PURCHASE: AND USE OF FERTILIZERS 341 



transpired per i gram dry matter produced in one experiment on 

 corn in pots as follows : 



Grams 



No fertilizer 1,012 



Phosphates 735 



Nitrates 555 



Phosphate and nitrate 1 78 



Bacterial action is undoubtedly affected by fertilizers, but to 

 what extent or of what importance is not known. 



It is claimed that the sulphate of lime which is present in acid 

 phosphate may liberate soil potash and so render it available to 

 plants. It is also possible that this sulphate of lime may supply 

 plants directly with sulphur, but this is a matter which requires 

 further study. 



Whitney claims that fertilizers destroy toxic substances in the 

 soil, but no direct evidence has been brought forward to show 

 that such is the case. 



Relation of Fertilizers to Losses and Changes of Plant Food. 

 When nitrogen, and, to a less extent, potash, is added to the soil, 

 the loss due to percolation increases. This is shown by analyses 

 of percolation waters from drain gauges or tile drains. See 

 Chapter XIII. There is also an increased los; due to denitri- 

 fication, which can be ascertained by analysis of the soil after a 

 number of years, provided loss by percolation and cropping is 

 also known. Little loss of phosphoric acid takes place, except 

 possibly on very light sandy soils. 



Fertilizers improperly used may diminish the fertility of the 

 soil. Thus acid phosphate alone will give good results on some 

 soils for a few years, but the increased crop increases the draft 

 upon the nitrogen and potash of the soil. Unless provision is 

 made to restore the loss of nitrogen and potash, the acid phos- 

 phate will become less and less effective. The same is true, 

 though to a less extent, of fertilizers containing large percentages 

 of phosphoric acid and small percentages of nitrogen and potash, 

 such as a fertilizer containing 8 or 10 per cent, available phos- 

 phoric acid, 2 per cent, nitrogen, and 2 per cent, potash, such as 

 are commonly used in the South for fertilizing cotton and corn. 



