Acid soil covers 30% of ice-free land in the world, mainly distributed in the tropical and subtropical regions where agriculture is the dominant business. Soil acidity, particularly aluminium (Al) and manganese (Mn) toxicity, often constitutes one of the critical constraints limiting crop production on theseacid soils. Research on acid-tolerance mechanisms of soil grown plants will have important implication in facilitating soil and crop management in the tropical and subtropical regions. Soil becomes acidic due to natural soil acidification process. In acidic soils, Al toxicity is common due to solubilisation of Al3+ ion which is toxic for plants. The main symptom of Al3+ toxicity is the inhibition of root growth. After Al3+ toxicity, Mn toxicity ranks as the second major concern for plant growth in acid soils. Unlike Al, Mn is an essential plant nutrient and is toxic when taken up in excessive quantities by plants. In addition to Al and Mn toxicity, low pH also affects plant growth in highly acid soils. Low pH stress facilitates H+ influx into root tissues resulting in poor plant growth. However, phosphorus (P) deficiency is also common in acid soils. Phosphorus leads to an Al-phosphate complex in acid soils that result in less P availability in these soils. Different Al tolerance mechanisms such as an increase in rhizosphere pH, plant tissue tolerance, exudation of organic acid and role of apoplast are discussed in this review. This review concludes that P may play an important role in Al tolerance. Thus, understanding acid tolerance mechanisms in soil grown plants has important implications for sustainable agriculture in the tropical and subtropical regions. This review suggests that introduction of Al-tolerant crops in acid soils will improve crop production in these soils.
Keywords: Organic acid exudation, Al and P interaction, apoplast, plant tissue tolerence
A study was conducted on soil moisture in Pasoh 50-ha demography plot, Pasoh Forest Reserve, Negeri Sembilan, Malaysia to assess the variations of moisture content for different soil types and depths and the association between soil moisture and tree community. The soil types examined were dry alluvial (DA), wet alluvial (WA) and ridge areas (RD). Soil moisture was measured at 15, 30, 45, 60 and 75 cm depths using AquaPro Frequency Domain Reflectometry (FDR) system. The average monthly soil moisture measurement for a two-year period varied between soil types with 48% for dry alluvial soils, 56% for ridge soils and 68% for wet alluvial soils. However, maximum moisture was recorded for wet alluvial soils at 100%, followed by ridge soils at 92% and dry alluvial soils at 80%. Wet alluvial soils showed highest soil moisture at all soil depths. Soil moisture increased with increasing soil depth with moisture at 75 cm depth being significantly different from moisture at other depths. Though soil moisture increased with soil depth, the difference was only significant at 75 cm depth. The species distribution based on soil types in the Pasoh 50-ha demography plot showed that Euphorbiaceae, Lecythidaceae, Myrtaceae, and Sapidaceae were abundant at wet alluvial soil. At DA, the abundant species were Annonaceae, Myrsinaceae, and Clusiaceae, while Burseraceae, Alanggiaceae, Anisophylleaceae, Fabaceae, Ulmaceae, and Sterculiaceae were abundant at RD. This indicates that species abundance at the Pasoh 50-ha demography plot is associated with site condition.
Keywords: Soil moisture, Pasoh 50-ha demography plot, monitoring, FDR
In order to reduce soil erosion on sloping lands, empty fruit bunches (EFB), Ecomat, oil palm frond heaps, or silt pit have been used by major oil palm plantations. Studies have shown that at 0-15 cm soil depth, organic matter content in EFB is highest among the four treatments. Besides, EFB had the highest humic acid content compared to the others, about two times higher than control. Our analysis showed that aggregate stability of EFB was the highest among four treatments at 54.88%, followed by Ecomat (47.7%), silt pit (44.76%) and finally, control (42.12%). We observed that organic matter content inversely correlated with Fe (p < 0.05) and Al (p < 0.05) oxides. Finally, yield of humic acids correlated with soil pH (p < 0.05), aggregate stability (p < 0.01) and aggregate size distribution (p < 0.01). Among the four treatments, application of EFB as a mulching material commonly practised in oil palm estates was found to be the best practice on sloping lands due to its high organic matter and humic substances content that retain soil particles by improving soil aggregate stability and aggregation.
