Assessment of sludge application in maize (Zea mays L.): influence on crop biomass and heavy metals bioavailability

Increasing population and subsequent increase in waste necessitate recycling of waste products to minimize the environmental burden. This study was conducted in semi-arid tropics of Punjab to evaluate different rates of sludge application as a supplementary source of nutrients to conventional fertilizers in maize. The grain yield was significantly higher with the application of 5 t ha(-1) sludge over control and marginally lower than in 10 t ha(-1). Cadmium (Cd), chromium (Cr), lead (Pb), and nickel (Ni) in grains were below international standards even after maximum dose of sludge treatment and can be declared as safe for consumption. The bioconcentration factor of Cd and Ni increased by 82% and 49% with 10 t ha(-1) over control, respectively while it remained same for Cr and Pb. Significant increase in exchangeable Cd, Pb in carbonate, and easily reducible oxide, Ni and Cr in residual fraction with 10 t ha(-1) sludge over control were found. Mobility of only Pb and Cd increased with increasing sludge treatment. Conclusively, sludge application can be beneficial in increasing plant biomass, however heavy metal accumulation in plants may limit its use. Long-term effect of sludge applications as nutrient sources must be evaluated to get more in-depth insights.