34 



AERATION AND AIR-CONTENT. 



from 0.35 per cent in January to 0.6 per cent in July, reached its 

 maximum at over 1.5 per cent in August and fell to 0.6 per cent in 

 November. Another series of determinations (1S73 : 250) of the 

 CO; content of soil-air at Munich at depths of 1.5 and 4 meters was 

 made from November 2, 1871, to November 29, 1873. It was found 

 as before that the C0 2 was greater at the greater depth, and in mid- 

 summer sometimes twice or nearly thrice as much. The mean for 

 July was 0.26 per cent at 4 meters and for January, 0.05 per cent. 

 The author also gave the results of Fleck's observations at 2 meters, 

 4 meters, and 6 meters in Dresden. The soil of the botanic garden 

 in Dresden contained several times as much C0 as the Munich 

 soil studied. 



Risler (1872; cf. Mangin, 1896) studied the variation in C0 2 in soil 

 at depths of 0.25 meter and 1 meter in relation to both tempera- 

 ture and weather. He found the maximum amount, 2 per cent, pre- 

 sent late in June, as well as a greater amount always at the 

 lower depths. 



Fleck (1872: cf. Pettenkoffer, 1873) found the intensity of the de- 

 composition process in the soil and the amount of C0 2 determined 

 by mechanical pressure, size of particles, and the water-content. 

 Garden soil without a plant cover showed more C0 2 in the lower 

 layer, while that covered with plants gave the largest amount in the 

 upper layer, as also did sandy soil covered with forest. The total 

 amounts in the latter were usually less than one-tenth those of the 

 garden soil. 



TABLE 5. 



Schloessing (1873 : 203) studied the intensity of oxidation in a 

 calcareous soil containing different amounts of oxygen, namely, 

 1.5, 6, 11, 16, and 21 per cent. The oxidation was considerably less 

 in the first, identical in the next three and somewhat greater in the 

 last. He later (1889 : 673) determined the composition of the soil- 

 air at 15 to 65 cm. of depth and at various places and times during 

 the growing-season. The amount of C0 2 varied widely from 0.5 

 per cent to 11 per cent, and the oxygen from 10 per cent to 21 per 



