Humic substances are natural compounds contained in soil, peat, brown coal or lignite. As an important component of soil, they are created by bio-chemical transformation (decay) of organic, mostly vegetal remainders as a part of natural humus. Ever since, their black colors have symbolised fertility of soil. The spectrum of humic substances consists of a scale of compounds that may be divided subject to their molecular weight to high-molecular (first of all humic acids and their salts) and low-molecular (first of all fulvic acids and their salts). Both groups influence plants in mutual harmony, and together and separately play a specific important role. In black soils, the content of these compounds is proportional to the content of humus and the ratio of the high and low-molecular parts is approximately 1:1. Humic acids and their salts effect the plant physiology mainly as a stimulator of the accumulation of nutrients that have been unavailable for a long time; also as a regulator of the nutrition of plants and a very important protective factor enhancing the immunity of plants against all stress factors, including resistance to various diseases. Fulvic acids and their salts act as a vital carrier, transferring factor, that reduces the surface tension of membranes of green parts of plants thus facilitating receipt of nutrition and active substances through leaves or, as the case may be, it facilitates the migration of nutrition from soil to the root system of plants.