This article throws light upon the three main ways by which water is lost from soil. The ways are: 1. Percolation Losses 2. Evaporation Losses 3. Transpiration Losses.
Way # 1. Percolation Losses:
Percolation losses are maximum under humid climate with high rainfall. Water loss through percolation is necessary otherwise poor drainage conditions and water-logging may develop. Percolating waters also leach out important plant nutrients from soil.
Peculation losses can be minimised by suitable management practices. High percolation rate is the characteristic of light (sandy) soil. In such type of soil, movement of water is more rapid, because of larger size of pores.
The downward movement may be minimised by the application of organic matter in the soil. The structure is also an important factor in percolation. The closer the arrangement, the less rapidly does the percolating water move.
Way # 2. Evaporation Losses:
Evaporation is the change from liquid to the vapour state and the resulting vapour is lost to the atmosphere. The evaporation of water from soil takes place almost entirely at the surface. A certain amount of water may be lost by evaporation from the lower layer also through cracks in the soil.
In temperate regions, 25 to 50 per cent of the water received by soil in the form of rain is lost by evaporation; in arid and semi-arid regions the loss is as high as 70 to 80 per cent of the annual rainfall. The rate of evaporation depends upon several factors viz., high temperature, less humidity, more wind velocity, high moisture content, fine texture soil, water-logged soil.
One of the best ways to check evaporation is mulching (covering soil with loose cover). It protects the soil from the direct rays of the sun and from wind currents, and keeps the soil cool. Vegetation (suitable cropping) also keeps temperature low. Use of wind break checks the movement of moist air resulting from high wind velocity.
Way # 3. Transpiration Losses:
Plant loses water through the stomata of leaves is called transpiration. Transpiration is a physiological phenomena and plants must transpire for their growth. Transpiration, like evaporation, is also influenced by temperature, humidity, wind velocity, moisture contents in the soil, and inherent characteristics of plant.
Transpiration being a natural characteristics of the plant, man has practically very little control over it. However, in water scarcity (dry) areas, crop selections can be made that have low transpiration ratios. Different plant species and even different varieties of the same species differ in their transpiration rates.
Transpiration rate can be minimised by the use of wind break or shelter belt. In crop husbandry, undesired transpiration losses through weed should be checked by proper weed control.