Effectivity of host-Rhizobium leguminosarum symbiosis in soils receiving sewage water containing heavy metals.

Disposal of sewage water in cultivated soils often containing considerable amount of potentially toxic metals such as Cu, Zn, Ni, Cd, Pb and Cr can be beneficial or harmful to plant growth, rhizobial survival, nodulation and nitrogen fixation. Soil samples from 14 such locations were collected. Symbiotic effectivity of host-Rhizobium leguminosarum symbiosis in these soils was assessed. The total metal contents of Cd, Cu, Zn and Ni in all the 14 samples collected from farmer's fields receiving sewage water ranged between 1.3 and 6.7, 55.8-353.2, 356.0-1028.0 and 90.0-199.7 mg kg(-1) of soil, respectively. In Rohtak 1 soil, levels of Cd, Cu and Zn were highest while Ni was highest in Sonipat 2 soil. The content of available Cd, Cu, Zn and Ni in these soils ranged from 1.0-29.3; 6.2-47.0; 2.4-13.5, respectively, and was 2-9 percent of their total metal contents. All the N2 fixing parameters in pea and Egyptian clover were adversely affected by the presence of heavy metals. Available Cd and Cu contents significantly affected the N contents of pea and Egyptian clover plants, whereas Ni contents were negatively correlated with the plant biomass of pea and Egyptian clover.