Vol. XII. No. 291. 



THE AGRICULTURAL XEWSr 



207 



An interesting note appears in the same publica- 

 tion in connexion with Isaria Paffrrsoni, Massee. This 

 fungus was erroneously stated to be indigenous to the 

 Gold Coast, the material having been received from that 

 Colony without definite information. The Kew authorities, 

 however, have learnt from Mr. Patterson, Government Ento- 

 mologist, Gold Coast Colony, that the organism was collected 

 in the island of St. Vincent, West Indies, on the Pentatomid, 

 Nezera riridula. Specimens of the fungus were recently 

 received at Kew from the island of Grenada llirough the 

 Imperial Department of Agriculture for the West Indies. 



A new process of timber preservation is described 

 in the !■: rperintent Station Ktrord, Vol. XXVIIl, No. 6. 

 The preservative is melted paraffin with suspended silica, 

 combined with a certain percentage of naphthalin. It is 

 stated that the naphthalin causes expansion of the pores 

 and ducts of the wood which expels the moisture and 

 draws in the [.reservative mixture. On cooling, the 

 mixture forms a solid coating over the interior ducts and 

 pores. Tests show that it does not leak out, that it is 

 impervious to water and all organic acid.s, and that it 

 prevents the entrance of bacteria and fungi, which destroy 

 the wood tissue. 



With reference to Fungus Notes which appeared in 

 the current volume of the Agricultural iVeios, p. 174, the 

 statement was made that the CoUetotrichum disease of sisal 

 hemp appeared to have not been noticed or described in the 

 Weft Indies. A communication recently received from 

 Mr. J. B, Korer, A.B., M.A, Mycologist to the Board of 

 Agriculture, Trinidad, indicates certain references which 

 were overlooked in the preparation of the article. The 

 disease has been observed in Antigua, and in Trinidad. 



THE EFFECT OF PARTIAL STERILIZ- 

 ATION OF SOIL. 



The following summary of a recent paper, by 

 Russell and Hutchinson of Rothanisted E.xperimental 

 Station, published in the Journal of Agricultural 

 Science, for March I9I3, is taken from the Journal 

 of the Board of Agriculture for ]\Iay 1913: — 



This communication forms the second part of the 

 report on an investigation of the zoological inhabitants of 

 the soil, which was suggested by the increase in bacterial 

 activity and consequently in the production of plant food in 

 the soil subsequent to the partial sterilization of the soil by 

 heating, or by the use of certain drugs. The authors con- 

 sider that the conclusions reached previously have been 

 confirmed and extended by the continuation of the work. 

 Fresh evidence is adduced that bacteria are not the only 

 inhabitants of the soil, but that another group of organisms 

 occurs, detrimental to bacteria, multiplying more slowly 

 under soil conditions, and possessing lower power of resist- 

 ance to heat and antiseptics. In consequence of the 

 presence of these detrimental organisms the number of 

 bacteria present in the soil is not dependent merely on the 

 temperature, moisture content, and other conditions of the 

 soil. It may indeed show no connexion with them; thus 

 rise of temperature may be accompanied by a rise in the 

 number of bacteria, or a fall, or the number may be 

 unaffected; increase in moisture content has also proved 

 without action. The number of bacteria depends on the 

 difference in activity of the bacteria and the detrimental 

 organisms. 



When soil has been partially sterilized, however, the 

 detrimental organisms are kill<d and the bacteria alone are 

 left. It is found that increase in temperature, up to 

 a certain point favours bacterial multiplication. 



The detrimental organisms are killed by any antiseptic 

 vapour, such as that of toluene, or heating the soil to -55° 

 to GO" C. ; they suffer considerably when soil is maintained 

 at even lower, but still higher than the normal, temperatures 

 (e.g., tO° C. for a sufficient length of time). Cooling to low 

 temperatures also depresses them, although it fails to kill 

 them. 



Once the detrimental organisms are killed, the only way 

 of introducing them again is to add some of the untreated 

 soil. 15ut the extent ot the transmission is apt to be erratic, 

 being sometimes more and sometimes less nearly complete 

 than at others. The precise conditions governing the 

 reintroduction have not yet been learned. 



The authors provisionally identify the detrimental 

 organisms with the active protozoa, but as the zoological 

 survey of the soil is yet incomplete, they do not commit 

 themselves to any particular organism or set of organisms, or 

 to any rigid and exclusive definition of the term protozoa. 



The increase in the number of bacteria following partial 

 sterilization by volatile antiseptics is accompanied by an 

 increase in the rate of ammonia production until a certain 

 amount of ammonia or of ammonia and nitrate has accumu- 

 lated, when the rate falls. Thus two cases arise: (1) when 

 only small amounts of ammonia and nitrate are present; here 

 the increase in the number of bacteria following on partial 

 sterilization causes a corresponding increase in the amount of 

 ammonia and nitrate; (2) when large amounts of ammonia 

 or of ammonia and nitrate are present, the increased numbers 

 of bacteria then causing no corresponding increase in the 

 amounts of ammonia and nitrate. There is a fairly well- 

 marked limit beyond which the accumulation of ammonia 

 and nitrate will not go, although bacterial multiplication 

 may still continue. The limit varies with the composition 

 and condition of the soil. 



Complications are introduced when the soil has been 

 partially sterilized by heat, because heat affects an obvious 

 decomposition of the organic matter, thus changing the .soil 

 as a medium for the growth of micro organisms. The 

 bacterial flora is also very considerably simplified through 

 the extermination of some of the species. These effects 

 become more pronounced as the temperature used is higher, 

 and the tendency is to reduce the numbers of bacteria. 

 Maximum numbers of bacteria are found in soils that have 

 been heated to the lowest temperature necessary to kill the 

 detrimental organisms (about 60°C.). In this case the 

 bacterial numbers and the rate of decomposition are similar 

 to those in soils that have been treated with volatile anti- 

 septics, and the relations between th^ numbers of bacteria 

 and the decomposition noted under (1) and (2) above also 

 hold. No relation was found, however, between the numbers 

 of bacteria and the decomposition in soils that had been 

 heated to 100°C. In this case, although the number of 

 bacteria was at a minimum, the decomposition effected was 

 at a maximum. When the bacteria are re-introduced into the 

 partially sterilized soil by the addition of untreated soil, a still 

 further production of ammonia and nitrate is brought about, 

 unless too large a quantity of those substances is already 

 present; but the depression in bacterial numbers that follows, 

 owing to the detrimental organisms being re-introduced at the 

 same time, generally does not. check the decomposition owing 

 to it< having already gone near to the limit before the check 

 could take effect. 



