Chapter 12 Summary
Soil forms from the breakdown of rock materials through mechanical, chemical, and biological weathering. Weathering rates are closely related to climate. The character of the soil reflects the nature of the parent material and the kinds and intensities of weathering processes that formed it. The wetter the climate, the more leached the soil. The lateritic soil of tropical climates is particularly unsuitable for agriculture: Not only is it highly leached of nutrients, but when exposed, it may harden to a bricklike solidity. The texture of soil is a major determinant of its drainage characteristics; soil structure is related to its suitability for agriculture. Agricultural practices may also alter soil chemistry, whether through direct application of additional chemicals or through irrigation-induced changes in natural cycles.
Soil erosion by wind and water is a natural part of the rock cycle. Where accelerated by human activity, however, it can also be a serious problem, especially on farmland or, locally, in areas subject to construction or strip mining. Erosion rates far exceed inferred rates of soil formation in many places. A secondary problem is the resultant sediment pollution of lakes, streams, and nearshore ocean waters. Strategies to reduce soil erosion on farmland include terracing, contour plowing, planting or erecting windbreaks, the use of cover crops, strip cropping, and minimum-tillage farming. Elsewhere, restriction of ORVs, more selective clearing of land during construction, the use of sediment traps and settling ponds, and careful reclamation of strip-mined areas could all help to minimize soil erosion.
