Effects of humic acid extracted from organic waste compost on maize seedlings under cadmium stress

Cadmium (Cd) contamination poses a major global threat to agricultural productivity and food safety by entering the human food chain. Our study investigates the potential of humic acid (HA), a naturally occurring substance in compost with potent metal-binding capabilities, to mitigate the impact of Cd stress on maize. Maize seeds were exposed to 2 mg L-1 Cd2+, with HA applied at varying concentrations (0 to 0.5 g L -1 HA-Cd) to assess its effects on germination and early seedling growth. Cd stress significantly impaired germination rates, indices, and root development. However, the application of 0.05 g L-1 HA-Cd improved the germination rate by 56%, while 0.05 and 0.1 g L-1 HA-Cd treatments enhanced root length by 17% and 34%, respectively. Conversely, the highest dose (0.5 g L-1) negatively affected growth. HA treatments also increased chlorophyll content and enhanced the uptake of essential nutrients like calcium, magnesium, and iron, while reducing sodium and sulfur levels in shoot tissues. These physiological improvements were closely linked to the growth-promoting effects observed at optimal HA concentrations. The findings from this study not only underline the role of humic acid as a promising ameliorative agent against cadmium toxicity but also establish the optimal concentrations of HA that maximize growth and physiological benefits in maize. This research could pave the way for developing cost-effective, environmentally sustainable strategies to enhance crop resilience against Cd stress, thereby safeguarding food security in contaminated soils.