It’s All One Piece: We continue to explore man’s traditional treatment of the soil, the results of this treatment, and the benefits that accrue through the planting and tending of natural landscapes, using native
plants.
This is an excerpt from the Wild Ones Journal
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Photosynthesis
Land plants and a few algae and bacteria can do something that no other naturally occurring entity on Planet Earth can do: Through the process of photosynthesis, they can harvest minute portions of the light energy from the sun and store it in chemical bonds. It is not an overstatement to say that life on Earth depends on the process of photosynthesis. It is through the manipulation of chemical bonds that all life persists. It happens that plants take in carbon dioxide (CO2) from the atmosphere, and water (H2O) from the soil, then, using the energy harvested from the sun, restring their component atoms together into molecules that most other organisms on the planet can use: Sugar molecules. These sugar molecules are the basic currency of life.
To complete their own life processes, plants can harvest the energy stored in these molecules to string together yet other molecules necessary for their own structure and functions – like reproduction. And they can exude the sugar molecules through their roots to influence their own growing environment. As was discussed in the last article, this growing environment, with the appropriate soil management techniques can be densely populated by a large variety of organisms – soil biota who make up the soil food web.
Among the soil biota are a specialized contingent of bacteria, called nitrogen fixers, that form symbiotic relationships with the roots of plants of the Legume family (Fabaceae). These bacteria are able to take in nitrogen (N2) from the air in the soil, harvest the energy from the energy-rich bond that ties two nitrogen atoms together, and fix single nitrogen atoms into organic molecules for use by the host plant, in exchange for the carbon-containing sugar molecules made by the plants. When the leaves and roots of the host plants die and decompose, nitrogen levels increase in the surrounding soil, improving the growth of other plants.
N, P, K and Soil Food Web
Nitrogen, phosphorus, and potassium, along with a number of microelements necessary for plant growth, are indeed available in healthy, soils that are rich in organic matter. Organic matter is made up of anything that is, or once was, living – plant or animal. It’s valuable in that it retains and filters water and nutrients, but it is not usable by plants in this form. Organic matter must be decomposed by the soil food web, and transformed into inorganic matter in order to become available to plants.
Nitrogen is made available by soil bacteria; phosphorus and potassium are tied up in mineral form in the soil itself and are made available by geochemical processes and the agency of algae and fungi.
As soil organisms consume organic materials, they retain (immobilize) nutrients in their cells. This process prevents the loss of nutrients, such as nitrogen, from the root zone. When fungi and bacteria die or are eaten by other organisms, nutrients are mineralized, that is, slowly released to the soil in plant-available forms. Nutrient immobilization and mineralization occur continuously throughout the year. This is what’s happening in the soil under our native plantings.
Contrast this with lawns and crop fields, which lack the full complement of soil microorganisms. Annual crops don’t allow sufficient time for the formation of a complex soil food web. They are fertilized to give the crops nutrients. And it is precisely because they are fertilized with chemicals that are destructive to the soil micro-organisms that the soil food web has trouble forming. The fertilizers are in concentrated form that rapidly dehydrates the bodies of micro-organisms. Further, fungicides and fumigants do exactly what they are designed to do: They kill soil fungi. It’s even been suggested that watering young seedlings with chlorinated tap water slows the establishment of the soil food web around the roots.
As mentioned earlier, plants produce sugars that they exude through their roots, while also sloughing off root cells. All the microorganisms that inhabit the soil are drawn to this special environment that is produced by growing plants. And when the plants cease to perform life-building processes (they die), the microorganisms proceed to dismantle all the fixed organic molecules and excrete inorganic molecules that continue the recycling process. The soil food web is cyclical and continuous; life forms ingest other life forms and excrete material in a form that plants can use.
The 6 to 10 inches of soil around plant roots is alive: In the case of native plants with roots that extend several feet into the soil, life extends for several feet into the soil.
The N, P, K exist in the soil around native plants and are immobilized in the bodies of microorganisms and in organic matter in general. Water carrying these nutrients is filtered by the organic matter in the soil. Our groundwater stays clean.
Fertilizers
We are familiar with the elements nitrogen (N), potassium (K), and phosphorus (P) that make up commercially available fertilizer. Let’s consider, for the sake of elucidation, why food-crop farmers and growers of lawns find it necessary to use fertilizers: Given their soil management techniques, there simply is not enough of these elements retained in the soils to produce the bountiful harvests that the market requires.
Both crop soils and lawns require the addition of chemicals that are in a form that plant roots can absorb directly. And, this feeding process, in some instances, may need to happen several times during the growing season because the chemicals do not persist in the soil – there is no soil food web to immobilize them. Biologists have realized that these chemicals sluice past the plant roots, through the soil, and on into our ground water, delivering nitrate and phosphorus pollution. The soil lacks the wherewithal to retain the chemicals.
Traditional proper farming practices have always required clean fields and monolithic crops. (Only one crop is grown at a time, for harvesting efficiency). The farmer plants his oats or corn, and at the end of the season is obliged to remove every shred of plant material that appears above ground. The seed is taken in by one method and the stems and leaves by another – leaving behind nothing but bits of stubble and meager, dead roots. In temperate climates that have winters, the earth stands naked in the off season, and dust devils whip around fine silt that ends up in drainage ditches and in our streams in the spring. There is little life in the soil, no living plant roots, and few microorganisms to stabilize the silt.
In the case of manicured lawns, the clippings (think organic matter) are removed each time the lawn is trimmed. The soil is purposely leveled and compacted, reducing any gaps and air spaces that might give room to microorganisms. In contrast to our native plants, lawn-grass roots rarely extend more than 6 inches into the soil, and this environment entertains few microorganisms to filter water or to retain and recycle nutrients.
Our soil management techniques and practices developed during a period of time when the soil retained fertility that had been laid down prior to the arrival of the first plows – and land was plentiful. Our attitude toward the soil was influenced by discoveries in science and by modern technology. We had the sense that technology would make up for our inattention to, if not outright misuse of the services provided by the natural world. These “services” were recently given a price tag by a Cornell University researcher – it was a staggering figure of several trillions of dollars annually. Those of us who promote the use of native plants in our landscapes recognize some of these services and are trying to turn the attention of others. For many of us, gardening with native plants has become more than a pastime, more than just another way of gardening, more than just another group of plants to collect – it has come to reflect a way of life.
In the next article we will explore some specific interactions between the soil biota and plant roots in healthy soil.
By Maryann Whitman