Sewage Sludge-treated Soils Research Articles

Rhizobium meliloti is less sensitive to heavy-metal contamination in soil than R. leguminosarum bv. trifolii or R. loti

A gradient of soils with increasing metal contamination was constructed by mixing uncontaminated farmyard manure-treated (FYM) and contaminated, sewage sludge-treated (S) soils from the Woburn Experimental Farm, and separate samples of these soils were inoculated with strains of Rhizobium leguminosarum bv. trifolii, R. meliloti and R. loti. The survival of rhizobia in these soils was monitored using most-probable number (MPN) plant infection tests. After 51 days incubation numbers of R. meliloti were similar in all of the soils irrespective of the heavy metal content, whilst the numbers of R. leguminosarum bv. trifolii and R. loti were reduced in soils containing more than 2 3 sludge-treated soil. The numbers of R. leguminosarum bv. trifolii were monitored in the same gradient of soils over a 171 day period and differences in survival between the soils were only apparent from 27 days in soil mixtures containing more than 5 6 sludge-treated soil. After 171 days the number of cells surviving had decreased even in the soil mixture containing 1 6 sludge-treated soil when compared with the uncontaminated FYM-treated soil. The populations of indigenous R. leguminosarum bv. trifolii were also monitored in the soil of the FYM-treated and S-treated plots in the field. Numbers of rhizobia remained at around 4 × 10 4 cells g soil −1 in the FYM-treated soil over 3 yr after clover was removed, but gradually declined in the S-treated soil to 1 × 10 3 cells g soil −1.

Behavior of zinc and copper in soil with long term application of sewage sludges

Abstract Two kinds of sewage sludge composts were applied separately to a crop field consisting of volcanic ash soil (Andosoil) twice a year at 10 t/ha for 12 years since 1978 and the changes in the concentrations of total and soluble Zn and Cu in the sewage sludge-treated soil were studied. The total amount of Zn in the surface soil of the sewage sludge-treated plots increased year by year. The total Zn concentration in the subsoil of these plots was higher than that of the non-treated plot after 12 years of application of the sewage sludge. Cu accumulated somewhat in the surface soil, but not in the subsoil during this period. These facts suggest that Zn moved down to about 20 cm in the Andosoil within 12 years. Sewage sludge application increased the ratio of soluble Zn to total Zn in both the surface soil and subsoil during a 9 year period.

The effects of pH and soil type on concentrations of zinc, copper and nickel extracted by calcium chloride from sewage sludge-treated soils

The effects of pH on concentrations of zinc, copper and nickel extracted by calcium chloride from a clay loam and two sandy loam soils that had been treated with sewage sludge were studied. Concentrations of all the metals increased rapidly as pH decreased below a threshold value ranging from 6·2 to 7·0 for Zn, 6·2 to 7·2 for Ni and 4·7 to 5·7 for Cu. Both the total concentrations and the threshold pH values were influenced by differences in soil texture and (between the two light-textured soils) by differences in soil cation exchange capacity. The amount of zinc and copper extracted from the mixtures was considerably less than that extracted from the same quantity of sludge alone.