Abstracts & Full Texts: Vol. 12, April 2008

Abstracts & Full Texts: Vol. 12, April 2008

Geochemical Distribution of Elements at Lipad and Tabin Mud Volcanoes, Sabah
A study was conducted to determine the chemical characteristics of mud volcanoes at Lipad and Tabin situated at Tabin Wildlife Reserve.  Both areas comprise of inner zone (with absence of vegetative cover) and outer zone (with vegetative cover).  The concentrations of Fe and Mn at the inner zone for both volcanoes ranged from 17390-24800 mg/g and 497-941 mg/g respectively.  The total concentrations of Mg, Na, Ca and K were highest at the inner zones ranging from 3653-6088 mg/g, 1543-19472 mg/g, 291-2875 mg/g and 722-2428 mg/g, respectively.  The concentrations of these elements at 200 m away from the periphery of the inner zone decreased to 588-1448 mg/g, 41-139 mg/g, 0.9-30 mg/g and 256-632 mg/g, respectively.  The element distribution decrease in the outer zone could be associated with the degree of mud volcanoes activity.  The concentrations of trace elements such as Zn, Cu, Cr, Pb, Co, Ni and Cd were of the same order of magnitude (<100 mg/g) with no apparent trend between inner and outer zones.  This indicates that the degree of mud volcanoes activity does not influence the distribution of trace elements.

 Hydrophobicity of Soils Formed over Different Lithologies

Using a free survey technique and special analytical methods, wettability of soils derived from different parent materials in central Southeastern Nigeria were investigated in 2005. Resulting soil data were subjected to Analysis of Variance (ANOVA) using PROC Mix-model of SAS, and some soil properties were regressed to identify leading predictors of soil hydrophobicity in the study area. Soil hydrophobicity varied among the soil groups and horizons (p<0.05) in response to differences in soil properties. Soil moisture, organic matter, clay, sand, sodium saturation were good predictors of soil hydrophobicity in soils of the study site although at varying levels of prediction and parameter combinations. Accuracy of predictions was very high. Further studies involving detailed sampling, increasing parameter combinations and geostatistical analysis should improve the quality of models used to study soil hydrophobicity in the study area.


Effects of Anthropogenic Disturbance on Soil Microbial Biomass C, N and P in a Tropical Rainforest Ecosystem of Assam, Northeast India

 The effect of anthropogenic disturbance on soil microbial biomass C, N and P dynamics in a tropical rainforest ecosystem of Northeast India was studied in undisturbed, moderately disturbed and highly disturbed stands.  Tree species richness in the community was drastically reduced due to disturbance, from 82 species in the undisturbed stand to 13 species in the highly disturbed stand. Soil organic C, total Kjeldahl nitrogen and P concentration was low in the disturbed stands compared to the undisturbed stand. With the increase in disturbance, the microbial-biomass C, N and P decreased significantly (P>0.001) because of lower inputs of organic matter to the soil. Microbial biomass C, N and P ranged between 226-1060 µg g-1, 27-92 µg g-1 and 15-52 µg g-1, respectively, in the undisturbed and highly disturbed stands. The seasonal pattern of microbial biomass C, N and P was influenced by the variation of soil moisture and temperature, with maximum during winter and minimum during the  rainy season. There were significant positive relationships among microbial biomass C, N and P and SOC, TKN and P concentration.  Destruction of above ground vegetation by selective logging and clear felling caused a significant reduction in microbial biomass in the disturbed stands.


Organic Matter, N and P Dynamics of Fine and Coarse Roots in Humid Subtropical Forest Ecosystem Exposed to Disturbance in Meghalaya, Northeast India

