2006 Volume 50 Issue 2 Pages 81-90
To clarify the factors affecting nitrification with nitrogen applied as high concentration, incubation experiments were conducted. Twenty-two soil samples obtained from arable lands in Hokkaido, more than half of which were Andosol, were used for incubation experiments. Addition of ammonium phosphate to the 22 soils at a rate of 0, 50, 100, 200, 300 mg N kg^<-1> and incubation for 14 d revealed that; (1) The higher concentration of added-N suppressed relative percent nitrification. (2) Comparing the 22 soils about nitrification at the highest amount of added nitrogen (300 mg N kg^<-1>), in the higher-organic matter soil (Haplic Andosol, total carbon content was 31.4-82.4 g kg^<-1>), percent nitrification was faster, than in the other lowerorganic matter soils (total carbon content was; Haplic Volcanogenous Regosol 13.6-25.8 g kg^<-1>, Low-humic Andosol 10.1-24.7 g kg^<-1>, Haplic Brown Lowland soil 9.3-12.5 g kg^<-1>). (3) Within the Haplic Andosol, nitrification was significantly associated with soil pH. (4) As for all 22 studied soils, percent nitrification was significantly associated with total carbon content firstly, and secondly associated with soil pH. Ammonium sulfate, ammonium phosphate, and urea (all 300 mg kg^<-1>) added to one soil with a relatively higher carbon content and pH were nitrified completely in 42 d. When added at 500 and 1000 mg N kg^<-1>, however, nitrification of these forms was suppressed; the percent nitrification was the lowest in ammonium sulfate, followed by ammonium phosphate and urea. Based on these results, applied nitrogen concentration, soil carbon content, soil pH, form of nitrogen source, and their interactions are factors that affect nitrification. These findings have implications for improving nitrogen fertilization.
