1474 Advances in Environmental Biology, 6(4): 1474-1476, 2012 ISSN 1995-0756 This is a refereed journal and all articles are professionally screened and reviewed ORIGINAL ARTICLE Corresponding Author Maryam Maneshdavi, Department of Soil Science, Science and Research Branch, Islamic Azad University, khouzestan, Iran. E-mail: maneshdavi88@yahoo.com Applicability of CDE Equation for Simulation of Escherichia coli Bacterial Leaching from a Silty Clay Soil 1 Maryam Maneshdavi, 2 Alireza Jafarnejadi, 3 Hossein Shirani, 4 Gholamabbas Sayyad 1 Department of Soil Science, Science and Research Branch, Islamic Azad University, Khouzestan, Iran. 2 Soil and Water Research Department of Agricultural and Natural Resources Research Center of Khouzestan, Iran. 3 Department of Soil Science, Vail-E-Asr University of Rafsanjan, Rafsanjan, Iran. 4 Department of Soil Science, Shahid Chamran University of Ahvaz, Ahvaz, Khouzestan, Iran. Maryam Maneshdavi, Alireza Jafarnejadi, Hossein Shirani, Gholamabbas Sayyad; Applicability of CDE Equation for Simulation of Escherichia coli Bacterial Leaching from a Silty Clay Soil ABSTRACT In this study, the equilibrium equation was used to predict the transfer and absorption of bacteria in the column of soil in during leaching time. The coefficient determination for direct modeling through the equilibrium equation was recognized 0.58 respectively. But, in the inverse modeling, bacterial movement in soil was predicted by using equilibrium equation had higher coefficient to amount 0.91 respectively. These results show the high efficiency of model through using the equilibrium equation (CDE) in the inverse method than its direct method in simulating the bacterial movement in the soil treated. The evaluation of model sensitivity was carried out by changing the soil hydraulic parameters in a specific range, it was revealed that the model has been sensitive to some changes of the soil hydraulic parameters and also it undergoes drastic changes when the parameters of the curve simulated by the model change. Finally, the validation of the inverse method using the equilibrium equation was 0.98. Both show the accuracy and correctness of the model. Key words: Escherichia Coli bacteria, simulation, HYDRUS-1D model. Introduction Manure is a valuable biological source and it has some ecologically and environmentally positive and negative effects, and it is much used in agriculture [2]. There are different kinds of poisonous gases, combination of mutation and solution, pathogenic microorganisms, drug-resistant bacteria, protozoa, and viruses in the waste matters of animals. For instance, one can refer to the fecal forms such as salmonella, shigella, escherichia coli, and dangerous protozoa such as cryptosporidium and giardia which are among pathogenic bacteria present in the waste matters of animals [4]. The model HYDRUS-1D is one of the advanced models in relation with the movement of water, minerals, and warmth in soil. This model was developed by Simonk et al. in Russian soil laboratory in the United States of America [1]. Through the use of HYDRUS-1D model, one can simulate the movement of bacteria and bacterial contamination resulting from using manure contaminated by different kinds of pathogens and some strategies can be presented for the correct use of manure and preventing the soil, surface and underground water from being contaminated by manure. Materials and Methods The samples of soil under study were put in PVC columns which were 35 centimeters high and 10.5 centimeters in diameter. Then, some weighted hen manure was added to the columns and it was mixed with 5 centimeters of soil. Then, the columns were studied for irrigation for 5 days. After every rinse, the drained water coming out the soil columns was put in sterilized containers. Afterward, the environment of culture was taken out from the incubator and some bacterial colonies were observed [3]. For every column of soil, the software of operation and the density of Escherichia coli bacteria in the drained water during the time have been simulated. The needed main inputs of the model for simulation consist of: information related to time and printing the results, soil hydraulic characteristics, introducing the primary and boundary conditions for the water flow. Results and Discussion Sensitivity analysis: