94 Report of the Acting Director and Chemist of the 



An examination of the foregoing table justifies the assertion, 

 when we consider all the conditions, that the smallest amounts of 

 plant-food we can expect to use on an acre of land with any satis- 

 factory results are the following : 



10 pounds of nitrogen, 



15 pounds of available phosphoric acid. 



20 pounds of potash. 



To state this in another form, the foregoing amounts of niti'ogen 

 would be contained in 200 jDOunds of a fertilizer having the follow- 

 ing composition : 



Nitrogen, 5 per cent. 



Available phosphoric acid, 7^ per cent. 



Potash, 10 per cent. 



This would be regarded as a high-grade fertilizer and on some 

 soils an application of 200 pounds an acre would be considered large, 

 while on others it would be entirely insufficient. The above rule 

 will probably be found fairly safe to follow in fertilizing average 

 crops, when we know nothing at all in regard to soil or crops. 



5. Specific Mixtures for Different Crops. 



We will now consider under a separate head in a more specific 

 manner the quantities of different forms of plant-food that can be 

 applied to advantage to one acre of land for different crops. 



We must make it clearly understood at the start that no rigidly 

 fixed formulas can be given for any one crop on all soils. The 

 question of quantity of application and of proportion must always, 

 in the very nature of the case, remain more or less a matter of in- 

 dividual experiment. Every field is constantly changing in the 

 extent and character of its needs. The farmer must constantly 

 study results and let the experience of one year suggest to him his 

 plan for the year following. With this preliminary precaution, it 

 may be of interest to consider briefly what has ordinarily been the 

 method of procedure in determining the proportions of nitrogen, 

 phosphoric acid and potash in making fertilizers for different crops. 



In making formulas, it was first proposed to make the formula 

 correspond to the analysis of the plant. This method was prac- 

 ticed for some time, when it was found that there was already in 

 the soil more or less available plant-food and that fertilizing material 

 was often applied where one or more constituents could be omitted 



