Page 83 - Enzymes in Tropical Soils

Enzymes in Tropical Soils 71

(Mollisols). The contents of soil organic matters are 1.5 – 2.0 times Organic C.
According to Amelung et al. (1998), soil organic matter is related to the soil texture.
Soil clay fraction is associated with 43% total Organic C, 56% of total N, and 62% or
total S. The percentage decreases with the increase in soil temperature and the
decrease in precipitation.
The vegetation grown may be one reason for the differences in organic
matter contents (Chan, 1997; Studdert et al.,1997; Salam et al., 2001). Some
reports (Chan, 1997; Studdert et al.,1997) showed that soil planted with grasses
contained organic matters higher than soils planted with food plants. This fact
indicates that grasses are potential to increase or restore the fertility of soils with
degraded organic matters (Table 5.5). Studdert et al. (1997) also reported that the
rotation of food plants with grasses significantly increases the soil organic C
contents. The increase in organic matter content will be more significant if grass is
more frequently used as a rotating vegetation.

Table 5.5. The differences in organic C and N contents of Vertisols planted
with grasses and food plants *.

Soil 1 Soil 2
Food
Food Plants Grasses Grasses
Plants
pH 7.27 6.87 8.01 7.80
Total Organic C
7.90 13.4 4.4 7.1
-1
(g kg )
Total N
0.9 1.5 0.7 0.9
-1
(g kg )
*Adapted from Studdert et al. (1997)

Based on a four years observation (1996 – 1999) in a coffee plantation of
West Lampung, Sumatra, Indonesia, Salam et al. (2001) also found that the soil
organic C and total N in coffee plots with Paspalum conjugatum were higher that
those with natural vegetation or control (Table 5.6). A consistent phenomenon
was observed from 1996 through 1999.
Salam et al. (1997c) also reported the effect of vegetation on the activities
of acid and alkaline phosphatase in soils planted with long-term cassava (Table

Abdul Kadir Salam - 2014