246 DENlTRfFlCATION 



The published reports of the various stations are voluminous and 

 only the general conclusions reached can be considered here. They 

 were as follows: 



1. The losses of ammonia from manure are comparatively slight, 

 but the setting free of elementary nitrogen which is due to micro- 

 organisms and not chemical means may be considerable. 



2. With a limited supply of air in manure, the loss of elementary 

 nitrogen and of organic substance are not extensive, but the greater 

 the access of air the greater the loss of nitrogen, in some cases 

 becoming as great as 40 or 50 per cent. 



3. In ordinary conservation materials when applied in the usual 

 quantities, do not stop entirely the loss of nitrogen, but burnt lime 

 is quite effective in stopping denitrification. Solid excreta and straw 

 lose their nitrogen very slowly and no conservation material is 

 needed. It is only the nitrogen of urine which requires conservation. 



It is sometimes found that the addition of large quantities of 

 organic matter to a soil cause a decrease in crop yield. This is 

 especially true with regard to the carbohydrates and it has often 

 been interpreted as indicating rapid denitrification, but Pfeiffer 

 and Lemmermann have pointed out that there are at least three 

 factors which may play a part, namely: (1) direct injury to the 

 growing plants by large quantities of organic matter; (2) fixation 

 of soluble nitrogen by the increased activity of different organisms; 

 (3) denitrification proper. 



It is quite probable that the last is of the least importance, for 

 Voorhees and Lipman after ten years' investigations under care- 

 fully controlled conditions conclude " that at least with cow manure, 

 used at the rate of sixteen tons per annum for a period of ten years, 

 no destruction of nitrogen takes place. In view of the long duration 

 of the experiment and of the comparatively large amounts of 

 manure used in the course of the ten seasons, we must assume that 

 denitrification is not a phenomenon of economic importance in 

 general farming and under average field conditions. We have no 

 hesitation in emphasizing again the view expressed above that 

 under the wide range of field conditions, denitrification is not a 

 phenomenon of economic significance to the general farmer." 



Moreover, at Rothamsted a plot of ground, 0.001 acre in extent, 

 has been kept free from vegetation by hoeing for thirty-five years. 

 During this time it has lost one-third of its original stock of nitrogen, 

 but all except 110 pounds of this is accounted for by the nitrates 

 in the drainage water, as may be seen from the following : 



