SOILS — FERTILIZERS. 217 



gases of the soil, but also to the absorption of gases by the soil at different tem- 

 peratures, and to the aqueous vapor." 



Soil temperatures as influenced by cultural methods, J. Oskamp {U. S. 

 Dept. Agr., Jour. Agr. Research, 5 (1915), No. 4, pp. 17S-179, figs. ^').— Two 

 years' field experiments at the Indiana Experiment Station on tlu-ee plats in 

 a young apple orchard, which included (1) tillage with a cover crop, (2) straw 

 mulch, and (3) grass land, are reported. The soil temperatures were recorded 

 l)y means of soil thermographs. 



The greatest variation in temperature between plats occurred during the sum- 

 mer months. In the spring and fall there was a transition period in which the 

 temperature differences were less. During the Avinter the temperatures were 

 quite constant from day to day, with very little variation between plats. In the 

 spring the diurnal range was considerable in the plat under tillage with cover 

 crop and the grass land, but varied little under the straw mulch, which exhibited 

 a very gradual warming up. During the summer season, fluctuations became 

 quite pronounced under tillage and grass, but the straw mulch still maintained 

 its uniformity. During the season of greatest daily range the maximum and 

 minimum temperatures occurred about 10 p. m. and 10 a. m.. respectively. In 

 the fall the temperatures and ranges were not radically different from those of 

 spring, except that the general trend of temperatures was reversed. 



" In conclusion it may be said that a system of clean cultivation with a winter 

 cover crop is characterized by extreme diurnal and annual fluctuations in soil 

 temperature; that a straw mulch equalized these fluctuations to a marked ex- 

 tent, as does also a grass crop, though in less degree." 



The biochemical reduction processes in the soil, C A. H. von Wolzogen 

 KiJHR, Jr. {Arcli. Suikerindus. Nederland. Indie, 23 {1915), No. 13, pp. 501-511; 

 abs. in Chetn. Abs., 9 {1915), No. 15, p. 2120). — The author discusses reduction 

 and oxidation processes in the soil in their relation to soil ventilation and drain- 

 age and the presence of aerobic or anaerobic conditions, and draws attention to 

 the so-called sulphate reduction process caused by Microspira desulfuricans, 

 which, according to Beijerinck," decomposed gypsum in the presence of organic 

 matter and set free hydrogen sulphid. The hydrogen sulphid was fixed as iron 

 sulphid, which is thought to account for the black color of many tropical soils. 



In chemical studies of swamp sugar-cane soils, rich in organic matter, it was 

 found that hydrogen sulphid was set free by treatment with dilute acids and 

 the soil was colored black with iron sulphid. In a solution containing sodium 

 lactate, asparagin, potassium phosphate, magnesium sulphate, and ferric sul- 

 phate, when inoculated with the soil and incubated at from 28 to 30° C. for 

 from four to five days, a strong sulphate reduction took place. Other culture 

 media with the same soils produced like results. Organic matter from the soils 

 also reduced ferric to ferrous salts in dilute solutions of hydrochloric or sul- 

 phuric acids, as indicated by potassium ferricyanid. It is thought, therefore, 

 that the reducing pov.er of such soils may be measured by the amounts of fer- 

 rous iron present after the action in weak acid solution, and that in all proba- 

 bility, since the reduction takes place only in neutral solutions, the appearance 

 of ferrous compounds is due to reduction by anaerobic bacterial activity. It is 

 also thought that cane soils showing local spots with poor growth will have a 

 greater reducing power than those showing normal growth. 



Separation of soil protozoa, N. Kopeloff, H. C. Lint, and D. A. Coleman 

 {U. S. Dept. Agr., Jour. Agr. Research, 5 {1915), No. 3, pp. i37-i40).— Experi- 

 ments made at the New Jersey Experiment Station are reported, the purpose of 

 which was to separate the different kinds of protozoa from each other and from 

 bacteria. 



« Centralbl. f. Bakt., 2. Abt, 1. Bd., 1895, p. 1. 



