Importance of Nitrogen Fixation 227 



of inoculated clover. All the subsequent reports point to large in- 

 creases in soil nitrogen due to the gro\Vth of leguminous plants in 

 the presence of specific bacteria. Poor soils usually show larger 



0.50 



0.45 



0.40 



0.35 



0.30 



0.25 



0.20 



0.15 



0.10 



0.05 



^H N obtained from soil 



E22 N added in NaNOj 



I I N obtained from atmosphere 



^ 



^ 



'/.. 







1200 



200 400 600 900 

 NaNOa pounds per acre 

 Fig. 93. Relation between soil and atmospheric nitrogen obtained by a crop 

 of inoculated alfalfa growing on soil variously treated with sodium nitrate ( from 



Giobel ) . 



gains than rich soils. Soils to which lime and phosphorus compounds 

 have been added show greater increases in combined nitrogen than 

 do soils in which these are lacking. Inoculated soils give higher 

 increases than uninoculated, especially if the particular legume has 



