130 PRACTICAL FARM CHEMISTRY. 



ticular circumstances of the case. The farmer him- 

 self knows these, and the diagnosis must largely be 

 left to his good judgment. 



This is also the case in regard to quantity to be 

 applied. Our old family physician, when asked 

 how much to give of a medicine prepared by him, 

 often used to say: "Use your own judgment." So 

 also the intelligent farmer will be required to use 

 his own judgment in modifying the general rules to 

 suit each particular case, bearing in 



Diagnosis. ^^^^ ^^^o the needs of the particular 

 crop. The most I can do in this connec- 

 tion is to give the reader some hints that will help 

 him in making a correct diagnosis, and to show him 

 how he can let the fertilizer fit his soil and crop. 



First of all we should know how much plant food 

 is removed from the soil in a good yield of our or- 

 dinary field crops. 



Suppose we raise a thirty bushel crop of wheat. 

 We then take off the soil, in the grain alone, about 

 thirty-seven pounds of nitrogen, nine or ten pounds 

 of potash and fourteen pounds of phosphoric acid, 

 and in the straw, perhaps twenty pounds nitrogen, 

 twenty-five pounds of potash and nine pounds phos- 

 phoric acid, altogether nearly sixty pounds of nitro- 

 gen, thirty -five pounds of potash and twenty- three 

 pounds of phosphoric acid, more or less, and this 

 quantity of plant foods we must return to the soil 

 after each thirty bushel wheat crop is taken off, if 

 we desire to preserve the original fertility of the 

 soil. There may be slight help from 



Plant Foods ^]jq atmosphere in furnishing nitrogen 



Grain Crops, as the rains and dews dissolve the 



fioating carbonate of ammonia and 



perhaps nitric acid, and carry it down to the soil; 



