11 



Professor Hilgard makes some incisive observations with regard to the* 

 threefold differentiation of plant food constituents in soils, which bear 

 directly on what we have said above. In order to appreciate his remark* 

 i:i this connection, some extracts, leading up to them, from his work al- 

 ready quoted are essential. He says: , 



" While the obvious importance of the physical soil-conditions has long ago rendered 

 { em subjects of close study by Schiibler, Boussingault, and others, the chemistry of soils- 

 vra^ very generally neglected for a considerable period, after the hopes at first entertained 

 by Liebig that chemical analysis would furnish a direct indication and measure of soil 

 fertility had been sorely disappointed in respect to the only soils then investigated, viz. 

 the long-cultivated ones of Europe. The results of chemical analysis sometimes agreed, 

 but as often pointedly disagreed, with cultural experiences ; so that after the middle of 

 the nineteenth century but few thought it worth while to occupy their time in chemical 



soil analysis Among the few who, during the middle of the past century, 



maintained their belief in the possibility of practically useful results from direct soil 

 investigation were Drs. David Dale Owen and Robert Peter, who prosecuted such work 

 extensively in connection with the geological and agricultural surveys of Kentucky and 

 Arkansas ; and the writer, who carried out similar work in the States of Mississippi and 

 Louisiana, with results in many respects so definite that he has ever since regarded this aa 

 a most fruitful study, and has later continued it in California and the Pacific North-west. 

 This was done in the face of almost uniform discouragement from agricultural chemists 

 until within the last two decades, with occasional severe criticisms of this work as a waste 

 of labour and of public funds. All this opposition was largely due to the prejudices 

 engendered by the futile attempts to deduce practically useful results from the chemical 

 analysis of .toils long cultivated, without first studying the less complex phenomena of 

 virgin soils ; and these prejudices persisted longest in the United States, even though in 

 Europe the reaction against the hasty rejection of chemical soil work had begun some time 

 before, as is evidenced by the methods employed at the Rothamsted Experimental Farm in 

 England, the Agricultural College of France, the Russian agronomic surveys, and at 



several points in Germany In the United States as well, the ancient 



prejudices have now gradually given way before the urgent call for more definite 

 information than could otherwise possibly be given to farmers by the experiment stations, 

 most of whose cultural experiments, made without any definite knowledge of the nature 

 of the soil under trial, were found to be of little value outside of their own 



experimental fields In many existing treatises so much emphasis is given to 



the alleged proofs of the inutility of chemical soil examination in particular that a special 



controversion of these arguments seems necessary In all these discussions the 



difference between the ascertainment of the permanent productive value of soils, as against 

 that of their immediate producing capacity, must be strictly kept in view. The former 

 interests vitally the permanent settler or farmer ; the latter concerns the immediate 

 outlook for crop-production, the ' Diingerzustand ' of the Germans. The methods for the 

 ascertainment of these two factors are wholly distinct, even though the results and their 

 causes are in most cases intimately correlated. The failure to observe this distinction 

 accounts for a great deal of the obloquy and reproach that has in the past BO often been 



heaped upon chemical soil-analysis and its advocates The abundant presence 



of the plant- food ingredients, as shown by analysis, will not avail, unless at least an 

 adequate portion of the same exists in a form or forms accessible to plants. Of course this 

 condition would seem to be best fulfilled by the ingredients in question being in the water- 

 soluble condition. But , . . substances in that form would be very liable to be washed 



or leached out of the soil by heavy rains or irrigation It is therefore clearly 



desirable that only a relatively small proportion of the useful soil-ingredients should be in 

 the water-soluble or physically-absorbed condition, but that a larger supply should be 

 present in forms not so easily soluble, yet accessible to the solvent action which the acids 

 of the soil and the roots of plants are capable of exercising. This virtually available 

 supply we may designate as the reserve food-store" 



Hilgards' remarks! have been quoted thus lengthily because his boolc 

 on the subject has all the qualities of a standard work of reference, em- 

 bodying, as the work of no other writer in recent years has done, in the 

 clearest language, the most reasonable present-day theories on the subject 

 dealt with. Following out his line of reasoning, it will be seen at once 

 tiiat, in a series of investigations of the nature, and earned on under the 

 circumstances of those that have been performed in the Government Ana- 

 lytical Laboratories here, quantitative determinations of the ingredients of" 



* Hilgard : Op. cit., pp. 313, 316-320. 

 t See also Snyder : " The Chemistry of Soils and Fertilisers," pp. 69, 70. 



