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Water and the Soil (2688 words) |
 | The water table is the dividing line in the soil profile separating the unsaturated zone, in which pore spaces are filled by a combination of water and gases, from the saturated zone, in which essentially all pores are filled with groundwater (fig. |
| Most soils are a combination of sand, silt, and clay, and the percentages of these various particle sizes determine the amount of water held in soil pores and the amount and rate of percolation to greater depths. |
| A clay soil may be unsuitable for crops because drainage is too slow, whereas a sandy soil may require irrigation because the water percolates quickly and does not remain in the root zone where it is available to plants. |
| Soil Mapping (565 words) |
| The soil profile is defined as a vertical section of the soil from the ground surface downwards to where the soil meets the underlying rock. |
| The soil profile can be as little as 10 cm thick in immature soils and as deep as several metres in tropical areas where the climate is conducive to rapid alteration of the underlying rock to form soil. |
| In some soils the B horizon results purely from the weathering of the underlying rock whereas in other soils this weathering is supplemented by the translocation of materials from overlying horizons. |
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