ABSTRACT
Although soil organic matter (SOM) forms a small portion of the soil body. Nevertheless, it is the
most important component of the soil ecosystem, as well as of the carbon global
cycle. In the semi-arid environment, there has been little research on the
spatial distribution of SOM and soil organic carbon (SOC) stock. In this study,
stratified random samples of total 30 soils were collected from two different
soil depth (topsoil, subsoil) of Al Balikh plain and used for mapping the
spatial variability of SOC and to estimating the SOC stock. The result showed
that the values were relatively homogenate, with the normal decreasing trend
with increasing the depth. The standard deviation (Std. D) for both SOC and SOC
stock indicates homogeneous and absence of outliers values, whereas the
coefficient of variation (C.V) indicates non-dispersion and clustering of
values around the average. SOC was 0.38%, 0.17% in topsoil and subsoil
respectively; the corresponding averages of SOC stock were 1.23 kg·m-2 and 1.14 kg·m-2 respectively, these values reflecting typical
characteristics of poor SOC semi-arid soil. The correlation between SOC and SOC
stock was (R2 = 0.996, p < 0.001) in topsoil and it was (R2 = 0.941, p < 0.001) for subsoil. The semivariograms were indicated that both
SOC and SOC stock were best fitted to the exponential model. Nugget, range, and
sill were equal to 0.002, 0.036, and 0.044, respectively for SOC in topsoil,
and 0.014, 0.071, and 0.081, for SOC in the subsoil. For SOC stock, it was 0.0,
0.036, and 0.0508, respectively in topsoil. In the subsoil, the values were
0.1899, 0.086, and 4.159, respectively. SOC and SCO stock in both two layers
are shown a strong spatial dependence, for which were 4.3, 17.2 for SOC in
topsoil and subsoil respectively, and 0.0, 4.5 for SOC stock in topsoil and
subsoil respectively, thus, which can be attributed to intrinsic factors.