Global tectonics and agriculture: A geochemical perspective

The global distribution of regions of sustained productive agriculture shows that an ample supply of fresh rock residues is vital to soil fertility. Once such rock debris is removed soil degradation will be evident in falling yields and trends within the clay fraction from chemically diverse smectite clays towards impoverished kaolinite-gibbsite soils. Increased erosion will follow the clay degradation. Reliance on N, P and K and organic residues alone will not be sufficient to counteract this trend unless Nature, through geological forces, or Man, through the application of appropriate rock dusts, intervenes to restore nutrient balance and a better clay spectrum. The geological evidence of natural weathering rates, and soil evidence of leaching rates, points to applications only of the order of 1 ton ha^?1 year^?1 being the amount of fresh rock replenishment required to hold the soil in balance for agriculture. Failure to achieve this makes way for a progressive trend towards soil degradation accelerating, as changes induced in the nature of the clay fraction enhance the leaching effect of the aerial environment.On a world scale these effects can best be seen by comparing the enhanced fertility of soils that have benefited from volcanic renewal near active plate boundaries or the fresh rock enrichment arising from the rock grinding involved in glaciation, with the almost ‘impossible’ soils typical of geologically quiescent areas, such as the Amazon and Congo basins where, merely to fertilise with N, P and K alone so impoverishes the soils of their critically limited supplies of other essential nutrients, that disaster is inevitable.