The Earth

What is this mysterious substance in the soil that makes it dark in color, very fertile, and which gardeners talk about so reverently? Growers affectionately call this substance Black Gold, but in the scientific world it is known as humus. Humus gives healthy earth its characteristic color, smell, and fertility. The object of the grower is to have rich healthy soil so crops will be vigorous and productive.

Chemically, humus is incredibly complex and defies precise analysis by soil scientists. It best can be described as consisting of decomposed organic matter, along with the remains of soil microorganisms, and is extremely rich in nutrients. When humus is increased in the soil it creates and maintains a soil that has the capacity to produce crops year after year without using chemical fertilizers.

In nature, humus accumulates very slowly over decades. But human intervention can speed up the process by incorporating large amounts of organic matter in the soil. When organic matter is digested (decomposed) by soil microbes – bacteria, fungi, etc. – humus is created.

A faster way to hasten the formation of humus is by composting garden and kitchen wastes and incorporating the finished compost into the soil. Compost is the mixing of organic matter that is high in carbon (such as dried leaves) with material that is high in nitrogen (such as fresh grass clippings). This combination leads to a population explosion of microorganisms and promotes rapid decomposition. Finished compost has reached a stage in its disintegration at which it is an ideal food for plants – a high-quality humus.

Applying a three-inch layer of finished compost and digging to a depth of six inches with a spading fork or tiller – three years in a row – accomplishes what it took nature at least 100 years to do – produce a rich fertile soil.

Though low in nitrogen, phosphorus, and potash when compared to chemical fertilizers, humus produces tremendous growth response in plants. One reason for such a response is its ability to release nutrients over a long period of time. Also, humus contains all the known trace elements plants need, thus ensuring against malnutrition.

Release of nutrients
Humus feeds the plants in two ways:

Fast nutrient release: As organic matter decomposition occurs, plant tissues break down into a number of substances. Some of the resulting products are released into the air and plant roots absorb others. Under these conditions humus is very soluble and will make available a flood of nutrients.

Slow nutrient release: Eventually, the easily decomposed food is exhausted, and more resistant compounds remain releasing nutrients very slowly and holding them in a stable form. This includes compounds of plant residues, such as waxes and lignin, that don’t readily decompose but become stable and fairly resistant to further decomposition. This is the humus that remains in the soil for long periods of time, some times up to a thousand years.

Benefits of humus
Some of the benefits that humus provides are:

Retains water. Like a sponge, humus retains moisture while at the same time aerating the soil. It can hold the equivalent of 80 to 90 per cent of its weight in water. Soil is more drought resistant when it is rich in humus.

Develops good soil structure. Humus gives soil a crumbly texture, which permits air to circulate. The secretions of soil microbes holds the soil particles together in a desirable crumb structure. This makes soil light and fluffy and easier to work.

Retains nutrients. Humus retains nutrients in the soil in a form that is readily available to plants. A reserve of humus provides additional plant nutrients in times of need. It is all but impossible to have too much humus in the soil.

Improves soil. With the help of humus the soil is improved. It resists compaction, is easier to cultivate, allows plant roots to penetrate, breaks up clay, and holds sand particles together. Stable humus improves the soil’s physical qualities and is most beneficial as a soil amendment.

Enhances plant health. Organic matter feeds the microorganisms that aid the plants and soil. These microorganisms protect plants from disease and insect damage by actively decomposing humus in such great numbers that they prevent plant-destroying fungi and other pathogens from establishing themselves.

Traps soil toxins. Humus can immobilize and prevent many toxic metals from becoming available to plants or other soil organisms.

Balances pH. Humus has a pH of about 7 (nearly neutral) and moderates excessive acid or alkaline conditions in the soil. When added to an acidic soil it will bring up the pH. When added to an alkaline soil it will bring down the pH.

Ways to build humus
As substitutes for the application of compost, organic matter can be increased by:

Green manures and cover crops which are grown to provide a source of organic matter. They are not harvested but tilled into the soil before the plants mature. This is one of the easiest ways to increase organic matter.

Mulch, which is used to control, weeds and protect the soil from extreme temperatures, but it also is a way of building humus if it is incorporated in the soil after the season is over. It will decompose as microorganisms and earthworms mix the mulch with the soil.

Sheet Composting which involves spreading organic material directly on top of the soil to decompose in place and to be turned under after decomposition. When sheet composting animal manure, it is best to apply it in the fall and to turn it under right away. This prevents the loss of nitrogen.

Trench-composting which is layers of buried organic material in a trench that is covered with soil and left to decompose for one season.

At the Rodale Institute they believe that a healthy soil is the foundation needed for a healthy food system. Healthy soil produces healthy crops, healthy livestock, and – ultimately – healthy people. This is why I work so hard to make sure there is an adequate supply of humus in my soil.

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