Malaysian Society of Soil Science

Abstract
The ability to produce the indole-3-acetic acid (IAA) by plant growth-promoting rhizobacteria (PGPR) is one of the mechanisms forpromoting plant growth. The survival of sweetpotato under low input farming could be associated with the production of such hormones.Studies were conducted to isolate IAA-producing rhizobacteria from rhizosphere of different varieties of sweetpotato grown on different soils. Media containing root exudate of sweetpotato var. Gendut was used to screen for rhizobacteria associated with sweetpotato. Growth performance of the IAA-producing rhizobacterial isolates was thenevaluated using sweetpotato var. Gendut cuttings under glasshouse conditions. A total of 115 rhizobacterial strains were isolated from the different sweetpotato varieties. Only 48 of the local isolates were able to grow in the root exudate medium with 18 of them producing 1AA ranging from 4.01 to 8.56 μg mL^-1). Inoculation of the IAA-producing isolates on Gendut showed significant differences in the root dry weight, shoot:root ratio and phosphorus uptake by the plants.

Abstract
A study was conducted to evaluate the hydraulic conductivity of saprolites and their potential use as a wastewater treatment in Malaysia. Samples of granitic, basaltic, schist and shale saprolites were taken from 16 locations throughout Peninsular Malaysia. These samples were morphologically described and air-dried for physical analyses. The infiltration rate study of the saprolites was conducted both in-situ and in the laboratory. The study showed that granitic saprolite had the highest K_sat value while basaltic had the lowest value in both laboratory and in-situ methods. Several factors influenced the K_sat value, namely clay and sand content, porosity, pore shape and pore sizes. Both pore size and shape analysis influenced the Ksat value especially mesopores, M_e (30 < 75 mm), macropores, M_c (> 75 mm), vugh and channel shapes. A model to predict the K_sat of saprolites was proposed as follows: K_sat = 16.859 - 0.182 θ_fc - 0.183 θ_wp - 0.128 S_i + 0.112 M_oist where, θ_fc and θ_wp is the moisture content retained at 9.8 kPa and 1500 kPa, respectively, S_i is the silt content, and M_oist is the air-dried moisture content. The study suggests that shale and basalt saprolites are suitable for in-situ wastewater treatment because of their slow to very slow infiltration rate. This will provide ample time for bacteria and viruses to be removed from the effluent by filtration and adsorption onto particle surfaces and for organics to stabilise the wastewater.

Abstract
Integrated farming of crop and animal enables resources from animal waste to be utilised. However, bacterial pollution is a concern. In this study, a bacterial model, ECOLI, was developed to simulate Escherichia coli density daily on land and its concentration in surface runoff. Loss of E. coli was assumed to occur through decay, runoff, sediment and percolation. E. coli decay was assumed to follow the first order decay affected by soil pH, soil temperature and soil moisture. In testing the model, the ECOLI model was interfaced with the GLEAMS-SWT hydrologic and erosion model. Calibration and evaluation was performed with field-scale data from Franklinton, Louisiana. Fresh cow manure was applied on grassed plots and runoff was collected and analysed. Predicted E. coli concentrations versus observed E. coli concentrations in surface runoff gave a regression line with coefficient of determination of 0.993, intercept of 0.011 and a slope of 0.995 indicating good agreement of model predicted concentrations with observed concentrations. The ECOLI model can be used to study the effects of various animal waste application practices such as waste loading rate, timing of application and frequency of application. More research needs to be conducted to incorporate databases so as to expand the capabilities of this model.

