426 IRRIGATION FARMING. 



it is useless expenditure of money to lay pipes where 

 the conditions are such that the water will not spread 

 laterally to the plants. In some localities the subsoil 

 is so porous or gravelly that the water applied beneath 

 the surface sinks immediately and cannot be utilized 

 by the roots of any of the plants except those in the 

 immediate vicinity of the source of supply. This is 

 especially the case on the bottom lands along streams 

 where the surface soil rests upon gravel or beds of 

 sand. Where, on the contrary, the subsoil is compara- 

 tively impervious, and above this the stru(5ture is such 

 that the water is transmitted horizontally, systems of 

 subirrigation can be introduced to advantage. 



Different depths have been tried, some being four- 

 teen inches, others eighteen, and still others two feet 

 deep. Some difficulty has been found in pipes laid 

 from eighteen to twenty-four inches beneath the sur- 

 face. By digging down it was found that the deeper 

 pipes were placed so low as to be imbedded in a 

 tenacious clay subsoil through which the water could 

 not spread freely. By raising the pipes about six 

 inches, well above the clay, the water percolated 

 freely. For vegetables it has been found that pipes 

 give the best results when laid from eight to ten feet 

 apart, while for orchards a single row of pipes is suffi- 

 cient between alternate rows of trees, the pipes being 

 placed from ten to twelve inches in depth. It has also 

 been found that the moisture was rendered more effi- 

 cient by using fertilizers. One of the most common 

 mistakes has been in giving too great slope or inclina- 

 tion to the pipes. If laid on ground which has decided 

 fall the water runs to the lower end before it can 



