TREATMENT OF ALKALI LAND 231 



with such a crop, the water is evaporated through the plant, and 

 not to any considerable extent from the surface of the soil. 



Alkali land when suitably treated is remarkable for yield- 

 ing good crops with a small rainfall ; the presence of alkali 

 becomes indeed a distinct advantage in an arid climate. 

 Hilgard explains this as due to the greater hygroscopic 

 character of the soil, but he quotes no facts bearing out this 

 opinion. We have already seen (p. 117) that the presence 

 of encrusting salts much diminishes the rate of evaporation 

 from a soil's surface. Probably, however, the main effect 

 of a copious supply of salts in the soil is tp diminish the 

 amount of evaporation from the plants growing on it, and 

 to render a small supply of water sufficient for their needs. 



The very important question of the proper mode of applying 

 water to alkali lands during the dry season is not apparently 

 as yet practically solved. The breaking up of pans, and 

 the provision of efficient drainage, would of course enable 

 water to be freely applied without any danger of its being 

 followed by a rise of alkali. Such treatment, apart from 

 its expense, would however entail the loss to the soil of 

 the large quantities of available plant food which the alkali 

 salts contain ; it is not therefore to be hastily recommended. 



Hilgard has suggested a system of sub-irrigation by means 

 of pipes ; the water to be used in such moderate quantity, and 

 delivered at such a distance below the surface, that no rise of 

 a solution of alkali salt to the surface need be feared. Such 

 pipes might also be used at other times of the year for drainage 

 purposes. The scheme has not apparently been tried. 



UNIVERSITY 



