Characteristics of Oil Palm Trunk Biochar and Its Effects on Physicochemical Properties of Ultisols in Productive Oil Palm Plantations

Abstract

Characteristics of ultisols commonly used for oil palm cultivation include low fertility, high acidity, and poor physical properties, which limit nutrient availability and, consequently, crop productivity. In this study, the characteristics of oil palm trunk biochar (OPTB) produced by a drum retort kiln were studied, and the effects of OPTB addition on the physicochemical properties of Ultisols and on nutrient uptake in commercial oil palm plantations were evaluated. OPTB was characterized using an X-ray diffractometer (XRD), scanning electron microscopy with energy–dispersive X-ray spectroscopy (SEM-EDX), and Fourier transform infrared spectroscopy (FTIR). An experimental field trial was conducted using a randomized block design (RBD) with three treatments: no biochar (B0), 1% OPTB (B1), and 2% OPTB (B2). Results demonstrated that OPTB primarily consists of amorphous carbon with a large surface area and contains many oxygen-containing functional groups. The elemental composition of OPTB is 71.83% C (wt%), 20.29% O (wt%), and some mineral elements, i.e., K, Ca, and Mg. Biochar addition resulted in significant improvements in soil chemical and physical properties compared with the control. Specifically, biochar affected soil pH, organic C, cation exchange capacity (CEC), base saturation, and exchangeable Ca, Mg, and K. Additionally, soil physical properties were improved as evidenced by reduced bulk density (BD), increased total porosity, increased field capacity (FC), and increased available water content (AWC). Furthermore, as a direct result of these improved soil conditions, higher concentrations of N, P, and K in oil palm leaves were observed across all treatments, with the greatest increase at the highest biochar rate (B2). Therefore, these results demonstrate that OPTB may be used as a sustainable means to improve soil quality and nutrient availability in Ultisols in productive oil palm plantations.