forestry

Soil Organic Matter

Soil Organic MatterOrganic matter is defined as the organic fraction of the soil. Organic matter in soil consists of the remains of plants and animals. When temperature and moisture conditions are favorable in the soil, earthworms, insects, bacteria, fungi, and other types of plants and animals use the organic matter as food, breaking it down into humus( the portion of organic matter that remains after most decomposition has taken place) and soluble nutrients. Through this process , materials are made available for use by growing plants. In addition, organic material has a very high cation exchange capacity, so nutrients are retained in plant available form. The digested and decomposing organic material also helps to develop good soil-air -water relationships. Organic matter is capable of absorbing large quantities of water and thus increases the water holding capacity of the soil.
In sandy soil organic matter occupies the space between the sand grains, thus binding these together and increasing water-holding capacities. In a finely textured or clay soil, organic material on and around soil particles creates aggregates of the fine soil particles, allowing water to move more rapidly around these larger particles. This grouping of the soil particles into aggregates makes soil mellow and easier to work.
Beneficial impacts of Soil Organic Matter on soil properties:

1. Physical : Stabilizes soil structure, improves water holding characteristics, lowers bulk density, dark color may alter thermal properties.

2.Chemical: Higher cation exchange capacity, acts as a PH buffer, ties up metals, interacts with xenobiotics.

3. Biological: Supplies energy and body-building constituents for soil organisms, increases microbial populations and their activities, source and sink for nutrients, ecosystem resilience, affects soil enzymes.
Each year , about 1 percent to 4 percent of nutrients in the soil organic matter are released through microbial transformation to become available to plants. Release is highest under warm, moist conditions and slowest in cool dry climates. Microorganisms are the driving force for nutrient release to plants.

By kamal bhusal