413 



[May, l9ia. 



SCIENTIFIC AGRICULTURE, 



NATURAL STERILISATION OP SOIL. 



(From the Gardeners' Chronicle, Vol. 

 *LVII., No. 1211, March, 1910.) 

 As our readers are aware, experiments 

 carried out by Messrs. Russell and 

 Hutchinson at Rothamsted have thrown 

 an entirely new light on the origin of 

 the enhanced fertility brought about by 

 soil-sterilisation. That soils sterilised by 

 heat or by certain poisons such as 

 carbon-bisulphide yield larger crops 

 than similar unsterilised soils has been 

 demonstrated by various observers. A 

 full account of the explanation, given 

 by the authors just referred to, of the 

 mode of action of the sterilising agent 

 was published in these columns on 

 October 23, 1909. Briefly, it amounts to 

 this, that heat or poisons kill out those 

 organisms, such as amasbae and in- 

 fusoria, which normally prey on the soil- 

 bacteria. Certain of the soil-bacteria are 

 also destroyed. Those which remain 

 have the fidld to themselves, and hence 

 increase and multiply exceedingly. In 

 the absence of competing organisms, the 

 supplies of nitrogen-compounds in the 

 soil are the more available for the crop, 

 which, in consequence, flourishes more 

 abundantly in the sterilised soil than 

 in one in which occur multitudes of 

 organisms all hungry for nitrogen. The 

 nitrogen compounds of the soil go into 

 the plant instead of being shared 

 between the plant and the teeming 

 " population " of the soil. An interest- 

 ing application of this sterilisation 

 hypothesis is made by Messrs A. & G. L. 

 Howard in a recent issue of Nature. 



It appears, according to these authors, 

 that the Indian ryot has practised a 

 kind of summer fallowing or weathering 

 from time immemorial. During the 

 months of April and May he exposes the 

 alluvial soil of the Indo-Gangetic plain 

 to the burning sun. Where the soil is 

 light it is ploughed by means of the 

 native wooden plough ; where it is 

 heavy, it is, however, not worked — 

 owing, apparently, to the lack of suit- 

 able tackle— until the arrival of the 

 monsoon rains. 



The effect of the exposure of the 

 worked, light soil to sunlight is remark- 

 able, the beneficial result on the succeed- 

 ing crop being equal to that which would 

 be obtained by the application of nitro- 

 genous manure. Messrs. A & G. L. 0. 

 Howard suggest that the effect of the 

 intense sunlight i9 to partially sterilise 

 the soil, and thus to induce in the soil 

 similar changes in micro-flora and fauna 

 as are effected by artificial sterilisation. 



Thus, if we accept this explanation, 

 the summer weathering has precisely the 

 same effect as a dressing of nitrogenous 

 manure, in that it renders nitrogen com- 

 pounds available to the crop. The des- 

 tructive action of sunlight on bacteria 

 has been demonstrated experimentally, 

 and is, of course, exploited constantly 

 by thrifty housewives, as, for example, 

 in exposing bedding and other house- 

 hold effects to bright sunshine. 



The detailed effects of sunlight on soil 

 bacteria have not yet been investigated. 

 We may predict confidently that results 

 of the greatest practical importance will 

 be obtained from such investigations. 

 It is, at all events, probable that the 

 secret of the origin of the nitrate beds of 

 S. America, whence are derived the bulk 

 of our supplies of nitrate of soda, is 

 bound up with the partial sterilising 

 effect of sunlight. 



Nor is it at all impossible that the soil 

 lying in the deep shade of trees might 

 not be ameliorated by sterilisation. 

 Anyone who has the opportunity might 

 well try the effect of sterilising such 

 soils in, which little will grow, by means 

 of copious waterings of carbolic acids or 

 permanganate of potash, and then 

 determining whether grass and other 

 plants would not succeed better than in 

 similar unsterilised soils, Of course, it 

 is not suggested that shaded soil so 

 treated will become fully fertile, for 

 evidently sterilisation cannot serve ' a 

 plant in lieu of sunsnine : nevertheless, 

 it is probable that some amelioration 

 might be effected. In any case, the 

 investigation of the bacterial flora of 

 the soil, which is bound to be of no small 

 service to horticulture, should receive a 

 powerful stimulus from the work of 

 Messrs. Russell and Hutchinson. 



AGRICULTURAL CHEMISTRY. 



(From the Chemist and Druggist, Vol. 

 LXXVI., No. 1566., January, 1910.) 



In the current number of the "Board 

 of Agriculture Journal," there is a paper 

 by Mr. E. S, Salmon, F.L.S., Mycologist 

 to the South Eastern Agricultural Col- 

 lege, Wye, Kent, on "The Making and 

 Application of Bordeaux mixture." 

 This subject is dealt with in the 

 Chemists' and Druggists' Diary, 1910, 

 but it is useful to emphasise anew 

 some of the points referred to in Mr. 

 Salmon's paper. The Bordeaux recom- 

 mended for spraying fruit-trees is of 

 the strength known as 4-4-50 (Imperial), 

 and the importance of using wooden 

 vessels is urged. The mixture should 

 always be freshly made, as it is diffi- 



