274 



NATURE 



December 6, 191 7 



INDIAN IRRIGATION.^ 



ONE of the earliest and most difficult problems, 

 towards the solution of which man has addressed 

 his ingenuity and resource, is that of artificial irriga- 

 tion. Thfe rain, we are told, descends alike upon the 

 just and the unjust, but, as regards its geographical 



Picottah worked by four men (Tuni, Vizagapatam district). 



distribution, us incidence is irregular, and at times 

 capricious. Of two localities within a few miles of 

 each other, one will receive copious and embarrassing 

 supplies, while the other will be given a scanty and 

 pitiful dole, which, apart from the satisfaction of 

 immediate human needs, is utterly inadequate for agri- 

 cultural purposes of any kind. In arid regions, re- 

 course is had to wells, storage reser- 

 voirs, and river dams, all of them 

 capable in some degree of alleviat- 

 ing the evil, provided means are at 

 hand to raise and distribute the sup- 

 plies obtained. 



It is particularly interesting, there- 

 fore, to read the account given by 

 Mr. R. Cecil Wood of the expedients 

 adopted in the less developed parts 

 of a country like India, where the 

 'rudimentary appliances of bygone 

 ages are still in vogue. In such dis- 

 tricts labour is cheap and plentiful, 

 and the installation of machinery 

 a costly and troublesome process. It 

 is, therefore, little wonder that the 

 mhote, the picottah,' and' the karim 

 still maintain an unimpaired popu- 

 larity. Yet, even in conservative 

 India, centuries old in tradition and 

 routine, modern innovations are 

 making headway, and machinery is 

 ousting the native and the bullock 

 alike from their accustomed tasks. 

 Centrifugal pumps, driven by oil 

 engines of the most recent type, are 

 now to be found at a number of stations 



3g-in. centrifugal pump, giving a total output of more 

 than 570 cub. ft. per sec, or nearly thirteen million 

 gallons per hour. 



The introduction of machine-driven pumps is, of 

 course, governed by the available flow of water, and 

 it is manifestly not economical to install a power 

 plant unless it can be effectively utilised. Experience 

 has shown that an engine must be 

 kept at work continuously for four 

 hours in the twenty-four, in order to 

 render its installation remunerative. 

 The Department of Industries in 

 Madras provides portable plant on 

 hire, so that actual tests may be 

 undertaken before any commitment 

 is made. 



It is, of course, not practicable in 

 a short notice to deal with all the 

 matters of interest touched upon in 

 Mr. Wood's brochure. Sources of 

 supply and their relative merits, 

 problems of distribution, cost of 

 working and upkeep, systematic 

 cultivation, minimum and maximum 

 requirements, are topics discussed at 

 varving length, and much valuable 

 advice is given for the benefit of the 

 ryot, or peasant land-holder. We 

 may, perhaps, allude to the special 

 difficulty which attaches to agricul- 

 ture in certain tracts in tropical 

 countries. The rapid and extensive 

 evaporation which takes place 

 causes an upward movement of the 

 subsoil water, with the resultant deposition of salts 

 at or near the surface ; certain of these salts, sodium 

 carbonate in particular, and the chlorides and sulphates 

 of magnesium and sodium, ape deleterious and produce 

 alkalinity of the soil, under the influence of which 

 crops become thin and' sparse, plants acquire an air 



of sickl 



and decline, and foliage is pale and falls 



and one 



of the largest, erected on the Divi island, in the Kistna' 

 district, consists of a battery of eight Diesel oil 

 engines, each of i6o-b.h.p. capacity, and driving a 



1 " Irrigation." By R. Cecil Wood, Principal of the Agricultural College, 

 Coimbatore. Pp. 62+33 figures and photographs. (Madras: Department 

 of Agriculture, 1917.) Price is. 6d. 



NO. 2510, VOL. 100] 



Fig. 2. — Karim (Godavari district). 



early. The remedies adopted are principally directed 

 towards a diffusion of the salts and the reduction of 

 the degree of concentration within limits, at any rate, 

 which admit of the maintenance of a state of pro- 

 ductivity. The simplest method is that of flooding 

 the areas affected, allowing the water to sink down- 

 wards, carrying the salts with it. But, as Mr. Wood 



