ABSTRACT
The weathering of various geologic materials under a given climatic regimen results in development of a biological system, the whole of which ultimately yields soil. Some of the soluble mineral fraction released via the weathering process and not lost from the soil system is tied up in both the living biomass and decayed organic matter. The biotic system within the soil, as well as the plant community growing from the soil, is nurtured by nutrients recycled from decaying plant residue and soil organic matter, along with nutrients released through solubilization of the mineral fraction. Gains and losses of nutrients in natural ecosystems are roughly in balance so that continued biological growth or net fixation of carbon depends upon the cycling of nutrients between the biomass and the organic and inorganic stores. The nutrients supplied by a soil to a crop within a year vary widely.
