THE WORK OF ROOTS 153 



immediate results: the use of such fertilizers (e. g., 

 guano and superphosphates) has revolutionized agri- 

 culture and made high farming and intensive farming 

 possible. For example, we now use from 100 to 200 

 pounds of superphosphates per acre where a hundred 

 years ago 1,000 to 2,000 pounds of bone were used; 

 i. e., for the same cost it is now possible to fertilize 

 six to eight times as much land. 



When the soil is deficient in one constituent only, a 

 small amount of fertilizer containing this constituent 

 will give results out of all proportion to its cost. 1 

 Hence it is important to know what elements of plant- 

 food are lacking in the soil before attempting to enrich 

 it. Chemical tests are useful, but in most cases the 

 question is practically settled by applying fertilizers 

 and noting the result. For the soil of our particular 

 region we may arrange an experiment as follows: Lay 

 out beds wherever convenient, or bring in the soil and 

 place it in pots. On each bed or in each flower -pot 

 place a single fertilizer or combination. We may use 

 whatever is obtainable. A good series is 



General fertilizers: Special fertilizers: 



(a) Well-rotted stable manure (6) Chili saltpeter 



(c) Superphosphates 



(d) Wood ashes 



(e) Quicklime . 



iSee Bailey: "Principles of Agriculture," Chapters V and VI; King: "The 

 Soil," Chapter III; Roberts: "Fertility of the Land"; also articles in the Year- 

 Book of the U. S. Dept. of Agriculture, for 1894 by Wiley and Webber; for 

 1895 by Snyder; for 1896 by Wiley; for 1898 by Means; for 1899 by Wiley; for 

 1901 by Woods; for 1902 by Holmes, Woods and McKenney. 



