Malaysian Society of Soil Science

Abstract
The rehabilitation of forest areas is not new to Malaysia as forest replanting activities have been carried out throughout the country for years to meet the demand for woody and non-woody products as well as to nurture degraded forestland. Thus it is important for a soil to be evaluated to ascertain the degree to which rehabilitation activities have succeeded in restoring forest health, particularly in sustaining soil quality in rehabilitated forests. This review article aims to provide a corpus of information for forest managers and related agencies who work closely with forestry. The aim is to provide an overview on the importance of soil quality in measuring the success of forest rehabilitation programs. Research articles on the evaluation of soil properties at selected rehabilitated forests in Peninsular Malaysia were included in the review. The impact of forest rehabilitation in relation to soil properties comprising soil compaction, moisture, acidity, macronutrients, cation exchange capacity, microbial count, microbial enzymatic activity, and microbial biomass is discussed. Natural forest is used as a benchmark to see the effect of forest rehabilitation programs. Our review indicates that rehabilitated forests that were established earlier and have gone through a longer period of time have better soil quality compared to the soil of forests established later. This shows that rehabilitated forests are able to restore their soil quality and achieve fertility on par with natural forests, if given longer periods of time for recovery. Soil quality analyses should be done regularly to measure the extent of success in rehabilitation programs.

Abstract
Accurate assessment of the spatial variability of soil properties is key component of the agriculture ecosystem and environment modelling. The main objective of the present study is to measure some of the soil properties and their spatial variability. Conventional analytical methods and geostatistical methods were used to analyse the data for spatial variability. During a period of 2018 – 2019, soil samples (n=23) were collected in the field through random sampling in the eastern part of Menoufia governorate (30˚ 50ʹ N and 31˚ N). Soil properties of soil Cation Exchange Capacity (CEC), electric conductivity (EC), percentage of soil Clay, Silt and Sand were estimated using the geostatistical approach methods. An ordinary kriging (OK) interpolation was used for direct visualization of soil properties. The semivariograms of the four soil properties were fit with Gaussian curve, except EC was fit with exponential curve. The results showed the effectiveness of statistical analysis and interpretation in sense of the obtained data. Cross-validation of variogram models through OK representing in ME showed that the spatial prediction of the selected soil properties is high. The present study suggests that the OK interpolation could potentially revealed the spatial distribution of soil properties and the sample distance in this study for interpolation.

Abstract
Most of the uncovered slope surfaces in tropical climates are highly susceptible to shallow, rainfall-induced soil erosion. The practice of re-vegetation is known to hold promise for a sustainable and long-term solution. Hence this study aimed to evaluate slope hydrological performance associated with vegetation and identify correlations among the parameters. Three experimental plots were set up comprising three density treatments; control (C; without the addition of plants), less dense (LD; 0.7 plant/m²), and dense (D; 1 plant/m²). The vegetated plots were grown with potential pioneers, namely Lantana camara, Melastoma malabathricum, and Bauhinia pupurea in a mixed species composition. A significant decrease in soil bulk density and an increase in soil total porosity, hydraulic conductivity, moisture content, organic matter, and organic carbon were found in D plot. These positive changes boosted plant growth, resulting in higher community-plants aboveground biomass and root length density resulting in the erosion rate being alleviated in LD and D plots by 50.1% and 74.04%, respectively. Soil infiltration capacity, soil structural dynamics, and soil water retention capacity explained the first three components of the principal component analysis (PCA). Thus, we suggest that the promising observations could improve our understanding of differential plant density responses to cut slope restoration performance, particularly for the eroded cut slopes in the tropics.

Abstract
This study investigated the effect of cow dung or rice husk ash amendment on glyphosate degradation in a Malaysian sandy loam soil under three moisture regimes. The control and soils amended with 10 tons ha^-1 of either cow dung or rice husk ash were spiked with 5000 μg g^-1 of glyphosate. Water was added accordingly to obtain soil moisture content equivalent to either a submerged condition, field capacity or permanent wilting point. Glyphosate degradation was monitored for 65 days and the data obtained was fitted to first order-double exponential decay model (FODED). The results revealed that glyphosate degradation occurred in two-phases; an initial high degradation rate followed by a slow rate representing degradation of labile and non-labile phases, respectively. The rate constants of the labile phases ranged from 0.0063 to 0.0604 μg day^-1 while those of non-labile phases were from 0.0077 to 0.0732 μg day^-1. The degradation rate was generally higher in the labile phase. Irrespective of moisture content, the degradation data from the cow dung-amended soil fitted the FODED model best (0.042 ≥ r² ≤ 0.909) followed by the rice husk ash-amended soil (0.023 ≥ r² ≤ 0.914) and the control (0.030 ≥ r² ≤ 0.756). Meanwhile, irrespective of the amendments, soils maintained at field capacity had the highest degradation rate in labile phases (k₁ = 0.0371 – 0.0604 μg day^-1) while at non-labile phases, soils maintained at permanent wilting point recorded the highest rate (k₂ = 0.0077 – 0.0732 μg day^-1). The soils maintained at field capacity generally had the lowest glyphosate half-life (11- 42 days) followed by soils at permanent wilting point (9 – 110 days), with the longest half-life being shown by the submerged soils (13-178 days). It can be concluded that the application of cow dung or rice husk ash increased glyphosate degradation in the soil especially when the soil moisture content was maintained at field capacity.