Standing fine (<2mm diameter) and coarse (>2mm diameter) root mass production, N And P accumulation, and turnover rate were studied in two pairs of protected and disturbed stands of a subtropical humid forest to examine the response of below-ground parts to mild disturbance caused by above-ground vegetation by humans.   Disturbance of mild intensity caused significant reduction in biomass accumulation and production of fine and coarse roots. The fine root (540-754 gm-2) and coarse root (307-387 gm-2) mass was higher in the protected stands, declining (fine root: 422-466 gm-2, coarse root: 247-305 gm-2) significantly in the disturbed stands. The total annual root production was also higher in the protected stands (1102 -1242 gm-2) than in the disturbed stands (890-940 gm-2).  Live roots (biomass) showed a higher N and P concentration than the necromass (dead root mass).  Nutrient concentration was higher in the fine roots compared to the coarse roots.  N and P accumulation in the roots was high (N = 99 - 132 kg ha-1, P =5 - 8 kg ha-1) in the protected stands and low (N = 76 - 85 kg ha-1, P= 4 -7 kg ha-1) in the disturbed stand.  The total input of N to the soil by roots ranged from 121-132 kg ha-1 in the protected stands to 96-100 kg/ha in the disturbed stands, whereas  P input was 5 to 7 kg ha-1 in all the stands. The study reveals that roots play a significant role in maintaining the organic matter, Nitrogen and P status of the soil and is influenced by soil conditions and vegetation   characteristics.  Soil and vegetation are affected due to disturbance, which in turn affects mass, production, N and P concentration and their accumulation in the roots. These results are discussed in the present paper and the information should help further understanding of the fragility of subtropical humid forest ecosystems.

 Carbon and Nitrogen Stocks of the Central Clay Plane: Irrigated versus Rain-fed Vertisols
Mitigation of atmospheric CO2 concentration and ensuring national food security could be achieved by increasing carbon sequestration in the soil. We estimated soil organic C and N sequestered in the long- (79 years), medium- (46 years) and short-term (22 years) crop rotation systems of cotton (Gossypium hirsutum), sorghum (Sorghum bicolor), groundnut (Arachis hypogaea), wheat (Triticum aestivum) and fallow in Vertisols, both irrigated and rain-fed, of the semi-arid tropics of Sudan.  Total C pool, comprising soil organic and inorganic C for the entire profile (0 - 0.90 m) of irrigated Vertisols was estimated to be 142, 174 and 99 t ha-1 C for the short-, medium- and long- term cultivation, respectively. Under irrigated soils, organic C made up 31 to 71% of the total C stored in the profile compared to 63 to 73% under rain-fed Vertisols. It was estimated that about 25% was lost from total profile (0 - 0.9 m) C as CO2 after about 79 years of cultivation (0.414 t C ha-1yr-1) of the Gezira cotton scheme. Similarly, loss from organic C was estimated at 29% with a rate of 0.208 t C ha/yr. Total profile (0 - 0.9 m) N under short- and medium-term cultivation (6.74 – 7.79 t  ha-1) was significantly higher than that under long-term cultivation (5.05 t N ha-1). However, cropping system had no significant effect on total N (an average of 8.0 t ha-1) under rain-fed Vertisols. About 65 to 68% of total profile N was found below the plough layer (0 – 0.3 m). Since Vertisols are heavy clay soils, reducing tillage operations, an alternative management practice (for example, using cover crops during fallow periods and retaining crop residues in situ) would help in reducing C loss in one of the largest cotton schemes in Africa.  


Enhancing Rice Establishment in Anaerobic Direct Seeding Through Control of Weedy Rice

A glasshouse and field trial was conducted to investigate the effects of pre-treated rice seeds on cultivated rice and weedy rice establishment in direct seeding planting system. Treatments applied were wet seeding (T1) and water (anaerobic) seeding at 10 cm flooding depth (T2). In the glasshouse trial, water seeding significantly reduced weedy rice seedling emergence almost three-fold compared to control; the usage of pre-treated seeds in both seeding methods significantly increased the viability of cultivated rice compared to weedy rice. The weedy rice population was significantly decreased (32%) in the water seeding plot compared to wet seeding at 90 DAS in season 2/04 in the field. The water seeding technique also profoundly reduced weedy rice population by about 50% at both 60 and 90 days after sowing (DAS) the following season (season 1/05) compared to wet seeding.   The use of pre-treated seeds for the anaerobic direct seeding technique had an advantage on seedling vigour that out- competed the growth of weeds, and increased rice seeds viability.

