Organic matter content in soil determines its suitability to grow plants. Organic matter is defined by the Food and Agricultural Organizations of the United Nations as any material produced by living organisms, whether excrement or decaying material, which is returned back to the soil.
Organic matter can improve the ability of a soil to retain water. Stabilized organic material acts like a sponge, able to absorb six times its weight in water states, University of Minnesota Extension.
Organic matter that holds water in the soil prevents the runoff of pesticides and fertilizers, states Oregon State University. Water retention prevents surface runoff of these materials, preventing the pollution of nearby lakes and streams. Better water retention also reduces the decay and erosion of valuable topsoil, keeping land fertile.
Revolving Nutrient Fund
Organic matter serves as a revolving nutrient fund, providing nutrients to the soil and holding nutrients in place. Plant residues that comprise the great majority of organic matter in soil contains all essential nutrients a growing plant needs. A large amount of organic matter provides essential fertilization. Stable organic matter holds decaying matter in place, holding nutrients in an easily absorbed form. Organic matter must be added to soil at a greater rate than decomposition to remain effective.
Improving Soil Structure
Soil structure is greatly improved with the addition of organic matter. Organic matter is easy for plant roots to travel through, improving root development. Crusting of soil in heat or extreme weather is often prevented with the addition of organic matter, due to its water-retention qualities. Compaction due to human or animal activity on the surface is greatly reduced with the addition of organic matter.
Using organic material in the garden also recycles plant waste and prevents disease. Decaying material left in the yard or garden may contain pests or disease, but when added to garden soil is decomposed and added to the nutrient cycle. However, too much organic matter in a garden may support these diseases in the soil.