SOIL HUMUS

Wairarapa Times-Age, 11 June 1940, Page 9

SOIL HUMUS

ITS MAIN CONSTITUENTS. A great deal is written about the value of humus in the soil, and it is of interest to know just exactly what is meant by this term. Typical humus is a black or brown substance formed by the action of bacteria and fungi (germs) on organic matter (the dead tissues of plants and animals). It really includes all of the substances intermediate between Hie undecomposed organic matter and the ultimate products of decomposition, like carbon dioxide, ammonia, etc.

The presence of humus is usually the cause of the dark colour of soils —the nvire humus the darker the colour. are three regularly occurring i/hes of humus, of which “mild humus" is the most desirable, and is the type which, is recognised as the most valuable constituent of any soil. It is formed chiefly in arable land, where there is sufficient air and lime to prevent the soil becoming acid. “Raw humus” is formed in humid zones where the supply of soil air is limited, and there is little or no available lime. This Causes the soil to become,acid. Such raw humus is common in swampy land, is readily con-' verted into milk humus by cultivation and liming. "Peat." the third form of humus, is normally formed under water by bacteria. This process is a kind of putrefaction during which gases are given off.