Effect of Water Reuse on Organic Matter Concentration of Soil and its Self Purification

Use of low quality water in agricultural irrigation lands has been common in many areas since long time ago. According to arid and semi-arid climate of Iran and the limitations of usable water resources, optimum application of each kind of available water (i.e.brackish and wastewater) is necessary. In this regard, the regional researches are needed by considering all local variables such as climate, native plants, culture, wastewater quality and so on.In order to investigate the effects of irrigation with domestic wastewater on soil organic matters content in the end of plant season and also the self-digestion rate of accumulated matters during non-plant period, a lysimetic study was carried out in Tehran area. A statistical “factorial experiments in form of randomized complete design” (3 * 3* 3) was used. Raw and treated domestic wastewater of Ekbatan complex and well water (control) have been applied for irrigation of raw eating vegetables such as parsley, carrot and tomato for two years.The results showed that the most increase of organic matter was happened by using the raw wastewater for irrigation of carrot planting, and the least for tomato. After two years and completion of self-digestion period, raw and treated domestic wastewater caused 48.8% and 17.4% increase in soil organic matter content respectively, but reduction of 31.59% was found in control treatment compared with the original amount (0.896%). There is direct relationship between the reduction rate of soil organic matter and the amount of organic matter exceeded by wastewater application. Therefore, the highest rate (14.9mg/100gr.day) was observed in raw wastewater irrigated lysimeters. Statistical analyses showed a significant difference in organic content and purification by means of irrigation water, quality crop, year and sampling time.