COMPOST PROPERTIES

Compost has been considered as a valuable soil amendment for centuries. Most people are aware that using composts is an effective way to increase healthy plant production, help save money, reduce the use of chemical fertilizers, and conserve natural resources. Compost provides a stable organic matter that improves the physical, chemical, and biological properties of soils, thereby enhancing soil quality and crop production. When correctly applied, compost has the following beneficial effects on soil properties, thus creating suitable conditions for root development and consequently promoting higher yield and higher quality of crops.

Physical properties

• Reduces the soil bulk density and improves the soil structure directly by loosening heavy soils with organic matter, and indirectly by means of aggregate-stabilizing humus contained in composts. Incorporating composts into compacted soils improves root penetration and turf establishment.
• Increases the water-holding capacity of the soil directly by binding water to organic matter, and indirectly by improving the soil structure, thus improving the absorption and movement of water into the soil. Therefore, water requirement and irrigation will be reduced.
• Protects the surface soil from water and wind erosion by reducing the soil-dispersion action of beating raindrops, increasing infiltration, reducing water runoff, and increasing surface wetness. Preventing erosion is essential for protecting waterways and maintaining the quality and productivity of the soil.
• Helps bind the soil particles into crumbs by the fungi or actinomycetes mycelia contained in the compost and stimulated in the soil by its application, generally increasing the stability of the soil against wind and water erosion.
• Improves soil aeration and thus supplies enough oxygen to the roots and escapes excess carbon dioxide from the root space.
• Increases the soil temperature directly by its dark color, which increases heat absorption by the soil, and indirectly by the improved soil structure.
• Helps moderate soil temperature and prevents rapid fluctuations of soil temperature, hence, providing a better environment for root growth. This is especially true of compost used as a surface mulch.

Chemical properties

• Enables soils to hold more plant nutrients and increases the Cation Exchange Capacity (CEC), Anion Exchange Capacity (AEC), and buffering capacity of soils for longer periods of time after composts are applied to soils. This is important mainly for soils containing little clay and organic matter.
• Builds up nutrients in the soil. Composts contain the major nutrients required by all plants [N,P,K, calcium (Ca), magnesium(Mg), and S] plus essential micronutrients or trace elements, such as copper (Cu), zinc (Zn), iron (Fe), manganese (Mn), boron (B), and molybdenum (Mb).
• The nutrients from mature composts are released to the plants slowly and steadily. The benefits will last for more than one season.
• Stabilizes the volatile nitrogen of raw materials into large protein particles during composting, thereby reducing N losses.
• Provides active agents, such as growth substances, which may be beneficial mainly to germinating plants.
• Adds organic matter and humus to regenerate poor soils.
• Buffers the soil against rapid changes due to acidity, alkalinity, salinity, pesticides, and toxic heavy metals

Biological properties

• Supplies food and encourages the growth of beneficial microorganisms and earthworms.
• Helps suppress certain plant diseases, soilborne diseases, and parasites.
• Research has shown that composts can help control plant diseases (e.g. Pythium root rot, Rhizoctonia root rot, chili wilt, and parasitic nematode) and reduce crop losses. Various researches have shown that cotton, fruit and vegetable growers were able to cut pesticide use by 60%-80% after three years of compost applications as part of an organic matter management system. Disease control with compost has been attributed to five possible mechanisms :

1. Successful competition for nutrients by beneficial microorganisms;

2. Antibiotic production by beneficial microorganisms;

3. Successful predation against pathogens by beneficial microorganisms;

4. Activation of disease-resistant genes in plants by composts;

5. High temperatures that result from composting kill pathogens.