On the Phosphoric Acid and Potash Contents of Wheat Soils. 11 



" A Chemical Study of the Phosphoric Acid and Potash Contents 

 of the Wheat Soils of Broadbalk Field, Bothamsted." By 

 Bernard Dyer, D.Sc, F.I.C. Communicated by Sir J. Henry 

 Gilbert, F.B.S. Eeceived November 9, — Bead November 15, 

 1900. 



(Abstract.) 



In the ' Journal of the Chemical Society ' for 1891 (vol. 65, ' Trans- 

 actions '), there appeared a paper by the author, " On the Analytical 

 Determination of probably available ' Mineral ' Plant Food in Soils," 

 in which the use of a 1 per cent, solution of citric acid was proposed 

 as a means of approximate differentiation between the total and prob- 

 ably available phosphoric acid and potash, the method proposed being 

 the result of an attempt to imitate, in the solvent, the acidity of 

 root -sap, based on a preliminary examination of the acidity of 100 

 specimens of flowering plants of some twenty natural orders. To test 

 the method, it was then applied to samples of the soils of the various 

 barley plots in Hoos Field, Kothamsted, kindly placed at the author's 

 disposal by the late Sir John Lawes and Sir Henry Gilbert. The 

 method, having yielded results fairly consistent with the greatly vary- 

 ing mineral history and known fertility of these various soils, has now 

 been applied by the author to the investigation of the soils of a num- 

 ber of the Wheat plots of Broadbalk Field, also kindly placed at his 

 disposal by Sir John Lawes and Sir Henry Gilbert on behalf of the 

 Lawes Agricultural Trust Committee. Twelve representative plots 

 were selected, and the samples examined include not only the surface 

 soils to a depth of 9 inches, but also, for each plot, the second and 

 third consecutive 9 inches of subsoil. The samples were drawn on 

 the completion of the fiftieth season of continuous wheat growing, 

 but earlier sets of samples, of both soils and subsoils, taken in 1865 

 and 1881, were also simultaneously examined. 



The present paper gives an account of this work. It includes a 

 summarised history of the manurial treatment and crop yields of each 

 plot at the different periods, and gives, for each sample of soil and 

 subsoil — fifty-one in all — the results of determinations of total phos- 

 phoric acid and of potash soluble in hydrochloric acid ; and also of 

 phosphoric acid and potash soluble in a 1 per cent, solution of citric 

 acid. 



The differences between the total percentages of phosphoric acid in 

 different soils, unmanured and variously manured, correspond fairly 

 well with their history ; but in the absence of a knowledge of such 

 history, these differences would not suffice to give any indication of 

 the profound differences known to exist in the phosphatic condition 

 and fertility of the soils. The relative proportions of citric acid 



