SEWAGE-SLUDGE AND HEAVY-METAL EFFECTS ON NODULATION AND NITROGEN-FIXATION OF LEGUMES

Effects of sludge-borne heavy metals on plant growth, nodulation, and nitrogen (NZ) fixation of alfalfa (Medicago sativa L.), white clover ( Trifolium repens L.), and red clover (Trifolium pratense L.) were exam ined. Plants were grown in the greenhouse in pots containing soil (Typ ic Paleudults) obtained from plots where heat-treated and Nu-Earth slu dges were applied in 1976 and 1978, respectively. Two soil pH regimes (low and high) were examined for each of the treatments. Nitrogen fert ilizer (NH4NO3) was applied to one-half the pots and each legume was i noculated with the appropriate Rhizobium culture. Soil pH and sludge t ype significantly affected uptake of metals with phytotoxicity observe d in the Nu-Earth, low pH soil. Nodulation was reduced, but not always completely eliminated in all low pH treatments, including the control s. Symbioses were generally ineffective in low pH treatments. In soils where pH was above 6.0, there was a significant increase in shoot wei ght and total shoot N with sludge addition. Plants derived significant quantities of N from soil, where sludge was applied many years ago. W hen pH was maintained at 6.0 or higher the results show that heavy met als in soil, and the resulting concentration in plants, had no effect on any of the parameters examined.