الملخص الإنجليزي
Oman faces problem of water scarcity. This is, obviously, a problem limiting the production of crops. Therefore, it needs to leverage the wastewater that is produced in the sewage system. Wastewater Company, Haya, converts the biosolid output of the wastewater processing into composting process. But unfortunately, this type of soil amendment is likely to contain various toxic materials. Therefore, it is important to identify the forms of various metals such as Mg, Ca, Al, Zn, Cu, Co, Cr, As, Cd, Fe, Mn and Ni which could exist in the soil as a result of the application of sludge fertilizer to land --- so as to enable us to spot their existence as also to evaluate the extent of their movement, hence determine e bioavailability and toxicity. It could also help us determine the bioavailability and toxicity of these metals. Sequential extraction technique has been used to analyze for metals associated with carbonate, iron oxide, manganese and organic matter. The presence of metals fractions in Omani soil and nutrients like Mg and Ca was studied; it had found that Ba was appeared as exchangeable in columns which were amended with 34.8 g/kg and others elements like Al, Ni. Na and Zn were available as organic fractions but Ca and Mg were available in all types of fractions. Other metals were not detected in extracts. Besides, most of the fractions were found to be more in columns irrigated at a rate of 60 ml/min than 120 ml/min.
The effect of two rates of sewage sludge compost (17.4 g/kg and 34.8 g/kg) and two irrigation rates (60 ml/min and 120 ml/min) on the soil properties was investigated; there were significant differences in the pH values in the last depths of soil columns which were amended with 34.8g/kg and irrigated with both irrigation rates (7.93 in line 1 and 8.33 in line 2). It was the same with moisture content; there were some significant differences between the last two depths of both columns which were irrigated with both rates and amended with 34.8 g/kg and they were 5.06 and 4.35% and between second depths in 17.4 g/kg column in both lines (4.14 and 2.81%). As regards the conductivity and percentage of organic matter, there were notable differences in their values (refer to table 2). In short, the high irrigation rate of 120 ml/min increased the mean values of soil properties compared to the low irrigation rate of 60 ml/min although there were significant differences in the values.
The plant uptake of metals was studied as well and it was found that the roots of the tomato plant recorded a high concentration of elements compared to the fruit, leaves and stem. The study also found that the metals had accumulated in the order of root, fruit, leaves and stem. Moreover, compost addition increased the yield of tomato plants in terms of height of stems and the weight of biomass of tomato organs.
The impact of the compost rates and the rate of irrigation on the metal concentration was obvious through total metals concentration analysis of the soil samples at different depths which showed that the concentration of metals decreased in the columns amended with 34.8 g/kg of compost in column which were irrigated with 60 ml/min. Moreover, metals in compost had been absorbed by the root part of the tomato plant in columns amended with 34.8 g/kg which caused reduction in the concentration of metals in soil samples. However, there was some release of metals from the compost to the soil which was confirmed through comparison between the controls columns and amended columns with compost rates in terms of hike in metals concentration.
