New York Agricultural, Experiment Station. 237 



ting power of the soil have become unfavorable to the growth of 

 agricultural plants, or because the soil has become charged with 

 compounds having a deleterious effect on plant growth. 



It is certainly important to a system of farm economics to 

 understand the relative importance of plant food supply. The 

 farmer should certainly be enabled to understand whether he 

 should continue to place emphasis upon the acquisition and sav- 

 ing of manurial substances or whether by certain methods of 

 management he may look with more or less indifference upon the 

 income and outgo of those substances, such as nitrogen, phosphoric 

 acid and potash, for which at the present time such enormous ex- 

 penditures are being made by farmers. 



It is firmly believed at the present time, by practitioners at 

 least, that under the conditions of agricultural practice that prevail 

 plant food supply is one of the determining factors in crop pro- 

 duction. If this belief is correct then measurements of soil 

 fertility and a study of the conditions which affect the ability of 

 the plant to appropriate the necessary materials for growth are 

 very important. 



We must at least consider the following factors : 



(1). The adaptability of the plant to the securing of the neces- 

 sary supply of food under given conditions.. 



(2). The forms in which the plant food is supplied. 



(3). The quantity of the supply. 



(4). The relation between soil composition and plant growth. 



During the past ten or more years the writer and his associates 

 have secured certain data, so far unpublished, which bear directly 

 upon the problems here suggested. The experiments that have 

 been conducted have been directed toward these questions: 



Are different forms of phosphoric acid equally available to 

 various species of plants ? 



Does the mechanical fineness of a crude phosphate influence its 

 availability ? 



How close is the relation of the supply of phosphoric acid and 

 potash to the amount appropriated by the plant ? 



