1914] Loughridge: Humus and Nitrogen in Calif ornia Soil Columns 175 



would be required." The experiments of Professor Harry 

 Snyder of Minnesota- on the humification of different materials 

 gave interesting results. Humification under favorable condi- 

 tions was allowed to proceed a year in each case, at the end of 

 which time the amount of humus obtained from each substance 

 and its composition was ascertained. Oat straw and sawdust 

 seemed unchanged even when humification was allowed to con- 

 tinue longer than a year. The following table illustrates some 

 of Snyder 's findings : 



Table 1. — Humus Obtained fkom Different Materials 



Fresh cow manure 33 parts for 1 part of humus 6.16% nitrogen in humus 



Green clover 25 parts for 1 part of humus 8.24% nitrogen in humus 



Meat scraps 11 parts for 1 part of humus 10.96% nitrogen in humus 



Sawdust 10 parts for 1 part of humus 0.30% nitrogen in humus 



Oat straw 6 parts for 1 part of humus 2.50% nitrogen in humus 



With ordinary green-manure crops and under field conditions it 

 will probably require a much larger amount of green material 

 to produce one part of humus, for there are losses from the 

 incomplete turning-under of the material and the drying-out of 

 the soil. 



It would naturally be supposed that as humus is formed by 

 the decay of roots, leaves, etc., it would be found only where 

 formed, whereas on the contrary, we find it quite evenly diffused 

 through the surface soil; this even distribution is not easily 

 accounted for without some outside agencies. Professor Hilgard, 

 in discussing the subject,^ attributes it chiefly to the action of 

 fungi, insects, and earthworms. 



The vegetative fibrils (mycelia) of several kinds of molds are constantly 

 present in the soil, and while consuming dead tissue of the higher plants, 

 spread their own substance throughout the soil mass. . . . All these being 

 dependent upon the presence of air for their life functions, remain within 

 such distance from the surface as will afford adequate aeration ; the depth 

 reached depending upon the perviousness of the soil and subsoil. In the 

 humid region this will usually be within a foot of the surface, but in the 

 arid may reach to several feet. . . . The earthworm nourishes itself by 

 swallowing, successively, portions of the surrounding earth, digesting a 

 part of its organic matter, and ejecting the undigested earth in the form 

 of "casts" such as may be seen by thousands on the surface of the 



2 Bulletin 53 Minn. Agr. Exp. Station. 



3 Soils (Macmillan & Co., 1906), p. 157. 



