PREVENTION OP DRAINAGE. 157 



lower temperature, and raise it sensibly, with beneficial 

 effect. A more moderate irrigation would, on the con 

 trary, be in danger of producing a contrary effect, be 

 cause it would be insufficient to overcome the loss conse 

 quent upon the increased evaporation. 



The nature of the soil needs to be studied in regard to 

 the quantity of water that should be applied, and the 

 periods of its application. A porous soil should be copi 

 ously irrigated for short periods and at short intervals. 

 The object is to supply nutriment to the grass, not to 

 cause an excessive filtration through the subsoil, which 

 might carry away valuable fertilizing matter. On a re 

 tentive soil the irrigation should be less copious, lest sur 

 face exhaustion should occur by washing away valuable 

 soluble matters, and it may be continued for longer peri 

 ods with longer intervals between them. The usual peri 

 ods of irrigation are, for 24 to 72 hours, at intervals of 

 four to twelve days. The condition of the soil is the only 

 guide for these. 



It is necessary that the irrigator exercise great watch 

 fulness over his field and become acquainted with all its 

 special characteristics, that he may direct the water in 

 this place or that ; that he may withdraw here or there ; 

 that he may regulate the supply of water according to 

 the condition of the vegetation, or the state of the 

 weather, which may change from day to day. Where ir 

 rigation is extensively practiced, a person whose sole 

 attention is directed to the application of the water, ought 

 to be employed. One capable man could attend to sev 

 eral hundred acres, and might earn his season s wages by 

 preventing in time one single mishap, which would prob 

 ably be overlooked by a person who had the care of many 

 other details upon his mind. Besides, there are frequent 

 occasions, where water is purchased by the inch, in which 

 attention during the night is necessary to prevent waste. 

 This special care is indispensable in the irrigation of field 



