500 STATE BOARD OF AGRICULTURE. 



soil formation. Zacharow^ maintains that the soil solution plays an 

 essential role to the extent in which it relates to the process of leach- 

 ing, dissolving and further advancement of the soil particles in the soil 

 layer. Finding that the soil extract from different soils varied in color, 

 reaction and amount and composition of the soluble constituents he was 

 able to differentiate the different soil types. The amount of humus 

 present has a marked influence upon the color and reaction of the soil 

 solutions. Soils of the same composition as to type except in organic 

 matter present will vary in their soil solutions as to color and reaction. 

 Varying in these, the other properties, chemical, physical and bio- 

 logical, vary. Not onlj'^ the humus, but certain of the mineral constitu- 

 ents of the soil that give it color, also have marked influence upon the 

 color of the soil solution. 



The second phase of importance from an ecological standpoint is the 

 soil solution as the medium for plant growth, the actual medium in con- 

 tac-t with the plant roots, which is the substratum for the microbial life. 

 The plant is susceptible to the neutral, alkaline, or so-called acid reaction 

 and is affected by the amount and kind of available substances present, 

 especially of potassium, ijhosphorus, calcium and of nitrogen in its 

 various forms. 



Cameron and BelP say ''The soil solution is physiologically of the 

 greatest importance, as it is the source from which plants absorb the 

 mineral constituents which have been demonstrated to be absolutely es- 

 sential to their continued existence and development. The study of the 

 soil solution therefore becomes of the first importance in the investiga- 

 tions of the relation of the soil to plant growth." 



Heretofore no available means has been devised for obtaining large 

 amounts of the true soil solution or a fair representative of the same. 

 From the study of synthetic solutions and of water extracts, much light 

 has been thrown upon soil fertility. With a true soil solution, much 

 more valuable information ought to be obtained. For example, we have 

 used the soil solution obtained by the method here described to study 

 the effect of the microorganisms in fertilized soils and also to show the 

 effect of soil reaction upon the number and kind of microorganisms pres- 

 ent. This phase of the work will be taken up in a later publication. 



PREVIOUS METHODS. 



1. Drainage Waters. 



Various investigators have tried to find some means of obtaining a 

 soil solution as it exists in the soil in order that they may become better 

 acquainted with the medium in contact with the plant roots and the 

 medium in which microbial activities must take place. Among the first 

 tried may be mentioned drainage waters.^ 



There are several methods of collecting the drainage water for study: 

 (a) Collecting the water from the soil drainage pipes at the point 

 of discharge. 



^Zacharow, S. A. : The SoU Solution : Its Role in the Soil Formation, The Method of Ex- 

 amination and Its Use in the Characterization of Soil Types. Rus. Jour, of Expt. Landw. 

 1906-7, No. 4, pp. 388-477. 



-Cameron, F. K. and Bell, J. M. The Mineral Constituents of the Soil. Bui. 30, Bureau 

 of Soils, 1905, p. 8. 



•■'Hilgard, E. W., "Soils" (1912) pp. 22-2.5; Deherain, P. P., Researches on Drainage Water. 

 Ass'n of Agron. Vol. 16-23, Comptes Rendus de I'Acad. des Sci., Vol. 116, 117, 120, 125; 

 Wclbel, B. M., Drainage at Plots Expt. Sta., E. S. R., 19, p. 923. Bckart, C. F., Lysimeter 

 Experiments. Haw, Sugar Planters' Sta., Div. Agr. and Chem., Bui. 19, (E. S. R. 18, p. 

 718; 14, p. 554). The amount and composition of the drainage through unmanured and un- 

 cropped land. Barnfield, Rothamsted, Miller, N. H. J. Journ. Agr. Sci. 1 (1906) No. 4, pp. 

 377-99. (List of 10 references). 



