Problem statement: The tropical rain forests in Southeast Asia have been characterized by several researchers. However empirical data on soil characteristics under degraded forest land in tropical rain forest and rehabilitated program are limited. A study was conducted to evaluate the soil morphology, mineralogical and sesquioxide properties of a rehabilitated degraded forest land (19 years after it was planted with various indigenous species) in comparison with an adjacent secondary forest. Approach: Soil samples were air-dried and pass through a 2 mm sieve. Soil morphology was determined based on field observation. The non-crystalline (amorphous) of Al, Fe and Si oxides and hydroxides (Alo, Feo and Sio) were extracted with ammonium oxalate while the dithionate-citrate-bicarbonate (DCB) method was used for extracting (crystalline) the Al, Fe and Si oxides and hydroxides (Ald, Fed and Sid). The concentrations of extracted Al, Fe and Si were determined by atomic absorption spectroscopy. Mineralogical compositions were identified by X-ray diffraction method. Results: The A-horizon of secondary forest was darker and thicker than that of the rehabilitated forest. Root mat at the secondary forest was well-developed compared to the rehabilitated forest. The clay minerals were dominated with kaolinite and illite to a lesser extent of goethite and hematite accompanied with low values of activity ratio of Al and Fe oxides and hydroxides, indicating that the soils were highly weathered. Conclusion/Recommendations: The difference between rehabilitated and secondary forests was root abundance where secondary forest had most. Good root penetration in the secondary forest indicates that the soil texture there was not heavy. Soils in the rehabilitated and secondary forests were strongly weathered (high presence of kaolin minerals), but the low presence of sesquioxides suggests that they are yet to reached the ultimately weathered phase. The soil properties in terms of morphology, sesquioxides and clay minerals should be taken into account for better management of forest rehabilitation program in tropical regions

An assessment of forest rehabilitation program in relation to soil fertility status by using soil indices could provide fundamental information on soil suitability for species preferences and improve the effective technique for future rehabilitation program in tropical rainforests. This study was conducted in order to characterize the soil properties and identifying the soil fertility status of rehabilitated and secondary forests. Soil samples were collected in year 2009 at rehabilitation forests (20 years after planting) and secondary forest of Nirwana Forest Reserve, Universiti Putra Malaysia (UPM) Bintulu Campus, Sarawak, Malaysia. The rehabilitation plots were planted with mixed dipterocarp and non-dipterocarp species since 1991. Prior to conversion of the areas into various land use types, the rehabilitation and secondary forests areas were considered as natural forests and subsequently subjected to forest logging with Selective Management System (SMS) in 1980s.The plot size for each site was 20×20 m for 18 experimental sites (at different ages after planting) were established, followed by soil sampling at 0-15 cm and 15-30 cm depth randomly using soil auger. Standard soil analysis for physical and chemical properties was used to analyze the soil samples. The soil fertility status was evaluated using two indices, namely Soil Fertility Index (SFI) and Soil Evaluation Factor (SEF) for both rehabilitated and secondary forests. The results showed that there were significant differences (p<0.05) in pH (water and KCl), exchangeable Mg, Na, Al and ammonium and granule composition (clay, silt and sand) between depths. The PCA result of 70% total variability (OM, TOC, TC and CEC) score in PC1 shows positive relationship, explaining nutrients in the soil stored in the organic matter in the surface soils. The correlation analysis indicated that there were positive relationship (p<0.05) between OM and TC, CEC and exchangeable Al for surface soils. We found that the selected physico-chemical properties had a significant differences based on the age of planting of rehabilitated forests. For subsurface soils, correlation between exchangeable Al and OM and CEC shows strong positive relationship, indicating that negative charge derived from organic materials plays important roles for cation retention capacity. The SFI and SEF for rehabilitation forests showed higher value as compared to secondary forests, indicating forest rehabilitation had improved the soil fertility status of degraded forestland. In conclusion, both rehabilitated and secondary forests have significant differences based on the selected physical and chemical properties. Moreover, the soil fertility status at rehabilitated plots was higher than secondary forest, which is proved that the forest rehabilitation technique is a suitable planting technique for rehabilitating and replenishing soil fertility status of abandoned degraded shifting cultivation land.

Heavy metal pollution of the soil environment has become a major source of concern and continues to pose serious health problems to both humans and ecological systems worldwide. Phytoremediation is a biological treatment whereby plants are used to remove pollutant from the environment. An experiment was conducted to evaluate the potential of Melastoma malabathricum as a phytoremediator to absorb heavy metals from soil contaminated with sewage sludge. Melastoma malabathricum seedlings were planted on six different growth media: T 0 -Control (100 % soil), T 1 (80 % soil + 20 % sewage sludge), T 2 (60 % soil + 40 % sewage sludge), T 3 (40 % soil + 60 % sewage sludge), T 4 (20 % soil + 80 % sewage sludge) and T 5 (100 % sludge). There were differences found in both growth parameters and plant biomass. The highest growth performance such as plant height and number of leaves was found in T 3 . Iron was highly accumulated in the roots, Cu in the stems in T 3 , while Pb was accumulated in leaves in T 5 . The results showed the lowest Translocation Factor (TF) and highest Bioconcentration Factor (BCF) values in relation to the following elements: Cu, Fe, Mn, Pb and Zn. Melastoma malabathricum roots are able to uptake and translocate the elements into the plant's shoots. Therefore, it can be considered a good accumulator plant due to its capability of concentrating contaminants in aerial tissue. Melastoma malabathricum were thus found to be suitable for absorbing heavy metals in contaminated soils, and this species can also be considered an effective phtyoremediator of contaminated soil and mitigator of soil pollution.

Soil fertility (both physical and chemical) is one of the important factors limiting plant growth. So, the fertility of the soils should be determined before growing crops and after the establishment of forest rehabilitation. A study was conducted to determine the fertility status of soils at rehabilitated degraded land in Universiti Putra Malaysia. The main objective was to compare the fertility of soils planted forest and pasture. Three sites studied were pines plantation (Pinus caribaea), mahogany plantation (Swietenia macrophylla) and pasture area. At each site, three squares of 20×20 m were selected and two depths of soil sample were collected, topsoil (0-20 cm) and subsoil (20-40 cm), from six points within the squares. The physical properties of the soils analyzed were bulk density, soil texture and moisture content, while the chemical properties were pH, total C and N, cation exchangeable capacity and exchangeable cations (Al, Ca, Mg, K and Na). The mean annual increment of height, diameter and volume of planted forest were also taken. The increment of height, diameter at breast height and volume of P. caribaea and S. macrophylla did not show any comparative difference for the cause of the similarity in the increment of patterns catalysed at the same location and climatic condition. P. caribaea showed higher SFI value compared to the other study plots, especially for the topsoil. In contrast, pasture plot had higher SEF, followed by P. caribaea and S. macrophylla plantation plots. P. caribaea showed the highest SFI value, while pasture plot had highest SEF, followed by P. caribaea and S. macrophylla plantation plots. Further study on bigger forest plantation having different types of plant species and land topography needs to be conducted to allow individuals and bodies in the field of forest plantation to gain the opportunity and implement the right approaches to establish forest plantation with good planting establishment practices.

Zulkeefli. This open access article is distributed under a Creative Commons Attribution (CC-BY) 3.0 license.