NITRATES AND NITRITES 157 



MUSTARD (Wagner). 



Yield of Grain and Straw. 



Soil without manure . . 1.6 grams. 



with nitrate of soda (2 



grams N.) . . 36.6 



with horse dung (2 grams N.) .5 

 with cow dung ( ) .4 



The amount of nitrogen recovered in the crop when 

 nitrate of soda was used alone in one case was 77 per 

 cent., whereas only 52 per cent, was recovered when the 

 nitrate was applied in conjunction with horse dung. 

 That the difference was due to the destructive action of 

 the horse dung on the nitrate was concluded from a 

 determination of the nitrates extracted with water from 

 soil treated with nitrate and nitrate plus dung in cases 

 where no crop was grown. A pot of soil to which 

 . 5 gram of nitrate of soda was added was compared with 

 one to which dung and the same amount of nitrate were 

 applied and left for an interval of six weeks. While 

 93 per cent, of the nitrate in the former appeared in the 

 extract, the pot receiving the dung in addition yielded 

 only 42 per cent. ; moreover, the filtrate from soil to 

 which no addition of nitrogenous manure had been made 

 was richer in nitrate -than that to which horse dung had 

 been applied, the latter having not only destroyed the 

 added nitrate, but also that naturally present in the soil 

 as well. 



The addition of chopped straw in large quantities 

 to soil containing nitrate has a similar effect to that 

 produced by fresh dung. 



The correct interpretation of the results of Wagner's 

 and Maercker's work is of importance since casual con- 

 sideration might lead to the conclusion that fresh horse 



