SOILS FERTILIZEES. 123 



121tii-12'ti), figs. 2; abs. in Internat. Inst. Agr. [Rome], Bui. Bur. Agr. Intel, and 

 Plant Diseases, 3 (1912), No. 2, pp. 376-378). — This is a report of a continua- 

 tion and extension of previous work by the author (B. S. R., 18, p. 1024). A 

 special form of apparatus used in these investigations is described, and the 

 results of studies of the effect of cultivation, fertilization, kind of crop, and com- 

 position of organic matter on the intensity of respiration of bacteria in the soils 

 are reported. 



The essential part of the apparatus used was a glass cylinder fitted with a 

 sieve at about 5 cm. from the bottom. The soil was placed in the upper part 

 of the cylinder, and sterilized air (or hydrogen for anaerobic bacteria) was 

 introduced into the bottom of the cylinder by means of a glass tube. A second 

 tube, projecting a few centimeters into the top of the cylinder, conducted the 

 carbon dioxid evolved from the soil through the apparatus for its absorption 

 and determination. The cylinder containing the soil was kept in a thermostat 

 during the experiment so that the temperature could be carefully regulated. 



The bacterial activity as measured by the amount of carbon dioxid given off 

 was influenced not only by the mechanical condition and fertility of the soil, 

 but also by the kind of crop grown. The greater the air space of the soil the 

 greater was the intensity of respiration of the bacteria. 



By sterilizing the soil and inoculating it with equal quantities of bacteria of 

 the same virulence it was possible to determine by means of the carbon dioxid 

 given off the power of the bacteria to decompose the organic matter in the 

 soil, and the author concludes that intensity of respiration of bacteria is a 

 better basis for judging the biological activities of soils than the amount of 

 organic matter present. Intensity of respiration shows the presence in the soil 

 not only of active bacteria but also of easily decomposed organic matter. 



The chemical composition of the drainage water was also found to furnish 

 a means of judging the intensity of the biochemical processes in the soil. It 

 was found, for example, that the calcium bicarbonate content of the drainage 

 water increased with the bacterial activity, irrespective of the lime content 

 of the soil, and stood in direct relation to the carbon dioxid produced by the 

 soil micro-organisms. This tends to show that the determination of the 

 carbon dioxid given off by a soil furnishes a reliable means of judging of the 

 transforming power of bolh autotrophic and heterotrophic bacteria in the 

 soil, and that the amount of carbon dioxid produced by a given quantity of 

 soil in a unit of time at a fixed temperature and known degree of moisture 

 represents accurately the physiological combustion taking place and makes it 

 possible to compare the bacterial activity in different soils. This varies widely 

 with (1) the air or water capacity of the soil, (2) the character and amounts 

 of decomposable organic matter in the soil, (3) the presence of organic and 

 inorganic nitrogenous substances and of easily assimilated substances contain- 

 ing phosphorus, potash, etc., (4) the number of autotrophic and heterotrophic 

 bacteria, and (5) the chemical reaction of the soil. 



The most active respiration occurs in neutral or slightly alkaline soils 

 abundantly supplied with air and with readily assimilable nitrogen, phos- 

 phorus, sulphur, chlorin, potash, soda, magnesia, lime, iron, alumina, and 

 manganese. The presence of alumina is necessary to the ready assimilation of 

 iron and manganese by autotrophic and heterotrophic bacteria. 



The form of nitrogen has a marked influence in determining the character 

 of bacteria predominating in a soil, and hence the intensity of respiration. In 

 forest soils, for example, bacteria which by preference assimilate organic 

 nitrogen predominate. In soils in which nitrification is active the predominant 

 bacteria are those which readily assimilate nitric nitrogen. On the other hand. 



51193°— 12 3 



