Iron sulfide nano-meerschaum composite (M-FeS) prolonged the release of bioavailable iron: Optimising accessibility, release kinetics and uptake in direct seeded rice under alkaline stress

Abstract

Iron bioavailability is a persistent challenge for sensitive crops such as rice which is usually exacerbated by electrochemical reactivity and rapid oxidation of iron, further aggravated under alkaline-stress. Sustainable alternatives are mandated over traditional practices to augment iron uptake, under which, the study leveraged the nanotechnological and chemical modification of iron as iron sulfide nano-meerschaum composite (M-FeS). M-FeS was prepared, characterized and statistically optimized by Response surface methodology (RSM) in alkaline loamy sand soil (pH 8.7) for maximum extractable Fe, subjected to varying organic matter (1.82–5 %), iron doses (5–500 μg/g) and incubation times (0–30 days). The soil incubation at an optimized dose of M-FeS (473.34 μg/g) presented extractable Fe at 54.72 %, with 39.31 % in bioavailable ferrous form, sustained over 29.47 days. In contrast, FeSO₄, optimized at 495.04 μg/g, achieved 64.1 % extractable Fe over 8.9 days with only 13.5 % in ferrous form. The Higuchi model was the best fit of release kinetic model indicating a Fickian diffusion-controlled mechanism facilitating sustained ferrous ion availability in alkaline soils. Direct-seeded rice (DSR) grown under pot studies in M-FeS treated soil showed significantly higher corrected iron uptake of 15.38 % in shoots and 28.56 % in roots relative to 5.45 % and 6.85 %, respectively, under FeSO₄ treatment on day 29. M-FeS, thus, represented a prolonged-release iron fertilizer, promoting sustainable agriculture through improved iron delivery in DSR under alkaline stress.