CARBON AND NITROGEN CYCLES IN THE SOIL 81 



TABLE XXXIII. RATES OF OXIDATION, ORDER OF PRODUCTIVENESS, AND ANALYTICAL 

 DATA FOR CERTAIN WOBURN SOILS. RUSSELL (238). 



darkness, and, therefore, unlike plants, derive no energy from light ; in- 

 deed light is fatal to many of them. So much are they dependent on 

 oxidation that in those soils where oxidation proceeds very slowly, as 

 in certain moorland soils, there is a corresponding diminution in the 

 micro-organic population. 



The chemical investigations of the nitrogen cycle in soils have 

 usually been confined to changes in the percentage of nitrogen and in 

 the amount of nitrate present, and consequently they throw little light 

 on the actual reactions taking place. Incomplete as they are, how- 

 ever, they have served a useful purpose by indicating the nature of the 

 problem and furnishing material that has helped in unravelling the 

 rather complex changes going on. Four cases have been studied. 



1. The simplest is that of an ordinary arable loam kept moist, aerated, 

 and at IO-I5C. these being normal conditions free from vegeta- 

 tion and from the washing action of rain these being abnormal condi- 

 tions. A considerable formation of nitrate then takes place, about 3 

 per cent, per annum of the nitrogen being converted, and generally 

 there is a small loss of nitrogen, presumably in the free state. How 

 far the accumulation of nitrate would go under these circumstances 

 has never been ascertained, because the experiment is necessarily very 

 slow. Boussingault (49) stated that in eleven years one-third of the 

 nitrogen of a rich soil changed to nitrate, and about one-half of the 

 carbon to carbon dioxide. 



2. If the conditions are made more normal by exposing the soil 

 (still kept free from vegetation) out-of-doors to the action of rain and 



