12 SEASONAL NITRIFICATION AS INFLUENCED BY CROPS, ETC. 



DISCUSSION OF RESULTS OF DETERMINATIONS. 



NITRATES IN THE FALLOW PLAT. 



Figure 1 shows the parts per million of nitrates calculated for the 

 oven-dried soil in each 6-inch layer in the fallow plat from April 27 

 to July 31 and the precipitation for the same period. About 1 inch 

 of rain had fallen from April 1 to April 27. The weekly periods are 

 laid off on the abscissa, and the parts per million of nitrates on the 

 ordinate. The precipitation scale is on the right-hand side of the 

 figure. 



The first two sets of determinations show decreasing amounts of 

 nitrates from the surface 6-inch layer downward, the second foot con- 



Fig. 1.— Diagram showing the parts per million of water-soluble nitrates in dry soil in the fallow plat in 

 each &-inch soil layer to a depth of 2 feet; also precipitation curve. 



taining very small amounts. There were no marked changes until 

 May 9, when the surface 6 inches of soil showed a considerable increase 

 in nitrates, and it is also seen that at this time this soil layer contained 

 a maximum amount of water-soluble nitrates. The nitrates in the 

 second layer, 6 to 12 inches, had more than doubled since the week 

 before, but there were no considerable changes in the lowest two 

 layers. By the next week, May 16, the surface 6 inches of soil had 

 decreased about forty parts per million, and there was also a decrease 

 in the 6 to 12 inch layer. By the next week, on May 22, a marked 

 increase in the amount of nitrates is evident in the 12-inch layer, it 

 having increased about seventy parts per million during six days, 

 and the surface 6-inch layer had decreased about ten parts per million. 

 At this date the 12-inch layer contained the maximum quantity of 



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