Page 163 - Ilmu Tanah

150 The Chemistry and Fertility of Soils under Tropical Weeds

Based on the fact that the primary forest was located higher that the
secondary forest, coffee plantation, and cultivated land, it is predicted that in the
beginning, the fertility of the coffee plantation and cultivated land was initially
higher than the primary and secondary forests. The land-use conversion drastically
decreased the availabilities of Cu and Zn in coffee plantation and cultivated land.

8
7
6
Avail. Zn (mg kg-1) 5

4

3
2
1

0
Primary Secondary Coffee Cultivated
Forest Forest Plantation Land

Topsoil Subsoil

Fig. 8.9. The changes in soil available Zn in different land-use systems of
Tri Mulya, West Lampung, Indonesia (Redrawn from Salam, 1999).

As those of Cu and Zn, the availability of Fe in general was higher in the
primary forest and secondary forest compared to those in coffee plantation and
cultivated land, both in topsoil and subsoil (Table 8.3, Fig. 8.10). This data shows
that land-use conversion also decreased the availability of Fe. This change was also
caused by the increased soil mineral weathering and organic matter decomposition
combined with the intensive Fe leaching and erosion. These changes are also well-
correlated with Organic C (r = 0.772 – 0.831), with Total N (r = 0.673 – 0.835), and
soil CEC (r = 0.560 – 0.940). The Organic C, Total N, and soil CEC are previously
reported to decrease by land-use conversion from the primary forest to secondary
forest, coffee plantation, and cultivated land.

Abdul Kadir Salam and Nanik Sriyani – 2019