PARENT SESSION
Oral Session #52: Carbon and Nitrogen Cycling: Soil processes and patterns. Presiding: F. Gilliam.
Wednesday, August 8, 2001. 1:00 PM to 5:00 PM. Hall of Ideas E.
Comparison of N dynamics in soil between dry dipterocarp forest and dry evergreen forest in central Thailand.
Tokuchi, Naoko1, Nakanishi, Asami1, Takeda, Hiroshi1, 1
ABSTRACT- A comparative study of N dynamics in soil between a dry dipterocarp forest (DDF) and a dry evergreen forest (DEF), that occur on the same soil group under similar climatic condition in northeastern Thailand. Nitrogen dynamics in soil was estimated using ion exchange resin core method and buried bag method. The soil N cycling was described by seasonal measuring of N mineralization and nitrification rates, inorganic N pool, soil microbial biomass, and extractable organic N pools. Soil C and N pools were 38 C ton/ha/30cm and 2.5 N ton/ha/30cm in DDF and 82 C ton/ha/30cm and 6.2 N ton/ha/30cm in DEF, respectively. In the respect to C accumulation, low C concentration was compensated by high bulk density in both sites. Higher C accumulation related with CEC in DEF. From these important C accumulation mechanisms are high soil density and CEC in tropical soil. In DEF extractable organic C (EOC) was also higher than in DDF. During the long-term incubation, inorganic N form changed from ammonium to nitrate, it was coincided with EOC concentration decrease. EOC is considered an index of C availability for microbes and C is important not only for nutrient accumulation, but also readily available nutrient dynamics. There was highest N dynamics in the onset of rainy season in DDF, while inorganic N production and uptake of N was shown throughout the rainy season in DEF. It is suggests that N dynamics in soil synchronizes with biological activity like life form of each forest.
KEY WORDS: N dynamics, dry tropical forest, available N , extractable C