BRIDGING THE DIVIDE: SOIL RESOURCES AND THE GEOSCIENCES ON A CULTIVATED PLANET

No particular division between soil science and geology existed as the two sciences emerged at the end of the Enlightenment. An institutional chasm emerged at the end of the 19^thcentury, however, when soil-related research and mapping were placed within the USDA – despite interesting efforts to combine the two led by Eugene Hilgard of Berkeley and John Wesley Powell of the USGS. It is certainly likely that the resulting institutional separation contributed to an academic divergence between the fields, an unfortunate division for both sciences as they now contend with emerging problems of societal significance.

Soil is the derma of the Earth. It has been suggested that the key attributes that define a soil’s quality are its texture, mineralogy, and organically-derived components (humus). These are in turn controlled by the variables of lithology, climate, biota, topography, and landform age. The earth is tectonically active; thus stable, level landscapes are rare. The rates and processes by which soil is eroded from sloping lands and replaced by the conversion of underlying rock into soil material contribute to the nature of the soil composition. James Hutton long ago recognized that these counteracting processes are largely in balance in many locations, leading to a local quasi-steady state or, in the terms of environmental vernacular: sustainability. Soils on hillslopes also have certain features characteristic of resilience, a feature where changes in the relative rates of either erosion or soil production produce feedbacks that in turn control the rate of the opposing process.

The major geological force capable of disrupting the soil and geomorphic resilience is the array of human activities, particularly cultivation. Cultivation removes vegetative cover and changes the mechanisms of soil transport, which can then rapidly accelerate erosion beyond the capability of soil production. Cultivation also greatly changes the rates of organic matter inputs and losses, generally resulting in large reductions in the soil’s store of C, N, and other elements associated with humus. Yet much remains to be understood about these and other problems. Multidisciplinary work involving the reconnection of the geosciences and soil science will result in more holistic means of sustainably managing a cultivated planet.