THE ESSEX EXPERIMENTS 



the winters of 1915, 1916, 1918 and 1919 a series of mamirial 

 experiments under the auspices of the East Anglian Institute of 

 Agriculture were laid down on permanent grass-land in Essex with 

 the object of ascertaining: 



(1) the relative fertilising value of the various forms of rock phos- 

 phate, the two types of open hearth basic slags, and 



(2) the extent to which the permanent grass on the heavy clay 

 soils could be profitably improved. 



The choice of grass as the experimental crop was influenced by the 

 fact that it is on grass, whether reserved for hay or pasture, that the 

 direct and indirect response to phosphates is most clearly felt. More- 

 over, in Essex, out of a total area of 981,000 acres approximately 

 300,000 are covered by permanent grass, and as a very large propor- 

 tion of this acreage is of the poorest quality, its improvement is of 

 considerable economic importance. 



CHARACTER OF THE SOIL 



Slightly over 600,000 acres, or about two-thirds of the county, is 

 covered by soils belonging to the London Clay and Boulder Clay 

 formations. 



The London clay beds form part of the Lower Eocene formation, 

 and in many parts reach a thickness of over 500 feet. It is a stiff 

 bluish grey or brown clay. Below the London clay lies a thin bed 

 of Thanet sands varying in thickness up to 60 feet. The Thanet sands 

 in turn rest upon an eroded surface of chalk. 



The boulder clay soils dominate the northern part of the county, 

 and vary considerably in thickness. In the extreme north and north- 

 west of the county the boulder clay rests immediately above the 

 chalk which comes close to the surface (see Map facing p. 1). South of 

 the line Bishop's Stortford Thaxted Twinstead, the boulder clay 

 lies immediately above the London clay. It nevertheless contains 

 a considerable admixture of chalk, sometimes up to 11 %, and it is 

 only the extreme southerly and easterly portions that are wholly 

 devoid of calcium carbonate. 



As a rule these heavy clay soils are very deficient in phosphoric 

 acid, the London clays being also deficient in calcium carbonate. 

 Unless the early autumn is favourable great difficulty is experienced 



