Vol. XI. No. 255. 



THE AGRICULTURAL NEWS. 



39 



THE QUANTITY OP SULPHUR IN SOILS. 



The A'jricidtimil Siivs of August 5, I'.ill, contained an 

 editorial article which pointed out that the importance of sul- 

 phur in the life of the plant had been under estimated, chieHy 

 because the methods of analysis commonly employed do not 

 serve for the detection of the whole of the quantity of that 

 element that is present: certain proportions are lost during 

 the manipulations concerned in the investigations, and are 

 therefore not accounted for in giving the results. 



The matter obtains further attention in an article by 

 V. de Sornay, Assistant Director of the Station Agronomique, 

 Mauritius, in the Intnnntioiml hwjar Journal ioi September 

 1911, which describes work devised to show thJK' the method 

 that is used for ascertaining the quantity of sulphur, as sul- 

 phuric acid, in soils, does not succeed in presenting a true 

 idea of the proportion of the element that i> present. 



It is first pointed out that, in Mauritiu.s, certain varieties 

 of sugar-cane take up a greater amount of sulphuric acid than 

 of phosphoric acid, frnm the soil; while in Hawaii the con- 

 trary condition ol)t'jins In both cases, the sulphuric acid 

 content of the leaves is about the same. Analyses of rain- 

 water in Mauritius have shown that this contains an amount 

 of sulphuric acid that serves to supply over 50 lb. of sulphuric 

 acid — equivalent to more than four times as much sodium 

 sulpbate^per acre; so that rain is a by no means unimportant 

 source of the sulphur required by the cane. Humus contains 

 a proportion of sulphur which becomes useful to plants by 

 being o.xidized to sulphates, in which form it is absorbed. 

 The special usefulness of the element for plants is constituted 

 in the fact that it is necessary for the formation of the im- 

 portant nitrogenous bodies known as albuminoids. 



In methods for estimating sulphur in .soils which entail 

 the use of concentrated nitric acid as a first step, the presence 

 of iron and aluminium in high proportions is sufKcient to 

 prevent the sulphur compounds from being completely dissol- 

 ved, so that they are not detected subsequently. When 

 hydrochloric acid is used, the preliminary solution is more 

 efficient, owing to the greater .solubility of iron and alumin- 

 ium in that acid. That this condition obtains in practice 

 was shown by extracting a sample of soil with nitric acid, 

 and then treating the insoluble residue with hydrochl"ri'^ acid, 

 when in all cases it was demonstrated that the employment 

 of nitric acid had not been sufficient for the solution of the 

 .sul|ihur. Further, calcination always gave still higher figures 

 for the sulphur content of the soil, because it causes the 

 oxidation of the organic sulphur that is present and. in addi- 

 tion, assists in the dissolving action of the acids that are 

 employed subsequently. There are losses, however, even 

 when calcination is used, for the carbon present causes reduc- 

 tion to sulphides, which are diiveii otl' liy heat, and the high 

 temperature is also sufficient to cause volatilization of the 

 sulphur contained in some of the organic matter in the soil, 

 before this can become oxidized, and fixed. 



'J"he researches of the author have led to the adoption of 

 a method of determining sulphur in soils, in which the effi- 

 ciency of calcination is increased by mixing with potassium 

 nitrate the samples taken, before they are heated, so that 

 complete oxidation to sulphate is obtained. Cases have been 

 found, however, in which the use of potassium nitrate in this 

 way did not result in the detection of sulphur in greater 

 amounts than those given when it was not employed, and 

 these occurred chietly in regard to examples that did not 

 possess a high humus content. 



The advice finally given in regard to tha.matter is that, 

 for the determination of sulphur in soils, calcination should 

 be carried out after the addition of potassium nitrate, and 

 that extraction of the calcined mass should be effected with 



hydrochloric acid. Details are presented of the manipulatioD 

 required in the adoption of this method. 



BENEFIT TO CROPS FROM GROWING 



THEM WITH LEGUMES. 



Work has been done recently at the Agricultural 

 Experitneiit Station of the College of Agriculture, 

 Cornell I'niversity, for the purpose of ascertaining, on 

 a practical .scale, if the growing of leguminous crops 

 with other plants results in any benefit to the latter 

 besides that arising from the addition of nitrogen that 

 legumes are able to effect with the aid of the nodule 

 organisms in the roots. A positive answer to the ques- 

 tion appears to have been obtained, and this is expressed 

 in the following way, in a summary to Bulletin Xo. 294 

 of the Station, flealing with the work :— 



Timothy grown with alfalfa contained a greater percent- 

 age of protein than did timothy grown alone. The same was 

 true of timothy grown with red clover. 



Oats grown with peas had a higher protein content than 

 oats grown alone. The yield of the mixed oats and peas, 

 when cut for hay, was considerably greater than the yield of 

 oats alone. 



The increased value of the non-legume, due to its greater 

 nitrogen content, when grown with a legume, is of some 

 economic importance. A method for increasing the protein 

 content of certain forage crops by growing them with legumes 

 is thus suggested. 



The increased sujjply of available nitrogen, which these 

 results indicate to be due to the presence of the legume, must 

 have a verj- important influence on the yield of the non- 

 legume on soils where nitrogen is the limiting factor in the 

 growth of the crop. 



Soil on which alfalfa had grown for five years contained 

 more nitrates than did soil which had grown timothy for the 

 same length of time. Sections of these same plants kept bare 

 of vegetation for the summer gave similar results. 



The rate of nitrification of ammonium sulphate was 

 greater in alfalfa soil than in timothy soil, thus indicating 

 an influence of the plant on the conditions favouring nitrifi- 

 cation. The higher protein content of non-legumes growing 

 with legumes than of the non-legumes growing alone is 

 probably due to the more active nitrification caused by the 

 presence of the legume. 



The nitrifying power of a soil which grew alfalfa for five 

 years and which was then kept bare of vegetation for a sum- 

 mer was greater than that of adjacent plots on which 

 timothy had been grown for the same length of time, and 

 which was likewise kept bare for a summer. This indicatps 

 a benefit arising from the infiuence of the legume on the 

 rate at which nitrification goes on in the soil even after tlie 

 crop has been removed. 



Alfalfa grown on .soil in need of lime contained a higher 

 percentage of protein when lime was added to the soil than 

 when none was added. The weed Erigemn annuux growing 

 with the alfalfa possessed a higher protein content when 

 grown on the limed .soil Ammonium sulphate, when added 

 to the limed and to the unlimed .soil, nitrified more rapidly 

 in the former. 



The greater protein content of a non legume when growa 

 with a legume on a soil containing sufficient lime, as com- 

 pared with one deficient in lime, is apparently due to the 

 more abundant formation of nitrates under these conditions.- 



