THE COMPOSITION OF THE SOIL 



145 



The Nitrogen Compounds in the Soil. 



It is convenient to collect together the main ^d:/'^ connected 

 with the nitrogen compounds of the soil. The total nitrogen 

 in arable soils is usually about 0*15 per cent, in pasture soils 



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about 0-3 per cent, ; higher amounts are present in chalk soils 

 and still higher in fen, moorland, and black prairie soils. 

 About half of the nitrogen in arable soils is contained in 

 compounds soluble in alkalis, and a small proportion in un- 

 stable compounds readily breaking down to ammonia. The 



10 



