AGEICULTUBAL BOTAIJT. 221 



10). — In continuance of work with soil bacteria (E. S. R.. p. 525), the 

 author carried out extensive analyses of soils in the \icinity of Pusa, India, 

 as to the kind and number of organisms present, as well as to their physiologi- 

 cal activities, with results and conclusions which may be summarized as 

 follows : 



The numerical bacterial content of a given soil as well as bacterial activity 

 therein, with resulting crop returns, may be greatly varied by conditions, and 

 the sequence of their alternation. Examples of this are rainfall, preceded or 

 followed by long drought; bacterio-toxins and influences affecting them, as 

 sunlight, heat, aeration, etc. ; protozoa and changes produced by and upon them ; 

 disinfectants and other means of bacterial limitation and selection; nutrient 

 materials and their changes of availability as affected by various agencies; 

 and physical character of the soil, and its alterations due to weather and to 

 cultivation. 



A study of weathering, that is repeated plowing of the soil during the hot and 

 dry season previous to the first rain of spring as practiced with Indian soils, 

 was made, the process being imitated by heating the soil up to a surface tem- 

 perature of 60° C. and stirring daily. It was found that most fungi were 

 eliminated, leaving such forms as Bacillus subtilis, said to possess superior 

 ammonifying power, suggesting that this selective action may be one of the 

 contributing causes of the resulting fertility. Weathering did not greatly alter 

 the nitrifying power of the soil. Comparative experiments show no decided 

 coincidence between the elimination of protozoa and increased ammonification. 

 It is found that in the process of weathering, by which the soil becomes practi- 

 cally air dry to a depth of about 9 in., the anaerobic bacteria suffer almost 

 total extinction, while the aerobic are affected in much less degree. It is 

 stated that this may in part account for the increased fertility, but that it may 

 also account for a certain loss of condition ascribed to a supposed disturbance 

 of the balance of nature in the soils so treated. Toluene apparently increases 

 the solubility of soils to air and bacterio-toxins gradually lose their toxicity in 

 water solutions and on exposure to air and light, weathering producing an 

 effect somewhat similar to boiling the soil extract. The effect of toluene upon 

 the production of carbon dioxid was greater in proportion to the amount applied, 

 suggesting that this was due to its action upon the physical or the chemical 

 constitution of the soil. It is thought possible that certain toxins in the soil 

 may be removed along with the soil wax said to be taken out by the toluene. 



A considerable loss of ammonia was observed to follow weathering. It is 

 suggested that the gradual air drying of successively lower layers of soil may 

 carry downward a zone of optimum conditions for nitrification, ammonifica- 

 tion, and other decay activities, resulting in the working over of a large portion 

 of the organic matter present. It is suggested also that the air drying of this 

 top 9 in. of soil results in preventing a wasteful degi-ee of bacterial activity, 

 thus in a measure compensating for the losses sustained in the escape of 

 ammonia and carbon dioxid. 



The conclusion is thought to be justified that the increase of fertility conse- 

 quent upon partial sterilization must depend not upon any one but upon numer- 

 ous complex factors, involving on the one hand the possibility of damage by 

 depletion of organic nitrogen and carbon and the alteration of the soil flora, and 

 en the other the rapid turnover of capital in the shape of organic nitrogen. 



The process of weathering appears to afford a means of rapidly converting 

 the nitrogen of green manures, root residues, and cattle manure into ammonia 

 and nitrates; the ultimate effect depending upon the regulation of the ratio 

 between supply and depletion of organic matter. It is thought that the effect 

 of weathering on the water supply may also prove to be very important 



