CH. iir] 



Nitrijication 



43 



upon by certain soil bacteria, the Nitrosomonas, and 

 converted into a nitrite, and this taken by another group 

 of organisms, the Nitrobacter, and converted into 

 nitrate; the process is called nitrification. Thus the 

 ammonia actually appears as nitrate which is readily 

 found in the soil by the simple test given in the Appendix 

 (p. 228). The amount of nitrate is commonly stated as 

 so many parts of nitrogen per million parts of soil ; they 

 can be expressed as parts of nitrate of soda by multi- 

 plying by 6, or they can be converted into lbs. per 

 acre in the top 9 inches by multiplying by 2|; the 

 results are not quite accurate but suffice for purposes 

 of comparison. 



The following amounts of nitrate were commonly 

 found in the author's investigations of various soils: 



Nitrates do not accumulate to any great extent in the 

 soil in our climate, and it is very unusual to find more 

 than 24 parts per milhon or 120 lbs. per acre (expressed 

 as nitrogen) in the top 18 inches. As soon as these high 

 values are reached further production ceases. It some- 

 times happens in dry regions that higher amounts are 

 present, but it is usually supposed that they got there 

 by evaporation of water which has soaked in from some- 

 where else, concentrating the nitrates from a wide area 

 over a particular spot. 



