^66 Journal of Agriculture. [lo JuiVE, 191 o. 



"earlier in the toluened than in the heated soil but does not last so long; 

 by the ninth day the heated soil contains more ammonia, a superiority 

 \vhich persists throughout. They conclude that the ammonia is mainly the 

 work of micro-organisms. 



Stoklasa determined that the bacteria in contmon field soils produce 

 daily per hectare (2| acres nearly) to a depth of 40 cm. (about 16 inches) 

 75 kilos, of CO^ (nearly 2,649 cubic feet) while an equal area of wheat 

 produces only 60 kilos. This carbonic acid before it escapes into the 

 atmosphere will help to disintegrate the rocky particles of the soil, dis- 

 solving carbonates and phosphates of lime and magnesia for the needs of 

 the plant, but, on the other hand, the healthy respiration of the root will 

 probably be interfered with. From this point of view, it follows that the 

 disinfection of a soil overcharged with microbes must have a very bene- 

 ficial effect on the healthy respiration of the roots, and consequently on the 

 well being of the entire plant, since after the microbes have been killed they 

 no longer use up the oxygen and manure. This continuous struggle for air 

 and food between the roots on the one side, and microbes on the other, is 

 thus interrupted in favour of the plant. 



At 125 deg. C. all organisms are killed. 



Partial sterilization causes two significant changes (i) An increase in 

 the amount of ammonia (2) Cessation of the nitrifying process. 



Bacteria reach far higher numbers in partially sterilized than in un- 

 treated soils. 



Untreated soil contains a factor, not bacterial, limiting the develop- 

 ment of bacteria, this factor being put out of action by partial sterilization 

 (Russell and Hutchin.son). The limiting factor is not a toxin but is in all 

 probability biological. Infusoria, amoebae, and ciliata, are killed by the 

 treatment, and these are all severe competitors with the bacteria by reason 

 of their large size (about 1,000 times that of the soil bacteria). 



As our experiments are far from being complete we can only make 

 the suggestion that the increased fertility is due to — 



(i) The new bacterial flora, being more active decomposing agents 

 than the original ones, cause an increased production of 

 ammonia. 



(2) The large organisms (Protozoa) being killed off by the treat- 

 ment, serve as food for the new bacterial flora. Their 

 decomposition also provides food for the new plant in the 

 shape of ammonia, and as some of these large organisms 

 are known to devour bacteria {e.g.. Colfoda cucidlus and 

 amoeba nitropJiilia), their destruction allows a rapid develop- 

 ment of the new bacterial growth to take place. 



The bacteria being found in greater abundance after a time in par- 

 tially sterilized soils, Stoklasa's theory that the production of COg by too 

 great a number of bacteria being present in the soil and interfering with 

 the respiration of the roots does not seem to hold good, though of course the 

 killing of the large organisms will greatly lessen the consumption of 

 oxvgen and the production of carbonic acid. 



A Soil Sterilizer. 

 A very effective plant for the sterilization of soil for the purpose of 

 securing a pure seed bed is at present in use at the nurseries of Mr. R. 

 Cheeseman at North Brighton. As will be .seen from the accompanying 

 illustration, it consists of a shallow pit, 18 inches in depth, floored with 

 bricks. The walls are formed of 9-inch brickwork, and divided into two 



