## 4 Materials and Methods
### Collection of Fine Roots Samples  
The study site was dominated by rubber monoculture planted in 1994, 2006, and 2003 with a conventional 2.5 m \(\times\) 8 m spacing arrangement (Figure 3). In June 2010, seven lines of the native _F. macrophilla_ species, well adapted to the tropical climate and local soil conditions, were interplanted in a section of each monoculture stand at a density of 0.8 m \(\times\) 1.0 m inter-row spacing with no further agronomic practices [40]. We collected soil cores from three sample subplots (25 m \(\times\) 20 m) in each of the six stands, namely 12, 15, and 24-years-old rubber monoculture and agroforestry (each age had two plantations mono and mix) in 1 hectare in March 2018. We extensively assessed samples for 3-month optimal intervals for fine root biomass, i.e., seasonal intervals (S1, March 2018; S2, June 2018; S3, September 2018; S4, December 2018, and S5, March 2019). S1, S4, and S5 represented the dry season, while S2 and S3 represented the rainy season. All sites were managed similarly, except _F. macrophilla_, which was clipped approximately 30 cm above the ground and subsequently covered at the end of each year. We extracted soil cores from 0-60 cm depth with the help of a soil drill hand-boring auger (9 cm diameter). We took 10 soil cores randomly in each subplot; hence for each stand age (mono/mix), 30 soil cores samples were collected, which provided a total of 900 soil core samples (6 subplots plots (3 mono/3 intercrops) \(\times\) 10 soil core \(\times\) 3 stand ages \(\times\) 5 seasons), for the determination of fine root dynamics. The extracted soil cores were kept in double-sealed plastic bags with name tags for identification. For nutrient determination, we took one soil core from each subplot and collected 18 soil cores in each season from a total of five seasons; we used 90 soil core samples for determining nutrients to explore how they varied amongst seasons and stand types and ages. Soil samples were air dried and sieved (2 mm) for further physio-chemical analysis. The descriptions of stand characteristics are shown in Table 4.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Age** & **MC** & **TN** & **TP** & **TK** \\
**(Years)** & **M.S** & **(g\(\cdot\)kg\({}^{-1}\))** & **(g\(\cdot\)kg\({}^{-1}\))** & **(g\(\cdot\)kg\({}^{-1}\))** & **(g\(\cdot\)kg\({}^{-1}\))** \\ \hline
12 & Mono & 9.4 \(\pm\) 1.5 ab & 0.3 \(\pm\) 0.0 a & 0.7 \(\pm\) 0.1 b & 20.1 \(\pm\) 1.6 b & 5.8 \\
12 & Mix & 7.9 \(\pm\) 1.2 b & 1.1 \(\pm\) 0.1 ab & 0.3 \(\pm\) 0.0 a & 17.5 \(\pm\) 1.0 c & 5.9 \\
15 & Mono & 9.8 \(\pm\) 0.5 ab & 0.3 \(\pm\) 0.0 a & 0.3 \(\pm\) 0.0 c & 16.2 \(\pm\) 0.9 c & 5.0 \\
15 & Mix & 8.9 \(\pm\) 0.5 ab & 1.2 \(\pm\) 0.0 a & 0.3 \(\pm\) 0.0 a & 15.2 \(\pm\) 0.6 d & 5.0 \\
24 & Mono & 10.6 \(\pm\) 0.7 a & 1.3 \(\pm\) 0.1 a & 0.3 \(\pm\) 0.0 c & 22.3 \(\pm\) 3.7 a & 5.0 \\
24 & Mix & 10.8 \(\pm\) 1.2 a & 1.2 \(\pm\) 0.1 a & 0.3 \(\pm\) 0.0 a & 17.3 \(\pm\) 1.6 c & 5.2 \\ \hline \hline \end{tabular} Note: MS; Management system, i.e., rubber monoculture (Mono) and rubber-_F. macrophilla_ intercropping (Mix), TC; represents total carbon, TN; total nitrogen, TP; total phosphorus and TK; total potassium. Data points (means \(\pm\) SE, n = 3) of the two systems; lowercase letters indicate the significant difference in different stand ages.  
\end{table}
Table 4: Basic characteristics of plots.