Humus generally refers to the decomposed organic residues which have undergone a series of degradation and synthesis cycles. The humic substances consist of a series of highly acidic, yellow to black coloured, high molecular weight compounds __________________, which can be separated using different extraction procedures:
In Pakistan there is general deficiency of rainfall. It varies from 125 mm annually in upper Sindh to about 900 mm in the sub-mountainous of northern Pakistan. In Balochistan the mean annual rainfall is about 200 mm, diminishing to ________ mm in the desert of Kharan:
_________ erosion is the removal of a thin layer of soil by water acting over the whole surface. This type of erosion damaged very fertile lands located on slopes, some of which have been eroded to a depth of about 15 cm.
Clay and humus particles are referred to as colloids and are less than 0.002mm. Due to their small size, colloids have ________________ surface area which provides surface for adsorption, catalysis, precipitation and microbial colonization: