l6o CHEMISTRY AND CROPS. 



has not, even now, 70 years after, received its jinal and complete 

 solution. These past 70 years have been years of strife — one feels 

 inclined to say unnecessary strife. Almost all the trouble has 

 arisen from the persistent confusion of and the fruitless endeav- 

 ours to combine two related but different problems, i.e., (i) The 

 determination of the immediate productivity of soils that have long 

 been subjected to the operations of cultivation, and (2) the deter- 

 mination of the permanent productive capacity of virgin soils. 

 Of the two problems, the latter is the simpler, and should have 

 been tackled first ; but, unfortunately, such an one did not present 

 itself in theo only continent where there was a scientific activity, 

 viz., in Europe; for all the lands there had long" been under the 

 plough. This was indeed a pity, for it certainly resulted in the 

 defeat of chemistry as an aid to agriculture. 



Going back to Liebig's time, I will briefly allude to the vari- 

 ous stages in the evolution of our present day methods. The 

 first step commenced with Liebig's assertion that if sufficient 

 quantities of the ash constituents of plants were present in the 

 soil good crops would be obtained. Soils were therefore sub- 

 jected to vigorous analysis, with the result that, as often as 

 not, analysis and cultural experience told very different tales. 

 The strong acids and fluxes wTiich it was then customary to use 

 as solvents were able to extract, even from exhausted soils, quan- 

 tities of plant food materials largely in excess of the require- 

 ments of crops. It is, therefore, not to be wondered at that the 

 analysis of soils came to be very much discredited, and looked 

 upon as a waste of so much time and money, that ever since 

 many writers have been at great pains to prove its uselessness. 

 The natural and violent reaction against chemistry led to the 

 practical abandonment of soil analysis, and for a time cultural 

 experiment was looked upon as the only means of salvation. 

 But salvation did not so much as come in sight ; it was soon found 

 that, in practice, this method was one of very limited utility. 



Agriculturists once more turned to chemistry for enlight- 

 enment, and obtained it ; for chemistry had not been idle — -it 

 had not been repulsed by one defeat ; but had gained strength 

 therefrom, and had quietly set out to win by other methods of 

 attack. It had been found that the use of weak-acid solvents 

 gave much more reliable indications of immediate productivity. 

 Among the pioneers may be mentioned Deherain, who was able 

 to obtain, using dilute acetic acid as a solvent, reliable indica- 

 tions in cases in which strong acids had signally failed. This 

 was indeed a triumph, and led to further experimentation with 

 other weak acids, among them citric acid, which, in Dyer's 

 hands, gave very gratifying results. Dyer was able to announce, 

 as the outcome of his investigations, that if a soil be extracted 

 with I per cent, citric acid for 7 days, and if it were found to 

 contain not less than .01 per cent, phosphoric acid and .005 per 

 cent, potash, then only did the soil contain sufficient quantities 

 of these materials for the production of good cereal crops. 



The use of dilute organic-acid-solvents was a piece of re- 

 markably good fortune, and may be attributed to the then uni- 

 versal belief that such acids were secreted by plant roots, and 



