Wood-waste bio-products for sustainable agriculture: exploring plant–soil interactions in treated lettuce under abiotic stress conditions

Many nations are promoting the use of renewable natural resources to address environmental and health challenges, using plant biomass management as a key strategy. Annually, 200 billion tons of lignocellulosic biomass are produced globally. Governments are implementing policies for a green, circular economy, focusing on high-value products and by-products, residues and waste reduction. Wood residues, for example, from managing forest and green areas, which are rich in bioactive compounds like tannins from plants such as chestnut, have a considerable potential for plant protection within the framework of truly sustainable agriculture by improving plant performance under climate stress, provided they are non-toxic to soil. Moreover, this approach is especially beneficial for marginal rural areas, offering economic opportunities and enhancing resilience to environmental challenges. In this study, a chestnut wood chip extract produced at both the lab and pilot scale was evaluated for its bioactivity and compared to several commercial biostimulants obtained through a pyrolytic process, for which limited scientific data are still available. After assessing the total phenolic content, several tests were performed on lettuce plants grown in arid frank sandy soil (Santomera, Murcia, Spain) under salt and water stress conditions, treated by fertigation with different concentrations of these extracts. The primary objective was to assess their potential in enhancing plant performance under stress factors. Chemical analyses were conducted on both treated and untreated plants to assess their content of micro- and macronutrients and heavy metals in order to evaluate the quality and safety of the final harvest. Additionally, the roots were examined to assess potential secondary, indirect effects of these treatments. Soil analyses were also carried out to investigate the impact of these extracts on the soil microbiome, soil enzyme activities, and overall soil quality. The results indicated no negative effects on soil quality, with values from treated soil being comparable to those of the negative controls. The extracts examined were shown to improve lettuce performance and yields under stress, thus ensuring greater product stability. However, the extracts differed in their overall effects on plant morphology and physiology, as well as in their bioactivity, exhibiting a dose-dependent effect.