Contents preface (VII) introduction 1—37

3.10.4. Sprinkler Irrigation
Sprinkling is the method of applying water to the soil surface in the form of a spray which is somewhat sililar to rain. In this method, water is sprayed into the air and allowed to fall on the soil surface in a uniform pattern at a rate less than the infiltration rate of the soil. This method started in the beginning of this century and was initially limited to nurseries and orchards. In the beginning, it was used in humid regions as a supplemental method of irrigation. This method is popular in the developed countries and is gaining popularity in the developing countries too.
Rotating sprinkler-head systems are commonly used for sprinkler irrigation. Each rotating sprinkler head applies water to a given area, size of which is governed by the nozzle size and the water pressure. Alternatively, perforated pipe can be used to deliver water through very small holes which are drilled at close intervals along a segment of the circumference of a pipe. The trajectories of these jets provide fairly uniform application of water over a strip of cropland along both sides of the pipe. With the availability of flexible PVC pipes, the sprinkler systems can be made portable too.
Sprinklers have been used on all types of soils on lands of different topography and slopes, and for many crops. The following conditions are favourable for sprinkler irrigation (1):
(i) Very previous soils which do not permit good distribution of water by surface methods, (ii) Lands which have steep slopes and easily erodible soils,

(iii) Irrigation channels which are too small to distribute water efficiently by surface irrigation, and

(iv) Lands with shallow soils and undulating lands which prevent proper levelling re-quired for surface methods of irrigation.
Besides, the sprinkler system has several features. For example, small amounts of water can be applied easily and frequently by the sprinkler system. Light and frequent irrigations are very useful during the germination of new plants, for shallow-rooted crops and to control soil temperature. Measurement of quantity of water is easier. It causes less interference in cultivation and other farming operations. While sprinkler irrigation reduces percolation losses, it increases evaporation losses. The frequency and intensity of the wind will affect the efficiency of any sprinkler system. Sprinkler application efficiencies should always be more than 75 per cent so that the system is economically viable.
The sprinkler method is replacing the surface/gravity irrigation methods in all developed countries due to its higher water application/use efficiency, less labour requirements, adaptability to hilly terrain, and ability to apply fertilizers in solution. In India too, the gross area under sprinkler irrigation has increased from 3 lakh hectares in 1985 to 5.80 lakh hectares in 1989. The total number of sprinkler sets in India now exceeds one lakh.

SOIL-WATER RELATIONS AND IRRIGATION METHODS