1 56 DENITRIFICATION 



K 



conditions, was shown in an experiment carried out by 

 Warington. A column of soil was saturated so as to 

 drive out the air from the small spaces within it, the 

 water being allowed to percolate through so as to extract 

 all the nitrate present. After no reaction for nitrate was 

 obtained, a certain amount of nitrate of soda was then 

 placed on the surface of the soil and watered into it 

 daily. It was found that only 2 1 per cent, of the 

 amount applied to the soil could be recovered, 79 per 

 cent, being lost by denitrification : transverse fissures 

 developed across the soil at some depth below the 

 surface, these being due to the evolution of nitrogen and 

 carbon dioxide gas. 



In 1897 Wagner and Maercker drew attention to 

 some remarkable results obtained from the growth of 

 oats, mustard, and other plants in pots, to the soil of 

 which fresh undecomposed farmyard manure had been 

 applied alone or along with nitrate of soda. They found 

 that where fresh horse or cow dung were added in large 

 amount the crop yield was less than where no manure 

 at all was used, and also discovered that under certain 

 conditions the application of dung greatly depressed the 

 produce from soil which had received nitrate of soda as 

 well. The following are typical results : 



OATS (Maercker). 



Yield of Grain and Straw. 



Soil without manure . .44.82 grams. 



with nitrate of soda (1.5 



grams N.) . . 128.37 (i 86% increase). 



, with horse dung (2.25 / 35.91 (i) (20% decrease). 



grams N.) I 23.33 (2) (48% decrease). 



