614 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



nite constituents given in earlier reports has been very greatly in- 

 rronsod by (lie isolation and identification of some 20 additional 

 c()Mij)()iinds, making a total ol" over J55 organic soil constitutents iilen- 

 tified to this time. There are now representatives of nearly every im- 

 portant chemical class among these compounds — hydrocarbons, acids, 

 bases, alcohols, esters, aldehydes, fats, waxes, resins, etc. — some con- 

 taining nitrogen, phosphorus, and sulphur in organic combinations. 

 The interrelationship between the compounds throws light upon the 

 biochemical transformations which take place in soils under the in- 

 fluence of the microorganisms of the soil, the various classes of bac- 

 teria, molds, protozoa, etc., as well as of the enzyms from these and 

 the influence of the roots of the higher plants. The discovery and 

 identification of these soil constituents have already brought order out 

 of the chaos that existed in regard to humus formation and transforma- 

 tion in soils under different conditions. The results have been made 

 possible by the installation of an equipment that has permitted the 

 handling of tons of soil in the course of these investigations. 



The most noteworthy discovery in connection with the effect of 

 these soil compounds on plants has been the fact that of the nitro- 

 genous constituents there are many that can serve directly as plant 

 nutrients without first undergoing further decomposition into am- 

 monia, nitrites, or nitrates as commonly accepted. Such nitrogenous 

 soil constituents as the decomposition products of the complex protein 

 and nucleo-protein molecules of plant and animal substance are shown 

 by these researches to l^e able to replace nitrates in plant growth, and 

 when present in soils or nutrient solutions are absorbed by plants, 

 with an increase in plant development, the nitrates wdien also present 

 being consumed by the plant in much smaller quantity than when the 

 organic nitrogenous soil constituents are absent. These nitrogenous 

 compounds are present in soils in quantities approximating the 

 nitrate content in normal soils, and this discovery of their function 

 in soils throws much light upon the relations between nitrification 

 and soil fertility and gives a new conception of the problem of the 

 nourishment of plants by soils. 



Certain of the biochemical factors in soils have also received de- 

 tailed consideration during the last j^ear, especially soil oxidation and 

 soil catalysis. These two properties of soils have been quantitatively 

 measured and their relations to each other and to other soil factors 

 studied. It has been found that both of these factors are most 

 strongly developed in virile soils and are weak in or absent from poor 

 soils. The.y are influenced by fertilizer treatment, especially by the 

 addition of soil ameliorators, such as lime, manganese salts, etc. 



The origin of some of the organic soil constituents has received 

 much attention. Their chemical relationships throw much light upon 

 the class of compounds from which they are derived, but the agencies 

 which effect these transformations are not yet clearly definite. Atten- 

 tion has therefore been given to the question of origin of these sub- 

 stances from plant debris, from plant roots by excretion, and from 

 microorganisms, especially molds. It has become quite clear as the 

 result of these researches that plant roots contribute some of these 

 compounds to the soil or water in which they grow, and also that 

 molds contribute such substances both as the result of their own life 

 processes and afier the death of the cells. 



