Sewage Sludge Application Enhances the Growth of Corchorus olitorius Plants and Provides a Sustainable Practice for Nutrient Recirculation in Agricultural Soils

The current study aimed at evaluating the effects of different sewage sludge (SS) amendment rates as biofertilizers on growth of Corchorus olitorius plants and soil properties, with an emphasis on heavy metal (HM) allocation in plant parts and postharvest soil. Then, the soil was supplemented with various SS rates (0, 10, 20, 30, and 40 g kg−1). The effects of these SS amendment rates on different growth parameters of Corchorus olitorius and soil properties were investigated. The SS amendment rate of 20 g kg−1 triggered the highest growth rates of Corchorus plants. Micronutrient HMs, including Co, Cu, Mn, and Ni, increased in the shoots of plants grown in soils amended with 20 g kg−1, but with levels sufficient for normal plant growth and below the phytotoxic limits. The sludge application significantly increased the content of organic matter in postharvest soil from 1.38 to 4.83% at the amendment rate of 20 g kg−1. Furthermore, our data showed that the quantities of the estimated HMs remaining in postharvest soils were below (Cu, Fe, Mn, Mo, Zn, and Pb) or within (Co, Ni, Cd, and Cr) the maximum permissible concentrations in agricultural soils at all of the SS amendment rates. Taken together, our findings suggest that soil application of SS can provide a sustainable safe practice for SS disposal and improve plant growth, while exerting no environmental threats provided there is no accumulation of HMs to toxic levels in shoots of the grown plants or in the amended soils.