40 THE POTATO 



Upon such soils as these applications of fertilizers 

 containing phosphoric acid, and, in some cases, potash, 

 have been found, by experience, to be most profitable — 

 a condition of affairs which could never be ascertained 

 from the analyses. It is seldom that the increase in 

 yield of crop bears any relationship to the quantity of 

 the fertilizers applied. Without either fertilizers or 

 manure, but given good tillage, yields of 300 bushels 

 of potatoes per acre have been obtained for four suc- 

 cessive years on the same piece of land.' 



The amount of plant-food removed by any crop is 

 small, and is obtained from all parts of the soil wherever 

 roots extend. Most soils contain certain sufficient plant- 

 food to supply the demands of any crop grown thereon 

 for an indefinite period of time. To maintain crop pro- 

 dudlion at a profitable point, attention must be paid 

 to factors other than the supply of plant-food. 



The ingredients applied as fertilizers will, no doubt, 

 be found to have a value other than their value as car- 

 riers of plant-food. Their value for this purpose may 

 be found to be small, while the benefits derived from 

 their use may be found to be largely due to their 

 chemical adlion upon the soil — e.g. , as sanitary agents, 

 promoters of the growth of desirable organisms or de- 

 stroyers of injurious ones, aids in the formation of de- 

 sirable chemical compounds in the soil or neutralizers 

 of undesirable compounds, to their influence as stimu- 

 lants, and upon the physical properties of the soil. 

 That their use is desirable in some cases is evident. 

 Why it Ghould be, and how, are matters for investiga- 

 tion. 



> (N. Y.) Cornell Bui. 191, p. 19J. 



