64 AGRICULTURE 



which the water is forced up through perpendicular pipe 

 outlets or holes. 



A third method of sub-surface watering is employed 

 where the land has a natural slope and a clay subsoil of 

 hardpan. The water is applied by the head ditch and al- 

 lowed to seep down through the soil to the hardpan. It 

 then rises to the surface by soil capillarity, where it is avail- 

 able for the use of the plants. This method is practical 

 only in a few localities where the source of water supply 

 and the physical conditions of the field are adapted to its 

 use. 



Overhead irrigation. Overhead irrigation is accom- 

 plished by a system of overhead piping so placed that wa- 

 ter can be applied to an entire field or garden at one time. 

 The pipes, are perforated with many small holes through 

 which are forced fine streams or a spray of water. This 

 method is very effective, but its expense limits its useful- 

 ness principally to gardening and trucking. Not only is 

 the cost prohibitive for large fields, but the piping is in the 

 way for cultivation when using horses and machinery. 



Determining the method of irrigation. What method 

 of irrigation is best must be decided by certain important 

 factors. Among these are (1) the available water sup- 

 ply, and its expense, (2) the location and level of the water 

 table, (3) the nature of the soil, (4) the variety of crops 

 to be irrigated, (5) the size of the field. Irrigating small 

 grain, forage crops, alfalfa, etc., is usually best accom- 

 plished by the surface corrugated methods, though flood- 

 ing may prove satisfactory if the land is well drained. 

 Orchard and trucking crops are most economically served 

 by the furrow method. 



