Rubber Tree (Hevea brasiliensis) Biomass, Nutrient Content, and Heating Values in Southern Thailand

Rubber trees (Hevea brasiliensis (Willd.) Muell.Arg.) are cultivated for latex production, but they also produce timber for industry, and logging residues can be used for power generation. In this study, we determined the biomass of above- and below-ground tree compartments (leaves, branches <3 cm in diameter, branches 3–5 cm in diameter, stumps and roots) of 20-, 25-, and 30-year-old rubber tree plantations in Songkhla province, southern Thailand, at the clear-cutting stage. We also studied the nutrient content and heating value of the compartments. The total dry mass (including leaves, branches, stems and stumps and roots) of the mature rubber wood stands was 157–289 Mg ha−1. The residual harvestable dry mass without leaves (39–68 Mg ha−1, branches <5 cm in diameter, stumps and roots) comprised 25% of the total dry mass. Nutrient concentrations were highest in the leaves, followed by small branches. In most cases, the stems and larger branches had similar concentrations. One ton of rubber tree biomass (leaves and stumps and roots included) contained an average of 2.4 kg N, 0.2 kg P, 3.4 kg K, and 4.8 kg Ca. Depending on the biomass of the stands, the rubber trees had 380–700 kg, 36–64 kg, 530–980 kg, and 750–1360 kg of bound N, P, K, and Ca per hectare, respectively. The effective heating value of the stumps and roots was the lowest (17.65 MJ kg−1). Stems and branches were similar (18.37–18.58 MJ kg−1), and leaves were the highest (20.34 MJ kg−1). The unharvested residual biomass in southern Thailand is a potential fuel source for power generation.