Soil Nitrate Studies 269 



NITRATE STUDIES ON PURDUE ROTATION FIELD 



No. 6. 



I. L. Baldwin, W. J. Nichter, and R. O. Lindsey, 



Purdue University. 



Nitrate formation in the soil, although primarily a chemical trans- 

 formation of protein nitrogen to nitrate nitrogen, is occasioned by the 

 activities of certain groups of micro-organisms in the soil. Since the 

 transformation is so dependent on the life processes of these organisms 

 it is subject to the factors which ordinarily control living matter as 

 well as those which regulate simple chemical phenomena. The following 

 factors seem, from a study of the literature, to be most important: 



Kind of soil, organic matter content of the soil, soil reaction, tem- 

 perature, moisture, aeration, presence of suitable organisms, and the 

 kind of crop grown. It was the latter point, the effect of the kind of 

 crop and cropping system, that has been considered primarily in this 

 study, although the other factors have been taken into consideration 

 to a certain extent. 



The plots on which this study was made, Purdue Rotation Field 

 No. 6, were admirably adapted to the work, as they have been cropped 

 and fertilized under a definite system since 1889, giving time enough 

 for the soil conditions to have reached a constant in so far as these fac- 

 tors are concerned. 



The work reported here is a continuation of work started in 1920 

 and first reported in the 1921 Proceedings of the Indiana Academy.' 

 Inasmuch as this is purely a continuation of the work reported in the 

 above paper and the technic used in the work is the same as that previ- 

 ously employed, with one exception, reference will be made to that 

 paper for a resume of the literature and a discussion of the technic em- 

 ployed. 



In any study of nitrate formation, the data secured from a one 

 year study of the problem are subject to considerable error as climatic 

 and cultural conditions influence the process so markedly. In continu- 

 ing the study over a series of years using the same plots, it is hoped 

 to minimize the inconsistencies due to factors which vary from year to 

 year and more closely narrow the problem down to a study of the one 

 factor of crop influence on nitrification. 



Tests were made every two weeks throughout the growing season 

 in this work, instead of every month throughout the year as in the 

 work previously reported. From past experience it seems that this 

 is a more accurate measure of the factors concerned. 



Effect of Various Crops on Nitrifying Power of Soil. 



The following set of tables shows the moisture content, and nitrates 

 in parts per million for the various rotations. The nitrates in all cases 



1 Baldwin, I. L., Coble, U. L., and J. W. Chamberlain. Crop rotation as affecting 

 nitrate production. Proc. Ind. Acad. Sci., 1921 (1922), pp. 283-293. 



"Proc. Ind. Acad. Sci., vol. 33, 1923 (1924)." 



