tte soil erosion process is modified by biophysical environment comprising soil, climate, terrain and ground cover and interactions between them (Figure 19.1). Soil erodibility - susceptibility of soil to agent of erosion - is determined by inherent soil properties e.g., texture, structure, soil organic matter content, clay minerals, exchangeable cations and water retention and transmission properties (Lai 2001). Climatic erosivity includes drop size distribution and intensity of rain, amount and frequency of rainfall, run-off amount and velocity, and wind velocity. Important terrain characteristics for studying soil erosion are slope gradient, length, aspect and shape. Ground cover strongly reduces the impact of the eroding energy before it has a chance to reach the soil; hence, most strategies to limit erosion begin with having some sort of vegetation, live or dead, covering the ground.
^e risk of soil erosion begins when natural vegetation, grasslands and forested areas, are either cleared for cultivation or used for grazing, ^e problem is accelerated by attempting to farm slopes that are too steep, cultivating up-and-down hills, continuous use of land for the same crop without rotation or fallow, inadequate use of fertilizers and organic manures, compaction of soil through of heavy machinery and pulverizing of the soil when creating seed-beds. Soil conservation strategies are also aimed at protecting the soil from direct exposure to natural elements such as establishing and maintaining good ground cover. Of particular importance in areas of the world where the first rains of a wet season area highly erosive, is the selection of crops that can establish ground cover rapidly. Where climatic conditions permit, early-season and between-season vegetation cover can be provided by off season crops that can be disked in or destroyed by pre-planting applications ofherbicide.
Soil conservation relies upon good management of soil combined with agronomic practices and the use of mechanical measures playing a supportive role (Figure 19.1). ^e basics of soil conservation practices to minimize soil erosion and enhance its prevention are shown in Figure 19.1. ^e initial task in adaptation of conservation practices to minimize the risk of water erosion, run off and soil loss would be to study the specific conditions in the study area or region that is con-
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Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.