XX OUTLINE AND TABLE OF CONTENTS 



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(2) Decomposition of non-nitrogenous organic 



matter (276). 



(3) Decomposition of nitrogenous organic 



matter (277). 



(a') Decay and putrefaction (278). 

 (b') Ammonification (279). 

 (O Nitrification (280). 



(1') Effect of organic matter on nitri- 

 fication (281). 



(2') Effect of soil-aeration on nitrifica- 

 tion (282). 



(3') Effect of sod on nitrification (283). 



(4') Depth at which nitrification takes 



place (284). 

 (5') Loss of nitrates from the soil (285). 



(4) Denitrification (286). 



(5) Nitrogen fixation through symbiosis with 



higher plants (287). 

 (a') Relation of bacteria to nodules on 



roots (288). 

 (b') Transfer of nitrogen to the plant (289). 

 (c') Soil-inoculation for legumes (290). 



(6) Nitrogen fixation without symbiosis with 



higher plants (291). 

 (a') Nitrogen-fixing organisms (292). 



(6') Mixed cultures of nitrogen-fixing 



organisms (293). 

 (c') Nitrogen-fixation and denitrification ' 



antagonistic (294). 



E. The Soil-Air 432 



I. Factors determining volume 432 



a. Texture (295). 



b. Structure (296). 



c. Organic matter (297). 



d. Moisture content (298). 



II. Composition of soil-air 434 



a. Analysis of soil-air (299). 



b. Production of carbon dioxid as affecting composition 



(300). 



