Amount oj Alkali Injurious 275 



which this additional water may have been instrumental 

 in producing from the soil on the spot through the 

 processes of weathering. 



Indeed, the more we study and reflect upon this 

 problem, the more we are led to fear that in all arid 

 climates, where irrigation is practiced, it will not be 

 found sufficient to apply simply enough water to the 

 soil to meet the needs of the crop growing upon the 

 ground at the time, but, on the contrary, there must 

 be enough more water applied to take up and carry 

 away into drainage channels and out of the country 

 to the sea not only the soluble salts which the irriga- 

 tion waters carry, but also those which it causes to be 

 produced from the soil and subsoil. In other words, 

 it appears that an excess of soluble salts in a thoroughly 

 irrigated field is not only a normal but an inevitable 

 condition, unless sufficient leaching takes place; and 

 if this is true, the sparing use of water can only 

 increase the number of years required to bring the 

 salts up to the danger point of concentration. 



AMOUNT OF SOLUBLE SALTS WHICH ARE INJURIOUS 

 IN SOILS 



Storer states that it is a matter of record that long 

 experience in the south of France has shown that any 

 soil which becomes visibly covered with a slight in- 

 crusation of salt in times of drought is improper for 

 cultivation, unless special pains are taken to prevent 

 the surface from becoming dry. 



Plagniol insisted, in his time, that soils containing 

 more than 2 per cent of salt are unfit for the growth 



