JWSS - Journal of Water and Soil Science

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Land application of sewage sludge is potentially beneficial as an inexpensive nutrient source. However, problem with the use of sludge may exist from high soil concentrations and subsequent uptake of heavy metals by plant and entering of the metals into the human and animal food chains. A field study with lettuce (_{Lactuca sativa} L.) and spinach (Spinacia oleracea L.) was conducted to examine uptake of heavy metals from a sludge amended soil as affected by sludge rate and time of sludge application. Sludge rates were 0, 22.5, and 45 ton/ha. To determine the effect of time on heavy metal uptake, a year after the first plants were harvested, one third of each plot was planted without sludge application and to the rest of each plot sludge was added in the same rates as before. Total and EDTA-extractable Cu, Zn, Pb, and Cd concentrations in soil were determined. The metal concentrations in shoots and roots of the plants were determined separately. Total metal concentrations showed an increasing trend with addition of sewage sludge. Copper, Zn, and Pb EDTA-extractable concentrations in soil and concentrations of these metals in the plants increased significantly with sludge rate. Time of sludge application did not have any significant effect on EDTA-extractable and plant uptake of metals. Sewage sludge also increased the crop yields significantly.

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A field study was conducted at the College of Agriculture, Ferdowsi University of Mashhad, to investigate the effect of irrigation with treated municipal wastewater on the yield and quality of lettuce and some soil characteristics. Five irrigation treatments were applied to a clay loam soil, classified as fine loamy mixed mesic Calcixerollic Xerochrepts, in a randomized block design with 5 replications. The treatments consisted of T1 (Irrigation with treated wastewater over all growing season), T2 (Alternate irrigation with treated wastewater and well water), T3 (Irrigation with well water and application of cattle manure), T4 (Irrigation with well water plus fertilizer N and P), and T5 (Irrigation with well water only as control). Chemical analysis of well water proved to be a suitable source for agriculture.

The results showed that the yield was higher in T1, T2, T3 and T4 as compared to the control treatment. Maximum fresh and dry yields were obtained from T3 & T1 and T1 & T3, respectively. Plant tissue analysis showed an increase in macronutrients (N, P, K) and heavy metal concentrations in shoots and roots of lettuce in the first four treatments as compared to the control. In T1, iron concentration was maximum while that of cadmium was minimum. Furthermore, microbial contamination was considerably higher in T1 and T2. Soil analysis indicated that in plots treated with wastewater, electrical conductivity, total nitrogen, available phosphorus, soluble boron and heavy metal concentration increased. However, their values were all below international standards. More experiments seem to be necessary in this regard.