E. J. Russell and A. Applbyard 



31 



alike the effect of the crop is not very great. Absolute identity of 

 conditions has not been attained, and we cannot yet be certain whether 

 the small effect of the crop still observed is due to uneliminated soil 

 differences such as the removal of water by the growing crop which 

 thus facilitates the escape of ('Oj evolved from the plant roots; or to 

 some direct interference of the growing crop with bacterial activity in 

 the soil. 



A wholly different argument in a previous paper i, led to the con- 

 clusion that the growing plant interferes with bacterial activity. 



Before leaving this subject attention must be directed to one 

 interesting point in connection with the two Broadbalk plots, the dunged 

 arable and the wilderness. The arable plot shows a persistent loss of 

 nitrogen amounting to over 100 lbs. per acre per annum, apparently 



21-0 



•8 



•6 



•4 



•2 

 20-0 



C 



ti '8 

 >-. 



K 



O .6 



•4 



•2 

 19-0 



bi.b. Mar, 



Fig. 13. Curves 



Apr. iM.iv June July Aug.Sept: Oct. 



showiii" 0, ill soil air 



Nov. Die. Jan. Fi-b. Mar. Apr. Miiv June July AuR.Sept. 



of Broadbalk dunged and wilderness plots 



not wholly by drainage. The wilderness, on the other hand, shows a 

 persistent gain of nitrogen amounting approximately to 100 lbs. per 

 acre per annum. We have hitherto been inclined to attribute this 

 remarkable difference to a supposed greater aeration influencing tlie 

 biochemical changes in the arable land. It is therefore of special 

 interest to compare the oxygen content of the air from the two jjlots : 

 this has been done in Fig. 13, from which it appears that there is little 

 if any difference between them. 



Amount of CO2 lender plants of various species. On some of the 

 Rothamsted grass plots and especially those that have become acid 

 there is a tendency for certain species to segregate; determinations 

 were therefore made of the percentage of CO., in the soil air of these 



1 ' The nature and amount of the fluctuations in nitrate contents of arable soils,' 

 J. A(pic. ,'^c). 1914, 6, 18-57. 



