1908.] Man'urial Value of Sewage Sludge. 



695 



sludge is very slow as compared with the effect produced by nitrogen and 

 phosphates supplied in ordinary artificial manures. 



"For such crops as mangolds, potatoes, and swedes, which have a short 

 period of growth, and require quick-acting manures, sewage sludges would 

 not appear to be well adapted, and if they are employed, they should be 

 applied in tons rather than in hundredweights per acre. 



" On the other hand, although these experiments do not supply the 

 evidence, it seems likely that sludge, used in proper quantities, would form a 

 good dressing for the slow-growing plants of many permanent pastures and 

 meadows. 



"Sludge is unlikely to give satisfaction on the very poor clay-soil pastures 

 which are so much benefited by basic slag, but for old grass land of 

 moderate quality it should prove useful." 



As regards the experiments with sewage sludge on grass land 

 at Woburn, carried out by Dr. J. A. Voelcker, which were on 

 similar lines to the above, Dr. Voelcker observes : — 



"There is, I think, little more to be said than that, for all practical 

 purposes, the sludges did not ' tell ' during this season, but that they require 

 longer time to show their influence, and that the only clear benefit was to be 

 traced to the more quickly acting ^because more soluble) material, sulphate 

 of ammonia. That even this increase will, in the end, be a beneficial one is 

 by no means certain, for the mere ' flushing ' of a grass field to give an extra 

 cut for hay by no means results necessarily in the improvement of the 

 pasture permanently. Here, again, continuation of the experiment for other 

 years is called for." 



In addition to the foregoing experiments with grass, Dr. 

 Voelcker also carried out experiments with wheat at the Woburn 

 Pot Culture Station. These are being continued for another 

 year, but Dr. Voelcker draws the following general conclusion 

 from the first year's work, so far as the wheat crop is concerned : — 



()) That the different sewage sludges, when used in quantity to supply 

 40 lb. of nitrogen per acre, are capable of increasing the yield of 

 both corn and straw by 10 to 12 per cent, above the unmanured 

 produce. 



(2) That " artificial equivalents " of the different sewage sludges applied 



as above, will give rather better results, the increase in corn and 

 straw being 16 to 17 per cent, over the unmanured produce. 



(3) That the tendency of the use of sewage sludges is to produce a 



greater length of straw. 



(4) That, as between different sewage sludges, those have done best 



which contain the most moisture and the most lime. 



(5) That the value of sewage sludge does not turn mainly upon the 



amount of nitrogenous organic matters contained, but that these may, 

 indeed, be in a form incapable of ready assimilation and requiring 

 lime for their decomposition. 



(6) That, from a practical point of view, none of the sewage sludges 



used would be worth 10s. a ton on the farm, for wheat-growing 

 purposes. 



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