Nitrogen mineralization in lowland rice soils: The role of organic matter quantity and quality

Ammonium production in wetland soils and sediments is the key process that impacts nitrogen (N) availability, wetland productivity and environmental quality. Significant relationships between organic matter content and mineralizable N have been reported for diverse groups of wetland rice soils. However, recent research also showed that in soils under intensified wetland rice production systems, the relationships between organic matter and mineralizable N are poor or not significant. The review of recent research suggests that both organic matter quantity and quality are influenced by prolonged submergence, which in turn affects mineralization and N supply in wetland soils. While organic matter quantity increases following prolonged submergence of soil; submergence also changes the chemistry and quality of soil organic matter, which influences N mineralization. The increase in N mineralization as a result of increase in organic matter quantity is countered by the change in the chemistry and quality of organic matter. The changes in chemical composition of soil organic matter and their influence on N mineralization in submerged soils are discussed with examples from recent research.