26 THE ESSEX EXPERIMENTS 



destitute of clover. During the more favourable season of 1920 the 

 clover reappeared towards the middle of June and, although it was 

 not so dense as in 1918, it constituted about 30 % by weight of the 

 crop (Table XXV). Throughout the whole of the winter the untreated 

 plot could be picked out a mile away owing to the contrast afforded 

 by its dark, reddish, unhealthy colour compared with the healthy 

 green of the treated plots. 



As at Tysea Hill, the effectiveness of the various phosphates during 

 the dry seasons (1917 and 1919) is again very noticeable, the crop 

 on the treated plots being about double that on the untreated. 



Hassobury Bishop's Stortford. The experimental field at Has- 

 sobury has been down to grass for over 90 years. The soil, although 

 classified as boulder clay, is of much lighter texture than the average 

 boulder clay soil. At Hassobury it lies immediately above the chalk, 

 which is only from two to four feet below the surface. (The photo- 

 graph shown in Plate V was taken standing in the ditch at the bottom 

 of the field. The chalk can be clearly seen rising to within two to 

 three feet from the surface.) The chemical and mechanical composition 

 of the soil, as will be seen by an examination of the data in Table VII, 

 differs considerably from that of the two previous centres. At Hasso- 

 bury the soil is comparatively well supplied with phosphoric acid and 

 is noticeably poorer in potash. Although so close to the chalk, the 

 surface 9 inches of soil is sour, judged either by its lime requirement 

 or its Ph. value. 



The pasture is of very poor quality, the bottom half of the plots 

 being covered with a thick almost impenetrable thatch of coarse 

 grass. From three-quarters to the whole of Plots 13 to 18 are covered 

 with a thick, matted growth, and it is only during favourable seasons, 

 and towards the end of the season, that the clover plant seems to be 

 able to push its way through in small scattered patches consisting 

 of a few plants. 



The meadow has been cut for hay practically every year owing 

 to the difficulty of getting water to the field, and the aftermath as 

 a rule grazed chiefly by horses. 



At this centre a large number of rock phosphates were tried, each 

 of them being applied in two degrees of fineness 1 . The weights of 

 hay on the various plots over a period of three years are given in 

 Table XI. 



1 The coarse grade was ground as fine as is usual in the manufacture of super- 

 phosphate (90-95% to pass a '60' sieve). The finer grade was obtained by setting 

 the Griffin mill so as to grind as fine as possible. It is not possible to sieve finely 

 ground North African phosphates satisfactorily owing to their woolly nature. 



