MOVEMENTS OF SALTS IN SOILS. 



109 



Mean distribution of phosphate*, silica, and bicarbonate* in six soi I 

 types under mulched and unmulched surfaces. 



In the case of the phosphates, silica and bicarbonates, the dis- 

 tribution, shown by the data of the table, is, in some respects, 

 the reverse of what occurred with the nitrates, chlorides and 

 sulphates ; with these, the amounts decrease with 2'reat rapidity 

 through the first three inches and continue to decrease, only 

 less rapidly to the bottom ; with the phosphates and the other 

 two radicles, there is but a small decrease, if any, through the 

 first three inches, but a well marked tendency for the amounts 

 to increase with the depth. This general difference, in the be- 

 havior of the two groups of salts, is clearly shown in the! dia- 

 gram, Fig. 7, p. 110, where the mean combined amounts of XO 3 , 

 SO 4 and Cl, have been plotted as a single curve, on one-third 

 the scale used for plotting the other three ingredients. From 

 this figure it will be seen how strong is the tendency for the 

 members of the nitrate group to concentrate at the surface, 

 while the others, and in a less marked degree, show the reverse 

 order of distribution. 



It should be observed, that in each case, more salts were re- 

 covered at the top from the soil which had sustained the greatest 

 evaporation. Moreover, there were more phosphates and silica 

 in the surface inch than there were in the second and third inch, 

 which shows that this reversal of the order in the distribution of 



