Vol. XI. No. 258. 



THE AGRICULTURAL NEWS. 



83 



evidence based on its behaviour in its own country was 

 brought forward as to the promising nature of the 

 species Castilloa costaricuna. Attention was ^ven, 

 further, to Funtumia elastica as a rubber pro- 

 ducer; close planting is best for this species, but even 

 under the most favourable conditions, as far as experi- 

 ence in Trinidad is concerned, the yield of rubber is 

 small and the product poor, quickly becoming tacky. 



Finally, in relation to rubber, opinions were 

 expressed as to the future of the industry that may 

 develop in the West Indies, and to the likelihood 

 of the serious competition of the artificial with the 

 natural product. As far as the first is concerned, 

 it is likely that plantations in the West Indies 

 will never have to compete directly with those in the 

 East; the competition will almost certainly be only with 

 the South American production, which suffers under 

 the disadvantages of the existence of export taxes and 

 of scarcity of labour. With regard to synthetic rubber, 

 any large manufacture of this is bound to increase its 

 price by enlarging the demand for the material — tur- 

 pentine — from which it is made; and while the practica- 

 bility of the ultimate extensive production of the com- 

 modity is not denied, it is likely that many years will 

 elapse before it will be conducted on such a scale as to 

 affect the interests of the grower of rubber. 



The business of the succeeding sessions had refer- 

 ence to the consideration of matters that are not con- 

 cerned purely with agricultural production. This article 

 therefore completes the series, commenced in the last 

 issue but one of the Agricultural News, in which it 

 has been intended to present a broad summary of the 

 results of the discussions at the recent Agricultural 

 Conference. 



THE FORMATION OF CALCIUM 



CARBONATE IN THE SOIL 



The Journal of Agricuhurnl SrivKcc for October 1911, 

 contains a paper, bearin? this title, which describes work that 

 was carried out at the suggestion of A. D. Hall, for the 

 purpose of ascertaining the nature of the organisms which are 

 concerned with the conversion of calcium oxalate into calcium 

 carbonate, in the soil. 



The paper commences by pointing out that some of the 

 processes in the soil tend continually to diuunish the amount 

 of calcium carbonate in it; nevertheless, soils remain fertile, 

 when in a normal condition, without additions of calcium c ir- 

 bonate. This suggests that there is a balancing action, by 

 means of which the calcium carbonate withdrawn is supplied 

 from another source, or sources. The first stage in the inves- 

 tigation was a repetition of Hall and Millers experiments to 

 show that organisms capalile of fermenting calcium oxalate 

 to carbonate are present in the soil. A culture solution con 



taining the necessary mineral salts, and including ammonium 

 sulphate, as well as glucose for providing a certain amount 

 of soluble organic matter to assi.st in the commencement of 

 the growth of the bacteria, was employed. A definite amount 

 of calcium oxalate was added to this, and it was inoculated 

 with soil and placed in an incubator at 2.5° C. In a period 

 varying from three to five weeks, it could be shown th it most 

 of the calcium oxalate had disappeared, and small crystals "f 

 calcium carbonate were found, mostly on the bottom and sides 

 of the flasks. The observation was completed by determining 

 by suitable means the amount of calcium o.xalate left. 



There is reference to the fact that attempts had been 

 made previousl}', by Mr. A. Amos, B.A., to bring about this 

 change in calcium oxalate, in pure cultures of various bacteria, 

 and that the only one with which he obtained any success 

 was the nitrogen-fixing organism, AioloUifter chroococcum. 



The authors made further investigations on these lines, 

 but found that, although a large number of bacteria, yeasts 

 and moulds were tested in pure culture, none seemed to be 

 able to effect the decomposition of the calcium oxalate. 

 In the nutrient solution containing ammonium sulphate, 

 there was usually little or no growth, among the species 

 exhibiting the latter characteristic being Azotoliarter chroo- 

 coccum. In cases where no growth occurred, a strong culture 

 of the organisms was taken, and aftpr a small quantity of 

 sterilized calcium oxalate had been introduced into it, the 

 flask was kept in an incubator for some lime. It was only 

 in cultures of Azotobacter that any conversion to calcium 

 carbonate took place, and this was only after all the soluble 

 organic matter had been exhausted; the observation of Amos 

 was thus confirmed A list is given of the organisms that 

 did not show any power of decomposing the calcium oxalate. 



The first attempts that were made for the purpose of 

 isolating from the soil an organism that is responsible for the 

 change were unsuccessful; better results followed the use of 

 a clear water extract of soil in the place of the amraoniacal 

 nutrient solution described above. 'The results were similar 

 whether the extract was prepared from a somewhat stiff loam 

 or from a light sandy soil, the production of carbonate being 

 however more rapid in the case of the sand, which was 

 extremely poor in organic matter. The lack of much soluble 

 organic matter seems to throw the organisms back on the 

 oxalate for their supply of carbon.' The action was shown 

 not to be due to enzymes, by making similar experiiiieuts in 

 which toluene or chloroform, as an antiseptic, was added to 

 the solution: when there was no formation of carbonate, even 

 after six weeks 



The solutions in which the change had been brought 

 about were used for making plates in ordinary gelatine or 

 agar nutrient media, and in most instances only one, two or 

 three types of colonies developed. The organisms were 

 obtained pure by sub culturing, and inoculated in fairly large 

 amounts into sterile soil extract containing calcium oxaldte 

 in suspension. In the result, six types of bacteria were 

 isolated, which possessed the power of changing calcium 

 oxalate to the carbonate. The rate at which the change focik 

 place varied considerably at different times, under similar 

 conditions, and appeared to be affected by the kind r,f 

 medium on which the organism had been grown previc.us^y. 

 An impure culture was found, on the whole, to bring about 

 the change more quickly than any of the pure cultures, and 

 in no case was the carbonate formed unless oxygen was 

 present. 



The conclusion is reached that it seems probable that 

 a number of bacteria in the soil are able to oxidize calcium 

 oxalate, if the lack of other food makes it necessary for them 

 to employ it in nutrition. 



