Page 161 - Ilmu Tanah

148 The Chemistry and Fertility of Soils under Tropical Weeds

8.3 Effects of Forest Conversion

Land-use conversion has long been suspected to change soil properties
including the soil chemical, soil physical, and soil biological properties important for
agriculture. As discussed previously, data showed that land-use conversion from
the primary forest to secondary forest, coffee plantation, and cultivated lands
lowered some soil chemical properties like soil CEC, soil organic C, organic matter,
and total N, soil enzymatic properties (urease, arylsulfatase, glucosidase, and
alkaline and acid phosphatases) (Salam et al., 1998b). The dominant vegetation
and soil life are also shown to change by land-use conversion (Salam, 2014).
The availabilities of heavy metal plant nutrients were also the important soil
chemical properties that changed by land-use conversion. This change is logical
based of their relationship with other soil chemical properties like soil pH, CEC , and
organic matter content (Parfiit et al., 1995; Rodella et al., 1995; Alloway, 1990;
McGrath et al., 1988). The changes in microclimate as affected by land clearing,
particularly the soil temperatures and the soil moisture content, may accelerate
the decomposition of organic matters and the weathering of soil minerals, that
may release various micronutrients that may be weakly adsorbed by soil solids or
leached by percolating water through the soil pore channels. Intensive tillage in
agricultural soils may also intensify the process of decomposition (Klein and Koths,
1980) causing the decrease in heavy metal micronutrient availability in soils.
The changes in vegetation, soil microorganisms, soil erosivity, soil organic
matter content, and fertilization practices may also change the availabilities of
heavy metal micronutrients (Klein and Koths, 1980; Herrero and Martin, 1993; He
and Singh, 1994; Gimeno-Garicia et al., 1996; McLaughlin et al., 1996; Salam, 1996).
Salam et al. (1998b) report that the organic matter content and CEC of topsoils and
subsoils decreased by land conversion from primary forest to secondary forest,
coffee plantation, and intensive cultivated land. This suggests that the land
conversion may also decrease the availabilities of heavy metal micronutrients.
Salam (1999) report that in general the availabilities of Cu and Zn were higher
in topsoil and subsoils of the primary and the secondary forest compared to those
in the coffee plantation and cultivated land (Fig. 8.8 and Fig. 8.9). The relative
concentrations of these heavy metal micronutrients compared to those in the
primary forest are listed in Table 8.3. The changes in the soil available Cu in each
location were linearly correlated with Organic C content, Total N contents, and CEC
with correlation coefficients ranging from 0.682-0.976, 830, 0,752-0.860, and
0.723-0.861, respectively. The availability of Zn was also well-correlated with these

Abdul Kadir Salam and Nanik Sriyani – 2019