## 3 Results
### The Physicochemical Properties of Produced Biochar  
The physicochemical parameters of raw sesame stalk (SF) and the corresponding biochar samples obtained by different pyrolysis conditions are presented in Table 1. Ash percentages in different sesame biochar types increased from 4.79% in SF to 11.07% in the conventional method (SB-3). At the same time, the volatile percentages decreased with increasing ash content. Compared to feedstock, the ash percentages of different biochar types were increased by about 19.62%, 69.73%, and 131.11% for SB-1, SB-2, and SB-3, respectively. Generally, the ash content and volatile gas percentages of SB-1 are approximately near those of SF. At the same time, the biochar collected from the upper part of the internal chamber (SB-2) was relatively close to that produced by the conventional method (SF-3). In general, from the volatile matter, ash content, and elemental constituents, the biochar that formed around the inner sidewalls of the internal chamber (SB-1) was more related to raw biomass (SF) due to the low conversion occurred (semi-biomass), while the biochar obtained from the upper part of the internal chamber (SB-2) was much more similar  
Figure 2: Photographs of sesame stalk feedstock and its different biochar types produced at 300 °C for 3 h: (**a**) sesame stalk feedstock (SF); (**b**) SB-1 biochar formed around the inner sidewalls of the internal chamber of the parabolic dish collector; (**c**) SB-2 biochar formed on the upper part of the internal chamber; and (**d**) SB-3 biochar of conventional method (muffle production). to that produced by the conventional method (SB-3) (Table 1). The biochar produced by the conventional process was more homogeneous compared to that produced by the parabolic dish collector (Figure 2). The pH value of biochar was higher than that of feedstock. It was observed that SB-3 became more alkaline (pH = 7.49) than SB-1 and SB-2. However, SB-2 and SB-3 were near neutral, but SB-1 appeared to be more acidic, and its value was near that of SF. Figure 3 showed a good exponential correlation (R\({}^{2}\) = 0.89) between the pH values and the percentages of oxygen content. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Parameter** & **Unit** & **SF 1** & **SB-1** & **SB-2** & **SB-3** \\ \hline Ash & \% & 4.79 & 5.73 & 8.13 & 11.07 \\ Volatile Gases & \% & 95.21 & 94.27 & 91.87 & 88.93 \\ pH & & 5.36 & 5.60 & 6.88 & 7.49 \\ EC & dS m\({}^{-1}\) & 0.62 & 0.65 & 0.77 & 0.91 \\ CEC & cmol kg\({}^{-1}\) & 100.48 & 59.59 & 57.61 & 51.42 \\ \hline Total Elements & & & & & \\ N & \% & 0.23 & 0.29 & 0.45 & 0.49 \\ C & \% & 43.26 & 49.39 & 53.20 & 62.61 \\ H & \% & 5.59 & 4.86 & 3.74 & 3.00 \\ S & \% & 1.47 & 3.32 & 6.08 & 7.49 \\ O & \% & 44.66 & 36.41 & 28.40 & 15.34 \\ P & \% & 0.31 & 0.47 & 0.78 & 0.72 \\ Ca & \% & 0.65 & 0.70 & 0.76 & 0.86 \\ Mg & \% & 0.27 & 0.67 & 0.41 & 0.40 \\ K & \% & 0.70 & 1.55 & 1.78 & 2.66 \\ Na & \% & 0.41 & 0.36 & 0.48 & 0.55 \\ Cu & mg kg\({}^{-1}\) & 7.78 & 9.37 & 9.52 & 12.59 \\ Fe & mg kg\({}^{-1}\) & 146.20 & 193.30 & 209.30 & 341.00 \\ Mn & mg kg\({}^{-1}\) & 7.09 & 10.32 & 11.94 & 16.93 \\ Zn & mg kg\({}^{-1}\) & 33.68 & 83.27 & 105.60 & 97.17 \\ \hline \hline \end{tabular} \({}^{1}\) Sesame feedstock: SF, biochar produced around the inner sidewalls of the internal chamber: SB-1, biochar formed on the upper of the internal chamber: SB-2, and conventional biochar: SB-3.  
\end{table} 
Table 1: The main physicochemical parameters of raw sesame stalk and its biochar produced by different conditions. Figure 3: Relationships between pH and oxygen content (%) for sesame stalk feedstock and corresponding to biochar produced at 300 \({}^{\circ}\)C by parabolic dish collector and conventional method. Electric conductivity (EC) of the water extraction is a factor used to assess the biochar salinity degree by measuring the total dissolved salts. The EC was higher in SB-2 and SB-3 than in SF and SF-1. All produced biochar types are generally characterized as non-saline materials, whose values are less than the unity.