Effects of Continuous use of Sewage Water on Soil pProperties and Plants

Sewage water of Bhubaneswar city is being used as a source of irrigation in E-block of Central Farm, Orissa University of Agriculture and Technology, Bhubaneswar for cultivation of different crops since last three decades. A study was carried during 2005 to characterise sewage water (SW) and its impact on soil properties, essential nutrients and heavy metal content in leaf of crop plants. Sewage water samples, sewage water irrigated soils and leaf of plants of rice, mustard, sunflower, maize, tomato, grain amaranthus, cabbage, cauliflower, brinjal, lady’s finger and water hyacinth(sewage channel) were collected and analysed for different plant nutrients and heavy metals. The data revealed that SW samples were non saline, acidic in reaction (pH 6.5-6.89) and had optimal level of BOD (48-55 mgl^-1) and COD (90 -105 mg l ^-1).The concentration of cations were in the order of Ca >Mg >Na >K. Residual sodium carbonate was nil. Based on SAR and EC rating, SW belonged to C1S1 category. Concentration of NH₄-N, NO₃-N, PO₄, Zn and B ranged from 48.3-52.6, 8.1-8.3, 2.4-2.5, 1.5-2.5 and 0.7-0.75 mgl^-1, respectively. Concentration of heavy metals was in the order of As > Pb >Hg >Ni >Co > Cd >Se. Available N, P₂O₅, K₂O and SO₄-S content of sewage water irrigated soils were higher than normal soil. The DTPA extractable Fe, Mn, Zn, Cu, Mo and B ranged between 63.3 to 122.2,13.4 to 62.6, 3.6 to 44.7 ,2.4 to 11.6, 3.8 to 4.0 and 0.52 to 1.15 mgl^-1 in SW soils and 60.6,15.1,0.8 ,0.8,0.6 and 0.52 mgl^-1 in normal soil, respectively. DTPA extractable heavy metals in SW soils were in order of As >Se > Pb > Cr >Ni >Hg > Cd. The leaf of crop plants grown in SW soils had toxic amounts of Fe, B and Mo. Toxic concentration of Zn and Cu were present in cabbage and cauliflower only. The concentration of Cd, Pb and Cr in rice, mustard, sunflower, maize, tomato, grain amaranthus, cabbage, cauliflower, brinjal and lady’s finger were below upper level of phytotoxicity. Maximum accumulation of Co and Hg was in cabbage and cauliflower. Grain amaranthus and water hyacinth contained higher amount of Ni and Se. Contents of heavy metals in leaf of crops grown in normal soils were lower than SW irrigated soils. Based on ISI standard, it is recommended to use sewage water of Bhubaneswar for irrigation after pre-treatment.