36 



AERATION AND AIR-CONTENT. 



there was no relation between the amount of C0 2 and of organic 

 matter found in the soil, and that the former depends primarily 

 upon permeability. The soil-air contained more carbon dioxid and 

 less oxygen at 4 meters than at 1 meter. 



TABLE 7. 



Salger (1882) confirmed the previous results as to the increase of 

 C0 2 , and found the amount greater at great depths, such as 20 meters. 

 Further, the amount increased with the contamination of the soil, 

 while regular ventilation diminished it rapidly in the surface layers, 

 but more slowly than at greater depths. Contrary to the usual 

 results, Bentzen (1882 : 446) stated that the atmosphere of the 

 upper layers was richer in C0 2 than that of the lower. 



Ebermeyer (1878 : 158) determined the amount of carbon dioxid 

 in soil-air with particular reference to the difference in this respect 

 between forest and field soils. His results for the four summer 

 months, May to August, are given in Table 8. 



TABLE 8. 



p. ct. 

 Bare, unfertilized, unworked soil at 1 



meter 2.3 



Same soil under an Acacia 1.4 



Free air 2 meters above the soil 0.04 



Forest air 2 meters above the soil . . 08 



Forest soil in the humus layer 



Forest soil at 0.5 meters 



Forest soil at 1 meter 



Soil of cultivated field at 0.5 meter. 

 Soil of cultivated field at 1 meter. . . 



p. ct. 



0.14 



0.45 



0.5 



2.6 



2.5 



He concluded that forest air contains twice as much carbon dioxid 

 in summer as free air and that forest soil is much poorer in CO 2 than 

 unforested soil, while a cultivated field contains 5 to 6 times as much. 

 With an increase of temperature, the C0 2 -content of the cultivated 

 field increases more rapidly than that of the forest soil. The move- 

 ment of C0 2 in the soil seems to be very slow, as shown by the differ- 

 ence in amount in contiguous places in the soil. 



He also (1890 : 15) found that the air in mineral soil is always 

 richer in CO 2 and poorer in oyxgen than ordinary air. The soil-air 

 in the upper layers was 4 to 5 times richer, and at 70 cm. deep, 10 

 to 20 times richer in CO 2 than the atmosphere. Among the soils, 

 quartz sand was poorest in carbon dioxid, while calcareous sand and 

 clay were at least once again as rich. Dry moor soil was far richer 

 in C0 2 than the pure mineral soils. This was true in the uppermost 

 layers, but especially at 70 cm. deep, where it was 22 times greater 

 than in sand and 10 times greater than in lime and clay soils. In 



