40 



AERATION AND AIR-CONTENT. 



material. A high content of CO 2 in the soil-air is identical with a high 

 degree of activity of the soil, and this, with the ability to bear a 

 flora of high requirement. A poisonous effect from soil-air with a 

 few per cent of C0 2 was nowhere found in the moor. It is regarded 

 as probable that it does not occur until the amount reaches such as 

 those which Mangin found in Paris. 



Jodidi and Wells (1911 : 146) measured the amount of carbon 

 dioxid and oxygen in the soil of 22 field plots during the months of 

 April, May, June, July, and August. The averages for each month 

 are shown in table 9. 



TABLE 9. 



The oxygen-content of the various plots varied little more than 

 1 per cent throughout the period, but the carbon dioxid showed a 

 maximum range from 0.04 per cent to 0.82 per cent. This bore 

 little relation to the previous treatment of the plots, as plots A and C, 

 with the same treatment for the preceding 4 years, gave values of 0.10 

 and 0.82 per cent respectively during the month of June. 



Harrison and Aiyer (1913) have determined the composition of 

 the gases from rice fields in India under various treatments and 

 shown that manure greatly increases the production of C0 2 . 



TABLE 10. 



Leather (1915 : 108) has made a comprehensive study of the gases 

 in the soils of fields with different treatments. In unmanured fallow 

 land in the spring of 1907, the amount of oxygen varied from 17.2 

 per cent at 3 to 6 inches to 15.5 per cent at 6 feet, the maximum being 

 18.6 per cent at 9 to 12 inches and the minimum 13.4 at 5 feet. The 

 carbon dioxid ranged from a minimum of 2.9 per cent at 3 to 6 inches 



