Humus and its Benefits:
Humus is often described as the 'life-force' of the soil. Yet it is difficult to define humus in precise terms; it is a highly complex substance, the full nature of which is still not fully understood. Physically, humus can be differentiated from organic matter in that the latter is rough looking material, with coarse plant remains still visible, while once fully humified organic matter becomes more uniform in appearance (a dark, spongy, jelly-like substance) and amorphous in structure, and may remain such for millennia or more.
Benefits of Humus
●The mineralization process that converts raw organic matter to the relatively stable substance that is humus, feeds the soil population of micro-organisms and other creatures, thus maintaining high and healthy levels of soil life.
●The rate at which raw organic matter is converted into humus promotes (when fast) or limits (when slow) the coexistence of plants, animals and microbes in terrestrial ecosystems.
●Effective and stable humus (see below) are further sources of nutrients to microbes, the former providing a readily available supply while the latter acts as a more long-term storage reservoir.
●Decomposition of dead plant material causes complex organic compounds to be slowly oxidized (lignin-like humus) or to break down into simpler forms which are further transformed into microbial biomass (microbial humus) or are reorganized (and still oxidized) in humic assemblages which bind to clay minerals and metal hydroxides.
●There has been a long debate about the ability of plants to uptake humus from their root systems and to use it for their nutrition. There is now a consensus about humus as playing a hormonal role rather than a nutritional role in plant physiology.
●Humus is a colloidal substance, and increases the soil's cation exchange capacity (CEC), hence its ability to store nutrients by chelation as can clay particles; thus while these nutrient cations are accessible to plants, they are held in the soil safe from leaching away by rain or irrigation.
●Humus can hold the equivalent of 80–90% of its weight in moisture, and therefore increases the soil's capacity to withstand drought conditions.
●The biochemical structure of humus enables it to moderate — or buffer — excessive acid or alkaline soil conditions.
●During the humification process, microbes (bacteria and fungi) secrete sticky gums and mucilage’s; these contribute to the crumb structure of the soil by holding particles together, allowing greater aeration (porosity) of the soil.
●Toxic substances such as heavy metals, as well as excess nutrients, can be chelated (that is, bound to the complex organic molecules of humus) and prevented from entering the wider ecosystem, thereby detoxifying it.
●The dark color of humus (usually black or very dark brown) helps to warm up cold soils in the spring.
source:
http://www.thesoilguy.com/SG/Humus-Technical-1