1922.] Experiments with Phosphates and Slags. 



521 



prove as important to distinguish between the extreme types 

 of rock phosphates as between those of basic slag. 



The Essex Experiments. — It was with the above considera- 

 tions in view that the Essex Experiments were designed and 

 laid down in the period 1915-19. As far as possible the various 

 types of basic slag likely to be produced in the future were 

 included in the field trials, and also a number of rock phos- 

 phates. ]\Ieadow land was chosen for the experiments because 

 such land in Essex does not as a rule receive artificial manures. 

 The soil was known to be poor in phosphoric acid, and a good 

 response to phosphates could, therefore, be anticipated. More- 

 over, it is on grass land, whether hay or pasture, that the direct 

 and indirect response to phosphates is most clear. The plots 

 were one-quarter of an acre in area. Three types of basic slag 

 have been used — Basic Bessemer, Basic Open Hearth Slag and 

 Basic Open Hearth Fluorspar Slag — and these have been com- 

 pared with the following rock phosphates : — Florida Pebble, 

 Tunisian, Algerian, Gafsa, and Eg}7)tian, and Cambridge 

 Coprolites. At some of the centres plots dressed with super- 

 phosphate, with superphosphate and lime, and with lime alone 

 have been included. The phosphates were applied during the 

 period December to February. Unless specifically mentioned 

 the initial dressings of the various phosphates contained 200 lb. 

 of phosphoric acid per acre (approximately equal to 10 cwt. per 

 acre of a 38-40 per cent, basic slag). No further dressing of 

 phosphates was applied at any time during the course of the 

 experiment and no other artificials have been applied to the 

 plots. The hay crop was cut and weighed at each centre over 

 a period of years, the whole of the crop being weighed on ea^h 

 plot immediately before stacking. 



Eifrht experimental centres were laid down, the following 

 soil formations being represented : London Clay, Boulder Clay 

 and Chalk. The results from three of these centres are given 

 below as they suffice to show the chief results obtained and the 

 main conclusions drawn from the experiments. 



Martins Hearne Farm: Boulder Clay Soil— The experimental 

 field at this farm had been down in grass for at least eighty 

 years before the experiment began. During that period no 

 artificial manures had been applied, but the meadow had re- 

 ceived during the last twenty years at intervals of seven to eight 

 years a dressing of about ten loads of farmyard manure per 

 acre. The herbage was of the poorest character. The results 



