United States Department of Agriculture - Agricultural Research Service
	Northwest Irrigation & Soils Research Lab,  Kimberly, ID
	Nutrient Cycling in the Soil-Plant-Animal System

Figure 1. Nutrient (elemental) cycling in the soil-plant-animal system (adapted from N.C. Brady, The Nature and Properties of Soils, 10^th ed., p. 353, 1990, Macmillan Publ. Co., New York). Primary minerals are the geologic parent materials of a soil or the original rocks of the Earth's crust, for example lava. Secondary minerals have been transformed by weathering processes into clay or silt. The circling nature of the process shows the interaction among soil, plants, animals, microbes, and soluble nutrients. The ultimate source of the "mineral" elements is the soil. For example, at any one time 98 to 99% of the phosphorus is associated with primary or secondary minerals and soil organic matter. About 1 to 2 % is in microbial tissue, and only 0.01% exists as soluble phosphorus. Elements are removed from the system by harvest and removal of plant and animal products, wind or water runoff (erosion), and to a lesser extent by water movement deep into the soil forming ground water flow. Note: this is a simplified and generic cycle, but certain elements such as nitrogen have more complex systems.



Last update on 17 April, 2001