140 SOILS: PBOPJERTIWS AND MANAGEMENT 



Other end products, such as methane (CH4), hydrogen 

 disulfide (HgS), free nitrogen (N), sulfur dioxide (SO2), 

 carbon disulfide (CS2), and the Hke, may also result. 

 They are relatively unimportant, however, as regards 

 the plant, in comparison to the rdle played by carbon 

 dioxide, ammonia, the nitrites, and the nitrates. The 

 production of the nitrates from ammonia particularly 

 is very clearly correlated with good soil conditions, es- 

 pecially optimum moisture and adequate aeration. The 

 proper handling of the soil, then, not only will tend to 

 eliminate toxic matter and prevent its further formation, 

 but will encourage the proper decay of the soil humus and 

 the production of end products which will function directly 

 or indirectly as plant foods. 



Snyder ^ found that when humus was extracted with an 

 alkali and then precipitated with an acid, it yielded from 

 five to twenty-five per cent of a reddish brown ash. This 

 ash contained silica, iron, and alumina, as well as mag- 

 nesia, potash, phosphorus, sulfur, sodium, and calcium. 

 While part of these mineral constituents may be chemically 

 combined with humus, it is probable that some may be 

 present because of the adsorptive capacity of the organic 

 colloids which are always present in humus generated 

 under normal conditions. Snyder has estimated that 

 in an ordinary soil containing a fair amount of organic 

 matter, one-sixth of the phosphorus and one-twelfth of 

 the potash may be present in such a state. They are 

 then fairly available, and are yielded much more readily 

 to the plant than if of a strictly inorganic nature. 



95. Carbonized materials of soil. — After the extrac- 

 tion of the soil for the study of the ordinary humus com- 



^ Snyder, Harry. Production of Humus from Manures, 

 Minnesota Agr. Exp. Sta,, Bui. 53, pp. 29-30. 1807. 



