Page 80 - Ilmu Tanah Book

The Chemistry and Fertility of Soils under Tropical Weeds 67

The degree of phosphatase activity with respect to soil pH is different from one
soil to another, depending on the types of land-use systems and on the sampling
locations. Observation showed that the difference was closely correlated with the
contents of organic C and total N. The activity of phosphatase in soils collected
from the primary and the secondary forests were in most cases higher than those
collected from the coffee plantation and the cultivated lands whose organic C and
total N were lower. The activity of phosphatase was also higher in soils collected
from Bukit Ringgis and Sekincau than those collected from Tri Mulya, Tri Budi
Syukur, and Pura Mekar. However, the pattern of phosphatase activity with
respect to soil pH was similar for all soils, independent of land-use systems and
sampling locations (Fig. 4.4).
Kumar and Wagenet (1984) also report the effect of CaCO 3 addition on the
activity of urease. The activity of urease decreased significantly upon CaCO 3
addition. The decrease in the urease activity reached a value of 29 -68% at CaCO 3
addition of 8%. Kumar and Wagenet (1984) argue that the decrease was attributed
to the inactivation of urease by amorphous CaCO 3 . The effect of CaCO 3 on the
increase in soil pH was also possible to affect the urease activity. The changes in
soil pH may also change the dominant microorganisms, especially fungi and
bacteria; fungi prefer acid soil environment while bacteria prefer neutral or alkaline
soil environment. This phenomenon may affect also the populations and activities
of the urease producing microorganisms.
The above observations clearly show that forest conversion such as that
occurred in West Lampung, Indonesia, induced a very significant influence on the
soil environment. Related to the soil enzymatic activities, forest conversion
changes not only the soil enzymatic activities but also the optimum pH values.

4.3 Effects on Soil Chemistry and Fertility

The changes in microclimate and soil microbial population and activities by
deforestation may drastically alter the soil chemical and fertility. Salam (2014)
shows that the changes in coverage of forest to monoculture plants and cultivated
lands may change the status of soil properties. Forest conversion in general
degraded significantly four of the important soil chemical properties, i.e. organic
matter and total N contents, available P, and CEC (Table 4.6). The soil CEC of the
-1
primary forest in 1998 was 43.2 cmol c kg while that of the secondary forest at the
Abdul Kadir Salam and Nanik Sriyani – 2019