Vol. XII. No. 295. 



THE AGKICULTLTRAL NEWS. 



259 



teriologist should give careful attention. As in the 

 case of the chemical c.xamiiiiUion of milk, so in the 

 biological, certain simple ar.il .luick tests have been 

 invented, one of the most useful being the Giir-reduc- 

 tase test, which depends on tht- fact that if a certain 

 colouring matter is added to a .sample of inilk.discoln- 

 ration gradually takes place, the rate depending upon 

 the number of germs originally uresent in the sample. 

 An officer in charge of milk supply would, however, 

 investigate further than this and endeavour to detect 

 any specific disease bacteria in suspected samples. 



The ndministrative side of the subject of the 

 control of milk supply must be li-ft to the local author- 

 ities. Undoubtedly the registration of milk vendors 

 is imperative. But that alone will not safeguard the 

 public. Individual energy backed by technical training 

 must move hand in hand with legislation. What 

 has btcn already said will serve to indicate the 

 necessity for this control, the proper person under 

 diflferent circumstances to carry it out, and the 

 lines of work to be followed. It remains for those in 

 authority to consider the neces-^ary expenditure, and to 

 take the initiative and start the machinery in motion. 



THE EFFECT OF COMMON SALT ON 

 THE GROWTH OF SUGAR-CANE. 



The island of Porto Iiioo ha.«, in proportion to its size, 

 a considerable area of swamp and niar^h land. The object 

 of the researches which Bulletin No. 4 of the Experiment 

 Station of the Sugar Producers' Association describe.", wis to 

 find out what means exist to make these salt marshes 

 produce cane at a profit. 



The most important point on which a definite decision 

 was necessary, was the exact limit of the cane plant for salt. 

 As regards the effect of salts in general on the grcnvth of plants, 

 sodium carbonate is the most toxic; sodium chloride, sodium 

 bicarbonate and magnesium chloride are less so. Sodium sulp 

 hate and magnesium sulphate are still less harmful, whilst 

 calcium salts are least toxic of all. It is said on the authority of 

 Maxwell, that, in ordinary soils, a percentage of sodium chlo- 

 ride exceeding 15 per cent. (OOi' percent, of chlorine) will 

 prevent a normal growth of cane. In .soiLs whi'-h are well 

 provided with nitrogen, the chlorine content may go 

 higher than O'lS per cent, of sodium chloride with- 

 out causing any harm. If the chlorine is combined 

 mainly with calcium, it may reach higher figures than 

 09 per cent. In Hawaii, it is concluded by Echart, 

 that if the salt content of the soil reaches over 01 

 per cent, an injurious effect is produced on the cane. It 

 appears that cane, in its later stages of growth, may 

 stand a much higher quantity of salt without visible injury. 

 It may further be mentioned in connexion with the point 

 under discussion, that in Jamaica, P.arbado,', Trinidad and 

 Demerara, an occasional flooding with sea-water, or the 

 application of sodium chloride to certain fields has been 

 found actually beneficial. This fact is explained by Prinsen 



(leerligs by the principle that a treatment with sodium 

 chloriile renders the potash, lime and magnesia contained in 

 the soil more available. 



With more particular reference to the conditions of the 

 Porto Itican experiments, the chief difficulty in gauging the 

 total effect of the salt content of the marshes was that the 

 effect of the different salts was not simply additive but rather 

 interactionary. That is to Siy, one salt may intensify the 

 action of others, whereas another one may lessen it. Thus 

 sulphates in general will mitigate the effects of carbonates, 

 bicarbonates and chlorides, nnd calcium salts in general will 

 counteract the influence of those of sodium and magnesium. 

 For this reason it was found very difficult to interpret the 

 results of analyse.'f. Nevertheless by collecting parallel 

 observations on the condition of the cane crops and the 

 composition of the soil of different fields, it was seen at once 

 that a very striking relation existed between the salt content 

 of the soil and the general condition of the cane grown 

 on it. To give but two examples: an area which contained 

 only "01 1 per cent, chlorine, produced as much as 60 tons of 

 cane per acre, wherea-f another containing '188 per cent, 

 chlorine, yielded only "JO tons per acre. Not only does salt, 

 when present in large quantities, lower the yield obtained, 

 but, as is shown by a table in the bulletin, it affects the 

 composition in a most deleterious manner. 



As already indicated, the application of lime greatly im- 

 proves saline soils, as does also the application of nitrogen in 

 the form of dried blood. But the conclusion of the bulletia 

 which is emphasized most, is the necessity for lowering the 

 water level of these .soils by drainage. Such methods are in 

 progress, and are likely to be extended. The id^-a is that 

 good drainage will lower the salt-water level, and enable the 

 excess of salt in the soil to be washed out by natural rainfall, 

 or, if necessary, by the aid of irrigation, until the concentration 

 of the salts falls below the danger point, as indicated by the 

 results described in the bulletin under consideration. 



Composition of Soil Suitable for Rubber 



Cultivation. — The Director of the Agricultural Institute 

 uf the University of Halle, has investigated rubber soils 

 from P>razil aud German East Africa. An interesting 

 abstract of hi.s conclusions are given in the Montli'y BuUethi. 

 of Agrindtwal Intellu/ence and Plant Diseases (.January 

 l913) from which the following notes are taken. 



In comparing the fertility of the soils of the two places, 

 it must be remembered that the annual rainfall in South 

 America is something like 120 inches, whilst in German East 

 Africa it amounts only to about 80 inches. The higher 

 rainfall is believeil to render the nutritive substances more 

 easily assimilated. Apirt from this consideration, Iferea 

 hrasiliensi^ is cultivated in South America, whilst the 

 }[aniho( Glatiovii. which requires a dry climate, is grown 

 in East Africa. Nevertheless, it is believed that generaliza- 

 tions, holding good for East Africa and South America 

 in regard to the soil requirments for rubber producing 

 trees can be formulated from the observations made. 

 These conclusions may be e.xpressed as follows: (1) The 

 soil should be fine, of medium coherence, rather loose 

 than heavy, and deep; (2) it is not necessary that the 

 nitrogen content should be higher than O'l per cent., whilst 

 a large percentage of humus was found to be actually 

 injurious; (3) lime and magnesia are needed only in very 

 limited amounts; (4) the rubber tree appears to have no 

 special requirements as regards the phosphoric content of the 

 soil: (5) it would seem that a large amount of potash in the 

 soil promotes growth and the formation of latex. 



