[Effect of iron oxides addition on organic acids content in paddy soil]

The addition of ferrihydrite into paddy slurries significantly reduced the concentration of acetate. In fresh paddy soil, due to the competitive consumption for acetate by addition of ferrihydrite, the concentration of acetate was reduced to 10-20 mumol.L-1 after 5d anaerobic incubation. However, in control slurries, the acetate concentration was still as high as more than 1200 mumol.L-1. In soil produced low acetate, the acetate was completely consumed by addition of ferrihydrite, resulting in a full inhibition of methane formation. Also, the application of lepidocrocite reduced methane genesis, but the reductive effect was less than ferrihydrite. The acetate was largely accumulated during a short-term anaerobic incubation from 1 to 10 days by hematite addition, but at the same time, the methane genesis was not extensively increased. The propionate concentration was also reduced under anaerobic incubation by addition of different iron oxides such as ferrihydrite, lepidocrocite and aluminum-substituted goethite, and the inhibitory effect was in order of ferrihydrite > lepidocrocite > Al-substituted goethite. The types and contents of organic acids in fresh soil were greatly different from those being incubated for 11 weeks under an anaerobic condition.