Amelioration of Cheringa Acid Sulfate Soil and Screening of Acidity-Salinity Tolerant Rice Varieties in a Simulation Study
A simulation study was conducted to evaluate the effects of basic slag (BS10: basic slag 10 t ha-1  and BS20: basic slag 20 t ha-1), aggregate size (A20: aggregate sizes of soil less than 20 mm and A30: aggregate sizes of soil, 20-30 mm) and groundwater depth (Gw0: no influence of groundwater and Gw50: groundwater beneath 50 cm of the soil surface) in pre-leached Cheringa acid sulfate soil (Typic Sulfic Halaquept) in relation to the production and screening of the acidity-salinity tolerance of 18 rice cultivars. The results obtained from the study showed that the physico-chemical properties of the pre-leached acid sulfate soil were strongly (p=0.05) influenced by the application of basic slag, aggregate size and maintenance of groundwater depth. Among the individual treatments, the application of BS20 ranked first with regard to the reclamation of soil and production of rice, followed by Gw50 > A30. The average soil data of all the treatments at post harvesting of rice cultivars were increased by 1.6 units for soil pH(water: 1:2.5) and 34 to 1803%  for the contents of N, P, Ca and Mg, while the saturations of Fe, Al and Na were decreased by 24 to 88% compared with the initial soil.  The maximum quantity (6.9 t/ha) of rice grain was attained by the local (Cox’ Bazar) Kajashail, followed by the Bangladesh rice (BR) line 5828-11-1-4 (6.7 t ha-1) > BR 23 (6.6 t ha-1).  Among the rice varieties, the BR lines were found to be the most effective for rice production in the soil, followed by the local varieties > BR varieties > international rice (IR) varieties. Almost similar and significant (p=0.05) effects were observed for plant height, tiller production, straw yield and yield components of the rice cultivated in the soil.

  Characterization of Malaysian Sewage Sludge and Nitrogen Mineralization  in Three Soils Treated with Sewage Sludge
Studies to determine the chemical composition of sewage sludges produced in Malaysia and potentially mineralisable nitrogen (No) and mineralization rate constant (k) of sewage sludge in three Malaysian soils are reported.  The sludges collected from ten wastewater treatment plants in Malaysia were acidic in nature and the N, P, K, Ca and Mg contents were variable. The heavy metal (Pb, Cd, Cu, Mn and Ni) concentrations of the sludges, except for Zn, were below the European Union Maximum permitted level in sludges. In an incubation study, three topsoils of Bungor, Jawa and Serdang series were treated with three rates (0, 140 and 420 kg N ha-1) of dewatered sewage sludge and incubated about 60% of the water holding capacity for 12 weeks. Mineralization of N exhibited a slow initial rate, followed by a rapid increase in rate in week 4 to 8. Accumulation of mineral N ranged from 50.5 to 147.6 mg kg-1 soil.  Bungor and Jawa series had higher N mineralization than Serdang series. Sludge added at 420 kg N ha-1 resulted in the highest concentration of net mineralised N. Values of potentially mineralisable N, (No), and mineralization rate constant, (k), ranged from 23.4 to 137.5 mg N kg-1 soil and 0.036 to 0.082 week-l, respectively. It was concluded that N mineralization of the sewage sludge treated soils was dependent on the application rate of sludge and soil type.

 Concentrations and Chemical Forms of Heavy Metals in Some Ultisols in Johore, Peninsular Malaysia
The concentrations of heavy metals in soil are associated with biological and geochemical cycles and are influenced by anthropogenic activities such as agricultural practices, industrial activities and waste disposal. A total of 36 surface soil samples (Typic Kandiudult, Rengam Series) were collected from some major vegetable growing areas developed over granite. Twelve soils from areas not cultivated with vegetables but also developed over granite were also sampled for background values. The pseudo-total heavy metals, (Cu, Pb, Zn and Ni) were determined by the aqua-regia method. Chemical properties such as pH, organic carbon and CEC were also analysed. Some selected cultivated soil samples (24 of Ultisols and 12 of background soils) were analysed for chemical partitioning using a modified Tessier’s procedure (F1: exchangeable fraction, F2: fraction bound to organic matter, F3: fraction bound to amorphous iron oxides and F4: residual fraction). Mean values of the total heavy metals for the cultivated soils are Cu (23.3 mg kg-1), Pb (18.0 mg kg-1), Zn (49.4 mg kg-1) and Ni (6.0 mg kg-1). Comparison of these values to the contents in the background soils show that Cu and Zn have significantly increased. However, all these values are below the contaminated levels established for the country’s agricultural soil limits (95th percentile). From the partitioning study, the general trend in the Ultisols for Pb and Ni is residual > oxalate >exchangeable>organic. For Zn and Cu, the oxalate extractable phase is highest followed by the residual phase. Zinc and Pb contents in the soils are also positively correlated with the pH of the soil.

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