Abstract
Water management is rarely a focus in Southeast Asian oil palm plantations, due to high rainfall all year long. However, this climatic condition is changing. There is increasing evidence that climate change is causing tropical regions to have reduced annual mean precipitation and increased prevalence of dry seasons. Thus, knowledge gaps in the area of soil-water relationship in these agricultural systems will result in inefficient water management. Therefore, this study was conducted to evaluate the potential of two approaches in monitoring and modelling soil water behaviour under oil palm canopies. The first approach used Neutron Moisture Meter (NMM), to obtain a time series on Θ, including evaluating soil-rainfall relationship. The second approach used Resistivity Imaging System (RIS), to provide data on stratigraphy that was used to further characterize the geologic setting of soil (6 m depth) and its effects on soil moisture. The results revealed a small significant variability in Θ values in the 20 different soil depths. Θ values also showed significant increases in response to high rainfall events (>30.0 mm) which decreased with time. Soil-water content percentage changes ranged from 9.5 to 23.8% at different depths. The resistivity imaging surveys successfully mapped the soil water content underneath the oil palm catchment up to 6 m depth, revealing leakages to groundwater flow at some study sites. Both techniques (NMM and RIS) were able to model the soil-water relationship in oil palm plantations. These methods can be used to charter better water management strategies in oil palm plantations in the future.

Abstract
Oil palm (Elaeis guineensis Jacq.) cultivation is said to have caused losses of soil carbon due to deforestation. However, current oil palm cultivation is carried out either on previously rubber and cocoa plantation or replanted on first- or second-generation oil palm. The present study was conducted to assess whether there is a build-up of soil carbon throughout the growth of oil palm and will those amassed carbon (if any) be lost during replanting. The study was conducted at oil palm ages 5, 10, 15 years old, and newly replanted oil palm. At each age, soils were sampled at the frond heap pile (FH), the harvesting path (HP), and the inter-row (IR). Soil carbon content at all plots was not significantly different between ages with a mean of 2.24%. Between sections, soil carbon content at FH (3.10±1.42%) was significantly higher than the other sections. Our results showed that age of oil palm did not influence the accumulation of soil carbon. Replanting was also found not to have caused losses of soil carbon. As the different sections of the plantation yielded different results, future measurements of soil carbon should consider these different sections to properly represent the whole plantation.

Abstract
Isotope measurements are associated with critical plant resources. Thus, stable rice crop's carbon isotope composition in response to potassium (K) fertilizer was determined,since K is a primary plant nutrient that plays a major role in achieving maximum economic yields. Rice plants were grown in the field and rain shelter under five treatments, which are T1 (no-K), T2 (MOP), T3 (SOP), T4 (Polyhalite) and T5 (conventional fertilizer). The fertilizers were applied 3 days after planting (DAP), 15 DAP, 55 DAP and 75 DAP. Leaf photosynthesis and stomata conductance measurements were taken 85 DAP. The samples were then dried and reserved for carbon isotope analyses. Photosynthesis declined due to K deficiency in the no-K treatment. From this research, we can conclude that stomatal conductance is affected by K fertilizer application where it controls the carboxylation efficiency which may affect the rate of photosynthesis. Later, photosynthesis may influence the discrimination of δ¹³ isotope value. There is discrimination against this heavier isotope of CO₂, this is because CO₂ diffuses through stomata by carbon 12 faster than carbon 13 so that is why there is discrimination against carbon 13 in the stomata.

