HARDPAN 123 



both roots and water. Harclpans are not always caused 

 by alkali, but are more likely to be formed if it is present. 

 Hardpan differs from the ordinary impervious subsoil in 

 that it has a limited thickness, usually varying from 2 to 

 18 inches with an average of 3 to 6 inches. A good ex- 

 ample is described by Gardner and Stewart (8) . A num- 

 ber of explanations of the genesis of hardpans have been 

 given. 



Hilgard (13) has the following to say about the cause of 

 hardpan: "The recognition of the cause of hardpan is of 

 considerable importance to the farmer because of the in- 

 fluence of the nature of the cement and the causes of its 

 formation upon the possibility and methods of its de- 

 struction, for the improvement of the land. 



"It may be said in general that inasmuch as the cause 

 of the formation of hardpan is a stoppage of the water in 

 its downward penetration, the reestablishment of that pene- 

 tration will tend to prevent additional induration; more- 

 over, experience proves that whenever this is accomplished 

 even locally, as around a fruit tree in an orchard, the hard- 

 pan gradually softens and disappears before the frequent 

 changes in moisture conditions and the attack of roots. 

 The use of dynamite for this purpose in California has 

 already been referred to; it seems to be the only resort 

 when the hardpan lies at a considerable depth. When it 

 is within reach of the plow, it may be turned up on the 

 surface by the aid of a subsoiler and will then gradually 

 disintegrate under the influence of air, rain, and sun. 

 But when the hardpan is of the nature of moorbedpan, 

 containing much humic acid and perhaps underlaid by 

 bog-iron ore, the use of lime on the land is indicated, and 

 will in the course of time destroy the hardpan layer. This 

 is the more desirable as in such cases the surface soil is 



