105 



and a larger proportion of the more active forms used, because in this 

 case quick-growing crops which belong to the high- value class are pro- 

 duced. For fruit trees, which feed slowly and continuously, the mine- 

 ral elements, as already explained, should be applied in greater 

 amounts, and may be derived from the cheaper and more slowly avail- 

 able forms. 



SUMMARY. 



(1) Commercial fertilizers are mainly valuable because they furnish 

 the elements — nitrogen, phosphoric acid, and potash — which serve as 

 food, not as stimulants. 



(2) The kind of farming in the past and the demands for special 

 products in the present make their use necessary in profitable farming. 



(3) In order to use them profitably the farmer should know — 



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

 manurial constituents ; 



(b) 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. 



(4) The agricultural value of a fertilizer bears no strict relation to 

 the commercial value ; the one is determined by soil, crop, and climatic 

 conditions, the other by market conditions. 



(5) The variations in the composition and value of manufactured 

 fertilizers which contain the three essential constituents are due to 

 variations in the character and in the proportion of the materials used. 



(6) The ton basis alone is not a safe guide in the purchase of these 

 commercial fertilizers. Low ton prices mean either low content of 

 good forms of plant food or the use of poorer forms. Fertilizers, high- 

 grade both in quality and quantity of plant food, can not be purchased 

 at a low price per ton. 



(7) The best fertilizers can not exert their full effect on soils that are 

 too dry or too wet, too compact or too porous. They can furnish but 

 one of the conditions of fertility. 



(8) The kind and amount to use should be determined by the value 

 of the crop grown and its power of acquiring food. 



(9) A definite system or plan should be adopted in their use ; " hit or 

 miss" methods are seldom satisfactory, and frequently very expensive. 



