CARBON AND NITROGEN CYCLES IN THE SOIL 179 



amounts of nitrogen found as nitrate in the drainage waters 

 were added up and found approximately to equal the total 

 loss of nitrogen from the soil (Table XLVIIL). 



The obvious uncertainty attaching to so prolonged an 

 experiment is reduced in this case by the fact that the 

 determinations were for the last twenty-eight years of the 

 period made by the same analyst. Miller found that the rate 

 of loss of nitrogen (estimated by the quantities of nitrates in 

 the drainage water) was about 40 Ib. per annum in the earlier 

 years, and fell below 30 Ib. and finally below 25 Ib. per 

 annum in the later years. The experiment is not fine enough 

 to justify any discussion of the small balance, but it shows 

 that the loss of nitrogen is mainly due to leaching out of 

 nitrates. 



TABLE XLVIII. CHANGES IN NITROGEN CONTENT OF A SOIL KEPT FREE 

 FROM VEGETATION FOR FORTY-SEVEN YEARS, BUT EXPOSED TO RAIN AND 

 WEATHER. MILLER (2006), RUSSELL AND RICHARDS (241^). 



It is unfortunate that this highly important experiment has 

 not been repeated with other types of soil, because there is 

 evidence that a richer soil would lose more nitrogen than is 

 accounted for by the nitrates formed, the rest presumably 

 escaping as gas. 



Consideration of the curves for the rate of washing out of 

 nitrate led Russell and Richards (24 1) to suppose that there 

 must be a nitrate immobiliser, probably certain organisms, 

 functioning in soils even when uncropped, taking up a part of 

 the nitrate formed and only slowly liberating it. 



1 After deduction of the amount brought down in the rain. The upper line 

 of figures refers to the 20 inch and the lower to the 60 inch gauge. Some nitrate 

 is no doubt contributed by the sub-soil. 



12* 



