THE ESSEX EXPERIMENTS 



47 



over a period of five years, whilst at Horndon the results are made 

 up from ten rock phosphate plots and two open hearth high soluble 

 basic slag plots for a period of two years. 



TABLE XXI. COMPARISON OF RESULTS ON SOUR AND SWEET SOILS 



* Open hearth high soluble basic slags. 



The results shown in Table XXI, although they do not agree with 

 those secured by Pfeiffer 1 , yet demonstrate that rock phosphates 

 compare more favourably with basic slag on 'sour' soils than on 

 chalky soils. 



Had the seasons of 1917 and 1919 been as favourable as those of 

 1916, 1918 and 1920, it is probable that the contrast would have been 

 more marked. 



Open hearth fluorspar basic slags are very uncertain in their action. 

 The improvement effected by their applications has in every instance 

 been considerable, but the lower soluble types have undoubtedly 

 proved to be less effective than either the high soluble slags or the rock 

 phosphates. At only one experimental centre (Lambourne End) has 

 the open hearth fluorspar slag of 20 % solubility given results com- 

 parable with the high soluble slag. The open hearth slag of 45 % 

 solubility has proved quite as effective as the best grades of slag and 

 rock phosphates. On the other hand, an open hearth slag of 30 % 

 solubility has given at Lambourne End inferior results to a similar 

 slag of 20 % solubility. The relation of citric solubility to the value 

 of the phosphate has been discussed elsewhere (18). 



1 Pfeiffer is quoted in the Inter. Inst. of Agric. Bulletin, September, 1913, p. 1316, 

 as follows: "on sour soils and on peat moss soils crude earthy phosphates (Algerian, 

 Gafsa, etc.) do better than basic slag." 



