544 NATURE AND PROPERTIES OF SOILS 



Not only do the products of the first stage of decay influ- 

 ence the crop growing on the soil, but they affect the biological 

 activities as well. 1 Nitrification in particular seems to be in- 

 fluenced, as nitrates do not begin to appear until the process 

 of humification is well advanced. Nitrification, however, is 

 probably not entirely suppressed as it is possible for soil or- 

 ganisms to use up the nitrates as rapidly as they are formed. 



TIME AFTER APPLICATION 



Fig. 64. — Diagram illustrating the three stages in the decay of a 

 green-manure. I, humus production dominant; II, a balance be- 

 tween humus production and destruction; III, humus destruction 

 dominant. A depression in nitrate accumulation generally occurs 

 in stage I followed by an increase. (After Martin.) 



As the humus destruction gradually dominates over humus 

 production, the end products of the decay become prominent. 

 The complex proteid decomposition is practically completed 

 and cellulose destruction is slowly progressing. Of the sim- 

 ple nutritive products, the nitrates are of particular impor- 

 tance. In fact, they have been chosen by a number of in- 



1 Briscoe, C. F., and Harned, H. H., Bacterial Effects of Green 

 Manures; Miss. Agr. Exp. Sta., Bui. 168, Jan. 1915. 



Hutchinson, H. B., The Influence of Plant Residues on Nitrification 

 and on Losses of Nitrates in Soil; Jour. Agr. Sci., Vol. IX, Part 1, 

 pp. 92-111, Aug. 1918. 



