186 



HIGHER PLANTS AND SOIL MICROORGANISMS 



considering the soil both about roots and at a distance from 

 roots, the soil microorganisms produce a much larger amount of 

 carbon dioxide. 



The development of plants not only increases the production 

 of carbon dioxide from soils by contributing some gas from root 

 respiration, but also favors microbial processes to such an extent 

 that the organic matter already in the soil is more rapidly decom- 

 posed. This is shown in Table 45. 



TABLE 45 



The Influence of Plant Development upon Formation of Carbon 



Dioxide from the Organic Matter Contained in the Soil Previous 



TO Planting (from Neller) 



Plant 



Soybeans. . 

 Soybeans. . 

 Soybeans. . 

 Soybeans. . 

 Buckwheat 

 Field peas . 



Wheat 



Barley .... 



Carbon Dioxide from the Soil (Mgm.) 



Planted 



2,093.4 

 2,128.2 

 4,795.2 

 2,403.6 

 953.1 

 751.6 

 2,403.6 

 3,274.9 



Unplanted 

 soil 



1,737.0 

 1,281.8 

 2,320.7 

 1,196.8 

 440.1 

 440.1 

 1,196.8 

 2,532.4 



Increase 



due to 



planting 



356.4 



846.4 

 2,474 . 5 

 1,302.1 



513.0 



311.5 

 1,206.8 



742.5 



Per cent 



increase 



due to 



planting 



20.5 



66.0 

 106.6 

 108.8 

 116.6 



70.8 

 100.8 



29.3 



It is further apparent from Fig. 71 that plants increase the 

 evolution of carbon dioxide in the soil, but the course of forma- 

 tion of the gas appears to be distinct for each plant and related 

 to differences in characteristics of growth of the plants. SHght 

 effects appear in the early stages of growth, and abundant forma- 

 tion of carbon dioxide occurs when the plants reach stages of 

 extensive vegetative development. During degeneration the gas 

 is produced in less abundance, and subsequent to death there is 

 little excess over that produced where plants are not developing. 

 Since biennials have a much longer growing period than the 

 annuals, their influences upon the soil are much more prolonged. 



