110 SOILS AND FERTILIZERS 



found in surface well waters. In the soil, the 

 ammonium compounds may be oxidized and form 

 nitrates. Compounds, as ammonium chloride or am- 

 monium carbonate, if present in a soil in excessive 

 amounts, will destroy vegetation in a way similar to 

 the alkaline compounds in alkaline soils. 



131. Nitrogen in Rain- Water and Snow. The 



amount of 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 form of 

 the nitrogen in rain water is ammonium carbonate 

 which is present in the air to the extent of about 22 

 parts per million parts of air. 



132. 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 nitrogen, while soils from the humid regions 

 contain 4 to 6 per cent. 45 In some soils the ratio of 

 nitrogen to carbon may be i to 6, while in others it 

 may be i to 18, or more. That is, in the organic 

 matter of some soils there is i part of nitrogen to 6 

 parts of carbon, while in others the organic matter 

 contains i part of nitrogen to 18 parts of carbon. In 



