Evaluation of metal nutrient from sewage sludge on growth of medicinal herbs

Abstract

Generally municipal sewage sludge can be used as fertiliser as it contains a lot of nutrients. However the level of each particular nutrient has not yet been established locally. By focusing on copper (Cu), iron (Fe), manganese (Mn) and zinc (Zn) contents in municipal sewage sludge from primary oxidation pond of Taman Sri Pulai, Johor and in plant tissue sections, this study attempts to explain the relationship between plant yield and metal concentrations and suggest alternative evaluation for future in-depth studies. Raw sludge samples were collected, then air dried and ground to powder form in the beginning of a field work. The metal concentrations of sewage sludge were copper 6.9 mg/kg; iron 330.2 mg/kg; manganese 6.7 mg/kg; and zinc 9.1 mg/kg. Curcuma longa (turmeric) and Orthosiphon stamineus (cat’s whiskers) were selected and the plants received different quantity of sludge application ranging from 1 g per plant to 4 g per plant weekly for six consecutive weeks while observations were done for eleven weeks inclusive of the first six weeks of sludge application and five weeks of post application period. The field experiments spanning 12 rows of vegetation and 65 pH grid points were carried out on iron rich soil. Physical parameters such as leaf length, plant height, rhizome yield, shrub width and shrub height were monitored parameters used to determine plant growth together with the chemical contents of both types of plants. All samples were acid digested using EPA Method 3050B and analysed using HACH DR5000 spectrophotometer. Soil pH readings during and after sewage sludge surface application at plant base section throughout the entire experiment did not display any statistically significant changes using one way ANOVA at a=0.05. Turmeric displayed 99% confidence level of negative correlation in the ironmanganese interaction in the plant using one way ANOVA at a=0.01 while cat’s whiskers displayed no definite pattern of metal relationships within the shrubs. Metal ratios between copper, iron, manganese and zinc were analysed to determine the occurrence of potential metal induced stress. Cu:Mn, Fe:Mn, Cu:Zn, Fe:Zn and Mn:Zn ratios suggested that turmeric suffered from manganese and zinc deficiency under high iron environment while Fe:Mn, Cu:Mn and Mn:Zn ratios suggested that cat’s whiskers suffered from manganese deficiency only. Through this study, the determined optimum sewage sludge dosage for turmeric was 3 g per plant while the optimum dosage for cat’s whiskers was between 2 to 3 g per plant