INFLUENCE OF NITRATE UPON NITROGEN FIXATION 121 



The presence of some nitrate in the soil appears greatly to bene- 

 fit growth of certain leguminous plants and fixation of nitrogen. 

 This is particularly the case with legumes, such as alfalfa and the 

 clovers, which produce tiny seeds. The reserve nitrogenous food 

 material in the seeds is insufficient to enable the plants to develop 



NaNOj-lb. 100 

 per Acre 



200 400 600 800 1,000 



Fig. 58. — Relation between soil and atmospheric nitrogen obtained by a crop 

 of inoculated alfalfa growing on soil variously treated with sodium nitrate 



(from Giobel). 



substantial root systems without drawing upon some nitrogen 

 from the soil. It is during this stage that nitrates greatly favor 

 the plants. After proper root development has taken place, inocu- 

 lated plants finding no combined available nitrogen in the soil 

 develop as well as those which are supplied with an abundance of 

 nitrate. Legumes having larger seeds, as beans and peas, are not 

 appreciably affected by the presence or absence of available forms 



