28 SEASONAL NITRIFICATION AS INFLUENCED BY CROPS, ETC. 



the time from June 19 to July 17; at the latter date the nitrates had 

 probably been reduced by the corn roots to the lowest limit possible. 



The wheat and corn plants reduced the nitrates to a constant 

 amount — about 15 parts per million in the dry soil. The wheat 

 removed the moisture also to a fairly constant degree, namely, about 

 15 per cent. 



Denitriflcation, as measured by the nitrites found, could not 

 account for the changes occurring in the nitrate content in the soil 

 layers. 



No correlation could be established between the amounts of nitrates 

 and the air temperature or between the nitrates and the soil moisture. 



Translocation of the nitrates by. rain could not account for the 

 seasonal changes in the amounts of nitrates in the different soil layers. 



The general increase and decrease in water-soluble nitrates followed 

 the same course in the fallow plat and in the cropped plats, the only 

 general difference being that there were more nitrates in the fallow 

 plat after May 16 than in the wheat plat. 



It is suggested: 



(1) That the marked increase in the amounts of water-soluble 

 nitrates in the individual soil layers, followed by marked decrease 

 in the same, and not at any time again reaching the same quantity, 

 is due to a seasonal physiological activity of the bacterial flora, 

 depending upon the climatic and nutritive factors in the soil, or else 

 the seasonal changes are due to a rythmic periodicity of activity in 

 the nitrifying organisms during tlie season, the nature of which 

 could not be made clear by the data obtained. 



(2) That the general decrease in amounts of water-soluble nitrates 

 from June 12 to June 19 may be due to the formation of albuminoid 

 nitrogen by other groups of bacteria which may have become most 

 active at this time; that the excessive accumulation of nitrates or 

 the accumulation of other by-products by the nitrifying organisms 

 may have inhibited further activity on their part. " 



(3) That, while the summer-fallow plat contained at the end of the 

 season more water-soluble nitrates than did the corn and wheat 

 plats, the same general phenomena of nitrification are found to take 

 place in both fallow and cropped plats; hence the extended practice 

 of summer-fallowing would seem to be of doubtful value so far as the 

 accumulation of nitrates in the soils represented by this station is 

 concerned. 



Note. — Since this bulletin was put into type, a review of Kansas Station Bulletin 

 161, appearing in the Experiment Station Record, vol. 22, no. 1, p. 21, gives as one 

 of the conclusions arrived at by the authors, that "bacterial life and activity seem 

 to rise and fall with more or less regularity. These periods of maximum and mini- 

 mum activity are to a certain extent independent of moisture and temperature, and 

 are possibly due to the presence of bacterial by-products." This conclusion corre- 

 sponds closely with the work herein described and shows that other bacterial groups 

 besides the nitrifying flora have the periodicity mentioned in this bulletin. 

 173 



