Fig. 4
Influence of H3PO4 and H4P2O7 modified on pH (a), electrical conductivity (EC) (b), total P (c), and relative proportion of each P fractions in the biochars (d); X-ray photoelectron spectroscopy (XPS) spectrum of the halophyte biochar (HBC), H3PO4-modified biochar (P-HBC), and H4P2O7-modified biochar (PA-HBC) (e); high-resolution XPS spectrum of P2p (f); and high-resolution XPS spectrum of O1s (g). Error bars are standard deviation of the means (n = 4). Different letters above the bars indicate significant (p < 0.05) difference between treatments