Mitigation of heavy metal bioavailability and uptake by fodder crops using organic and mineral amendments in a sewage-irrigated peri-urban agroecosystem

Abstract

Long-term irrigation with sewage wastewater can increase the bioavailability of potentially toxic metals in peri-urban soils and promote their entry into fodder-livestock systems. This greenhouse study evaluated six amendments namely biochar, bentonite, zeolite, humic acid, vermicompost and farmyard manure (FYM), for reducing lead (Pb), cadmium (Cd), nickel (Ni) and chromium (Cr) availability and uptake by fodder maize, fodder sorghum and Cumbu Napier grown in contaminated soil. Each crop was evaluated in a separate completely randomised experiment with 8 treatments and 3 replications. Zeolite was consistently the most effective amendment. Compared with the unamended control, it reduced post-harvest diethylenetriaminepentaacetic acid (DTPA)-extractable Pb, Cd, Ni and Cr by 66.7 % across the three crop soils and lowered metal concentrations in plant tissues by approximately 57.6 %. Vermicompost and farmyard manure (FYM) were the next most effective treatments, whereas recommended fertiliser alone and the unamended control retained the greatest metal availability. Metal concentrations followed the order root > leaf > stem, indicating restricted movement to above-ground tissues. Fodder maize had the lowest overall tissue concentrations, while Cumbu Napier accumulated more Pb, Cd and Ni; Cr accumulation was comparatively greater in sorghum and maize roots. All bioaccumulation and translocation factors were below one. The first two principal components explained 99.79 % of the variation and clearly separated low- and high-metal treatments. The integrated amendment-crop assessment identifies zeolite-amended maize as the lowest-transfer combination under the tested conditions and provides a practical basis for safer fodder production in sewage-irrigated peri-urban soils.