2 Irrigation and Drainage 



growing parts of plant life, than because it is the 

 medium in which the transformation of the crude 

 materials into assimilable food -products takes place, 

 and through and by means of which these products 

 are transported to their destinations at the various 

 points of growth. It is only when we fully appreciate 

 the important role played by water in crop production, 

 that we are in position to see how necessary to large 

 yields is the right amount of water at the right time, 

 and thus be led to insure to our crops a sufficient 

 irrigation and an adequate drainage. 



Since the falling of rain upon soils has always 

 been intermittent in its character, and during the in- 

 tervals of fair weather a part of the water so given 

 to the soil has been lost by drainage, land vegetation, 

 during its evolutionary stages, has become fitted to do 

 its best work when the soil is watered once in about 

 so often, and when that soil retains a certain amount 

 of the rain which falls. But the intervals between 

 rains in almost all countries are irregular in length, 

 and the amount of rain which falls at one time also 

 varies between very wide limits, so that in many if 

 not in the majority of climates, those seasons are rare 

 indeed when a crop can be carried to maturity with 

 the soil containing at all times the best amount of 

 moisture. This being true, there will occur times with 

 almost all soils when they would give larger yields if 

 they could be artificially irrigated or artificially drained, 

 according as the period is one of deficient or of exces- 

 sive rain. 



But not all soils are alike in their capacity for re- 



