Adsorption of npk fertiliser and humic acid on palm kernel shell biochar

Abstract

To date, no study has been reported on adsorption capacity (Qe) of palm kernel shell (PKS) biochar for plant nutrients NO3-, NH +4, PO3-4 and K+ (NPK) while most biochar adsorption investigations have not considered the effect of dissolved soil organic matter e.g. humic acid (HA). In our study, we produced PKS biochar at different temperatures and holding times and conducted sorption experiments with a commercial NPK fertiliser and HA. HA-coated PKS biochar was investigated for its capability in adsorbing NPK. Equilibrium adsorption experiments showed that NH +4 and HA were adsorbed with no effect for NO-3 and PO3-4, while K+ concentration in solution increased exponentially over time. The highest Qe of NH +4 (0.522± 0.036 mg g-1; p<0.05) and that of HA (0.649 ± 0.073 mg g-1) were observed for 400°C PKS biochar. The best-fitted HA sorption with Freundlich isotherm (R2 = 0.904) reveals a heterogeneous surface and arguably multiple layer sorption of HA. A 55.9% reduction in Qe of NH+4 for HA-coated 600°C PKS biochar suggests that performances observed in the laboratory cannot be directly extrapolated to the field. Furthermore, a realistic mechanistic understanding of PKS biochar sorption efficiency on NPK associated with soil matrix components such as humic substances, microorganisms and colloidal clay particles is essential.