New York Agricultural Experiment Station. 279 



Table XII. — Computed Maximum Acre Yield of Dry Substance in Crops 

 Grown in Boxes, in Plant-food Requirement Experiment. 



growth. Indeed, it may be said safely that there was in practically 

 all cases a quite regular increase in the proportion of phosphorus 

 and potassium compounds in the plants of the several species corre- 

 sponding to the supply of these compounds in the soil. 



It was hoped that by repeating these experiments during several 

 seasons some quite definite minimum relation between the neces- 

 sary phosphorus and potassium and the dry matter produced would 

 be established. The data secured do not establish such a relation. 

 It is quite possible that other factors obscured the limitations of 

 the plant food supply. 



The results reached do strongly emphasize the fact that the amounts 

 of soil compounds used by agricultural plants are materially 

 influenced by the chemical environment of the roots. 



It is therefore not necessarily true that what a given crop con- 

 tains of certain elements is to be regarded as a measure of what 

 must be supplied in order to meet the needs for maximum growth 

 under the existing conditions. It seems more than probable that 

 in field practice a liberal supply of highly available plant food com- 

 pounds increases the amounts of these compounds utilized out of 

 proportion to the growth of dry matter. 



Formulae based on crop analysis are therefore only approxima- 

 tions to the real needs of the crop. 



