3.1 | Physicochemical analysis of the soil
samples
Soil physicochemical properties that could be directly influenced by the
soil depth and forest type are shown in Figure 1 and Tables 1 and 2.
There were no significant differences in the five physical indicators
evaluated, namely soil moisture content [SMC], pH, electric
conductivity [EC], total dissolved solids [TDS], and specific
soil weight [GS] in the soil samples from different depths (P> 0.05; Figure 1). In contrast, the slope position and
forest type did influence the physical indicators (Figure 1). The EC
decreased from the -base to the top at different slope positions, while
intercropping caused fluctuations in the soil EC and the TDS.
Preliminary analysis results for the soil chemical parameters are
presented in Table 1. The TOC, SOM, TN, TC, NH4–N, and
AP content were highest in the 0–20 cm depth layer. The increase in the
soil chemical parameter values of the surface soil was likely due to the
decomposition and transformation of forest tree litter and biological
residues, which are major sources of organic matter accumulation. The
slope position did not significantly affect the soil physical and
chemical indicators. The TOC, HC, SOM, TN, TC NH4–N,
AN, and AP contents in the GLF were significantly higher than for the
other stands, indicating that G. jasminoides plays an important
role in modulating the fertility of the soil in the C. oleiferalow-yielding forest.
A comparison of the soil nutrient content at different soil depths
determined that the NH4–N and AN levels were the lowest
in the 40–60 cm depth layer and that the AP levels were highest in the
0–20 cm depth layer (Table 2). The NO3–N and AK levels
did not significantly vary by soil layer. No significant differences in
NO2–N levels were recorded among the different
plantations, but the highest NO3–N levels were observed
in LF. Comparing the soil nutrient content from the different forest
types revealed that the NH4–N level for the
intercropping was significantly lower than that of the
monoculture(p < 0.05). It could be due to theG. jasminoides and newly planted C. oleifera substantially
increasing plant uptake of tNH4–N. Therefore, the
nitrogen supplying capacity of the forest soil became insufficient.