Assessing the bioaccessibility of aluminum in an acidic soil with the diffusive gradients in thin films (DGT) and DIFS

To assess the bioaccessibility of aluminum (Al) by DGT, and to clarify the main factors affecting Al plant accessibility.

An acidic soil amelioration with Ca(OH)₂ and peanut straw biochar was established by determining the acid-neutralizing capacity of amendments with constant pH automatic titration, to determine the amount of amendments required to achieve the target soil pH. A pot trial was conducted, Al available to DGT (C_DGT) was compared to plant Al content. Plant accessibility of different Al species in the soil solid phase and solution was analyzed. The DIFS model was used to predict the diffusion potential of labile Al from soil solid.

The dynamic of C_DGT showed an opposite trend to that of soil pH, with a significant decrease in C_DGT as pH was increased. There was a highly significant positive linear correlation between C_DGT and Al contents in shoots and roots. C_DGT showed highly significant positive correlation with Al-Ex and Al-Solid, and highly significant negative correlation with Al-Hy. In soil solution, Al species of Al³⁺, Al-OH, Al-F, and Al-SO₄ were significantly positively correlated with C_DGT. Sorption rate k₁ values of labile Al in soil solid phase were predicted as 108.15 ~ 495.32 × 10^–5 s⁻¹, and desorption rate k_-1 values as 30.09 ~ 204.6 × 10^–7 s⁻¹ by DGT-DIFS.

DGT was an effective tool to assess plant-accessible Al. The co-application of peanut straw biochar with lime better promoted the conversion of soluble Al to low-toxicity Al-OM and Al-Or and reduced the bioaccessibility of Al.