Volume VII MARCH, I 'J 15 Part I 



THE ATMOSPHERE OF THE SOIL: ITS COMPOSI- 

 TION AND THE CAUSES OF VARIATION. 



By EDWARD JOHN RUSSELL and ALFRED APPLEYARD. 



(Rothamsted Experimental Station.) 



LIBKAKY 



(With 17 Text-figures.] "^^^^ ^^^"^ 



tiUTAISiCAl. 



Introduction. bakoiSN. 



The remarkable relationships existing between the microorganisms 

 of the soil and the growth of plants have given rise to numerous 

 researches on the bacteria, fungi, and more recently the protozoa of 

 the soil, and considerable knowledge has now been obtained of the 

 organisms present in normal soils. The earlier investigations were 

 necessarily confined largely to methods of isolation, descriptions of the 

 organisms found and studies of their behaviour in certain culture 

 solutions, but sufiicient of this preliminary work has been done to 

 enable us to attack the real problem and try to obtain a picture of the 

 life in the soil as it actually is. For this purpose it is necessary to 

 know the relative abundance of the various organisms, to find out 

 which are active and which inert, and to discover what the active forms 

 are doing and what is their mode of life. Before the bacteriological 

 and zoological work can be fully interpreted, however, it is necessary 

 to discover the conditions under which life in the soil goes on, and in 

 the series of papers, of which this is the first, it is proposed to deal with 

 the air supply, water supply, and temperature of our own soils and 

 by comparison with other investigations to see how far the observed 

 relationships hold generally. 



In the present paper we shall confine ourselves to the atmosphere 

 of the soil. The soil mass is porous and the volume of solid matter 

 in our case^ is approximately two-thirds of the whole, leaving one-third 

 pore space. The pore space, however, is not empty but contains a 

 considerable amount of water, and the actual space empty except for 



1 For analysis of the soil, see p. 44. 

 Journ. of Agric. Sci. vii 1 



