families should rotate over the available ground in succeeding seasons. A diversity of sources of organic matter should be used—composts, mulches, cover crops, etc.
- Feed the soil using sources of fertility grown on the homestead or found close by Deep-rooted cover and fertility crops can “mine” minerals from the deep subsoil and make them available to more shallow-rooted plants. Nitrogen-fixing legumes (clovers, alfalfa, beans and peas) can boost nitrogen for heavier-feeding crops. Recycle autumn leaves and crop residues by composting or using them as mulches. Manures and mulching materials may be available from nearby farming operations. If a soil test does indicate the need to add minerals, use slow-release rock powders (greensand, colloidal rock phosphate, etc.) rather than highly soluble chemical fertilizers, which quickly leach to groundwater.
- Protect and improve soil structure Plant in wide beds and never compact the soil by walking in the growing spaces. Keep the soil constantly covered—by closely-planted crop plants, cover crops, mulches. Addition of lime to clay soils can help “floculate” the almost microscopic soil particles into aggregate clumps, resulting in a looser, more open soil structure with better air and water penetration. When tight soil must be loosened, do it with a broadfork rather than a power tiller (or even a spading fork) to avoid inverting soil layers. Chickens can also be used to till in cover crops without serious disruption of soil structure.
The “Soil Care Basics” articles, “Increasing Organic Matter and Mineral Availability” and “Protecting Soil Structure with Alternatives to Tillage”, present specific soil care practices based on the above ideas.