NITROGEN, NITRIFICATION, NITROGENOUS MANURES 



fixation. See Chapter VI. They cannot accumulate 

 in arable soils, because of nitrification and fixation. 

 Usually they are to be found in surface well waters. 

 In the soil, the ammonium compounds are acted upon 

 by nitrifying organisms, and nitrites and nitrates are 

 formed. Such compounds as ammonium chloride or 

 ammonium carbonate, if present in a soil in excessive 

 amounts, will destroy vegetation in a way similar to 

 the alkaline compounds in alkaline soils, but in small 

 amounts they are beneficial. 



142. Nitrogen in Rain Water and Snow. Ordinarily 

 the nitrogen which is annually returned to the soil in 

 the form of ammonium compounds dissolved in rain 

 water and snow is equivalent to from 2 to 3 pounds 

 per acre. At the Rothamsted Experiment Station the 

 average amount for eight years was 3.37 pounds. 44 

 When a soil is rich in nitrogen the gain from rain 

 and snow is only a partial restoration of that which 

 has been given off from the soil to the air or lost in the 

 drain waters. The principal forms of the nitrogen in 

 rain water are ammonium carbonate and nitrates and 

 nitrites, present in the air to the extent of about 22 parts 

 per million parts of air. 



143. Ratio of Nitrogen to Carbon in the Organic 

 Matter of Soils. In some soils the organic matter is 

 more nitrogenous than in others. In those of the arid 

 regions the humus contains from 15 to 20 per cent of 