Abstract
Recycling of sewage sludge to agricultural land can be beneficial from the aspect of essential plant nutrients and organic matter supplement to the soil and plant system. However, sewage sludge also contains varying amounts of heavy metals which may pose a metal toxicity hazard to crops and consumers of these crops. Thus, the uptake of heavy metals by crops and the fate of these heavy metals in soils need to be monitored. In general, domestic sewage sludge has lower concentrations of heavy metals compared to the mixed light industry and domestic sludge type. Therefore, domestic mixed with light industry type sludge is hazardous and unsuitable for agricultural use. The concentration of heavy metals in domestic sewage sludge does not exceed the maximum permitted concentrations (MPC) of the European Community Standard (ECS) for land application. Sewage sludge application appears to have little effect on increasing heavy metal concentrations in the soil and grain after the third maize cycle. The concentration of heavy metals in the soil was below the MPC of the ECS and ranged from 12.44-35.44 mg kg-1 Zn, 5.00-9.80 mg kg-1 Cu, 0.60-2.44 mg kg^-1 Cd , 7.16-24.04 mg kg^-1 Pb and 7.44-11.36 mg kg^-1 Ni. The concentration of heavy metals in maize grain which ranged from 4.95-19.18 mg kg^-1 Zn, 0.56-2.60 mg kg^-1 Cu, 0.037-0.052 mg kg^-1 Cd, 0.034-0.052 mg kg^-1 Pb and 0.66-1.22 mg kg^-1 Ni was below the MPC values of the Malaysian Food Act 1983 and Food Regulation 1985 (fresh weight basis and 60% moisture content). Correlations were found between (i) total Pb concentration in the soil (r=0.53**) and Pb content in maize grain; (ii) available heavy metals or 1 M NH₄NO₃ extractable Cu (r = -0.25*), Pb (r = O.40**) and Ni (r = 0.51**) in the soil and metal content in the grain(significant); (iii) total concentrations of Cd r=-0.43**, Pb r = 0.43**, Zn r=0.30* and Ni r = -0.40** in soil and the metal content in leaves and stem: (iv) available heavy metal concentration of 1 M NH₄NO₃ extractable Zn (r = 0.41**) and Ni (r = 0.55**) in soil and leaves and stem content (significant); and (v) concentration of Cd (r = -0.40**) and Ni (r = -0.52**) in soil and content of these metals in sheaths band cobs and between available or 1 M NH4NO3 extractable Cd (r = 0.28*), Pb (r = 0.39**) and Ni (r = 0.86**) in soil and content of the metals in sheaths and cobs. From this study, it can be concluded that soil extracted with NH₄NO₃ is suitable for determining available heavy metals in sludge-amended soils.

Abstract
Burning and dumping of coffee bean residue has brought on environmental problems. On the other hand, low soil fertility has resulted in declining crop production. For efficient use, mineralisation of N from coffee residue applied as surface mulch was evaluated using four rates of residue (0, 3, 6, and 9 Mg ha^-1) combined with five periods of incubation (0, 30, 60, 90, and 120 days) in a pot experiment with three replicates. The low quality coffee residue resulted in immobilisation of soil N (varied between -7.1 to -2.8 g kg^-1), which ((R² = 0.72**) which persisted linearly up to the end of the experiment. The regression equation indicates that mineralisation of N is controlled by lignin, L/N and cellulose (R² = 0.99**), while residue N at each period of incubation is controlled by L/N ((R² = 0.56**). Increased application rates of coffee residue reduced immobilisation of N (a quadratic response). N mineralisation rate (Nk) was significantly higher (1.5 mg kg^-1 d^-1) in the first 30 days of incubation, whereas 3 Mg ha-1 residue had a significantly high Nk value (1.3 mg kg^-1 d^-1) compared to higher rates. The regression equation to predict N mineralisation rate (Nk) indicates that time of incubation and concentration of N in the residue control N mineralisation rate (R² = 0.80**).

Abstract
This research was conducted to study the kinetics processes of microbial denitrification and the kinetics processes of plant absorption. The test plants were spinach, peanut and grass. The test solution contained nitrate of 24 mg N/L, glucose of 64 mg C₆H₁₂O₆/L and phosphate of 0.5 mg P/L. The results showed that the kinetics of nitrate biodeconcentration processes were exponential: Ct = Co*e^-kt. The rate constant for microbial denitrification was stated as kd which was equal to 0.0786 day-1. The rate constant of plant absorption was stated as ks, and the rates for spinach, peanut and elephant grass were 0.0745, 0.0921 and 0.1226 day^-1, respectively. The time to process 50% of nitrate biodeconcentration efficiency (t½), as the half time of nitrate biodeconcentration, for microbial denitrification it was 8.8 days and for nitrate absorption by spinach, peanut, and elephant grass, the times were 9.2, 7.5, and 5.6 days, respectively. Therefore, elephant grass they was more effective in suppressing nitrate than peanut, denitrifier and spinach.