Introduction
It has long been recognized that humic substances (HS)
have many beneficial effects on soil and plant growth.
These heterogeneous and complex molecules, ubiquitous
in the environment, can produce various morphological,
physiological and biochemical effects on higher plants
(Chen and Aviad, 1990; Vaughan and Malcom, 1985).
The influence of humic material on plant growth, have
been investigated on biometric factors and numerous studies
have shown that humic substances enhance root, leaf
and shoot growth but also stimulate the germination of
various crop species (Piccolo et al., 1993).