28 COMPOSITION OF EOTHAMSTED SOIL 



the earliest samples available (1856) show more than 5 per 

 cent, in the surface soil of Broadbalk field. This amount is 

 always being reduced by the action of the rain washing it away 

 as calcium bicarbonate ; it is still more rapidly reduced by the 

 action of many of the manures applied, particularly by the 

 ammonium salts, so that at the present time there is only about 

 3 per cent, present on any of the plots. In other fields less is 

 to be found, practically none at all in the soil of some parts of 

 Agdell and of the Park. The subsoil below the depth of 9 

 inches also contains little or no calcium carbonate, and this 

 fact together with the varying proportion in the surface soil 

 indicate that the original soil was almost devoid of calcium 

 carbonate, and that the quantity still found in the surface soil 

 has all been applied artificially. We read, indeed, that the 

 chief form of manuring known to Hertfordshire farmers in 

 the eighteenth century consisted in digging pits through the 

 clay soil until the chalk was reached, extracting chalk and 

 spreading it over the land, and all of the Rothamsted fields 

 show a depression or "dell" from which the chalk had thus 

 been formerly obtained. Arthur Young, the elder, in his 

 General View of the Agriculture of Herts, drawn up for the 

 consideration of the Board of Agriculture, and published in 

 1804, writes of "the prevailing practice of sinking pits for the 

 purpose of chalking the surrounding land," and mentions the 

 application of 60 loads of chalk every ten years as customary. 

 The chalk now present in the arable soil is visible in small 

 grains varying in size from that of a pea downwards, additional 

 evidence of its extraneous origin. But the amounts so added 

 to the soil are enormous : if we assume that the wastage in 

 the past had been at all comparable to that going on during 

 the last half-century on the unmanured plot, then Broadbaik 

 field must have begun the nineteenth century with something 

 like 100 tons of chalk per acre in its surface soil. 



The proportion of organic matter, carbon and nitrogen, 

 present in the various soils is very variable and entirely 

 dependent on the character of the manuring and cultivation. 



