THE EFFECT OF REMOVING THE SOLUBLE HUMUS 

 FROM A SOIL ON ITS PRODUCTIVENESS. 



By WILLIAM WEIR, M.A., B.Sc. 

 Carnegie Research Scholar. 



(Rothamsted Experimental Station.) 



The decay of plant and animal residues in soils produces brown 

 organic compounds coiunionly designated as humus. Some of it is 

 soluble in dilute alkaline solutions, and agricultural chemists and 

 investigatois have often assumed that this part plays an importaiit 

 function in the nutrition of plants by reason of its solubility. As a 

 result numerous methods have lieen devised for determining this reatlily 

 soluble material, and its amount has been regarded as a measure of 

 the fertiUty of the soil. Since however the amount of nitrogen in the 

 soluble humus material is commonly 40 per cent, to .50 per cent, of the 

 total nitrogen, the results for ordinary soils gave no better indication 

 of potential fertility than did the total nitrogen determination itself. 



Few experiments seem to have been made to ascertain directly if 

 the soluble humus really does play any considerable part in plant 

 nutrition. The only one that has been found is recorded by Grandcau- 

 in 1872. A kilogramme of Russian Black Earth was divided into two 

 parts; one was treated with dilute hydrochloric acid and ammonia 

 solution to remove soluble humus, or, as he termed it, matiere noire; 

 the other was left untreated. 



The two lots of soil were put into flower pots and watered to 

 saturation point with distilled water, the untreated soil taking 7 per cent. 



' "Results of Investigations on the Rothamsted Soils," liK)2. by Bernard Dyer. 

 N. H. J. Miller's "Determinations," p. 179. 



- "Reeherchcs siir le role des matiercs organiques du sol dans les phenonicnes do la 

 nutrition des vegetaux," par M. L. Cfrandeau. Publication de la Station agronomiquc 

 de VEsl. 1872. 



