INFLUENCE OF MOISTURE 



229 



slightly with the physical properties of a soil. Twenty-two soils 

 varying widely in physical properties yielded maximum nitrification 

 when the soil contained from 50 to 60 per cent, of their water- 

 holding capacity, as indicated in Fig. 30. Furthermore, the opti- 

 mum moisture content for maximum nitrification is correlated 



10 20 30 40 X 60 70 80 90 IOC 



FIG. 32. Average percentages of nitric nitrogen produced in soil receiving various 

 quantities of water. The quantity produced at 60 per cent, is taken as 100; on the 

 ordinate is given the per cent of nitric nitrogen formed, whereas on the abscissa is 

 given water applied as per cent, of water-holding capacity. 



with the other soil constants with a set of equations similar to 

 those given for ammonification, page 201. Thus, 



Mn = .55 C 



Mn = .8525E + 11.55 



Mn = 1.472 W + 11.55 



Mn = 2.163 H + 11.55 



