Potential of Composted Macrophytes as a Sustainable Organic Fertilizer: Environmental and Agronomic Insights

Abstract This study evaluated the agronomic potential and environmental impact of a macrophyte-based fertilizer (OMF) in maize cultivation. OMF was previously characterized in accordance with regulatory standards and applied to sandy loam and clayey soils at six rates (0, 2, 4, 6, 8, and 10 g dm⁻³). The experimental design also included a mineral fertilizer (MF) control receiving N, P, and K amounts equivalent to the 10 g dm⁻³ application, arranged in a randomized block design. After 45 days in greenhouse conditions, maize biomass and total nutrient accumulation, soil macronutrient concentrations, and the activities of arylsulfatase, β-glucosidase, and acid phosphatase were quantified. Basal soil respiration (BSR) and nutrient leaching were also evaluated through laboratoy-based analyses. OMF increased BSR, with CO₂ release in sandy loam and clayey soils highest under OMF (11.5; 10.7 mg g⁻¹), moderate under sludge compost (7.06; 7.51 mg g⁻¹), and lowest in unfertilized soil (2.34; 3.40 mg g⁻¹). OMF also promoted linear increases in soil P, K, Ca, Mg, and S, as well as in maize biomass and total N, P, and K accumulation. However, the highest OMF dose achieved only 20–31% of MF biomass. Moreover, organic fertilizers consistently reduced NO₃⁻-N, NH₄⁺-N, and K⁺ leaching compared with MF. In sandy soil, NO₃⁻-N leaching decreased by 31.2% and 38.5%, NH₄⁺-N by 45.6% and 37.4%, and K⁺ by 71.3% and 24.3% under SSC and OMF, respectively. In clayey soil, reductions reached 44.6% and 46.4% for NO₃⁻-N, 24.0% and 20.9% for NH₄⁺-N, and 35.9% and 15.7% for K⁺ under SSC and OMF, respectively. OMF offers environmental advantages by decreasing NO₃⁻-N leaching and supplying a slow-release K⁺ source, although it remains less effective than mineral fertilizer in promoting maize growth.