This article throws light upon the three ways by which water enters into the soil. The ways are: 1. Infiltration 2. Percolation 3. Permeability.
Way # 1. Infiltration:
Infiltration refers to the downward entry or movement of water into the soil surface. Infiltration is affected by many factors. Infiltration is surface characteristic so primarily influenced by the condition of the surface of soil. A compact surface permits infiltration. Soil surface with vegetative cover have more infiltration rate than base soils.
Warm soils absorb more water than cold one. Coarse surface texture (sandy), granular structure and high organic matter content in surface soil, all help to increase infiltration (Fig. 4.7). Infiltration rate is comparatively lower in wet soils than dry soils.
Way # 2. Percolation:
The movement of water through a column of soil is called percolation. Percolation is important for two reasons. First, percolating water is the only source of recharge of ground water which can again be used through well for irrigation. Second, percolating waters carry plant nutrients down and often out of reach of plant roots (leaching). Percolation is dependent on rainfall.
In dry region, percolation is negligible but in region of high rainfall, percolation is usually high. Sandy soils permit greater percolation in comparison to clayey soils. Vegetation and high water table reduce the percolation losses.
Leaching Losses of Nutrients. Percolation losses of water are not harmful but the nutrients that are leached along with the percolation water are of serious consideration. Losses of calcium and magnesium are the greatest but phosphorus is lost by leaching in trace (very less).
Way # 3. Permeability:
Permeability indicates the relative ease of movement of water within the soil. The characteristics that determine how fast air and water move through the soil is known as permeability. The term hydraulic conductivity is also used which refers to the readiness with which a soil transmits fluids through it.
The permeability is basically dependent on the pore-size distribution in the soil. The larger the number of macrospores, the greater is the permeability. The pore size distribution is greatly determined by the extent of aggregation in the soil. The larger the aggregates, the greater is the amount of non-capillary (macro) pores.
The permeability of soil usually decreases with depth, as the sub-soil layers are more compact reduces the macro pores. More content of organic matter and vegetation increase permeability. Normally permeability decreases with increasing fine texture, but the extent of aggregation in fine-textured (clay) soils may override the effects of texture. If irrigation water is high in sodium content, it would cause dispersion of soil (soil becomes compact) and thus reduces permeability.
Like infiltration, the permeability can also be controlled to a large extent by suitable management practice. Continuous tillage reduces permeability, while the growth of deep- rooted grasses, legume and trees increases permeability.
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