226 



THE AGRICULTURAL NEWS. 



July 20, 1912 



importance. Russell and other experimenters are not, 

 however, prepared to agree as to the relative insignifi- 

 cance in which the effect of the chemical properties of 

 soils on their fertility is held by Whitney and others. 

 The simplicity of the composition of the coarser soil par- 

 ticles is not possessed by those that are of the smallest 

 dimensions, and investigation is tending to show that 

 their smallness of size will not accouiu alone for their 

 properties. Those who have madi' the chemical inves- 

 tigation of soils a large part of their work are most 

 prone to follow van Bemmelen in his view ihaf, in the 

 soil, the various decomposition products are largely 

 deposited on the particles in a special state known as 

 the colloidal form, the matter of importance being that, 

 owing to their condition, changes of temperature, of 

 strength of the soil solution, and other circumstances, 

 cause the continuous further decomposition of these 

 products, rather than any sudden completed changes 

 in them. It is therefore the composition of this mixture 

 of colloidal products that determines the strength of 

 the soil solution, so that the latter may be altered to 

 a certain extent by the addition of soluble salts, includ- 

 ing artificial manures. 



This view is thus seen to depend upon the cir- 

 cumstance as to whether or not the strength of the 

 soil solution is constant, and thus great importance 

 attaches to the investigation of this matter. Chemical 

 examination of the solution itself is so far impos- 

 sible because no means has been devised for its 

 extraction from the soil. If well water or the soil 

 surface drainage water are taken to be representative 

 of soil water, then there is a large amount of evidence 

 that its composition does vary considerabl}', and this is 

 true even when consideration is given to the figures upon 

 which Whitney based his contrary conclusion — that the 

 composition of the soil water is virtually constant". The 

 observations and experience of Russell and others lead 

 to the view that the strength of the soil solution is 

 dependent upon the amount of carbon dioxide present 

 (which depends in turn on the distribution of roots 

 and living beings in the soil), on the disposal of 

 water and of calcium carbonate, and on other factors. 

 There is the further consideration that, even if it were 

 possible to obtain .some of the soil water by itself, for 

 analysis, it would not necessarily follow that the 

 average composition found would be that of anything 

 occurring in the soil. 



The argument advanced against these criticisms is 

 that, even where the strength of the soil solution may 

 vary, the differences are without effect on fertility, as 

 they are incapable of influencing the growth of plants- 



The opponents of Whitney, again, cannot agree with 

 this view of the matter, and point to the fact that the 

 amount of growth of plants in nutrient solutions 

 increases with the strength of these, up to a certain 

 limit of concentration. Further, the concentration 

 may be increased beyond this limit, over a fairly wide 

 range, without causing any enhanced growth, and this 

 is why e.x-perimeiits in plant physiology may be cirried 

 out with a number of culture solutions possessing 

 different strengths; there is, however, nothing to show 

 that the concentration of the soil solution approaches any 

 of these strengths. In relation to the action of manures, 

 it is difficult to, deny to these the effect of increasing 

 directly the fertility of the soil, especially as all the 

 substances employed in this way are particularly rich 

 in the very bodies that are necessary for the nutrition 

 of plants. Whitney, even, holds that this action is 

 complex, and it is not obvious why their nutritive 

 function should not be agreed to exist as part of this 

 complexity. 



The theory that infertile soils contain substances 

 classed generally as toxins, that are poisonous to plants 

 is held to be supported by the circumstance that 

 organic substances possessing such poisonous properties 

 have been isolated from the soil. Though these may 

 be toxic in water cultures, it does not follow that they 

 retain the property in the soil; in fact its removal has 

 been demonstrated by the addition of various sub- 

 stances, and even of soil itself. So that it has not been 

 proved that toxic substances taken from the soil have 

 been affecting injuriously the plants in it, though the 

 fact is admitted that soils poor in calcium carbonate 

 have given indications of the presence in them of such 

 substances. Agreement with Whitney is therefore 

 expressed: that in soils deficient in calcium carbonate 

 — 'sour' soils — infertility may be caused by the presence 

 of toxic organic bodies. 



Russell and other investigators have found no 

 evidence whatever of the existence of plant excretions 

 in the soil. Experiments have been made at Rotham- 

 sted in which plants were grown continously in nutrient 

 solutions, in sand cultures and in soils, and no signs 

 were obtained that the later plants suffered fi-om 

 excretions of the firs^t. Interesting particulars of other 

 trials from which the same result was obtained are 

 given in the article quoted; all lead to the significant 

 statement; 'it is asserted by the American workers 

 that the continued growth of one and the same crop on 

 the same soil leads to a low crop production, whilst we 

 on this side are unable to obtain any evidence to this 

 etfjct.' It must be realized at the same time that the 



