32 THE ESSEX EXPERIMENTS 



The summer is equally trying on this type of soil. The dry and hot 

 weather which is usually experienced in Essex in June and the latter 

 part of May 'caps' or bakes the soil the soil sets hard and cracks 

 and the crops receive a check. It is but seldom that the crop of hay 

 exceeds 10 cwts. to the acre, and it is only too frequently left uncut 

 altogether. The meadows which have recently been laid down contain 

 a small reserve of calcium carbonate, a residuum from the heavy 

 dressing of lump chalk (40-60 tons per acre) fairly frequently applied 

 up to the eighties or nineties. 



The soil is exceedingly poor in both 'total' and 'available' phos- 

 phoric acid, but is well supplied with potash. 



Nineteen quarter-acre plots (1-19) were laid down on this field in 

 1918, and the manures sown on February 27th, 1918. Subsequently 

 Plots A, B, C, D, E, F, G, H and K were added and sown on February 

 3rd, 1919, and finally Plot L was sown during May, 1919. 



The weights of hay on the various plots for the seasons 1918 and 

 1920 are given in Table XIV. 



In this experiment an attempt was made to ascertain whether 

 better effects could be obtained from rock phosphates by finer grinding. 

 With this object in view the Florida pebble, Algerian, Gafsa, Tunisian 

 and Egyptian phosphates mentioned in the above tables were specially 

 ground under the writer's supervision by Messrs Walter Packard, of 

 Ipswich. 



All the phosphates were passed through a Griffin mill. For coarse 

 grinding the mill was set to grind for the standard usually adopted 

 when the rock phosphates are used for the manufacture of super- 

 phosphates (90 % to pass a '60' sieve). In actual fact about 80 % 

 of the material will pass the ' 100 ' sieve. For fine grinding the mill 

 was closed down so that the output per hour was reduced by a half. 

 A much finer product was obtained, but it has not been practical, 

 owing to the 'woolly' nature of the rock phosphates, to satisfactorily 

 distinguish by means of sieves between the 'fine' and the 'coarse' 

 grinding. During 1918 no superiority due to fine grinding was noticed. 



Throughout the whole season of 1920 the writer was able to visit 

 this centre at least every week, and a close watch was kept on the 

 progress of the various plots. The high soluble slag and the "super- 

 phosphate and lime " plots were the first to make a start, followed by 

 those plots receiving the finer ground rock phosphates. During the 

 whole of May the superiority of the plots receiving the finer ground 

 rock phosphates over those receiving the same phosphate only more 

 coarsely ground could be distinctly seen. As the season progressed 



