HOW TO DETECT SOIL DEFECTS 35 



successfully grown in soils containing very considerable quantities 

 of Glauber salt. 



In connection with consideration of the possible natural alkali- 

 content of the soil, it is essential to guard against its increase by the 

 use of alkaline water for irrigation which will be mentioned in the 

 chapter on irrigation. 



Prospecting for Soil Defects. For subterranean prospecting, 

 Professor Hilgard commends a steel rod not less than a quarter of 

 an inch in diameter (round or square, preferably the latter), well 

 pointed at one end, and provided at the other with a stout iron ring 

 for the reception of a stout cross-handle, such as is used for post-hole 

 augers. With such a prod, or sounding rod, not less than five feet in 

 length, the exploration of the subsoil for hard-pan or dense clay 

 layers becomes a matter of a few minutes. It is easy also to detect 

 thus the presence of underlying layers of quicksand, gravel, or other 

 loose materials through which irrigation water would waste, or 

 which would prevent the rise of bottom water within reach of plant 

 roots, by the large interspaces between their grains. Any remaining 

 doubts as to the nature of such underlying material at particular 

 points can then quickly be solved by the use of a post-hole auger 

 or by digging, for thorough inspection of each foot of depth which 

 may be found desirable. Subsoil prospecting or sampling can also 

 be very easily done by boring with an ordinary carpenter's auger, 

 iy 2 inches in diameter the shank being lengthened by welding-in 

 a piece of steel, three or four feet in length, according to the depth 

 it is thought desirable to penetrate. Separate samples for each foot 

 of depth are thus easily taken. 



