THE AGEICULTUEAX, NEWS. 



Ffbeuaey 26, 1916. 



PLANT DISEASES. 



THE EFFECT OF SULPHUR ON CROPS. 



In connexion with the use of sulphur as a fungicide or 

 iiii^ecticide, the question sometimes arises as to the direct 

 f tt'tct of its application to the soil. It has often been remarked 

 that certain crops so treated liave shown a marked improve- 

 ment in appearance, apart from the benefits derived from the 

 check to the pest or disease towards which the treatment is 

 directed. 



The subject is still far from lieing fully investigated, but 

 papers have recently appeared which afford some information 

 upon it. 



It is clear that the effect is liable to wide variations, 

 ranging from toxicity to highly beneficial action, according to 

 the species of plant and the composition of the soil concerned. 



It has been shown that elemental sulphur added to the 

 soil gradually undergoes oxidation to sulphates, in which 

 form it serves as a source of supply for the sulphur needed in 

 certain organic compounds. There would appear to be 

 danger from acidity unless lime is present in the soil, or is 

 added along with the sulphur, and danger even in the 

 presence of lime from the intermediate formation of sulphites. 



In a series of plot experiments on Leguminous, Crucifer- 

 ous, and Graminaceous plants it was indicated that growth 

 in certain cases in the first two orders was measurably 

 increased by the addition of sulphates, and in both barley and 

 oats seed production was stimulated. Calcium sulphate was 

 more effective than the more soluble sodium sulphate. 

 Elemental sulphur was generally harmful. In field trials on 

 alfalfa in Oregon, the use of eitlier sulphur or sulphates has 

 given increased yields, amounting in a number of instances to 

 from 200 to 300 per cent., and in one case, with iron sulphate, 

 to 1 ,000 per cent. 



It has been contended that apart from its manurial 

 effect, sulphur acts on the soil flora and stimulates the break- 

 ing down of organic matter, and it has been shown that very 

 heavy applications (900 B). per acre) while highly injurious 

 on poor soils, had no ill effect on a loam rich in humus. 



It would be interesting, especially in view of the 

 existence of local sources, to study the effect of sulphur in 

 tropical soils. 



A Chart of Tropical Plant Diseases.— A copy has 



been received from the Hoard of Agriculture of British Guiana 

 of a chart, measuring approximately 2 x 21 feet, entitled. 

 The Fungoid Diseases of Garden and Field Crops in British 

 Guiana, prepared by C. K. Bancroft, M.A., F.L.S., Govern- 

 ment Botanist. The middle of "the sheet is occupied by 

 parallel columns giving, opposite to crop headings, a list of 

 diseases under their common names, short diagnoses for 

 their identification, and condensed instructions for treat- 

 ment. The bud-rot of coco-nuts, for example, is dealt with 

 as follows: — 



DEscisii'i'ioN. 'Appearing usually in trees which are 

 liearing, younger trees being frequently free of the disease. 



'Young and immature nuts frequently fall. 



'Flowers blacken and die, sometimes before the sheath 

 opens. 



'Leaves break and hang down, frfi|ucnt!y yellowing 

 previously. 



'The bud finally rots and emits an offensive smell.' 



TREATMENT. 'Drain well and practise good cultivatioir. 

 methods which will establish a good growth of the trees. 



'In trees recently affected, a bag of common salt may be 

 tied to the central shoot above its base. 



'Dying and dead palms .should be cut down at once and 

 the crowns and trunks burnt or buried in the ground.' 



The marginal columns of the chart contain instructions- 

 for the preparation and application of fungicides, and a note 

 on Plant Sanitation and the Nature of Diseai^es in Plants. 



W.N. 



SOLUBILITY OF ROCK IN PURE WATER. 



Professor J. B; Harrison, C.M.G., M.A., Director 

 of the Department of Science and Agriculture, British 

 (luiana, has furnished this Office with the following 

 extract from a paper by him, published in the Geologi- 

 cal Magazine, Vol. VII (1910), concerning the very 

 interesting subject of the solubility of rock constituent* 

 in pure water. It will be realized that tl>e action 

 referred to results in only minute quantities of mineral, 

 matter being dissolved at any one time. Nevertheless, 

 with continually repeated washings a very large quan- 

 tity will become dissolved, resulting eventtially in com- 

 plete degradation of certain rocks. The nature of the 

 action concerns the interchange of 'ions' between the 

 water and the salts in the rocks. It is a phenomenon 

 which does not appear to have received the recog- 

 nition it deserves as being important in the weath- 

 eiing of rocks and consequent improvement of soil 

 fertility: — 



Some ten or eleven years ago, whilst lecturing on 

 agricultural science, I used the following experiment to 

 illustrate the action of pure water on rock. Itock powder 

 was prepared from various tyjies of rock by grinding on 

 a bucking plate. About 2(1 grams of the rock powder 

 was placed in a beaker, and from 100 to 1-50 c.c. of cold^ 

 recently boiled distilled water poured on it. To the water 

 thus freed from carbonic acid a few drops of a solution of 

 phenol-phthalin were added. In the course of a few minutes 

 the water commenced to change to purple, and after ten 

 minutes or so had elapsed, the depth of colour produced 

 served as a measure of the rates of decomposition of the 

 various rocks by the water. I found that the most readily 

 decomposable rocks Irere felspar-porphyry and porphyrite, 

 the next being granitite-gneiss, followed by granite 

 and granitite. The basic rocks were more slowly attacked 

 by the water. After standing for some time when the 

 colour of the water had ceased to deepen, it was poured or 

 filtered eft' completely, the rock powder again treated with 

 fresh quantities of "the boiled water and phenol-phthalin, 

 when the gradual colourization again ensued. This, if 

 desired, could be repeated many times, using the same rock 

 powder. The experiments well illustrated the action of 

 water free from carbonic acid on the rocks, and its repetition 

 with successive <iuantities of water showed it to be a mass 

 action The rates of decomposition of the various rocks 

 thus indicated were found to correspond with the extent of. 

 their denudation and degradation on the lower-lying lands of 

 the colony. 



