18 MASS. EXPERIMENT STATION BULLETIN 333 



which they have reported in Soil Science. Both soil and soil bacteria showed 

 active fixation of nitrogen from the air under laboratory conditions. 



Legume bacteria, the ability of which to fix nitrogen from the air has been 

 accepted for years, have been shown by Allison in the Journal of Agricultural 

 Research, and by Hopkins and by M. Loehnis in Soil Science, to be unable to 

 do so when the roots of legumes are not present in the soil. Legume influence 

 in the nonlegume subplots must have been reduced to the minimum, if not 

 wholly eradicated. 



Discussing in Soil Science the work of the First International Congress of 

 Soil Science, Waksman asserted that the literature about Azotobacter pre- 

 sented no valid proof that such bacteria were of any use in the soil under field 

 conditions. Winogradsky, in the Congress, pointed out that organic matter 

 and temperatures used in laboratory studies were wholly unlike known con- 

 ditions in the field. Nevertheless, the studies by Bradley and Fuller showed 

 that there were possibilities of fixation of nitrogen in these plots from the air 

 about them, though their laboratory temperature was 82 3 F., which is possibly 

 never reached in our soils, although even higher temperatures are found in 

 soils of some sections of our country. Vandercaveye and Villanueva of the 

 Washington Agricultural Experiment Station have recently reported labora- 

 tory experiments with virgin soil, which showed in 80 days, at temperatures 

 between 69° and 76° F., fixation of nitrogen from the air, equivalent to 216 

 pounds per acre in the field, with only the soil organic matter. When filter 

 paper was supplied together with lime, the amount of fixed nitrogen was more 

 than doubled. These observations of Bradley and Fuller and of Vandercaveye 

 and Villanueva aid in explaining the greater content of nitrogen in the summer 

 crops like corn and the millets, which are growing during the season of highest 

 temperatures. 



Waksman, describing the decomposition of organic matter in the soil, states 

 that it finally becomes humus and most of the soil nitrogen is contained in soil 

 humus. This material is often so stable that its nitrogen cannot be used by 

 plants, and plants will not thrive without added nitrogen in available forms. 

 Our repeated analyses of these soils indicate a somewhat stabilized percentage 

 of nitrogen, equivalent to approximately 3000 pounds per acre in the depth 

 of soil sampled. It has been already noted that legume fixation has not ap- 

 parently caused accumulation of nitrogen beyond the capacity of the growing 

 crops to use it. It is equally apparent that nonlegume crops have not lessened 

 the nitrogen in the soil as analyzed. It appears reasonable that continued 

 growth of nonlegumes on a soil wtihout nitrogen fertilizers maintains the soil 

 nitrogen, but limits crop production to a lower level than is possible when 

 legume crops are alternated with nonlegumes. 



USE OF NITROGEN FROM THE AIR 



The classic experiment of Lawes and Gilbert in 1858 proved that plants 

 could not use nitrogen from the air through their leaves as they were known 

 to use carbon dioxide, and their use of air nitrogen was doubted in 1883, when 

 Field A was laid out. By 1889, when the plots were devoted to a comparison 

 of nitrogen fertilizers, it had just been shown by Wilfarth and Hellriegel that 

 nodules on the roots of clovers, peas, and similar plants contained bacteria 

 that supplied the plants with nitrogen which came from the air and not from 

 the soil. Soybeans and clovers were introduced into rotations from time to 

 time. The importance of such crops in agricultural practice had long been 



