LIN Xiaolan1, YOSHIDA Koshi2, MAEDA Shigeya2, KURODA Hisao2
1 The United Graduate School of Agricultural Science, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo, Japan, 183-8509, [email protected]
2 College of Agriculture, Ibaraki University, 3-21-1, Chuuo, Ami, Inashiki, Ibaraki, Japan, 300-0393
The characteristics of oxidation-reduction (redox) layers were reviewed under natural conditions. This study was carried out a field survey from 2014 to 2015. The survey was conducted in a paddy field. Soil temperatures, air temperatures, and T-N concentrations of water had been measured. The dissolved oxygen (DO) concentrations of redox layers in flooded soil were measured per 0.2 mm with a special DO concentration sensor through surface to 6 cm depths of soils. Based on the DO concentration results, the soil of the oxidized layers where the concentration was over 1 mg L-1 was sampled, along with reduced layer of less than 0 mg L-1. The denitrification activities of redox layers were measured by acetylene blocking technique.
The DO concentrations in paddy field soil have a seasonal change and changed in a thin layer. A positive correlation is observed between the thickness of the oxidized layer and soil surface temperature in the range of 12 ~ 24 °C. The oxidized layer denitrification activities are little, denitrification of paddy fields is dependent on the reduced layer.