Agronomic Potential and Limitations of Factory-Derived Tea Waste in Kale Cultivation Under Drought Stress

Plant-derived wastes are increasingly explored as organic matter sources for sustainable agriculture. Tea waste, a by-product of industrial tea processing, is often regarded as an environmental pollutant, yet its potential for agricultural use remains conditional and requires careful evaluation. This study examined the effects of factory-derived tea waste on kale (Brassica oleracea var. acephala) under drought stress. Plants were grown in soils amended with 5% or 10% tea waste and subjected to mild (75% field capacity) and moderate (50% field capacity) water deficits, compared with full irrigation (100% field capacity). Fifteen morphological and physiological parameters were assessed, and data were analyzed using principal component analysis (PCA) and correlation heatmaps to identify trait associations and stress markers. Drought stress significantly reduced all growth and yield traits, with stronger effects under more severe water deficit. Tea waste generally exacerbated stress impacts, increasing damage indices, reducing plant height, and lowering chlorophyll values. However, 10% tea waste under non-stress conditions increased plant and root dry weights without negatively affecting other traits, suggesting a partial nutrient contribution. In contrast, 5% tea waste aggravated stress effects, likely due to phenolic and caffeine toxicity. Overall, raw tea waste was found to be unsuitable for kale production under drought conditions. To harness its potential, bioactive compounds must be degraded or removed, and the material stabilized through composting or biochar conversion for safe integration into drought-resilient systems.