The Science behind Compost

Composting is a natural recycling process performed by micro organisms that exist naturally in the soil. Large quantities of food, garden, lawn, and/or farm waste can be reduced in a relatively short time to a pile of black, crumbly humus which makes an ideal soil conditioner.

Regular addition of compost to soil will inevitably provide benefits for the growth of plants. The soil structure will improve, since humus contains substances that cause aggregation of soil particles. In clay soil this means that the microscopic individual particles will be clumped together and more air spaces will be opened up between clumps. Without these air spaces the clay particles stick tightly to each other, forming a nearly impenetrable barrier to water and gases. This is why the clay is so sticky when wet and hard when dry. In sandy soils, the large sand particles are aggregated with humus as well, which increases the nutrient content and moisture-holding capacity of the sandy soil. Normally, water and nitrogen fertilizers leach quickly from sandy soil, making it necessary to add them frequently.

A less widely recognized benefit of compost lies in its humic and other organic acids content. Humic acids bind salts, heavy metals, toxics, pesticides, and a variety of other reactive or ionic materials, making them unavailable for plant uptake. This translates to healthier crops. Organic acids also improve soil physical properties, boost trace nutrient availability through chelation, and improve overall plant nutrition by regulating nutrient release. These nutrients, or ions, are held by the humus particles which contain many ion exchange sites on their surfaces. The ions are released into soil water, and plant roots are able to take them up. Because there are so many ion exchange sites on humus particles, humus also increases the buffering capacity of the soil. This condition helps to prevent rapid leaching of lime and nutrients as well as reducing the effects of over-liming and over-fertilizing.

For example, when a soil’s pH is increased too much by adding too many wood ashes, the most economical way to correct the condition is to add compost, which will bind the extra basic ions that would otherwise result in a high pH.

Consistent use of compost and other organic matter will result in dark brown or blackish soil, which increases heat-absorbing capabilities to some extent. Compost reduces soil erosion by holding water so it can percolate into lower soil layers rather than run off, carrying soil particles with it. Compost also reduces crusting of the soil surface by slowing evaporation. Compost provides nutrition for earthworms, soil insects, and micro organisms, many of which will help balance the populations of less desirable soil fauna over time.

Mycorrhizal fungi, which have been proven to benefit plants through their association with plant roots, are also prolific in high humus soil.

Finally, the products of the composting process contain common nutrient elements (Nitrogen, Phosphorous, Potassium, Magnesium, etc.) found in synthetic fertilizers, as well as many trace elements not available from commonly used synthetic fertilizers.