Humus 



Humus differs according to the manner in which 

 it is produced. 



ist. In arable soils, properly aerated and 

 sufficiently moist, and containing carbonate of 

 calcium. It is produced when the temperature is 

 favourable by bacteria and moulds. This formation 

 of humus is accompanied by a considerable reduction 

 in volume of the matter from which it is formed. The 

 losses are heaviest in oxygen, less in carbon, and 

 lightest in nitrogen. 



This is the finest humus. 



2nd. Another variety of humus is formed when 

 the surroundings are slightly acid and well-aerated, 

 but the bacteria are not so active because of the ab- 

 sence of carbonate of calcium, and soon give place 

 to moulds. This condition will be found in heather 

 lands and some pastures. 



3rd. A variety of humus is formed in marshes 

 by anaerobic bacteria. This formation of humus 

 under water is accompanied by the formation of 

 marsh gas. During periods of atmospheric depres- 

 sion this gas escapes sometimes in large quantities, 

 lights spontaneously and produces the will-o'-the- 

 wisps {ignis fatuus). This formation of humus 

 gives peat. 



As humus possesses all the animal and vegetable 

 matter of the soil, it gives off ammonia in decomposi- 

 tion, which later, under favourable conditions, is 

 transformed into nitrate and other bodies. 



This formation of ammonia will be the more rapid 

 in action because it will have the influence of more 

 carbonate of calcium and at a suitable temperature. 

 It is an important point in agriculture, for upon it is 



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