Biochar effects on phosphorus sorption-desorption kinetics in soils with dissimilar acidity

To describe phosphorus (P) dynamics with progressing reaction time entails an adequate understanding of P sorption and desorption kinetics in soils. To this end, the present study examined P sorption and desorption kinetics via batch experiments in four different soils with dissimilar acidity that were incubated for 90 days with 6% (w/w) wheat straw-derived biochars produced at 300 (B300) and 600 °C (B600). P sorption and desorption kinetics were measured in incubated soils and fitted to several models (zero, -first, -second-order, parabolic diffusion, simple Elovich, and exponential equations). Based on the results, the properties of wheat straw-derived biochars were affected by the pyrolysis temperature. The time required to reach the near-equilibrium state of incubated soils was about 48 and 24 h for P sorption and desorption kinetic experiments, respectively. Moreover, as pyrolysis temperature rose from 300 to 600 °C, P sorption and desorption decreased and increased, respectively in acidic soil samples (pH 4.6 and 6.0). An opposite result was obtained for the alkaline soil (pH 8.3). Adding B300 to the alkaline soil (pH 7.4) decreased P sorption, but increased P desorption. On the contrary, B600-treated alkaline soil (pH 7.4) demonstrated a slight increase in P sorption, although with a marked reduction in P desorption. P sorption kinetics was found to successfully follow simple Elovich, pseudo-second-order, and exponential models. Similarly, P desorption kinetics were duly described by pseudo-second and first-order and simple Elovich equations. The findings of the study confirmed that biochar application and pyrolysis temperature influence P sorption and desorption kinetics in soils and these effects were most likely determined by soil reaction. All this can bear implications for further studies on biochar applications and P sorption-desorption kinetics.