MEANING OF IRRIGATION 



4. Conservation of rainfall on farms. It is the business 

 of the farmer so to handle his farm that the largest possible 

 proportion of the rain that falls may be made to enter the 

 soil, and to remain there until needed by plants, unless, 

 indeed, the rainfall is too heavy, when provision must be 

 made for relieving the soil of the harmful surplus. To 

 accomplish this, the farmer must resort to methods for 



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FIG 1. Progressive averages of annual rainfall (1834-1906). 



preventing, or reducing largely, the loss due to the run- 

 off, evaporation and seepage. Where the annual rainfall 

 is fairly large and well distributed, these methods are 

 not applied extensively; but where the annual rainfall is 

 light or is not in the growing season, moisture-conserv- 

 ing methods are indispensable. There are relatively 

 few localities on earth where special efforts to conserve 

 the rains for plant-growth are not rewarded by large 

 crop yields. The smaller the annual rainfall, the greater 

 is, naturally, the return for careful moisture-conservation. 

 5. Conditions of dry-farming. If the annual rainfall 

 be very light, it frequently happens that, with the best 

 available tillage methods, the water conserved in the soil 



