Soluble Salts in Soils. 



99 



115. Variation of Soluble Salts with Different Crops. 



There is a marked difference in the amount of soluble salts, 

 and especially in the amount of nitrates, in soils under 

 crops like corn and potatoes, where inter-tillage is prac- 

 ticed, and under such crops as clover and oats, where the 

 ground is not cultivated at any time of the season. This 

 is very clearly shown in Fig. 32 ; the nitrates are plotted 

 in the lower two sets of curves and the total soluble salts 

 in the upper two sets. 



The nitrates in the first foot under the corn and potatoes 

 increased rapidly until July 1st, when they were five times 

 as concentrated as in the fourth foot ; but in 30 days more 

 the nitrates had been reduced from over 400 Ibs. to 40 Ibs. 

 per acre. 



PARTS PER MILLION Of 



Fio. 81. Shows the mean amount of nitrates and total soluble salts 

 In the surface four feet of soil under cultivated and not cultivated 

 crops. Heavy shading Is uncultivated ground. 



In the case of the uncultivated crops the fields started 

 with about 40 Ibs. per acre and increased to only 70, June 

 1st, when they were highest; from this date they fell to 

 little more than 10 Ibs. per acre in the surface foot, but 

 rose again to 60 Ibs. at the end of August. 



With the total soluble salts there was at first a more 



