Abstract:
For accurate estimation of soil organic carbon (SOC), storage and SOC turnover, assessment
of soil organic carbon quality is important. However, most of the carbon researches in
Ethiopia focus only on the actual SOC present in the soil. Prediction of soil organic matter
(SOM) decomposition rate and litter stabilization factors are also useful to estimate how much
carbon (C) is lost from the soil as CO
2
. The main objective of this study was to assess the
effect of different land use types on SOC quality, decomposition rate and litter stabilization in
North Gondar, Ethiopia. Three sites (Ambober, Chiliga, Gorgora) were selected which all had
four different land use types next to each other: agroforestry, cropland, eucalyptus plantation
and grazing land. Three soil samples per pit, from three depth intervals (0-10 cm, 10-20 cm
and 20-30 cm) were taken in four replications. Totally 12 samples per land use, 48 samples
from each site and 144 samples were collected. The soil samples were analyzed for pH, soil
texture, decomposition rate (k), stabilization factor (S) as well as for SOC. A stepwise thermo
gravimetric (STG) method was applied to analyze SOC quality. Croplands had generally
higher clay content whereas agroforestry and eucalyptus plantation were higher in silt content
that confirm long-term land use impacts on soil particle size distribution. Crop and
agroforestry were higher with soil pH in average than grazing land and eucalyptus plantation.
Cropland showed the highest soil pH (7.07) in the top soil in Ambober, but contrasting, the
lowest pH value (5.73) in Chiliga. Slightly higher thermo labile SOC were accumulated in the
top 10 cm of the soil. Croplands showed lower thermo stable SOC which may be due to the
effect of long-term tillage and fertilization. Land use affected both the litter stabilization
factor (S) and the decomposition rate (k). There was no correlation between SOC components
(thermo labile, total SOC and thermo stable) and soil clay content and only a weak positive
correlation with silt content. On the other hand, a weak negative correlation was found with
sand content. Total SOC and thermo stable SOC were strongly positively correlated SOC
analyzed with CN analyzer but only a weak positive correlation was observed between thermo
labile SOC and SOC analyzed with CN analyzer. Generally land use types had a significant
effect both on SOC quality, litter decomposition rate and stabilization factor those may
influence SOC dynamics. Characterization of SOM quality across land use types and
ecologies should gate future research attentions for accurate modeling of climate change.