Abstract
An experiment using leaching columns was conducted for 72 weeks to determine the impact of biochar treatment on a sandy Spodosol. Biochar treatment was found to have a positive impact on soil chemical properties. The treated topsoil had higher exchangeable K, Ca and Mg compared to the control. Due to low clay and organic matter content, much of the cations released by biochar could not be retained in that zone. This is evidenced by the increased concentration of elements in leachates collected from the leaching columns. It means that a significant portion of the nutrients, initially in insoluble form, was susceptible to leaching or podzolization. Some of the nutrients were transported downwards and subsequently retained in the spodic horizon. The biochar treatment increased soil pH, total C and the CEC of the spodic layer with the CEC increase being positively correlated with C content. Notwithstanding, the ameliorative impact of biochar treatment is at best short-term. The application of high amounts of biochar is necessary to raise soil fertility to the level suitable for crop production. Hence, it is recommended that biochar be applied in combination with some NPK fertilizers to sustain crop growth/production in the long term.

Abstract
The present study investigated the spatial variation of the physico-chemical characteristics of lateritic soil profiles (up to 60 cm in depth) in a sloping mango orchard (1 ha; slope gradient = 6%) in North Peninsular Malaysia. The study revealed that horizontal variation for the exchangeable Al and Mg, and the particle size fractions in the topmost soil layer (0-15 cm) within the orchard was higher than their vertical variation within the soil profile, and that, in contrast, the opposite trend was found for the total N, cation exchange capacity, and base saturation. Furthermore, preferential accumulation of soil organic matter and nutrients such as total N and available P were found at the lower (LS) and/or middle (MS) slope positions than the upper (US) one, while the lower clay content with the higher clay activity index was observed at LS compared to MS and US. These results suggest that these variations occur by the scattered accumulation of fertilizer-derived nutrients (i.e. N, P, K, and Mg) in the surface soil layers and the translocation of the surface litter, soil and nutrients towards the downslope in addition to enhanced eluviation process with the residual of clays at the downslope in the sloping orchard.

Abstract
To better understand soil nitrogen (N) sequestration by Acacia mangium Willd. in the plantations of the Southeastern region of Vietnam, a study was conducted to examine soil N content and storage in three different-aged A. mangium stands (4, 7 and 11 years old). Soil samples were collected at different depths from 0-50 cm. Field measurements were taken based on established national standard methods. We used the modified Kjeldahl method to determine soil total N concentration. Soil total N concentration at the various soil depths for each plantation decreased significantly with increasing depth, but increased significantly with plantation age. Soil total N stocks at the topsoil (0-50 cm) increased from 6.13 Mg. N. ha^-1 in 4-year-old stands to 9.71 Mg. N. ha^-1 in 11-year-old stands. Soil total N storage showed obvious topsoil aggregation with more than 60% of soil total N storage in the 0-30 cm depth for each stand. Hence, protection of total N stocks present in the topsoil of planted forests is very critical in the context of N sequestration. Furthermore, stand characteristic parameters (i.e., stand age, plant biomass, stand density, tree height and diameter at breast height, and canopy closure) significantly affected soil total N storage. The findings from this study indicate that taking stand age into consideration is greatly beneficial for forest soil N storage assessment and highlights the potential of A. mangium for N sequestration in plantation ecosystems.

Abstract
Rehabilitation of degraded forestland is critical because it aids in reducing soil nutrient loss, improving vegetation stand and/or composition, and addressing environmental concerns. Thus, the purpose of this study was to determine the soil fertility condition in soils in rehabilitated forests after 30 years of planting. This study was conducted in 16 plots of a 47.5-hectare rehabilitated forest at Universiti Putra Malaysia Bintulu Campus in Sarawak, Malaysia. As of 2010, around 350,000 seedlings from 128 Sarawak native species had been planted. Soil samples were taken from different depths at each site (0-15 cm and 15-30 cm). Soil chemical properties were determined using standard laboratory methods while soil compaction analysis was determined using the fall-corn-type soil penetrometer (Hasegawa Type H-60). Soil Fertility Index (SFI) and the Soil Evaluation Factor (SEF) were used to estimate soil fertility and site quality. The compaction rate for the soil at rehabilitated forest plots was inversely proportional to cumulative depth. The compaction rates for plots in years 1991 to 2000 showed an increase in compaction rates with the depth of soil. The total cumulative depth for plots 2001 to 2008 had a longer graph trend compared to the previous years. The principal component analysis (PCA) showed that pH, OM, exchangeable Mg, CEC, and available P all contributed positively to factor loading in PC1. Our data showed a moderately positive correlation between CEC and exchangeable (Exch.) Mg, CEC with OM and Exch. Na and Exch. K indicating that negative charges derived from organic matter played an important role in cation retention capacity, nutrient supply, and soil fertility. The SFI analysis (9.26) in rehabilitated forest planted in year 1991 indicated greatest accumulation of organic matter from litter fall. In addition, the SEF values of the rehabilitated forests in relation to planting years indicated an undulating trend. Generally, SFI and SEF exhibit strong correlations with soil chemical and biological features, implying that these two indices can be used as indicators of soil quality.