Initial Performance of Joannesia princeps in Degraded Soils Amended with Decomposed Aquatic Macrophyte Biomass

Aquatic macrophyte biomass removed from reservoirs represents a residue with potential for agricultural reuse, but its agronomic effectiveness and environmental safety require evaluation. This study assessed decomposed aquatic macrophyte biomass (DB) as a soil amendment for the initial growth of Joannesia princeps in soils from Piraí (RJ) and Jaboticabal (SP), Brazil. Plants were grown in 50 L pots under a completely randomized design with five replicates, using DB at 10, 20, and 40% of pot volume, applied alone or combined with mineral fertilization, plus a mineral-fertilized control. Soil chemical attributes, plant biometric traits, foliar nutrient concentrations, potentially toxic metals, and principal component analysis were evaluated. Increasing DB rates generally increased soil organic matter, sum of bases, cation exchange capacity, base saturation, and the availability of P, K, Ca, Mg, and micronutrients, while reducing potential acidity and aluminum saturation. Intermediate and high DB rates enhanced plant height, leaf number, leaf area, and dry biomass, although responses varied between locations and fertilization strategies. Ni and Pb remained low, with no consistent accumulation pattern. Overall, decomposed macrophyte biomass improved several soil chemical attributes associated with fertility and promoted the initial growth of J. princeps, supporting its potential use as an organic soil amendment under the evaluated conditions.