244 SYSTEMS OF PERMANENT AGRICULTURE 



tion because the addition of hydrochloric acid produced a white 

 precipitate. The Professor asked: "How do you know that this 

 precipitate is not due to lead or mercury? " and the student replied, 

 " Because I was not testing for lead or mercury at all." 



Similarly one may apply wood ashes to ascertain if the soil is 

 deficient in potassium, or he may turn under a spring growth of 

 clover to ascertain if the soil needs more nitrogen, and from the 

 increased yield he may think both of these elements are deficient; 

 but in the one case the increase may be due, not to the potassium 

 as plant food, but to the basic or alkaline properties of the lime 

 and other carbonates in correcting soil acidity, and in the other 

 case not to the nitrogen supplied, but to the liberation of phos- 

 phorus from the meager supply in the soil by the action of decaying 

 organic matter. 



It is never safe to assume that the action of soluble fertilizers, 

 such as sodium nitrate, acid phosphate, kainit, or other potassium 

 salts, is due entirely to the respective plant-food elements for which 

 those materials are valued, especially when heavy applications 

 are made, as must be done with sodium nitrate and kainit if suffi- 

 cient nitrogen a-nd potassium are thus provided to meet the needs 

 of good crops, more than 900 pounds of sodium nitrate and 700 

 pounds of kainit being required for a hundred-bushel crop of corn. 



About 400 pounds of acid phosphate would be required for such 

 a crop, and this would contain more manufactured land plaster 

 (calcium sulfate) than monocalcium phosphate, as will be seen by 

 computation from the reaction expressed by the equation: 



Ca 3 (P0 4 ) 2 + 2 H 2 S0 4 = CaH 4 (P0 4 ) 2 + 2 CaSO 4 . 



Dried blood and steamed bone meal are among the most trust- 

 worthy materials for culture experiments to determine if the soil 

 is in need of nitrogen or phosphorus, and potassium sulfate is 

 probably the least objectionable form of potassium, although solu- 

 tions of such soluble salts have some power to liberate phosphorus 

 contained in, or applied to, the soil, and by this indirect action to 

 bring about more or less increase in crop yields not due to potas- 

 sium as plant food. Steamed bone meal contains a small amount 

 of organic nitrogen, but even if it were all made available, the 



