Foliar Application of Scenedesmus obliquus to Mitigate Water Deficit in Maize Grown in Mining Tailings

The recovery of areas affected by mining tailings is one of the main challenges for the sustainability of the mining industry, particularly under increasing water scarcity. This study aimed to evaluate the feasibility of growing maize (Zea mays L.) in a substrate composed of mining tailings, quantify crop water use, and investigate the potential of foliar application of cell-disrupted microalgal lysate of Scenedesmus obliquus to mitigate the effects of water deficit. The experiment was conducted in a completely randomized design with seven treatments and three replicates, totaling 21 lysimeters. The treatments combined two periods of water deficit (V10-VT and VT-R1), the presence or absence of foliar application of the microalga, and two substrates (mining tailings and natural soil). Physiological, biometric, and yield-related variables, as well as crop water use and water use productivity, were evaluated. Maize grown in mining tailings was agronomically viable and showed performance similar to that observed in natural soil when no water deficit was imposed. Water deficit reduced gas exchange, plant growth, crop water use, and grain yield, while increasing water use productivity, with the greatest effects observed when the stress occurred between V10 and VT. Foliar application of S. obliquus cell lysate partially mitigated water deficit, with statistically significant benefits (p ≤ 0.05) restricted to the V10-VT stage, increasing root dry mass (+29.2%) and grain yield (+57.8%, from 3600 to 5679 kg ha–1). The microalga was also associated with greater water use productivity under water-deficit conditions, without a statistically significant increase in total crop water use. These results indicate that integrating irrigation management with the microalgal biostimulant S. obliquus is a promising strategy for maize cultivation in mining tailings.