Chapter XL 



THE ORGANIC CONSTITUENTS OF THE SOU SOLUTION. 



The organic substances in the soil are tissue remains, to a large 

 extent of plants, and to a less extent of animals; and it is to be 

 expected that there may be found also in the soil the substances 

 which were in the organisms at the time of their death, and de- 

 gradation and decomposition products derived from these. More- 

 over, there are to be anticipated numerous products of bacterial 

 origin, secretions of algae, fungi, etc., so that the organic com- 

 plex in the soil may contain numerous substances of widely 

 different chemical characteristics. Degradation products of pro- 

 teins, fats, and carbohydrates, as well as decomposition products 

 may be expected in almost any soil. But it does not follow that 

 any particular organic substance (excluding, of course, carbon 

 dioxide or nitrates) is to be found in every soil. No general- 

 ization regarding the organic substances in the soil can be made 

 such as that formulated for the inorganic compounds. It is 

 probable that further investigation will show qertain organic 

 substances or classes of substances to be common to most soils, 

 but it is reasonably certain that many other organic substances 

 will be found in only a few soils, or occasionally, and these latter 

 will be often a prominent factor characterizing the particular 

 soil in which they may occur. 



Although no broad generalization is justified regarding the 

 composition of the soil solution with respect to organic sub- 

 stances dissolved, nevertheless the extension of the methods 

 developed in the study of the inorganic substances dissolved has 

 led to a considerable knowledge of the organic ones. 



In view of the facts shown in the preceding chapters, and 

 at the same time recognizing that good and poor soils respec- 

 tively must show differences in the soil solution if the funda- 

 mental thesis is valid as to the relation of soils to crop produc- 

 tion, experiments have been made to investigate in a comparative 

 way solutions obtained from good and poor soils of the same 

 type, locality, and physical characteristics. For this purpose 

 two samples of soil were taken from adjacent fields which had 



