REMOVAL OF NUTRIENTS FROM THE SOIL 295 



carried by acid phosphate, the effect does not seem to be 

 towards acidity CTen after long periods of application.^ 



This discussion, brief as it is, brings out a little studied 

 phase of crop and fertilizer interaction. How the plant util- 

 izes a particular fertilizer after it is once in the soil, what 

 residues are left, and the importance of such residues, are 

 questions of fundamental concern. The possibility of plants 

 influencing the soil and the fertilizers added, as well as the 

 soil and fertilizer influencing the crop, is well worth attention. 



156. Do plants directly aid in the preparation of their 

 nutrients? — The conception commonly held regarding the 

 plant is that its direct relation to the soil is more or less 

 passive. Indirectly, of course, it may exert a considerable 

 influence on the availability of the nutrients. In view of the 

 knowledge regarding fertilizer residues and the new concepts 

 as to possible root exudates, the idea that the plant may 

 directly aid in the preparation of its own nutrients is becom- 

 ing more and more plausible. 



Such influences, if recognized, might occur in three ways: 

 (Ij through the action of carbon dioxide, known to be given 

 off in large amounts by roots; (2) through the influence of 

 organic and inorganic acids other than carbonic acid; and 

 (3) by catalytic agents, enzymic or non-enzymic. 



In a rich, moist soil the number of root-hairs is very large 

 and the relationship between the rootlets and the soil particles 

 very intimate. When in contact with a particle of soil or 

 colloidal complex^ the root-hair in many cases almost incloses 

 it, and by means of its mucilaginous wall forms a contact so 

 close as to make the solution held between the particle and the 

 cell-wall distinct from that in the soil proper. Carbon dioxide, 

 excreted under such conditions, may assume a solvent power 

 entirely unique and independent of the amount produced. 



^Conner, S. D., Acid Soils and the Mffect of Acid Phosphate and 

 Other Fertilisers Upon Them; Jour. Ind. and Eng. Chem., Vol. 8, No. 1, 

 pp. 35-40, Jan. 1916. 



