Abstract:
Mineralization of annual leaf fall is considered as an important source
of N in Hevea plantations. The objectives of this study were to quantify the N
pool in the leaf litter of two Hevea clones with different canopy architectures,
and to determine the rates and pattern of N release from Hevea leaf litter in
three major rubber growing soils.
Two //eveaclones (RRIC 121 and RRISL 203) planted in 1992 were
selected to quantify the N pool in the leaf litter. Leaf litters under each clone
were collected manually and the dry mater and total nitrogen contents were
determined. Soils from three rubber growing areas were used for N
mineralization study. Soils (air-dried and 2-mm sieved) from each group were
packed into cores to a bulk density of 1.3 Mg m'3. Half of the cores of a given
soil group were mulched with 90 mg of ground leaf litter. The soil cores were
incubated under controlled conditions and NH4+-N and N 0 3'-N contents were
determined at the end o f 2, 4, 8 and 12 weeks of incubation.
The N pool in the leaf litter were significantly different between the
two clones (25.7 and 13.6 Kg N ha''for RRISL 203 and RRIC 121,
respectively). The SMN contents in all three soils increased during the first
eight weeks of incubation, reached a maximum and then the rates of increase
were slowed down. However, the highest mineralization was observed in
Kegalle soils and the lowest in Monaragala soils through out the incubation
period, possibly due to the differences in clay content in the three soils. The
SMN contents were significantly higher in residue added soils throughout the
incubation period. The largest residue effect was observed at about 8 weeks
after incubation. On the average, SMN content was higher in residue added
soils by about 9.0 mg kg'1 during the entire period. The N release from the
decomposition o f added residue was not influenced by the soil type.
