114 SOILS AND FERTILIZERS 



the soil and passes off as drainage. The quantities of these 

 materials that are annually lost from an acre of soil, as found 

 by lysimeter experiments, are shown in Table 24. 



It will be noticed that there is a much greater loss from the 

 unplanted soil than from the planted. The quantities of 

 these materials taken up by some crops is much less than the 

 difference between the quantities in the drainage in the 

 planted and unplanted soil, hence the growth of these crops 

 on land is really a means of saving lime. 



138. Effect of plant growth on soil acidity. — Plant growth 

 may promote soil acidity in the following ways : (1) by re- 

 moval of the bases in the ash of the plants ; (2) by leaving 

 in the soil the acids with which these bases were combined ; 

 (3) by formation of organic acids during decomposition of 

 plant remains. 



It will be seen from Table 27 that the quantities of 

 potash and lime removed in crops of average size vary 

 considerably and in some cases are very large. When, 

 as in a state of nature, the vegetation on the land is returned 

 to it after life ceases, and its organic material is again 

 incorporated with the soil, there is no loss in this way, but 

 in ordinary farming most of the above ground portion of 

 the crop is removed from the land. The manure of growing 

 animals returns to the soil only a small proportion of the 

 lime that was originally in the plants because the animal 

 has used it, and the potash is likely to be leached from the 

 manure unless it is carefully handled. 



Crops in growing remove more potash and other bases 

 from the soil than they do the acid-producing substances, 

 which latter are left in the soil and contribute still more to 

 its tendency to assume an acid condition. 



139. Effect of fertilizers on soil acidity. — It has been 

 shown very conclusively that the continued use of considerable 

 quantities of sulfate of ammonia on land may result in bring- 



