NOTES AND ABSTRACTS. 



415 



(Frankland), a typical spore-forming bacterium, and the two Pseudomonas forms 

 soon attain an ascendancy. 



In field soil where no organic matter has been added for many years P. 

 fluorescens and P. caudatus are rarely found, but B. cereus is common. All 

 three organisms are vigorous ammonhiers when tested in pure culture. 



Pseudomonas fluorescens has been compared with other fluorescent forms 

 isolated from the soil, but definite limits cannot be fixed for this species. Pseudo- 

 monas caudatus is similar to the " orange-liquefying type " previously described 

 by one of the authors, and appears to be identical with the organism described 

 by Wright (1895), and it is commonly found in soil and water. 



A short bibliography is appended. — A. B. 



Soil Factors affecting the Toxicity cf Aikali. By F. S. Harris and D. W. Pittman 

 (U.S.A. Jour. Agr. Res. vol. xv. No. 5, Nov. 191S, pp. 287-319). — The authors' 

 conclusions, based upon some thousands of determinations of the effects of 

 alkali salts on plant germination and growth under different conditions, were 

 as follows : 



The size of the particles of sand, independently of other factors, does not 

 seem to influence appreciably the toxicity of alkali. 



Loam soils are more tolerant of alkali than either sand or clay ; the coarser 

 loams are more tolerant than the finer ones at the same moisture content, but 

 if the heavier loams are maintained at an equivalent moisture content they are 

 more tolerant. Organic matter increases the resistance to alkali when the soil 

 containing it is given sufficient moisture, but where present in large quantities 

 organic matter decreases the resistance if the moisture supply is low. The 

 toxicity of sodium chloride and sodium sulphate seems to depend on the relation 

 between concentration of salt and percentage of moisture present, while the 

 toxicity of sodium carbonate is more largely affected by the presence of organic 

 matter. Organic matter has the apparent power to remove sodium carbonate 

 from the soil solution in large quantities. This probably explains why, when 

 sodium carbonate is added to a loam soil, it is less toxic than sodium chloride, 

 while in field studies where the salt is determined by analyses, and in solution 

 and in sand cultures, the sodium carbonate is more toxic. 



Loam soils and soils with a high water-holding capacity may be successfully 

 farmed at a higher alkali content than others. Soils in which alkali reduces 

 crop results should be kept as moist as possible. Manure or other organic matter 

 should be beneficial to alkali soils, especially those high in carbonates. — A. B. 



Soil Reaction and Growth 01 Azotobacter. By P. L. Gainey (Jour. Agr. Res. 

 xiv. pp. 265-272, August 1 91 8). — Azotobacter was found to exist in soils con- 

 taining none or only traces of calcium carbonate, and also in soils showing some 

 acid reaction, the latter being a more important check than the presence of cal- 

 cium carbonate an encouragement. The paper should be consulted for details. 



F. J. C. 



Soil Reaction, Influence on Nitrogen-assimilating Bacteria. By E. B. Fred 

 and A. Davenport (Jour. Agr. Res. xiv. pp. 317-336, August 1918). — The 

 nodule-forming bacteria were found to vary according to their host-plant in their 

 powers of resisting acid- concentration in the soil. Azotobacter was found to be 

 much more sensitive to alterations in reaction of the soil than are the nodule 

 bacteria, a concentration of acid represented by N/ 1333' 3 being fatal. — jF. /. C. 



Soil Solution as an Index of the Biological Changes in the Soil. By J. F. 

 Morgan (U.S.A. Exp. Stn. Mich., Tech. Bull. 39, Sept. 1917, pp. 24; 9 

 tables, 6 figs.). — The soil solution as obtained by the oil-pressure method was 

 discussed in a previous Bulletin, No. 28. The writer now attempts to show the 

 value of such a soil solution for the study of the microbial changes that are 

 believed to be the essential factors in fertility. In the experiments, soils were 

 treated with several organic manures : dried blood, tankage, cotton seed meal, 

 bone meal, and hoof meal ; and also with ammonium sulphate and sodium nitrate. 

 The soil solutions from the treated soils were more concentrated than from 

 untreated (control) soils, due to the decomposing organic matter added. The 

 dried blood gave quicker results than the other organic substances. Nitrification 

 is well illustrated by the study of solutions obtained by extracting at definite 

 intervals soils similarly treated. The treated soils contained more micro- 

 organisms than the controls, indicating that when more food for the bacteria 

 is added these organisms will multiply to take care of the increased work de- 

 manded of them. The only change in the nitrogen cycle that could be expected 

 when ammonium sulphate and sodium nitrate were added would be the nitri- 

 fication of the former and denitrification of the latter. 