Keywords: Oil palm fronds, empty fruit bunches, Ecomat, silt pit, humic and fulvic acid
Rubber, Hevea brasiliensis is one of the important commodity crops that has contributed much to the nation’s economy as this country was the third largest producer of pure latex and the fifth in terms of consumption of natural rubber in the world. The precise use of fertilizers is very important in a rubber nursery establishment to ensure quality production of planting materials and optimizations of the fertilizing cost. This study will assess the suitability of the current fertilizer application rate for latex timber clones and suggest a fertilizer rate for use in advanced planting materials nurseries. The study was conducted using a complete randomized design (CRD) with four replications. Four different rates of RISDA 1 compound fertilizer were used; T1 (0 g plant-1) acted as control, T2 (50% or 18.75 g plant-1), T3 (100%: 37.5 g plant-1) and T4 (150%, 56.25 g plant-1). T3 (100%) is the rate recommended by the Malaysian Rubber Board (MRB). The soil was a Tropeptic Haplorthox, Munchong Series. Data on growth such as height, girth and dry weight were taken. Tissue analysis was conducted at the end of the study. Results show that plant growth increased significantly with fertilizer application. Results show that K and Mg contents were highest in T4 (150%) and significantly different from other treatments. Compared to established nutrient critical values for immature rubber, T4 met the nutrient sufficiency range for rubber, while current recommendation showed insufficient K and Mg. Visual observation also showed symptoms of nutrient deficiencies. Efficiency of nutrient use showed decreasing efficiency with increasing rates of fertilizer application. Based on biomass production and comparison of leaf nutrients with critical nutrient value, this study concludes that the current recommended fertilizer rates are insufficient for optimum growth, and precise fertilizer application should be considered to optimize fertilizer use efficiency.
Keywords: Rubber, Tropeptic Haplorthox, compound fertilizer RISDA 1, nursery trials, advanced planting materials
Black pepper is a high nutrient demanding crop. Fertilizer use and management is therefore of crucial importance to sustain growth and high yield. This experiment was carried out to study the effect of chemical and organic fertilizers on some physiological characteristics, yield and soil fertility of pepper in the first 30 months of planting. The treatment consisted of T1: chemical fertilizer; T2: organic and foliar (seaweed) fertilizer; T3: organic and chemical fertilizer and T4: no fertilizer. These selected integrated fertilizer treatments out-yielded organic and chemical fertilizer by 75.38% and 16.14%, respectively, with the higher yield being associated with various phenotypical alterations, which are reported here. Significant measureable changes were observed in physiological processes and plant characteristics, such as large leaf area index, more chlorophyll content and high photosynthetic rate coupled with lower transpiration rate in integrated fertilizer treatment compared with other treatments. The high fertility level in organic fertilization reflected the importance of organic fertilizers in improving soil quality. However, the 75.38% reduction in pepper yield should be compensated by premium price of organic pepper. In conclusion, to achieve high growth performance and yield in pepper, organic fertilizer alone is insufficient whilst integrated fertilization gave a significant increase in yield and growth of pepper.
