100 SOILS AND FERTILIZERS 



When sulfate was added annually to soil in one of the tanks 

 already mentioned, for a period of five years, as much as 

 two-thirds of the quantity applied was removed in the drain- 

 age water, in addition to what would have been removed if 

 the soil had received no sulfate. The potash previously 

 mentioned as having been applied to this soil, and the sulfate 

 here spoken of were one substance called sulfate of potash. 

 The latter was held by the soil and the sulfate largely leached 

 through. It is evident that the substance was decomposed 

 in part or in whole. 



It is thus apparent that there are certain soluble fertilizers 

 that may be applied to soils without much danger of loss 

 by leaching and other fertilizers that are likely to be partly 

 carried out of the soil in this way. 



117. The availability of absorbed fertilizers. — When a 

 soluble fertilizer is absorbed by a soil, a part of it, at least, 

 is held in a condition in which it is more readily available 

 to plants than is the large mass of plant-food material origi- 

 nally in the soil. Thus there may be in a soil several 

 thousand pounds to an acre of nitrogen, phosphoric acid or 

 potash in the three or four feet through which roots ramify, 

 and yet the yield of crops on this soil may be materially 

 increased by the application of less than a hundred pounds 

 of one or more of these substances. 



The ability of soil to hold fertilizers in a readily available 

 form is strikingly illustrated by an experiment at the Rotham- 

 sted Experiment Station in which soil from plats that had 

 been treated with certain fertilizers for many years was 

 thoroughly extracted with water and the extracts analyzed. 

 Complete analyses of the soil from the several plats were 

 also made. The yields of crops on these plats had been 

 recorded for many years and the annual average of these, 

 together with the analytical data, is given in the accompany- 

 ing table : 



