Application of Sewage Sludge for Growing Alfalfa, Its Effects on the Macro-Micronutrient Concentration, Heavy Metal Accumulation, and Translocation

Abstract

Alfalfa (Medicago Sativa) was grown by mixing sewage sludge at 0 (control soil), 20 (SSA2), 40 (SSA4), 60 (SSA6), and 80 (SSA8) t ha-1(w/w) amendment ratios to the soil. The soil pH decreased but, the electrical conductivity, organic matter, total N, available and total P, exchangeable and total K and Na, exchangeable Mg, DTPA-extractable Fe, Zn, Mn, Cu, Ni, Pb, and total Zn, Cu, Cr, and Pb increased in the soil. The shoot P, K, Ca, Mg, Fe, Zn, Mn, Cu, and root N, P, K, Na, Fe, Zn, Mn, Cu, Ni, and Cr concentrations increased but the root Mg concentration decreased in the plant. The translocation factor (TF) for Fe, Zn, Mn, and Cu (nutrients) increased at SSA2 and SSA4 as compared to SSA6, SSA8, and control soil. The TF was mostly higher than 1 for Zn, Cu, and Mn and for Fe it was lower than 1. The TF for Ni, Cr, and Pb (non-nutrients) was the highest in the control soil. The TF was lower than 1 for Ni and Cr in all treatments. For Pb it was more than 1 at SSA2, SSA4, and the control soil. The shoot bioconcentration factor (BCF) for Fe, Zn, Mn, and Cu at SSA2 and SSA4 were mostly higher than SSA6, SSA8, and the control soil. While the root BCF for Fe, Mn, Ni, and Cr were highest at SSA8, for Cu it was highest in the control soil. Both shoot and root BCF for all elements at all treatments were lower than 1. The total fresh and dried biomasses increased at SSA 2 , SSA 4 , and SSA 6 compared to the control soil, however, they were reduced by SSA 8 . The tolerance index (TIN) was greater than 100% for SSA 2 , SSA 4 , and SSA 6 . Although, the TIN was higher than 100% at SSA6, the value was lower than SSA2 and SSA4. It indicates that the plants are stressed at the amendments of sewage sludge at more than 40 ton ha -1 to the soil.