SOILS AND FERTILIZERS 441 



conditions, but improves the quality of the fruit and prolongs the 

 bearing period of the orchards and vineyards. 



It will be thus seen that commercial fertilizers can be used most 

 advantageously either in reenforcing farm manures in general, or in 

 providing a generous supply of quickly available plant food in spe- 

 cialized, intensive farming. It should be the aim in applying such 

 fertilizers to supplement rather than to replace entirely the manurial 

 resources of the farm, for the best results from their application may 

 be secured only on soils well stocked with organic matter (humus), 

 a material that can be maintained in the soil only by the systematic 

 application of the bulky barnyard or green manures. 



The use of commercial fertilizers is necessary to maintain the 

 fertility of farms upon which live stock is not kept. The use of 

 these fertilizers is constantly increasing and their advantages for 

 special crops ; ease of handling ; quick availability to plants, as well 

 as freedom from weed seeds, are being appreciated. 



WHAT THE FARMER SHOULD KNOW. 



Commercial fertilizers are mainly valuable because they fur- 

 nish the elements nitrogen, phosphoric acid, and potash which 

 serve as food, not as stimulants. The kind of farming in the past 

 and the demands for special products in the present make their use 

 necessary in profitable farming. In order to use them profitably 

 the farmer should know 



(a) That nitrogen, phosphoric acid, and potash are the essen- 

 tial manurial constituents. 



(6) That the agricultural value of these constituents depends 

 largely upon their chemical form. 



(c) That these forms are contained in specific products of a well- 

 defined character and composition, and may be purchased as such 

 from dealers and manufacturers and may be mixed successfully on 

 the farm. 



In making up the manure for a crop, the farmer should be 

 guided chiefly by two considerations. He must ascertain wherein 

 the soil, upon which the crop is to be grown, is deficient, and he 

 must know the requirements of the plant which is to live upon it. 

 These matters are best ascertained by actual experiment, carried on 

 by the farmer himself on his own land, using different fertilizing 

 ingredients to show him what elements are lacking. We will sup- 

 pose that the farmer has determined what he is going to use, and 

 how much per acre, and will endeavor to explain how different fer- 

 tilizing materials are to be combined and prepared. 



There are two distinct cases. In the one case, the plant food of 

 the materials to be used is already in sufficiently available form, and 

 the different ingredients need only to be well mixed in the proper pro- 

 portions. In the other case, some of the materials need to be changed 

 before they are put in the soil, and must be composted, or rotted. 



A rapid growth of foliage and a deep green color of the same 

 give evidence of an ample supply of nitrogen in the soil ; if the foli- 

 age seems watery and the growth of the plants is more or less rank, 

 there is most likely a need, of phosphoric acid, and probably of lime. 



