مجله آب و خاک (Sep 2016)
Studyof Wastewater and Compost Effects on Some of Soil Physical and Chemical Characteristics
Abstract
Introduction: Arid and semi-arid areas are confronting increasing water shortages. In these regions of the world, planners are being forced to consider other water sources that could be used economically and effectively to promote further development. Wastewater is the only potential water source, which will increase as the population grows and the demand on freshwater increases. Composting municipal solid wastes (MSW) and sewage sludge is a good way to reduce the amount of wastes generated in densely populated areas. Municipal solid waste production in Asia in 1998 was 0.76 million tons per day, with an annual growth rate of 2- 3% in developing countries and 3.2- 4.5% in developed countries. (MSW) compost is increasingly used in agriculture not only as a soil conditioner but also as a fertilizer. Despite the growing interest in wastewater and compost usage, excessive application of them may have some harmful effects such as human health problems, runoff and leaching of nutrients to surface and groundwater, undesirable chemical constituents, pathogens, accumulations of heavy metals in plants and soils, negative environmental and health impacts. So, using of wastewater and compost application should be under controlled conditions that minimize health risks of agricultural products. Materials and Methods: This study was conducted in greenhouse of Bu-Ali Sina as a factorial completely randomized design to evaluate the effects of wastewater and compost on physical and chemical properties of soil. The factors included four types of watering: raw wastewater (W1), treated wastewater (W2) combined 50% of raw wastewater and fresh water (W3) and tap water (W4) and also four compost levels: 0 (C1), 40 (C2), 80 (C3) and 120 tha-1 (C4). Therefore, 16 treatments (W1C1 to W4C4) were considered for investigation. It is noted that Compost added and mixed just with top layer of the soil. 48 volumetric lysimeters were applied as Cultivation beds (26 × 30 × 30 cm). The soil had three layers: the upper layer (Clay texture), the middle layer (clay loam) and the bottom layer (sandy clay loam). After beds preparation, basil (Ocimum Basilicum) was planted in them. Due to the lack of an active wastewater treatment plant in the region, raw and treated wastewaters were transported from Kermanshah, the nearest city to Hamedan. Also, municipal compost was prepared from Kermanshah Compost Company.At the end of cultivation period, the soil samples (from 0-15 cm) were collected and the amount of physical (hydraulic conductivity, bulk and particle density and porosity)and chemical (nitrogen, phosphorus and potassium) properties were measured. Results and Discussion: The results showed that the water quality has a significant effect on all parameters and the amount of compost has significant effect on all parameters except bulk density. But, the amount of all parameters (except hydraulic conductivity) was not influenced by interaction between water quality and compost levels. In all treatments, the range of hydraulic conductivity, bulk density, particle density and total porosity were varied between 23.82 to 35.61 mmh-1, 1.41 to 1.43 grcm-3, 2.51 to 2.57 grcm-3 and 42.88 to 45.19 %, respectively. Also the range of nitrogen, phosphorus, and potassium were varied between 0.06 to0.08 %, 14.64 to232.28mgkg-1,and 393.22 to519.84mgkg-1,respectively.Overall, the results indicated that using compost and wastewater increased hydraulic conductivity, porosity, nitrogen, phosphorus, and potassium of the soil in comparison to the control. Whereasbulk and particle density of soil decresed by using compost and wastewater (as a mixed material). Conclusion: In this study, we investigated the effect of wastewater and compost on some of soil physical properties (hydraulic conductivity, bulk density, particle density and total porosity) and also some of chemical properties of soil nitrogen, phosphorus and potassium).The results showed that the use of wastewater and compost on soil physical condition has a positive effect.Wastewater and compost by improving the soil pore size distribution, decreased the bulk and particle density and increased porosity and hydraulic conductivity of the soil. The impact of wastewater and compost to improve the physical properties, commensurate with the level of wastewater treatment and composting rate in the soil. Also using the wastewater (raw wastewater, treated wastewater and combined 50% of raw wastewater and fresh water) and compost (40, 80 and 120 tha-1), compared to the control (fresh water and soil without compost), increased total of nitrogen, phosphorus and potassium of soil. But, due to the risks of soil salinity and nitrogen leaching, it is suggested that longterm exposure to wastewater and compost needs a careful practical management.
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