Vol. XI. No. 266. 



THE AGRICULTURAL NEWS. 



211 



number of surfaces which hold the soil moisture and 

 enable it to travel to the places where it is required. 

 Thus the differences shown by soils, with respect to 

 their fertility, ^r usefulness to plants, are not due to 

 variation in the compusition of the soil (solution, as this 

 does not exist: but to the efficiency of the soil as a 

 water-carrying medium — a characti-ristic depending on 

 the nature of the mineral particles and on the presence 

 of organic matter, as well as other circumstances. All 

 this means that it is argued that fertility does nut 

 depend on the chemical composition of the soil, for the 

 constitution of the soil solution is the same in all soils; 

 and even if it were not, differences in composition 

 would have no influence on plant growth. 



The holders of this view of soil fertility were soon 

 confronted by special instances that did not bear them- 

 selves in accord with the simple e.xjilanation. Cases 

 were adduced in which soils possessing very similar 

 physical characteristics showed striking differences in 

 fertility, either when plants were grown in th<' soils 

 themselves or when they were raised in solutions ob- 

 tained by extracting the soils with water; as was ex- 

 pected, however, these solutions were found on an.tlysis 

 to be similar in composition. It was therefore con- 

 cluded that the infertility of the poor soil could not be 

 due to any deficiency in its content of plant food, so 

 that another cause must be found. The short explana- 

 tion may be made that, as the result of a large amount 

 of work in connexion with the matter, carried out both 

 in the United States and other countries, it was sup- 

 posed that the inferiority of the poor soil in such c:i3es 

 is due to the presence of some organic substance that is 

 a poi.son (toxin) in relation to the life of the higher 

 plants. The solution obtained by treating such soils 

 with water was so poisonous to plants in some cases 

 that they were found to develop to a greater degree in 

 distilled water than in the solution. This toxicity 

 could be reduced in various ways, such as diluting the 

 solution, shaking it with various substances and bodies, 

 and adding artificial or natural manures — the latter 

 kind being the more efficient. 



All this led to the suggestion by Whitney that 

 the infertility of soil is caused by the presence of toxic 

 bodies, probably of an organic nature; and the next 

 step in the investigations was to find, by means of 

 water cultures, the effect on plant growth of organic 

 substances likely to occur in the soil, and to try to dis- 

 cover in the soil itself such organic compounds among 

 these as had been identified. Several of these bodies 

 were found and examined, and it was demonstrated 



that a toxic water solution in which two crop3 are 

 grown is less poisonous to the second than to the first — 

 piobably because of the oxidizing action of the roots 

 that had already developed in it — and that this action 

 was especially powerful in the presence of manure. 

 The attempt to find harmful organic compounds in the 

 soil resulted in the isolation of several such substances, 

 one of which — dihydroxystearic acid — received special 

 investigation.* Attempts to find the way in which 

 these poisonous compounds are formed in the soil led it 

 to be concluded that some arise from the decomposition 

 of organic matter already present, and that others are 

 excreted by plants; the latter consideration led to the 

 revival of the old supposition of de Candolle that, 

 while such products may be harmful to the kind of 

 plant that produces them, they may not necessarily 

 interfere with the growth of other kinds — a supposition 

 that was brought forward to explain the decreases 

 in yield that sometimes take place when the same 

 soil is used for growing successive crops of the 

 same plant. Lastly, it was suggested, as a result of 

 all the work that has been reviewed, that the bene- 

 ficial action of manures arises — not because they feed 

 the plant — but because they assist in the proper dis- 

 tribution of the soil solution and are effective in 

 destroying the toxic bodies that are formed or pro- 

 duced in the soil. 



What has been said shows the directions in which 

 investigations concerning soil fertility must be made, 

 and presents the conclusions concerning this that 

 have been reached in work which takes account of 

 physical and chemical considerations of the soil, rather 

 than of the effect of the life -processes that occur in it 

 continually. The presentation of the criticism by 

 Russell, of this work and of the views to which it has 

 led, as this is unfolded in the article by that investi- 

 gator, quoted above, is reserved for the next issue of 

 the Ar/ricultural News. 



According to The Board of Trade Journal ior Miy 16, 

 1912, of the exports from Venezuela in 1911, valued at 

 £428,960, classified as being sent to the United Kingdom 

 and British Colonies, about £262,440 went to the United 

 Kingdom and £162,000 to Trinidad. The imports from 

 Trinidad during the same year were valued at about £26,000 

 only, owing to the surtax of 30 per cent, levied in Venezuela 

 on imports from the West Indie.s. 



* Bulletin No 70; Bureau of Soils, United States Depart- 

 mont of Agriculture. 



