INFLUENCE OF ENVIRONMENTAL CONDITIONS 



795 



of growing plants on nitrification in soil. Lawes, Gilbert and War- 

 ington 113 were among the first to note that nitrogen of unmanured land 

 nitrifies with greater difficulty than nitrogen of land that has yielded 

 large crops. More than twice as much nitrate nitrogen was formed, 

 including the nitrogen in the crop and soil nitrate, in the plot growing 

 oats, than in the corresponding bare plot. 114 Certain plants, like 

 maize, may, during the most active periods of growth, stimulate the 



TABLE 91 

 Influence of plant upon the numbers of bacteria and evolution of CO2 



Triticum vulgare . 



Secale cereale 



Avena sativa 



Beta vulgaris .... 

 Medicago sativa . . 

 Trifolium pratense 



MILLIGRAMS OF COl 



PRODUCED BY 



1 KGM. OF SOIL IN 



24 HOURS AT 20°C. 



69.4 

 68.2 

 79.0 

 74.3 



86.8 

 82.4 



TABLE 92 

 Evolution of CO2 from 1 kgm. portions of different soils in 24 hours at 20°C. and 25 



per cent moisture 



formation of nitrates; during the latter periods of growth, when the 

 roots cease to grow and begin to undergo decomposition, the same 

 plants may exert a depressing effect. 115 This depressive influence was 



113 Lawes, J. B., Gilbert, J. H., and Warington, R. Nitrogen as nitric acid 

 in the soils and subsoils at Rothamsted. Jour. Roy. Agr. Soc, 19: 331-367. 1883. 



114 King, F. H., and Whitson, A. R. Development and distribution of nitrates 

 in cultivated soils. Wis. Agr. Exp. Sta. Bui. 93. 1902. 



115 Lyon, T. L., and Bizzell, J. A. Some relations of certain higher plants to 

 the formation of nitrates in soils. Cornell Univ. Agr. Exp. Sta. Mem., 1. 1913; 

 Jour. Frankl. Inst., 171: 1-16. 1911. 



