E. J. Russell and A. Appleyard 35 



33 hours failed to show any systematic variation as between the day 

 and the night. The results are given in Table VIII. The CO2 tends 

 to rise and the oxygen to fall from the 18th hour onwards {i.e. from 

 3.30 a.m. on the 15th) when the barometer is steadily falling, but there 

 is no sign of any relationship with the temperature either of the air 

 or the soil. 



Table VIII. Hourly fluctuations in composition of soil air, 

 'd-kour periods over 33 consecutive hours. 



Hour 



Time Nov. 14 







X.M. 



:i.:50 



3 



P.M. 



12.. 30 



(i 



P.M. 



3..30 



9 



P.M. 

 (j.30 



12 



P.M. 



9.30 



Hoiir 



Timc Nov. 15 



15 

 12.30 



IS 



A..AI. 



3.30 



21 



A.M. 



0.30 



24 



A.M. 



9.311 



27 



l'..M. 



12..30 



30 



P.M. 



3.30 



33 



P.M. 



6.30 



(4) Cultivation. We have not made systematic investigations into 

 the effects of the various cultivation operations, but we find that 

 ploughing usually increases the percentage of oxygen and diminishes 

 the CO3 in the soil air, the fall in CO2 being particularly marked when 

 the ploughing is done early. The details are given in Table IX, where 

 also are set out the analvtical data for the uncultivated wilderness. 



The relation between carbon dioxide prod act ion, nitrate 

 formation and bacterial numbers. 



The curves showing the amounts of carbon dioxide in the soil air 

 and of nitrate in the soil are so similar in character as to justify the 

 view that both essentially represent the rates of formation (p. 12). 

 Closer comparison of the curves with those for bacterial numbers 



3—2 



