QUANTITY OF POTASH REMOVED BY CROPS 537 



may still be mixed with other organic matter and then it requires 

 treatment as above, for it is not safe always to rely solely on the 

 solubility of the potash mineral, and the solution, moreover, in 

 such cases, is likely to contain organic matter. In some States, 

 only that portion of the potash soluble in water is allowed to be 

 considered in official fertilizer work. In these cases it is evident 

 that the organic matter present should not be destroyed in the 

 original sample, but only in the aqueous solution. Since, how- 

 ever, the potash occluded in organic matter becomes constantly 

 available as the process of decay goes on, it is not advisable to ex- 

 clude it from the available supply. It may not be so immediately 

 available as when in a soluble mineral state, but it is not long 

 before it becomes valuable. In the opinion of some investigators 

 phosphorus, nitrogen, and potash are all more valuable finally 

 when applied to the soil in an organic form. This fact is not irre- 

 concilable 'with the theory already advanced that all mineral com- 

 pound bodies are probably decomposed before they enter as com- 

 ponent parts into the tissues of the vegetable organism. 



It is highly probable, therefore, that the potash existing in 

 organic compounds, finely divided and easily decomposed, is of 

 equal, if not greater value to plant life than that already in a 

 soluble mineral state. For analytical purposes the organic matter, 

 when present, is destroyed, either by ignition at a low tempera- 

 ture, or by moist combustion with an oxidizing agent before the 

 potash is precipitated. For agricultural purposes the plant food 

 represented by the potash occluded in the organic substance is 

 held with some degree of tenacity, preventing its leaching by 

 heavy rains, and permitting its gradual release as required by the 

 growing plant. 



457. Quantity of Potash Removed by Crops. The quantity of 

 potash removed from the soil annually by the principal crops in 

 the United States is equivalent to 2,500,000 tons of muriate of 

 potash or 1,250,000 tons of potash. 27 



The foregoing discussion of the sources and kinds of potash 

 presented to the analyst is sufficient to clearly set forth the ob- 

 jects of the examination. 



17 Voorhees, Journal of the Franklin Institute, 1905, 160 : an. 



