1905.] 



On the Retention of Bases by- the Soil. 



3 



and induced by the application of saline manures, are taking place. In most 

 cases the plots have received the same manures, year after year, for more 

 than fifty years, and though unfortunately samples of the soil were not taken 

 at the starting of the experiments, yet in the case of the Broadbalk Field, 

 on which wheat has been grown continuously since 1843, a set of samples 

 drawn in 1856 has been preserved, in addition to samples drawn in 1865 and 

 in 1893. From the Hoos Field (continuous barley since 1852) samples were 

 drawn in 1868, 1882, and 1904 — 5, and from Agdell Field (under a four- 

 course rotation since 1848) samples exist which were drawn in 1867, 1874, 

 1883, and 1905. 



Furthermore, the calcium carbonate in the Ptothamsted soil is of 

 extraneous origin, and is entirely localised in the surface layer which is 

 stirred by the plough. The subsoil, from which the surface soil is 

 undoubtedly derived, belongs to the drift formation of " clay-with-fiints,"' 

 characteristic of the chalk plateau, and consists of the debris of the chalk 

 formation largely mixed with sands and clays of the Eeading series.* It 

 normally contains little or no calcium carbonate, although it is partly 

 derived from the chalk formation and rests upon the solid chalk at a 

 varying depth of 8 to 12 or 20 feet. 



In the eighteenth century, however, a characteristic feature of the 

 agriculture of this district of Hertfordshire was to manure the land by sinking 

 pits through the clay to the chalk, which was then lifted and spread in 

 considerable quantities. Arthur Youngt quotes from "Walker's Survey of 

 1795 — " the now prevailing practice of sinking pits for the purpose of 

 chalking the surrounding land therefrom . . . The most experienced Hert- 

 fordshire farmers agree that chalking of lands so circumstanced is the best 

 mode of culture they are capable of receiving." Evidence of the former 

 prevalence of this practice of chalking may be seen by the existence in 

 each of the Eothamsted fields of a " dell," a depression representing the 

 fallen-in pit from which the chalk was extracted. A certain rawness of the 

 soil round the edges of these " dells " still bears witness to the disturbance 

 created by the excavation, though it is known that nothing of the kind was 

 done during the late Sir John Lawes' possession of the estate, which dates 

 back to 1834. Probably the pits were but little worked after the close of the 

 eighteenth century, and certainly neither chalk nor lime has been applied to 

 the plots since they were put under experiment. At the present time the 



* See H. B. Woodward, " Report of the Soils and Subsoils of the Eothamsted Estate. 

 Summary of Progress of the Geological Survey, 1903." 



t " Eeport on the Present State of the Agriculture of Hertfordshire,'' presented to the 

 Board of Agriculture, 1804 



B 2 



