14 SEASONAL NITRIFICATION AS INFLUENCED BY CROPS, ETC. 



however, soon results in the soil becoming moistened deeper than 

 6 feet within one year after breaking the sod and cultivating the 

 soil. It is fair to assume, therefore, that nitrification in the un- 

 broken land can not take place to any great extent much below a 

 depth of 1 foot. 



NITRATES IN THE SPRING-WHEAT PLAT. 



Figure 2 shows the results obtained from determinations made 

 on the spring-wheat plat. These determinations were not begun 

 until May 9, but a vertical section made in figure 1 on May 9 will 

 show that the order is about the same at this point on both figures. 



Figure 2 does not contain the precipitation curve, but in addition 

 to the curves showing the amounts of nitrates in the 6-inch soil layers, 



KIG. 2. — Diagram showing the parts per million of water-soluble nitrates in dry soil in the spring-wheat 

 plat in each C-inch soil layer to a depth of 2 feet; also weekly increase of wheat plants. 



it shows the curve representing the weekly increase in the dry weight 

 of the wheat plants. The increase was determined each week by 

 cutting four 3-foot squares, two near each end of the 2 by 8 rod plat, 

 both green and air-dry weights being obtained. Only the dry 

 weights are platted in the figure. 



"A comparison of figure 1 and figure 2 shows the same general fact, 

 namely, that the maximum amount of water-soluble nitrates in any 

 soil layer is shifted every two weeks to the next lower layer. The 

 detailed variations are about the same in the two plats, but there is 

 one general difference — the date of the maximum accumulation of 

 nitrates in the respective soil layers in the two plats is shifted one 

 week forward in the case of the spring- wheat plat — that is, each of 

 the 6, 12, and 18 inch layers, respectively, attained its maximum 



173 



