1917] SOILS FERTILIZERS. 515 



aridity of the climate in wliicli tliey laave formed. Tlie concentration of phos- 

 phorus in the surface layers, while it may be attributed to the prairie vegeta- 

 tion, is not dependent upon a corresponding concentration of organic matter, 

 the difference between the first and the twelfth inch being much the greater 

 with the latter." The average phosphorus contents of the soils of the six areas 

 were 0.141, 0.137, 0.147, 0.122, 0.132, 0.145, and 0.137 per cent. 



In addition attention is drawn to the importance of considering the relative 

 densities of soils when taking samples for comparisons of the phosphorus 

 content of long cultivated soil with that of virgin prairie or prairie fields. 



The mobilization of soil phosporic acid under the influence of bacteria, IV, 

 S. Severin (S. a. Severin) {Viestnik Bakt. Agron. Sta. Y. K. Ferreln, No. 21 

 (1914), PP- 53-83). — Continuing investigations previously reported (E. S. R., 31, 

 p. 721), experiments with chernozem soil on the influence of the activity of 

 certain soil micro-organisms on the solubility of phosphoric acid, carbon dioxid 

 production, the quantitative variation of nitrate content, total nitrogen, and on 

 bacteral numbers are reported. 



In the first series three soil samples were used, one sterile, a second sterilized 

 and inoculated with pure cultures of Azotobacter, and a third sterilized and 

 inoculated with cultures of Bacterium radieicola and Azotobacter. The phos- 

 phoric acid soluble in acetic acid increased in the inoculated soils from 8 to 14 

 per cent over that in the sterile soil. 



In a second series one soil was sterilized, a second sterilized and inoculated 

 with pure cultures of B. fliiorescens liqtiefaciens, and a third sterilized and 

 inoculated with pure cultures of Bacillus mesentericus vulgatus. The soluble 

 phosphoric acid decreased about 5.8 per cent in the second soil and increased 

 about 12.9 per cent in the third soil. Carbon dioxid production was about the 

 same in both soils, but the numbers of Bacterium fluorescens liquefaciens far 

 exceeded those of Bacillus mesentericus vulgatus. Both bacterial types were 

 accompanied by a similar increase in soil nitrogen (about 20.6 mg. in 100 gm. 

 of dry soil) and a .slight decrease in nitrate content, the latter being more 

 marked in the case of Bacterium fluorescens liquefaciens. 



In the third series one soil was allowed to stand two months in its natural 

 state, a second was sterilized, and a third was sterilized and inoculated with 

 pure cultures of Bacillus mijcoides. The bacterial numbers in the third soil 

 differed but slightly from those in the first soil. Carbon dioxid production was 

 four times as great in the first soil as in the third. B. mycoides showed no 

 effect on the soil nitrate content or on the total nitrogen content, while both 

 were decreased in the unsterilized soil. The soluble phosphoric acid decreased 

 about 12.6 per cent in the unsterilized soil and increased about 4.2 per cent in 

 the soil containing B. mycoides. 



The influence of salts on the bacterial activities of the soil, J. E. Greaves 

 {Soil Sei., 2 (1916), No. 5, pp. U3-480, figs. 4).— Experiments conducted at the 

 Utah Experiment Station on the influence of the chlorid, nitrate, sulphate, and 

 carbonate of sodium, potassium, calcium, magnesium, manganese, and iron on 

 ammonification in a productive sandy loam soil are reported. 



It was found that the toxicity of the salts tested as determined by ammoni- 

 fication was controlled largely by the electro-negative ion. As a general rule, 

 to which there were exceptions, the chlorids were the most toxic and nitrates, 

 sulphates, and carbonates followed in the order of decreasing toxicity. The 

 quantity of a salt which could be applied to a soil without decreasing the 

 ammonia formed varied with the salt, and for the soil under investigation the 

 order of decreasing toxicity of the salts was as follows : Calcium chlorid, cal- 

 cium nitrate, sodium sulphate, potassium sulphate, magnesium nitrate, ferric 



