SOILS FERTILIZERS. 223 



tween successful inoculation and successful crop production. For alfalfa the 

 conditions favoring successful inoculation seem identical with those favoring 

 the alfalfa crop. While the limitations for either inoculation or crop produc- 

 tion with vetch are less sharply drawn, their relationship or interdependence 

 is perhaps as marked as with alfalfa. Crimson clover, on the other hand, may 

 be inoculated even on soils which redden litmus, yet under these conditions 

 liming or manuring is often of great benefit in crop production." 



Studies in soil oxidation, O. Schreiner, M. X. Sullivan, and F. R. Reid 

 (Z7. S. Dcpt. Agr., Bur. Soils Bui. 13, pp. 57).— This bulletin, which is based 

 upon investigations by the authors and by others, deals with " reduction and 

 oxidation by roots, concurrent oxidation, and reduction by roots, and oxida- 

 tion within the soil itself. The fact that roots possess the power of reduction 

 was shown by the precipitation of tellurium and selenium from sodium tellurite 

 and seleuite, respectively. The oxidative power of the roots was shown by 

 means of organic compovmds, which, on oxidation, yield dyes which either 

 ■<;olor the solution or are deposited on the root surface. These two opposite 

 properties may occur separately or concurrently, depending upon the reaction 

 of the medium. The oxidation within the soil itself is shown by the same 

 reagents as those showing oxidation by the roots. The reagent most success- 

 fully used in the case of soil is aloin, a yellow water solution of which is 

 changed to a claret red by the oxidation. The depth of color can be measured 

 and is taken as an indication of the extent of the oxidation. 



" This oxidation appears to be mainly nonenzymotic, the result of interaction 

 between inorganic constituents and certain types of organic matter. It may also 

 be brought about by organic matter in a state of autoxidation and by inorganic 

 oxygen carriers, such as manganese and iron. Both processes activate oxygen. 



" The oxidation in soils was increased by the addition of salts of manganese, 

 iron, aluminum, calcium, and magnesium, especially in the presence of simple 

 hydroxyacids, such as citric, tartaric, malic, glycolic, and their salts. The best 

 oxidation was obtained by the addition of manganese, and the stimulating 

 action of manganese used as a fertilizer is attributed to its oxidizing power ; 

 i. e., to its amelioration of soil conditions rather than its function as a plant 

 nutrient. Fertilizer salts augment the oxidizing power of roots, and the 

 fertilized soil has an increased oxidizing power after cropping. The fertilizer 

 salts alone sometimes increase, sometimes decrease, the oxidative functions 

 of the soil itself, thus showing that the fertilizer salts are effecting changes 

 directly or indirectly in the soil constituents, more particularly in the organic 

 matter. Some types of organic matter, such as dihydroxystearic acid, isolated 

 from certain soils, inhibit oxidation in the soil, but in the main the oxidative 

 power is augmented by a plentiful supply of organic matter, the nature of 

 which in the soil is the limiting factor of oxidation. Excessive oxidation is 

 harmful to vegetation. , . . 



" Soils oxidize substances in a manner analogous to an oxidase, and the in- 

 crease noticed by the addition of certain hydroxyacids is closely paralleled by 

 the recently discovered activating action of salts of tartaric and citric acids on 

 the oxidative action of manganese acetate. This analogy between the oxidative 

 power of a soil and the action of an oxidase is especially significant in that an 

 oxidizing enzym, laccase, of alfalfa, has been found to be more simple in com- 

 positon than formerly supposed and to consist of neutral salts, mainly calcium, 

 of glycolic, mesoxalic, malic, and citric, and probably glyoxylic acid. . . . 



" Whatever decreases the oxidation in soils tends also to bring about the 

 conditions which decrease growth, and the factors which favor oxidation are 

 the factors which favor soil productivity." 



77543°— No. 3—11 3 



