THE PRINCIPLES OP FERTILIZER PRACTICE 489 



be charged to this factor. Many farmers make the mistake of 

 applying too much fertilizer. Any information along such 

 lines, however, can only be suggestive, rather than literal, 

 it being understood that the general formulae suitable to vari- 

 ous crops, and the quantities ordinarily applied, are subject 

 to wide variations. 



276. Fertilizer formulae.^ — In the popular mind, the nu- 

 trition of a plant is considered as similar to and as easy as 

 the proper feeding of an animal. With animals, the food is 

 compounded with the correct balance of nutrients and if other 

 conditions are favorable, normal results should be obtained. 

 The nutrition of a plant is by no means as simple as the proper 

 feeding of an animal. In the first place, the plant receives 

 most of its nutrients from the soil and air and not from the 

 fertilizer, since the latter usually merely supplements the nu- 

 trients already present in the soil. Again, the food for the 

 animal remains balanced as it is utilized. In the case of plants, 

 the fertilizer nutrients undergo great changes on addition to 

 the soil, the soil influencing the availability of the fertilizer 

 as well as the fertilizer influencing the soil in a great number 

 of different ways. Moreover, the question of fertilizer resi- 

 dues, especially those of an acid nature, is always paramount 

 when fertilizers are used over long periods. The proper for- 

 mula for a given crop and a given soil under a probable series 

 of weather conditions is thus more or less of a guess and will 

 always remain so. 



*The following example of fertilizers similarly named but carrying 

 strikingly different guarantees are taken from Bull. 206 of the Yt. 

 Agr. Exp. Sta. 



Potatoes and Maize Potatoes and Tobacco 



4-7-8 2- 6-7 



4-8-4 2- 6-4 



4-8-0 242-0 



Vegetables Top Dressings 



3- 7-10 7-6-5 



4- 8- 4 7-6-2 

 5-10- 7-6-0 



