236 Report of the Department of Chemistry of the 



ured by the amount appropriated, was greatly influenced by the 

 degree of fineness, the amount taken up from the floats being at 

 least one-half more than what was used from the coarsest ma- 

 terial. With bone meal the degree of fineness has little influence, 

 if any. Much the largest appropriation of phosphoric acid was 

 from the acid phosphate. 



(5) The proportion of phosphoric acid to the growth of dry 

 matter in the plants increased with the increase in fineness of 

 division of the Florida rock, or, in other words, in proportion 

 to the availability. 



(6) Similar tests proved the phosphoric acid in an iron ore 

 waste to be of slight availability for plant growth. 



INTRODUCTION. 



Soil problems in their relation to crop production are complex 

 and difficult. This is necessarily so because of the numerous fac- 

 tors that are involved in soil fertility. As our knowledge has 

 broadened, we have come to see that the maintenance or develop- 

 ment of the productive capacity of a farm requires attention to 

 much more than the mere saving or purchase and application of 

 manures. 



The factors which have a practical relation to soil fertility 

 may be classified in a general way under three heads : 



(1). Soil conditions, such as color and texture, in their rela- 

 tion to the welfare of the plant, these conditions depending pri- 

 marily upon soil composition. 



(2). The supply of plant food both as to its kind and quantity. 



(3). The life activities of the soil that have to do with the ac- 

 quisition and development of available plant food. 



Formerly the plant food supply was the factor chiefly considered 

 and emphasized. It is now minimized by some writers and in- 

 vestigators to a position of much less importance than is attributed 

 to soil conditions. It is urged that land becomes infertile not 

 because of a depletion in the quantity of the needed elements of 

 plant food but because, for instance, by unwise management the 

 texture and consequently the water-holding and water-transmit- 



