Abstract
The conversion of invasive weed biomass into functionalised soil amendments presents a promising strategy for sustainable agricultural management. This study evaluated the effects of pristine Lantana biochar (BC, pyrolysed at 500°C to 600°C) and iron-modified Lantana biochar (FBC) on soil physicochemical properties, nutrient dynamics, and biological activity in a rice pot culture system. Eight treatments were assessed: absolute control (T1), RDF; recommended dose of fertilisers (T2), and graded applications of BC (T3-T5) and FBC (T6-T8) at 5, 7.5, and 10 t ha-1. Chemical modification significantly altered the biochar, reducing its pH (10.42 to 5.41) and potassium content (0.93% to 0.07%) while increasing ash content and fixed carbon. In the soil, FBC application, particularly at 10 t ha-1 (T8), significantly outperformed pristine biochar by maximising soil organic carbon (OC%;0.68%) and cation exchange capacity (36.09 cmol (+) kg-1), while effectively reducing electrical conductivity (0.66 dSm-1). Furthermore, T8 significantly enhanced the availability of nitrogen, phosphorus, and sulphur, though available potassium was highest under high-dose pristine biochar (T5;10 t ha-1) due to leaching losses during FBC synthesis. Biologically, FBC at 10 t ha-1 induced a massive proliferation of actinomycetes and bacterial populations and significantly stimulated dehydrogenase, alkaline phosphatase, and urease activities compared to both the control and BC treatments. The results demonstrate that engineered Fe-modified Lantana biochar is a superior soil amendment for enhancing carbon sequestration, nutrient retention, and microbial health in flooded rice ecosystems, although it necessitates supplemental potassium management.