Occurrence of nitrification-denitrification and gaseous nitrogen loss process in flooded rice soil

摘要

Flooding in wetland rice fields soon after transplanting results in displacement of soil air (including O_2). Thus any dissolved O_2 in the pore water is consumed out by microbial respiration in a short period. Supply of O_2 to the flooded rice soil is by diffusion of O_2 through the standing floodwater and consumption at the soil-water interface, and by exudation of O_2 by rice roots and subsequent diffusion of O_2 into the rhizosphere. The greater potential consumption of O_2 compared to the renewal rate results in the development of distinct soil layers: oxidized soil layers under soil-water interface and in the rhizosphere, and reduced soil layers or reduced bulk soil. Nitrification in oxidized soils and denitrification in reduced soils have been known. Currently, denitrification in oxidized soils, even in standing floodwater, has also been identified. In this article, we present a modified nitrification and denitrification occurring mechanism in flooded rice soil.