Patterns and Factors Controlling Nitrogen Mineralization in Paddy Soils in Tropical and Temperate Regions

Abstract

The process of soil ammonification was analyzed in 121 paddy soils from 11 South East Asian countries, three Mediterranean countries and Japan. The rate of nitrogen mineralization was determined in samples subjected to 4 week’s submerged incubation every week. The pattern of nitrogen mineralization varied widely from soil to soil. We employed a numerical taxonomic method for cluster analysis of the soils on the basis of the similarity of the percentage of ammonification recorded every week. Based on the cluster analysis, the soils were assigned to 12 classes and finally divided into four groups. The four groups were identified with a nonlinear mapping algorithm and designated as P, Q, R, and S groups.

Based on data fitting, the nitrogen mineralization patterns of the P and Q groups were fit to the first order rate kinetics and those of the Rand S groups were fit to the logistic function. Group P soils showed a slow rate of mineralization and a low value of ammoniacal nitrogen released. Group R soils showed a slow rate of mineralization and a high value of nitrogen mineralized. In the soils of groups Q and S, ammoniacal nitrogen was released rapidly after water-logging.

The soils of the P group were characterized by both low percentages of a-amino-N in total-N and polysaccharide-C in total-C. When the soils rich in α-amino-N (previously reported as A group), contained large amounts of polysaccharide or readily decomposable organic matter with a low C/N ratio, rapid nitrogen mineralization occurred after waterlogging and the mineralization patterns were characteristic of the Q or S group. The amount of nitrogen produced during the 4 week incubation was regulated by the content of polysaccharide- C, according to the regression analysis. In the other soils and in the soils with a Iow content in a-amino-N (previously reported as B group), nitrogen mineralization occurred slowly and the mineralization pattern was characteristic of the P or R group. The amount of nitrogen released after 4 weeks was regulated by the content of α-amino-N.

Key Words:

• nitrogen mineralization pattern
• tropical soils
• α-amino-N
• polysaccharide-C