XIV CONTENTS. 



CHAPTER III. POSITION OF NITROGEN IN 

 AGRICULTURE. 



The Rothamsted experiments and the nitrogen question . . 115 



Different forms in which nitrogen exists in nature . . .116 



Relation of "free" nitrogen to the plant . . . .117 



Combined nitrogen in the air . . . . . .118 



Amount of combined nitrogen falling in the rain . . 119 

 Nitrogen in the soil . . . . . . . .120 



Nitrogen in the subsoil . . . . . . .121 



Nitrogen of surface-soil 121 



Amount of nitrogen in the soil . . . . . .123 



Soils richest in nitrogen 123 



Nature of the nitrogen in the soil . . . . .124 



Organic nitrogen in the soil . . . . . .125 



Differences of surface and subsoil nitrogen . . .126 

 Nitrogen as ammonia in soils . . . . . .127 



Amount of ammonia in soils ...... 127 



Nitrogen present as nitrates in the soil . . . .128 



Position of nitric nitrogen in soil . . . . .128 



Amount of nitrates in the soil . . . . . .129 



Amount of nitrates in fallow soils 129 



Amount of nitrates in cropped soils . . . . .130 

 Amount of nitrates in manured wheat-soils . . . 131 



The sources of soil-nitrogen 131 



Accumulation of soil-nitrogen under natural conditions . 133 

 Accumulation of nitrogen in pastures . . . .134 



Gain of nitrogen with leguminous crops . . . 1 35 



The fixation of " free " nitrogen ..... 136 



Influence of manures in increasing soil-nitrogen . . 136 

 Sources of loss of nitrogen . . . . .137 



Loss of nitrates by drainage . . . . . .137 



Prevention of loss of nitrogen by permanent pasture and 

 "catch-cropping". . . . . . . .138 



Other conditions diminishing loss of nitrates . . .139 

 Amount of loss of nitrogen by drainage . . . .140 



Loss of nitrogen in form of " free " nitrogen . . .141 

 Total amount of loss of nitrogen . . . . .142 



Loss of nitrogen by retrogression .... 



Artificial sources of loss of nitrogen . . . . .144 



Amount of nitrogen removed in crops . . . .144 



