26 SEASONAL NITRIFICATION AS INFLUENCED BY CROPS, ETC. 



Stoddart, and McLeod found that the difference in the amount of 

 nitrogen between virgin land and cropped land was not enough to 

 account for the crops removed, and they suggest that this fact is due 

 to the removal of nitrogen by bacteria. Their work was carried on in 

 humid regions, however, where leaching would affect the distribution 

 of nitrogen in the soil. 



In an area such as the prairie region represented, where the amount 

 of rainfall is rather limited, there would be an accumulation in the 

 fallow plat of both water-soluble and albuminoid nitrogen. The crop 

 would have the advantage of the nutritive condition of the soil solu- 

 tion represented on July 31 in figure 1, as compared with the less 

 favorable conditions obtaining on April 27 in figure 2. 



It should be kept in mind that the plats on which the determina- 

 tions were made were "dry farmed," and it is not intended strictly to 

 apply to irrigated lands the conclusions derived from this work. 

 Irrigation would in all probability cause disturbances in the bacterial 

 processes in the soil, and so, to some extent at least, mask the seasonal 

 activities of the bacterial flora by translocation of the nitrates and by 

 intermittent wetting and drying. It is likely, however, that by 

 properly controlling the work the same general phenomena would be 

 observed. 



RELATION OF NITRIFICATION TO SUMMER FALLOW. 



As will be noticed from figure 3, the summer-fallow plat contained 

 on July 31 about 35 parts per million more of water-soluble nitrates 

 than did the wheat plat, which would present a more favorable nutri- 

 tive condition than found in the cropped plat. In view of the fact, 

 however, that the fundamental phenomena underlying nitrification 

 are the same in both the cropped plats and the fallow plat, it would 

 seem that summer fallow would be of doubtful economic value so far 

 as the use of nitrates is concerned. The various curves distinctly 

 show that nitrification is affected in degree but not in kind by the 

 presence of a growing crop, and it is certainly likely, with this point 

 in view, that nitrates were formed to as large an extent in the wheat 

 plat as in the summer-fallow plat ; interest on the investment would 

 be lost from the fallow land while lying idle, when by suitable treat- 

 ment of the soil use could as well be made of the products of the 

 nitrifying organisms each year as to allow the land to lie idle. The 

 bacterial groups active in producing soluble nitrates and albuminoid 

 nitrogen, feeding largely on the organic matter in the soil, would of 

 course reduce their food supply more rapidly in a system of fallowing 

 than in a system of crop rotation, where organic matter is continually 

 being added to the soil. Another serious objection to summer fal- 



oWhitson, A. R., Stoddart, W. C, and McLeod, A. F. Twenty-Third Annual 

 Report, Agricultural Experiment Station of the University of Wisconsin, 1906, pp. 



160-170. 

 173 



