[July, 1909. 



SCIENTIFIC AGRICULTURE 



THE CAUSE OF INFERTILITY 

 IN SOILS. 



By C. Dbiebbrg 



(Paper read at the Annual General 

 Meeting of the Agricultural Society on 

 June 8, 1909.] 



This brief note deals with a subject of 

 the very greatest importance to the 

 agriculturist, and upon which important 

 deliverances have recently been made 

 by two leading schools of scientific 

 thought. 



The cause of infertility and the means 

 of maintaining fertility in cultivated 

 land have been matters for great diver- 

 gence of opinion from the time of de 

 Candolle and Liebig to the present day. 

 Within comparatively recent times the 

 purely chemical theory of soil exhaustion 

 has had to be modified so as to admit 

 the all-important influence of bacteria 

 in their relation to the soil and plant. 

 More recent researches in America by 

 Whitney and Cameron have tended to- 

 wards what may be said to be a rever- 

 sion to de Caddolle's excretory theory, 

 and the attributing of infertility to an 

 insanitary state of the soil arising from 

 the presence of toxic bodies consisting 

 of plant excreta. The means of main- 

 taining a sanitary condition are said to 

 be aeration provided by proper culti- 

 vation, rotation of crops, green manur- 

 ing, and the judicious use of fertilizers — 

 all of which, according to the American 

 view, act directly or indirectly as cor- 

 rectives or disinfectants, and result in 

 the soil being purged of the poisonous 

 substances which reduce the yield of 

 crops grown continuously on the same 

 land, or cultivated without due regard 

 to the requirements of the soil. The 

 American school goes so far as to deny 

 that soil exhaustion in the chemical 

 sense of the term takes place at all, since 

 all soils contain solutions sufficiently rich 

 in the elements of plant food to nourish 

 a full crop, provided some other factor 

 does not come into play. Humus as an 

 ingredient of soil is looked upon as a 

 sort of "cure-all," giving to it those 

 qualities which make for sanitation and 

 productivity. 



The above is a very brief statement of 

 the American theory of infertility in 

 soils. 



The British view of the question is 

 that expounded by Hall of Rothamsted. 

 He is not prepared to allow all the deter- 

 minations claimed by the American 



scientists, and certainly does not agree 

 with their theory of plant food, and the 

 denial of its exhaustion ; but, on the 

 other hand, recognizes the need there is 

 for some fertilizing agents, of which the 

 composition has to be determined more 

 by the soil than the plant, to rectify the 

 deficiencies of the soil as regards the re- 

 quirements of the crop in question. A 

 knowledge of these requirements can, 

 we are told, only be decided by experi- 

 ment, with a view to ascertaining the 

 " idiosyncracies " of plants which are 

 sometimes somewhat paradoxical (note 

 the attitude of wheat and swedes to- 

 wards phosphoric acid. 



The best notion of fertility, according 

 to Hall, is got by extending Liebig's "law 

 of minimum" to all factors affecting 

 yield— plant food, temperature, soil tex- 

 ture, water supply, &c. 



Hall finds fundamental difficulties in 

 accepting the poison theory. In fact, he 

 doubts whether the toxins extracted by 

 Whitney were really excreted by the 

 roots, and whether theyj are really toxic 

 in the soil because they were found 

 so in dealing with seedlings and through 

 water culture. He instances the case of 

 ammonia under similar conditions. 



Experience in the continuous and suc- 

 cessful cultivation of wheat at Rotham- 

 sted for fifty years with proper culti- 

 vation and fertilizing, in his opinion, 

 negatives the excretory theory. 



He is prepared to admit that there is 

 such a thing as the "sickness" of land 

 which is kept continuously under one 

 crop, and further that most crops (some 

 specially so) effect changes in the soil 

 which unfit it for the continued growth of 

 thecrop. This injurious factor may be the 

 excreted toxins of the American theory 

 or some " secondary effects due to the 

 competition of injurious products of bac- 

 teria and other micro-flora " in the soil. 

 If we assume that there is some kind of 

 "debris "(not of the nature of excreta) 

 left by the plant as the result of bac- 

 terial action upon it, we may, he thinks, 

 ultimately obtain a clue to certain pheno- 

 mena at present imperfectly understood. 



The value of a rotation is readily ad- 

 mitted, but its beneficial effects are 

 attributed mainly to good tillage and 

 the clearing away of weeds, insects and 

 fungoid pests, though, it is thought, 

 there may possibly also be certain bene- 

 ficial effects beyond these. It is also ad- 

 mitted as possible that there is a clue in 

 " disinfection " of so mo kind, as indicated 

 by the iacrease of fertility which follows 



