30 THE ESSEX EXPERIMENTS 



bility would have done equally well at Martin's Hearne and vice versa; 

 that the slag of very low solubility 20 % would have also given 

 inferior results at Tysea Hill. The rock phosphates both at Martin's 

 Hearne and Tysea Hill give consistently good results. On this type 

 of soil Gafsa rock phosphate may safely be said to be equivalent 

 to the better grades of basic slag. Other North African phosphates, 

 such as Egyptian and Algerian phosphate, are not far behind Gafsa 

 phosphate in this respect. 



Although at Tysea Hill there is apparently no discernible difference 

 between the various types of phosphate, yet on a very similar soil 

 though slightly poorer in phosphoric acid, such as that at Martin's 

 Hearne, a study of the results reveals some important variations in 

 their action. During a moist season with a long growing period the 

 rock phosphates are on the whole more effective than even the highest 

 soluble basic slag. When the season is dry and the growing period 

 consequently short the advantage is decidedly with the more highly 

 soluble phosphate. 



Under the soil and climatic conditions existing at Martin's Hearne, 

 there is over a period of years nothing to choose between the effective- 

 ness of rock phosphate and the best grades of basic slag for the im- 

 provement of grass-land. The open hearth basic slags of 20 % solubility 

 or less, although they give good and profitable results, are clearly less 

 effective even in favourable seasons than the high soluble types. 



The lack of response to phosphates at Farnham and Hassobury 

 indicates that phosphates are not the most important manurial factor 

 on all the boulder clay soils in Essex, and that even where the soil 

 is very deficient in available phosphoric acid as at Farnham, a 

 deficiency in some other constituent may prevent a profitable response 

 to phosphatic manuring. 



FIELD EXPERIMENTS ON LONDON CLAY SOILS 



Horndon-on-the-Hill. A 20 acre meadow which had been laid 

 down to grass in or about the year 1890 was selected for these trials. 

 The soil is a heavy, impervious London clay, known in Essex as 

 three-horse land and always put up in 7 ft. 6 in. stetches so as 

 to secure the maximum amount of surface drainage. 



The field, as do all the fields whether grass or arable on this type 

 of soil, lies cold and wet during the autumn and winter, and unless 

 there is a good natural slope and good under drainage, water stands 

 in the furrows during the greater part of the winter and early spring. 



