In order to quest the effects of Fe oxide on nitrification in soils

a acidic fluvo-aquic soil (pH 4.9) and neutral fluvo-aquic soil (pH 7.2) with low total iron were selected as materials. Indoor incubation method?was used to investigate the time-dependent kinetic of net nitrification after the two soils were amended with 0% (control)

0.5%

1%

3%

5%

10% Fe oxide by weight. The results showed that

nitrification was best fitted by a first-order kinetic model for neutral soil with less than 3% Fe oxide amendment. However

it was best fitted by a zero-order kinetic model when more than 3% Fe oxide were added. For acid soil

nitrification was best fitted by a first-order kinetic model regardless of the addition amount of Fe oxide. Net mineralization rate of the acid soil increased significantly after the addition of different amount Fe oxide

and the highest mineralization rate was found for 10% Fe oxide amendment (4.12 mg/(kg·d))

which was 7.82 times higher than unamended soil. With the increase of iron oxide addition amount

the net nitrification rate of acid soil significantly increased while the net nitrification rate of neutral soil decreased significantly. The net nitrification rates of acid soil with 3% and more Fe oxide amendment were extremely significantly higher than that of soils with less amendment. Overall

Fe oxide addition stimulated net nitrification rates in the low pH soil (pH 4.9)

while the opposite occurred in the high pH soil (pH 7.2)

and the greater amount wereadded

the more significant effects were observed. 3% Fe oxide amendment was the critical value that significantly influence nitrification of the acid fluvo-aquic soil and neutral fluvo-aquic soil.