IRRIGATION 271 



Irrigation and special cultivation. Adjacent fields 

 with or without irrigation require different cultivation. 

 That on which large amounts of water are applied should 

 be plowed deeper, and subsoiling is sometimes necessary 

 in heavy soils, receiving much water. Irrigation tends 

 to make the soil denser, less porous, colder and heavier 

 to handle with tillage implements. In regions so drouthy 

 that irrigation is necessary, lands not irrigated are quite 

 as well managed if they are not plowed so deeply, and 

 they are kept mellow with much less cultivation than is 

 sometimes necessary in lands heavily watered. Among 

 corn and other crops which may be cultivated between 

 the rows, the surface should be broken up with the cul- 

 tivator as soon after applying the water as the soil is 

 sufficiently dry to be handled. This cultivation pre- 

 vents the rise of the water to the surface, and conserves 

 it for the use of crops and provides suitable mechanical 

 conditions for the roots of the crops. Coarse and green 

 manures, also artificial fertilizers, are especially profit- 

 able where the land can be kept so uniformly moist that 

 it is adapted to the best use of the available fertility. 



Subirrigation. Various forms of subirrigation have 

 been devised. A very simple form is one in which the 

 water is supplied from below, as in greenhouse benches. 

 Supplying water is also accomplished by means of 

 tile drains laid one or more feet below the surface in the 

 fields. Instead of these drains being used to run the 

 water out of the soil, they serve to carry the water into 

 the soil. This method has the advantage of not causing 

 the surface to bake, as in surface irrigation, where dry, 

 bright weather following the application of large quan- 

 tities of water to a surface of heavy soils causes the sur- 

 face soil to become baked and hard. This form of irriga- 

 tion, however, is limited to gardens where valuable crops 

 are grown, and where water is plentiful, or to green- 

 houses where the water is under full control. 



