Contamination-Dependent Mobilization of Vanadium in Alkaline Soils with Chelator-Assisted Phytoextraction

Chelator-assisted phytoextraction can alter metal mobility in soils by modifying soluble and extractable fractions. However, the role of oxalic acid (OA), especially in combination with synthetic chelators, in regulating vanadium (V) mobility in alkaline soils remains largely unexplored. This study evaluated the effects of CA and OA, applied alone or in combination with EDTA, on V mobilization and plant uptake by Brassica juncea grown in alkaline soil spiked with 200 or 400 mg V kg⁻¹. A 13-week greenhouse experiment was conducted using five treatments (control, CA, OA, EDTA + CA, and EDTA + OA), with chelators applied in two split applications during plant growth. At 200 mg kg⁻¹ soil V, combined EDTA + OA significantly increased pore water V (5.6 mg L⁻¹) and NaNO₃-extractable V (9.6 mg kg⁻¹), resulting in greater leaf V accumulation (6.6 mg kg⁻¹) among treatments without visible phytotoxicity. In contrast, natural chelators alone did not significantly alter V mobility. At 400 mg kg⁻¹ soil V, pore water V, NaNO₃-extractable V (21–23 mg kg⁻¹), and plant V were all significantly higher than at 200 mg kg⁻¹, and chelator application did not further increase V mobilization. Increased V availability at this higher contamination level reduced plant biomass and showed mild phytotoxic symptoms. The findings demonstrate that V phytoavailability in alkaline soils is governed by contamination-dependent changes in soil solution V and NaNO₃-extractable fractions, underscoring the contamination-dependent control of soil solution and labile V fractions in regulating V mobility in alkaline soils.