TWO VIEWS OF HOW SOILS SUSTAIN US: AGRICULTURAL VS. GEOCHEMICAL CYCLES

Agriculture and geochemistry differ in their views of soils as sustaining resources. In agriculture, the goal of fertility places a premium on conservation of available pools of rock-derived nutrients, which are replenished dominantly by fertilization and biotic cycling. In geochemistry, soil plays a “pass-through” role linking the Earth’s rock and ocean-atmosphere reservoirs; the important pools are weatherable, not available, and are replenished by landscape renewal; and leaching of nutrients is essential for maintenance of planetary habitability. These views intersect quantitatively in the rate of chemical denudation of the continents, which is nicely constrained over geologic time but may be considerably affected on human timescales by agriculture. Discussion will be encouraged.