| Abstract: |
| The main objective of this study is to test to what extent the amount and quality density fractions respond to differences in input of residues through two-step experiment fractionation of soil organic matter (quantity aspect) and incubation of these fractions (quality aspect).
The soil organic matter ( >150 pm ) of various soils under species plots of forest; sugarcane; and Alley Cropping systems i.e : Peltophorum dasyrrachis, Gliricidia sepium; Leucaena leucocephala, Calliandra calothyrsus, Flemingia congesta, and control (without alley) which had received different inputs of organic residues for 10 years was fractionated into light, intermediate, and heavy fraction ( <2 mm and litter fraction ( > 2mm ). All of these fractions are mixed with quartz sand. The mixture were incubated in the leaching tubes to determine mineralization rates.
The dry Weight, the C, N, P content, and C : N ratio of soil organic matter fraction were much affected by residue treatments (species plots). For all species plots it is shown that the dry weight of litter > light > intermediate > heavy fraction. Whereas...all fractions of plot species showed that forest > Calliandra > Peltophorum > Flemingia > Gliricidia > Leucaena > Sugarcane > Control. Mineralization rates of soil organic matter fractions for all species plots were, in increasing order as follows : light > litter > intermediate > heavy. Whereas based on all fraction it is shown that : Leacaena > Gliricidia > Peltophorum > Calliandra > Flemingia >1 Control > Forest > Sugarcane. For all species plots, the fractions with high C : N ratio is mineralized faster than those with low C : N ratio. However, the fractions of species plots with high C N ratio is mineralized more slowly than those with low C : N ratio.
It was apperent from this study that not all alley plots were mineralized quickly, despite the high nitrogen concentration in the fractions. Nitrogen and P released by fractions of alley plots with high C : N ratio would be slower than those with low C : N ratio. It appeared that mineralization rates of various fractions in this incubation- method (quartz sand as media) was faster than those in incubation method with soil as media due to the absensce of complex of organo-mineral in the sand media, so that the rate of mineralization was dominantly controlled by its chemical composition besides the higher biological activity in the sand media. |
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