354 



MICROBIOLOGY OF SOIL 



of water. Clay soils and clay loams are, on the other hand, late soils; 

 it means, therefore, that in the more open soils microbial activities be- 

 come intense earlier in the spring. Market gardeners usually attempt 

 to improve matters still further by the use of large quantities of readily 

 fermentable manure that develops enough heat to raise slightly the 

 soil temperature. 



PRODUCTION AND ASSIMILATION OF PLANT FOOD. It was observed 

 by Moller that slight amounts of carbon dioxide may be evolved 

 from frozen soil. Kostychev could detect a considerable production 

 of carbon dioxide at o to 5. In a series of experiments carried out 

 by Wollny the amounts of carbon dioxide produced were as follows: 



CO 2 IN 1,000 VOLS. OF AIR 



The increased production of carbon dioxide at the higher temperatures, 

 as shown in the above table, corresponded with the observations that had 

 already been made by Ebermayer, Schloesing and others, that carbon 

 dioxide production in the soil is greater in summer than it is in winter. 

 These facts, taken together with the early observations of Forster on 

 the multiplication of photo-bacteria at o, and the more recent ob- 

 servations of numerous investigators on the multiplication of in- 

 dividual species, or of mixtures of species in milk, water, soil, butter, 

 etc., at o, or even below that, make it evident that bacterial activities 

 are not entirely suspended at relatively low temperatures. As the 

 latter rises these activities become more intense as gauged by the 

 formation of carbon dioxide. 



Coming down to specific groups of soil bacteria, it may be noted that 

 at 12 nitrification is already quite perceptible; that urea bacteria grow 

 slowly at 5; Ps. radicicola at 4; members of the B. subtilis group at 

 6 to 10, etc. At 15 the breaking down of organic matter is fairly 

 rapid, and at 25 the optimum is reached for many species. It follows, 

 thus, that the production of plant food namely, ammonia, nitrates, 

 sulphates, phosphates, etc. gains rapid headway as the optimum tem- 

 peratures are approached. The organic matter itself, apart from serv- 



