Key words: drying effect, kinetics, mineralization of N, paddy soil in the tropics
The kinetics of mineralization of soil organic nitrogen
(N) in samples of several air-dried and fresh soils in the tropics was
studies, Four different paddy soil samples in the IRRI lowland field were
used. Parameters for mineralization of soil organic N were computed by
using Arrhenius' law and Michaelis-Menten's equation, The following results
were obtained:
1) The mineralization pattern of organic N in the wet
soil samples were represented by an exponential equations as a function
of reference days, which were determined by the duration of the incubation
period and apparent activation energy. Although significant differences
in the mineralization rate and mineralization potential among the soils
were observed, there was no appreciable difference in the value of apparent
activation energy, which were relatively low compared with those Japanese
paddy soils.
2) The mineralization pattern of the dried soil samples
was represented by an equation consisting of two exponential equations.
When a large amount of extractable carbon was detected by diluted sulfate
or hot water in the soils, the mineralization pattern was represented by
an equation which consisted of three exponential equations.
3) The difference in the amount of inorganic N between
the dried and wet soil samples increased rapidly up to 5 weeks after the
start of incubation and then became almost constant. The mineralization
pattern of the decomposable organic n which appeared with the changes of
the soil conditions from wet to dry (DON) could also be represented by
an exponential function of reference days.
4) There was no appreciable difference in the mineralization
rate and apparent activation energy between the organic N of the soil samples
and slowly mineralizable organic N of the dried soil samples, and between
DON and the rapidly mineralizable organic N of the dried soil samples.