## 2 Materials and Methods  
### Experiment Setup  
A pot experiment was carried in a net house at Universiti Putra Malaysia Bintulu Sarawak Campus, Malaysia. The test crop used in this study was Thai Super Sweet hybrid F1 maize (_Zea mays_ L.). Pots (22 cm in height, 30 cm in width, and 30 cm in diameter) were filled with 7 kg of a mineral acid soil (from 5 mm bulked soil sample). Nitrogen, P, and K fertilizers were used based on the requirement of Thai Super Sweet hybrid F1 maize. Urea, triple superphosphate (TSP), and muriate of potash (MOP) were applied at 60 kg N ha\({}^{-1}\) (130 kg ha\({}^{-1}\) Urea), 60 kg P\({}_{2}\)O\({}_{5}\) ha\({}^{-1}\) (130 kg ha\({}^{-1}\) TSP), and 60 kg K\({}_{2}\)O ha\({}^{-1}\) (105 kg ha\({}^{-1}\) MOP), respectively. These rates were based on the recommendation of MARDI (Malaysian Agricultural Research and Development Institute) [13]. Based on these recommendations, the rates were scaled to per pot basis (Table 1). The amount of P fertilizer was further varied and reduced to 75%, 50%, and 25% (Table 1) whereas, the amounts of N and K fertilizers were the same except for the treatment without N, P, and K fertilizers. The fertilizers were applied in two equal splits (at 10 and 28 days after sowing). The CLB was applied at a rate of 5-ton ha\({}^{-1}\). Based on this rate, the CLB was scaled to 180 g of biochar per 7 kg of soil per pot (Table 2).  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Treatment Code**} & \multicolumn{2}{c}{**Treatments**} \\ \cline{2-3}  & **Biochar (5 t h\({}^{-1}\))** & **P (60 kg h\({}^{-1}\))** \\ \hline T1 & 0\% & 0\% \\ T2 & 0\% & 100\% \\ T3 & 100\% & 0\% \\ T4 & 75\% & 25\% \\ T5 & 50\% & 25\% \\ T6 & 25\% & 25\% \\ T7 & 75\% & 50\% \\ T8 & 50\% & 50\% \\ T9 & 25\% & 50\% \\ T10 & 75\% & 75\% \\ T11 & 50\% & 75\% \\ T12 & 25\% & 75\% \\ \hline \hline \end{tabular}
\end{table}
Table 1: Percentages of chicken litter biochar, nitrogen, phosphorus, and potassium fertilizers.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Treatment Code**} & \multicolumn{2}{c}{**Biochar Rate**} & **Fertilizers Rate** \\ \cline{2-3}  & \multicolumn{2}{c}{**g plant\({}^{-1}\)**} \\ \cline{2-3}  & \multicolumn{2}{c}{**TSP**} \\ \hline T1 & 0 & 0 \\ T2 & 0 & 4.8 \\ T3 & 180 & 0 \\ T4 & 135 & 3.6 \\ T5 & 90 & 3.6 \\ T6 & 45 & 3.6 \\ T7 & 135 & 2.4 \\ T8 & 90 & 2.4 \\ T9 & 45 & 2.4 \\ T10 & 135 & 1.2 \\ T11 & 90 & 1.2 \\ T12 & 45 & 1.2 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Scale down of chicken litter biochar, nitrogen, phosphorus, and potassium fertilizers rate in a pot study.  
The CLB used in this study was from the Black Earth Company, Australia. It was produced by the combusting chicken litter in oxygen-limited conditions and relatively high temperature (controlled) through pyrolysis. Chemical properties of the chicken litter biochar (Table 3) are consistent with Australia Certified Organic Standard, 2010.  
Soil and CLB were thoroughly mixed and moistened with a tap water at 60% water holding capacity before sowing. Maize seeds were soaked with water and fungicide (Thiram) for 24 h before sowing. This was done to ensure good germination, avoidance of seed infection, and plant establishment. Sowing depth was 3-4 cm and the maize seeds were sown in planting holes (two seeds per hole) after which the holes were partially covered with loose soil. At seven days after sowing, maize plants were thinned to two. The pot experiment was conducted in a completely randomized design with three replications. During the pot experiment, soil water holding capacity was calculated based on the amount of water retained at field capacity. The moisture was then maintained at 60% water holding capacity. The maize plants were monitored and harvested at tasseling stage (52 days after sowing) because this growth stage is a major determinant of maize yield [16; 17]. Nutrient and dry weight accumulation can also increase greatly around tasseling stage.