SOILS — FEKTILIZEES. 823 



gen fixation. These characteristics " help to explain the favorable physical 

 and chemical constitution of the soil and also the deep rooting of plants so 

 characteristic of the arid regions." 



The law of minimum, I. Pouget and D. Chouchak (Compt. Rend. Acad. 

 Sci. [Paris], 155 {1912), No. i, pp. 303-306, figs. 2 ) .—Referring to an article by 

 P. Maz6 noted elsewhere (E. S. R., 27, p. 721), the authors offer what is 

 claimed to be strong experimental evidence in favor of a law of minimum 

 which, it is claimed, plays an important part in large scale cultivation, espe- 

 cially in dry soils. 



A contribution to the knowledge of the black cotton soils of India, W. H. 

 Harrison and M. R. R. Amaswami Sivan {Mem. Dept. Agr. India, Chem. Set:, 

 2 {1912), No. 5, pp. 261-280, pis. I,; ahs. in Jour. Soc. Chem. Indus:, 31 {1912), 

 No. 20, pp. 999, 1000). — The authors review previous investigations on the sub- 

 ject by Leather (E. S. R., 10, p. 421) and by Annett (E. S. R., 23, p. 316), and 

 report studies of the geological distribution of the regur or black cotton soils 

 of India and the chemical and physical characteristics of the soil particles, with 

 a view of determining the cause of the black color of the soils. 



It is concluded from the results that " the black cotton soils of India are not 

 derived from any specific geological formation, such as trap, but are formed 

 from many diverse formations and generallj', when not alluvial, bear a close 

 relationship to the underlying rocks. 



" Titaniferous magnetite is not a constant factor in the regur soils of the 

 Madras Presidency, and, even when found, the amount is small, but its presence 

 in quantity is characteristic of the soils of the trap area. It can not, therefore, 

 be looked upon as the cause of either the color or the physical properties of 

 these soils, but only as a modifying agent. 



" The color and peculiar physical properties of black cotton soils are asso- 

 ciated with the compound particles of low specific gravity, which are found in 

 all these soils. 



" Two classes of substances have been recognized as conferring the color and 

 physical properties. One is probably a colloidal hydrated double iron and 

 aluminum silicate, which is mainly concerned with the formation of compound 

 particles and which possesses, in a modified form, the properties of ordinary 

 clay. The other is organic in character and may possibly be an organic com- 

 pound of iron and aluminum." 



The soils of Webster County, A. M. Peter and S. C. Jones {Kentucky Sta. 

 Bui. 162, pp. 135-169, pi. 1). — This bulletin, which is based on woi'k done in 

 cooperation with the Kentucky Geological Survey, reports a survey with map 

 of the soil types of the county, including mechanical and chemical analyses of 

 typical samples and pot experiments with a soil similar to the upland type of 

 the county, to determine the fertilizer and crop adaptation. 



The area is typical of the western' coal field of Kentucky, including about 

 4,500 square miles or about one-eighth of the total area of the State. The soil 

 tyiies established are the yellow silt loam (hilly), the yellow silt loam (undu- 

 lating), gray silt loam, gray clay loam, and a dark-brown clay loam covering, 

 respectively, 36.1, 27.3, 25.3, 8.1. and 3.2 per cent of the area. 



The results of preliminary pot fertilizer tests seem to indicate on the whole 

 that "phosphorus decidedly increased the yields of wheat, oats, and clover, 

 but not that of tobacco ; that nitrogen decidedly increased the yields of wheat, 

 oats and tobacco, but not that of clover; that potassium moderately increased 

 the yields of wheat and oats and slightly increased that of clover, but did not 

 have a marked effect on that of tobacco. Rock phosphate, used alone, gave 

 consistent gains, except with tobacco. Used with manure, however, its effect 

 seems to have been negative, contrary to the usual teaching. Limestone pro- 

 70257°— No, 9—13 3 



