Biomass Production, Metal And Nutrient Content in Sorghum Plants Grown on Soils Amended with Sewage Sludge

Sludge generation from wastewater treatment plants in Uruguay has increased in recent years. Agricultural soils may be a final destination. A greenhouse experiment was conducted to quantify the effect of this sludge on: 1) plant biomass production and nutrient concentration of sorghum plants ( Sorghum bicolor var. vulgare); 2) the chemical properties of amended soils; and 3) assess whether heavy metal concentrations in sludge are appropriate according to environmental regulations. Two soils (S1 and S2) were amended with pure sludge (PS) and limed sludge (LS), with low dose (LD) of 16.0 and 17.3 Mg ha -1 and high dose (HD) of 32.0 and 34.6 Mg ha -1 respectively. Sludge increased plants' nutrients absorption and dry matter production. Lime addition to PS favored production, its increment depended on soil pH and on its impact on nutrient availability. Sludge effect on elements concentration in aboveground biomass, depended on the element, treatments and soil type. The mineralized N and residual P-Bray 1 values increased with the addition of sludge, without exceeding the critical level of P-Bray 1 of the crop. The PS did not increase metal concentration in soils. The LS slightly decreased soil Pb and slightly increased Cr and Zn soil concentration; levels were according to Uruguayan environmental guidelines. Therefore, agriculture soils are a viable final destination for both PS and LS. Sludge has acceptable levels of metals and promotes crop development.