Valorization of Water Hyacinth Biomass as a Soil Amendment: Long-Term Impacts on Soil Properties and Tomato Growth Under Two Water Regimes

Résumé fourni par la source

Water hyacinth (Eichhornia crassipes, WH) is a highly invasive aquatic plant. Although its surplus biomass has been proposed as an agricultural amendment, uncertainty remains regarding its safe use. Based on this knowledge gap, two working hypotheses were addressed: (i) WH application would enhance soil physicochemical and enzymatic attributes, particularly under water stress, and (ii) WH application would stimulate plant growth through nutrient release. To verify this, two WH amendment rates (2.5% and 5% w/w) were evaluated under normal (45%) and severe (22.5%) WHC using tomato (Solanum lycopersicum L.) as a bioindicator. WH incorporation significantly altered soil conditions, inducing progressive acidification and increasing electrical conductivity (EC), particularly at the 5% rate under well-watered conditions, where EC values reached approximately 3000 µS/cm. Although WH amendments increased soil relative humidity owing to the hydrophilic nature of the biomass, these moisture-driven benefits were transient. Acid phosphatase activity increased markedly by day 60 in WH-amended soils, especially at 45% WHC, indicating enhanced microbial activity and phosphorus mineralization associated with organic matter decomposition. Plant responses were strongly driven by water availability, with severe water restrictions consistently limiting germination and growth and potentiating osmoprotectant retention. From day 60 onward, germination and biomass declined markedly in the 5% WH treatment, likely due to the accumulation of salt and osmotic stress arising from the decomposition of biomass. Surviving seedlings in WH-amended soils exhibited increased shoot biomass relative to their roots, suggesting stress-related biomass reallocation. Overall, the results indicate that the direct application of untreated WH biomass at moderate to high rates may generate short-term benefits but may impair long-term plant establishment. Lower application rates (≤2.5% w/w) may offer limited early stage benefits, whereas higher rates pose risks under prolonged exposure, highlighting the importance of dose, water regime, and amendment processing when considering WH valorization for agricultural use. This valorization approach may contribute to incentivizing control of this invasive species while promoting plant waste valorization within circular economy goals.

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