ORGANIC COMPOUNDS OF SOILS 93 



Hurnic phos- Humic 



phoric acid. potash. 



Sawdust humus : Grams. Grams. 



In original sawdust and soil 0.85 0.67 



In final humus product 0.78 0.70 



Oat straw humus : 



In original straw and soil 1.02 2.42 



In final humus product 1.03 2.41 



100. Comparative Value and Composition of Hu- 

 mates. — The humus produced from nitrogenous 

 bodies, as meat scraps, is more valuable than that pro- 

 duced from cellulose bodies as sawdust, because the 

 former have a greater power of combining with the 

 phosphoric acid and potash of the soil. The non- 

 nitrogenous compounds, as cellulose, starch, and sugar, 

 undergo fermentation but seem to possess little, if any, 

 power to form humates. There is also a great differ- 

 ence in soils as to their humus-producing powers. 

 Soils deficient in lime or alkaline compounds possess 

 only a feeble power to produce humates. There is 

 also a marked variation in the composition of the 

 humus produced from different kinds of organic matter. 

 Straw, sawdust, and sugar, materials rich in cellulose 

 and other carbohvdrates, vield a humus characteris- 

 tically rich in carbon and poor in nitrogen. Materials 

 rich in nitrogen, like meat scraps, green clover, and 

 manure, produce a more valuable humus, rich in nitro- 

 gen and possessing the power to combine with the 

 potash and phosphoric acid of the soil to form 

 humates. 



