FERTILIZERS 31 



greater solubility. There is no element less soluble 

 than Phos. A. while potash is present in the drain- 

 age water in quantity greater than a trace. Even 

 silica is more soluble than phosphoric acid. 

 CONCLUSIONS. 



50. The amount of soluble matter is greater in 

 wet, peaty soils. Poor soils yield to water the least 

 amount. Very rich soils, and well manured soils 

 yield more to water than poor soils. From the 

 table it is seen that where water extracted most 

 organic matter, it extracted large quantities of other 

 elements. Cultivation and irrigation use up organic 

 matter rapidly. So the supply of humus materials 

 must be constantly renewed. Humus and organic 

 matter are the key to availability but are also prob- 

 ably the means of exhausting other plant foods 

 through the production of larger growth and crops. 

 (86). 



INSOLUBILITY DESIRABLE. 



51. It is well known that the nitrates may easily 

 be lost by leaching, because they are soluble. This is 

 not the case with the phosphates, or phosphorus 

 compounds, as these are always insoluble even in the 

 most fertile soils. Numerous analyses of the "run 

 off" waters show this. The nitrates being always 

 available to the plant, stimulate its feeding powers 

 and force it to act on such insoluble compounds as 

 the phosphates, which, in turn, by yielding slowly, 

 regulate growth and maintain for a longer time the 

 soil's productive power. 



It can readily be seen that the loss would be 

 many times greater if the phosphates and other com- 

 pounds were soluble as well as the nitrates. 



