191 2.] Summary of Agricultural Experiments. 939 



SUMMARY OF AGRICULTURAL EXPERIMENTS.* 

 Soils and Manuring. 



Sewage Sickness in Soil and its Treatment by Partial Sterilisation. 



Dr. E. J. Russell and Mr. J. Golding. (Jour. Soc. Chem. Indust*, 

 April 29th, 191 1). — The method known as the land purification of 

 sewage consists in allowing the sewage to drain through soil which 

 retains most of the fertilising material. By the agency of bacteria this 

 decomposes, and is utilised by crops grown on the land, giving some 

 financial return for the treatment. The system, however, has the 

 serious disadvantage that the soil gradually becomes "sewage sick," 

 in which state its efficiency as a filter is low, and the effluent conse- 

 quently impure. 



A soil in such a condition has to be rested for a longer or shorter 

 period, in which time no sewage can be run on it. 



To some extent this "sickness" is due to physical causes. Owing 

 to the continuously wet condition of the soil receiving sewage, the 

 clay — of which there is some in even the lightest soils — gradually 

 becomes deflocculated or more gluey in its consistency. Drainage is 

 retarded, and the amount of air in the soil is too little to meet the 

 requirements of the bacteria which bring about the decomposition of 

 the organic matter. 



The authors, however, show that the bacteria, and consequently 

 the decomposition, are affected in another way. 



The fact has been established that even in an ordinary soil there is 

 some factor that keeps down the number of useful decomposition 

 bacteria, and the experiments of Russell and Hutchinson indicate that 

 this factor consists of larger organisms, probably protozoa. 



These larger organisms are more readily killed than are bacteria ; 

 by heating the soil or treating it with antiseptics they may be com- 

 pletely destroyed, while many of the useful bacteria survive, and after- 

 wards develop at a very rapid rate, with consequent rapid liberation of 

 available plant food and improved growth of crops. 



From their experiments, carried out at the Kegworth Sewage Farm, 

 the writers conclude that one of the causes of sewage sickness is the 

 great increase in the number of the injurious organisms, owing to the 

 specially favourable condition of a soil treated with sewage. When 

 soil from the farm w 7 as partially sterilised by heating, or by treatment 

 with toluol or carbon disulphide, the number of bacteria after a short 

 time rose greatly (in some cases to more than ten times that observed 

 in untreated soils), with correspondingly rapid decomposition of organic 

 matter in the soil, and recovery from sewage sickness. Analysis of the 

 effluents showed that treated soils were more effective as filters, and 

 did not so quickly lose their efficiency. 



* A summary of all reports on agricultural experiments and investigations recently 

 received is given each month. The Board are anxious to obtain for inclusion copies 

 of reports on inquiries, whether carried out by agricultural colleges, societies, or 

 private persons. 



