RESPIRATION AND OXYGEN. 41 



to 8.2 per cent at 6 feet, the maximum being 8.5 per cent at 1 and 5 

 feet approximately. In manured land in October, the oxygen was 



11.4 and 13.2 per cent, and the carbon dioxid 1.98 and 5 per cent at 

 9 to 12 and 29 to 30 inches respectively. In December, the oxygen 

 was 14.7, 14.7, 13.6, and 17.8, and the carbon dioxid 6.8, 4, 10, and 

 4.3 per cent at 9 to 12, 19 to 20, 29 to 30, and 40 to 43 inches re- 

 spectively. Fallow land after green-manuring gave a range of 10 to 



12.5 per cent of oxygen at various depths, and of 3.5 to 10.1 per cent 

 of carbon dioxid with one crop and a maximum of 18.4 per cent with 

 another. The gas from swamp rice-land yielded the following aver- 

 ages: nitrogen, 85.57 per cent; oxygen, 0.54 per cent; carbon dioxid, 

 4.42 per cent; hydrogen, 5.75 per cent; methane, 2.81 per cent; argon, 

 0.893 per cent. The amount of oxygen in soil at various depths up 

 to 15 inches about the roots of Crotolaria juncea ranged from 2.23 to 

 9 per cent, and the C0 2 from 4.84 to 16.99 per cent; about the roots of 

 Indigofera arrecta, the respective ranges were 3.33 to 5.24 per cent 

 and 12.62 to 21.14 per cent, and about those of Zea mays, 6.28 to 

 13.82 per cent and 3.34 to 12.30 per cent. The amount of oxygen 

 in fallow land decreased about 1 per cent after nitrification, and the 

 carbon dioxid increased slightly, while nitrification in vessels usually 

 reduced the oxygen from 20.93 per cent to less than 1 per cent, and 

 resulted in the production of 12 to 24 per cent of carbon dioxid. The 

 outstanding results are the relatively low content of oxygen and high 

 carbon-dioxid content about the roots of plants, and the great 

 amounts of oxygen used and carbon dioxid evolved in nitrification. 



Russell and Appleyard (1915 : 1) have studied the free air of 

 Rothamsted soils and found that to a depth of 6 inches it differs 

 from atmospheric air in containing about 10 times as much carbon 

 dioxid, namely, 0.25, in contrast to 0.03 per cent, and practically the 

 same amount of oxygen, 20.6, as against 20.96 per cent. During 

 rapid nitrification there is a perceptible falling-off of oxygen and a 

 still greater one in water-logged soils. The air dissolved in the water 

 and the colloids of the soils consists chiefly of carbon dioxid and nitro- 

 gen, and contains practically no oxygen. Variations in the compo- 

 sition of the free air arise mainly from fluctuations in the chemical 

 processes of the soil, the curves following those of the amount of 

 nitrate and the bacterial counts. Weather conditions appear to 

 have little effect upon the soil-air, and no evidence was obtained 

 that growing crops greatly increase the carbon dioxid in it. The 

 dissolved oxygen brought in by rainfall is a factor of considerable 

 importance in renewing the soil-air and facilitating chemical change. 



Hole and Singh (1916) find that when rain-water with an initial 

 content of 1 mg. of carbon dioxid and 7 mg. of oxygen was kept in 

 contact with the loam of a sal forest, the oxygen fell to 1 mg. and the 

 CO 2 rose to 60 to 70 mg. in 2 days, and then to 230 mg. in 28 days. 



