The theoretical reasons for the soil fertility (a trophic function of ecosystem) have been demonstrated. Higher green plants were regarded as heterotrophic organisms with symbiotic digestion and feedding. He supposed that the soil trophic function is connected with soil organic matter to a great extent. Firstly, soil organic matter (especially humic substances) is the source of compound organic molecules, which are consumed and assimilated by plants together with mineral nutrients. Plants "are economical" with an energy in addition. Secondarily, humification of plant litter is conductive to decrease of negative allelopathic influence by intermediate products of litter transformation. From ecological point of view, soil plays transformatic-trophic rather than substratum role in ecosystem.