48 IRRIGATION 



IRRIGATION . 



Irrigation is practised chiefly in dry countries, where, in many 

 cases, the cultivation of crops is entirely dependent upon it, as in 

 the northern part of Ceylon. In a moist climate, as in the south- 

 west of Ceylon, irrigation is adopted only in the cultivation of Rice 

 or other water-plants. In countries where the rainfall is limited, 

 however, intermittent irrigation is applied with good results in the 

 cultivation of fruits and other crops. The methods of accom- 

 plishing irrigation depends upon the facilities which the situation 

 offers, the water being conveyed from natural sources or artificial 

 reservoirs to the land by means of canals, streams (called "ellas" 

 in Ceylon), pipes, or spouts. In parts of India and in the Jaffna 

 district in Ceylon, irrigation water is hauled up from deeply sunk 

 wells by means of rope and pulley with buckets, and distributed 

 along diverging and transverse channels. A general mode of rais- 

 ing water in parts of India is by means of a large bag made of 

 bullock-hide ; the bag is suspended from a pulley over the well, 

 and this is drawn up by a pair of bullocks as they are made to run 

 down a declivity. The "Persian wheel" method of raising water 

 is commonly adopted in Northern India. This consists of a large 

 vertical wheel, fixed in the mouth of a well ; over it a looped 

 chain of earthenware pots is suspended, the lower part of which 

 reaches the water. As the wheel revolves, one length of the chain 

 is continually rising with pots of water, which discharge them- 

 selves into a trough fixed at the summit, and return empty to be 

 filled again. By means of a horizontal wheel and a beam, bullocks 

 are made to work the apparatus. Wind-mills also are sometimes 

 employed very successfully for raising water from wells. 



Different systems of irrigation are adapted for different 

 countries, according to circumstances. A simple system is to 

 conduct water through the land by small canals, the soil obtaining 

 its supply by the water percolating through the porous earth. The 

 "catch-work" method of irrigation is adapted for sloping land, and 

 consists of a series of transverse trenches or channels ; the w r ater is 

 conducted through the upper trench, runs along the surface and 

 escapes through regular outlets into the next trench, and thence to 

 the one below, and so on. Similar to this is the "terracing system," 

 which is carried out extensively in rice cultivation on the hill-sides 

 in Ceylon, where it forms a striking feature in the landscape. (See 

 under Rice). Artesian wells and tube- wells are largely used in 

 some countries, being especially suitable where the soil is loose 



