Ob 



Shoddy showed a residual effect which would improve its 

 position. The differences are less than might have been expected. 

 No evidence could be obtained that the nitrog-en in rape cake is 

 superior in crop-producing- power to the nitrogen of sulphate of 

 ammonia or nitrate of soda. No larger crops were obtained from 

 rape cake than from an equivalent of sulphate of ammonia and 

 superphosphate, and actually less was obtained than from nitrate 

 of soda. 



There is very little evidence for the \ iew that rape cake and 

 Peruvian guano permanently benefit the soil. Where very large 

 dressings of rape cake (10 cwt. to 1 ton per acre) are applied year 

 after year to the same land there is, in course of time, an accumula- 

 tion of nitrogen, but this proves of little value to wheat or barley ; 

 on the other hand, it may be more useful to mangolds, though the 

 evidence is not conclusive. 



In ordinary farm practice, where smaller dressings are given 

 and less frequently than every year, there is little reason to antici- 

 pate any residual effect. 



If this were the whole case there would be no reason why rape 

 cake and guano should ever sell at prices above those obtaining for 

 sulphate of ammonia or nitrate of soda. Yet farmers and manure 

 makers have always been willing to pay more. There appear to be 

 three reasons for this preference. Rape cake and guano are safer 

 than artificial manures in the hands of inexperienced cultivators. 

 No one would be likely to apply too much ow'ing to high prices, 

 and there is no necessity to mix with other fertilisers. 



Further, from the manure makers' point of view, these sub- 

 stances have the enormous advantage of improving the condition 

 of compound fertilisers, a property to which farmers rightly 

 attach great importance in view of the w^idespread use of manure 

 drills. 



Lastly, from the special point of view of the horticulturist, who 

 uses in the aggregate large quantities of manure, rape cake and 

 guano, ha\'e the advantage that they can be applied once for all, 

 whilst artificials w'ould have to be given in several small doses, 

 otherwise they might injure the soil. 



XLVIIl. W. E. Brenchley and E. H. Richards. " The 

 Fertilising Value of Sewage Sludges/' Journal of 

 the Society of Chemical Industrv, 1920. Vol. 

 XXXIX. pp. 177-182. 



The sewage sludges produced by the old methods of tank 

 treatment have very little fertilising value. Two new processes 

 yield sludges of a different class. Slate-bed sludge and activated 

 sludge are aerobically produced while the old precipitation and 

 septic-tank sludges are essentially anaerobic. This difference 

 accounts for the marked increase in manurial value of the newer 

 sludges. The most valuable constituent is nitrogen. The average 

 content in the old sludges tested by the Sewage Commission i\t 

 Rothamsted and elsewhere, was 1.22%. Harpenden slate-bed 

 sludge contains 2.63% and Withington activated sludge 7.09% cf 

 nitrogen ; the availability of the nitrogen being 26% in the former 

 and 66% in the latter. 



Pot culture exi)eriments made with the two sludges and an 

 equivalent dressing of nitrate of soda showed that activated sludge 



