Nitrate fertilization doubles chemical weathering and boosts crop yield in olivine-amended acidic soils

Enhanced silicate weathering (ESW) can contribute to carbon dioxide removal (CDR) while improving acidic soils, but the interplay with fertilization remains poorly understood. We performed pot experiments with water spinach (Ipomoea aquatica) to examine how fertilizer, KNO₃ and K₂SO₄, interact with powdered olivine to affect CO₂ removal and plant growth. We estimated CO₂ uptake via extractable Mg and measured the Mg budget in our pot experiments, including: accumulated Mg in leachate, extractable Mg in soils, and Mg stored in plant tissues. Results showed that both fertilizers, KNO₃ and K₂SO₄, can accelerate Mg dissolution. The addition of 1.0 g KNO₃ with 20 g olivine could remove 1.97 t CO₂ ha⁻¹, nearly twice the amount removed by olivine alone (0.92 t CO₂ ha⁻¹) and more than K₂SO₄ (0.69 t CO₂ ha⁻¹). Compared with the control, KNO₃ increased dry biomass by 217% and Mg uptake in plants by 3.8–4.2 times, indicating that EW can also enhance vegetation uptake and lower soil acidity (pH increased from around 4.1 to 4.5). The Mg mass balance revealed that less than 2% of dissolved Mg was found in leachate, while roughly 40–54% remained in soil, about 7–13% in plant biomass, 3–5% in extractable pools, and 26–60% in residual pools that could not be explained. Our study suggests that combining powdered olivine with nitrate fertilization offers a synergistic approach to boost crop productivity, enhance CO₂ removal, and mitigate soil acidity. It is noted that the leachate measurements of Mg would not represent the short-term CO₂ removal and closure of Mg budget is not easy due to the uncertainties in soil extraction.