NON-SYMBIOTIC NITROGEN FIXATION 153 



ural conditions and which may be attributed to non-symbiotic 

 nitrogen fixation. 



There are, however, several' cases in which this has been meas- 

 ured with a fair degree of accuracy. Lipman, in pot experiments 

 carried on with a soil containing about 5,000 pounds of nitrogen 

 per acre-foot of soil, found a gain of more than one-third this 

 amount in two short seasons. Much of this must be attributed to 

 non-symbiotic nitrogen fixation. To these soils had been applied 

 solid and liquid manure which furnished to the organisms readily 

 available supplies of energy and various necessary inorganic con- 

 stituents. This fixation was not nearly so rapid where legumes 

 were turned under as green manures. Koch found a gain of 

 0.019 per cent in soil nitrogen during two seasons which must 

 be attributed to non-symbiotic nitrogen fixation. In addition to 

 this there was a threefold gain in the nitrogen content of the 

 crops — oats, buckwheat and sugar beets — which must also be 

 attributed to the action of Axotohacier, Hall noted an annual 

 gain of 100 pounds of nitrogen on Broadbalk field at Rotham- 

 sted and twenty-five pounds on Grescroft field. He feels that 

 much of this gain must be due to the action of non-symbiotic bac- 

 teria. Lipman points out that the actual gains of nitrogen are 

 even greater, for this does not take into consideration the various 

 losses which occur even under the best of conditions. 



The analysis of a great number of soils in Utah showed that 

 the average nitrogen content of the soil which had grown wheat 

 and other non-leguminous plants for from twenty to fifty years 

 was 0.2009 per cent, whereas adjoining virgin soil on the average 

 showed only 0.1984 per cent of total nitrogen. The evidence is 

 very strong that considerable nitrogen has been added to these 

 soils by microscopic organisms, as is shown by the following: 



1. In nearly every case the cultivated soil fixed much more 

 nitrogen in the laboratory than did the virgin soil. This was the 

 case when the soil was incubated with or without the addition of 

 carbonaceous material. 



2. There is a richer nitrogen-fixing bacterial flora in the cul- 

 tivated than in the virgin soil. 



