218 MOVEMENTS OF SALTS IN THE SOIL 



In speaking of the proportion of alkali salts which is 

 sufficient to cause injury, we must regard in the first place 

 the proportion in the surface soil, as it is here that the 

 actual injury is generally done. It is indeed exceptional 

 for the proportion of soluble salts in the subsoil to be so 

 great as to be productive of much harm. It is when the 

 salts are highly concentrated by the evaporation of their 

 solution on the surface of the soil that active mischief takes 

 place. 



In Table XXXVII are given some determinations of the 

 quantity of alkali salts found in land of known fertility 

 belonging to the Experiment Station at Tulare, California. 

 The salts in the first three inches of the soil, and in the first 

 foot, were extracted and analysed. The results found would 

 doubtless have been still more striking if the composition of 

 the first inch had been ascertained. 



The land growing a good barley crop is seen to have con- 

 tained on March 31, 0-178 per cent, of soluble alkali salts in 

 the first three inches of soil ; the barley, which was probably 

 sown in January, was then 2, ft. high. In May the pro- 

 portion of alkali at the surface of the soil has nearly doubled, 

 but at this stage of growth the presence of an excess of salts 

 is not nearly so hurtful as when the crop is young. The 

 barley in May was 4 ft. high, and yielded i\ tons of barley 

 hay per acre. The alkali on this land, though moderate in 

 quantity, was of a particularly hurtful type, about one-half of 

 the salts consisting of sodium carbonate. 



The land on which the crop of barley was small, amounting 

 to only one ton of hay per acre, was not examined till Sep- 

 tember, or nearly at the close of the hot weather ; the results 

 are thus not strictly comparable with those already quoted. 



