DISCUSSION OF RESULTS OF DETERMINATIONS. 13 



nitrates. Up to this time there were no great changes in the nitrates 

 in the 18 and 24 inch layers, but from May 22 to June 5 these layers 

 accumulated considerable amounts, and on the latter date the 18-inch 

 layer contained the maximum, which remained constant until the 

 next week, June 12. In the mean time, the 24-inch layer accumulated 

 considerable quantities of nitrates, reaching its maximum on June 12. 



It will be noticed in general that from April 27 to June 5 the 

 maximum amount of water-soluble nitrates shifted every two weeks 

 to the next lower layer and that once any layer had accumulated 

 a maximum it decreased and in general never again contained as 

 large amounts as the maximum of the next lower layer, which was 

 reached at a later date. 



From June 12 to June 19 there was an interesting change, in that 

 every soil layer which had recently been actively accumulating 

 nitrates suddenly showed a marked decrease in amounts of water- 

 soluble nitrates, and all of the layers on June 19 contained nearly 

 the same amount of nitrates. The upper 6-inch layer did not show 

 any such decrease, the reason for which will be discussed later on. 

 From June 19 till July 31 there were no regular changes, all of the 

 curves zigzagging irregularly. 



In view of the marked increases in the amount of nitrates in the 

 18 to 24 inch layer, it is to be regretted that determinations were not 

 made in the third foot also, but time did not permit the increased 

 work. The 18 to 24 inch layer never contained a maximum amount 

 of nitrates in comparison with the other layers, but the results cer- 

 tainly indicate that nitrification is quite active at a depth below 2 

 feet in these prairie soils when they are brought under cultivation. 

 Bazarewski a found very few nitrifying bacteria, however, at a depth 

 of 50 centimeters and reports that they were "plentiful at a depth 

 of 10 centimeters." It will be noticed from figure 1 that the 18 to 24 

 inch soil layer accumulated as much water-soluble nitrate as did the 

 to 6 inch layer, so nitrifying organisms are presumably active in 

 this prairie soil to a depth considerably greater than 2 feet. Hunt b 

 likewise reports that nitrification took place to but a small extent 

 below a depth of 2 feet, and the figures given by him show that under 

 the conditions discussed nitrification was not very active in even 

 the second foot. 



In this connection it may be of interest to mention, that the un- 

 broken prairie "gumbo" never becomes moistened deeper than 

 about 8 to 10 inches even after the heaviest rains. Cultivation, 



a Bazarewski, L. von. Nitrification and Denitrification in Soils. Reviewed in Ex- 

 periment Station Record, vol. 21, no. 1, July, 1909, pp. 20-21. 



b Hunt, T. F. The Importance of Nitrogen in the Growth of Plants. Bulletin 247, 

 New York (Cornell) Agricultural Experiment Station. 

 173 



