NON~SYMBIOTIC NITROGEN FIXATION 155 



found it to be at least twenty-five pounds, Lohnis thirty-seven and 

 seven-tenths pounds, and the senior author tv^enty-five pounds per 

 acre annually. It is, therefore, conservative to state, as has Lipman, 

 that these organisms under favorable conditions add from fifteen 

 to forty pounds of available nitrogen to each acre of soil yearly. 