Keywords: Black pepper, organic fertilizer, integrated fertilization, growth performance, yield
Rice Husk Charcoal (RHC) is a by-product of rice processing mills which can be found in very large quantities in these mills. This industrial waste is largely unutilized, causing environmental pollution especially in the state of Kelantan. In order to increase its utilization, RHC was characterized and investigated for its potential in enhancing the composting process. Physico-chemical properties of RHC such as pH, nutrient content, ash content, CEC, adsorption kinetics, surface area, functional groups, surface structure and pore sizes were studied. The composting treatments were carried out by mixing 4% (wt/wt) and 6% (wt/wt) RHC with organic substrates and with no RHC amended as control. Parameters such as daily temperature, CO2 flux, nutrient content, pH, moisture and total microbial count were measured during the composting process. Results showed that RHC is a highly alkaline material (pH 8.9) with a carbon content of 16% (wt/wt dry basis), CEC of 17 cmol/kg soil, BET surface area of 401 mg/g and a methylene blue adsorption capacity of 38.8 mg/g. The presence of C=O carboxyl-C, ketones and ester, aliphatic C=H, C=C benzene ring and C-H aromatic hydrogen suggests that RHC mainly comprises amorphous char, a random mixture of thermally altered molecules and aromatic polycondensates.The addition of RHC to organic matter accelerated the composting process through higher decomposition rates due to higher microbial population at the thermophilic stage with RHC acting as a bulking agent, as well as higher moisture and nutrient retention during composting. N losses were found to be lower with RHC composting.
Keywords: Rice husk charcoal, composting, physico-chemical, decomposition, nutrient retention
The efficiencies of different particle sizes (< 63, 63-93, 93-106 and 106-125 µm ) of mined phosphate rock (PR), as well as other phosphate sources (processed and biogenic) as a chemical stabilization remediation technology and stability (in terms of heavy metals) were assessed in contaminated urban soils. The results demonstrate that the application of PR substrate with smaller particle size (< 63 µm) was significantly more effective than larger particle size for Cu, Co, Cd and Pb immobilization. Depending on phosphate solubility, the decrease in of metal availability was highest in biogenic ground fish bones) (0.02; 0.0; 0.005 and 0.017 mg kg-1 for Pb, Cd, Co and Cu, respectively) and processed phosphates (0.05; 0.02; 0.22 and 2.01 mg kg-1 for Pb, Cd, Co and Cu, respectively) than mined phosphate rock (0.03; 0.011; 1.11 and 0.005 mg kg-1 for Pb, Cd, Co and Cu, respectively). It is noted that lower dissolution of phosphate rock may be advantageous for long term maintenance.
Keywords: Mined PR, processed PR, biogenic PR, TCLP, sequential extraction study
Microbes are theoretically the driving force for the dynamics of greenhouse gases, especially nitrous oxide (N2O) and methane (CH4) which are trace gases but have high global warming potential (i.e., 23 and 296 times higher than that of CO2). Little is known about the population and genetic diversities of bacteria related to N2O and CH4 in peat soils, though an understanding of microbial aspects of N2O and CH4 may explain better the dynamics of these gases across wide ranges of peat conditions and human impacts. Conventional cultivation and molecular methods were carried out to determine the population and genetic diversities of N2O and CH4-related microbes in peat soils with different site locations and land-use covers. The results showed that the population of nitrifying bacteria varied with site locations and land-use covers and ranged from 0.33 x 103 MPN g-1 in an oil palm field in Wanaraya (KW site) to 4.43 x 103 MPN g-1 in a forest in Gambut (GH site). Similarly, the population of methanogenic bacteria was varied with site locations and land-use covers and ranged from 0.15 x 105 MPN g-1 in a paddy field in Barambai (BB site) to 34.46 x 105 MPN g-1 in a paddy field in Balangan (P site). The genetic diversity of denitrifying bacteria increased as forested peat lands (i.e., AH and GH sites) were converted to agriculture lands (other sites). The genetic diversity of nitrifying bacteria seemed to be site specific and less affected by land-use cover. Type I methanotrophic bacteria existed in forest in Gambut (GH site), but disappeared as the soils were cultivated for rice and applied with chopped-swamp weed or silicate fertiliser. The methanotropic bacteria type II existed in all sites and diversity was not affected by land-use cover or soil amelioration, suggesting that type II methanotrophic bacteria was less sentitive to environment shifts or human activities.
Keywords: Nitrous oxide, methane, denitrifying bacteria, methanotrophic bacteria, peat soil