Abstract:
Cashew (Anacardium occidentale L.) is an important perennial crop with significant
potential for carbon sequestration in tropical dry zone agroforestry systems. However,
information on the influence of planting density on biomass carbon and soil organic
carbon (SOC) accumulation under long-term plantation conditions remains limited.
This study evaluated the effect of five planting densities on above-ground biomass
carbon (AGB), below-ground biomass carbon (BGB), SOC, and total ecosystem carbon
(TEC) in a field experiment established in 2012 at the Puttalam Plantation of the Sri
Lanka Cashew Corporation. The experiment was arranged in a Randomized Complete
Block Design (RCBD) with three replicates using cashew variety WUCC 19. Five
spacings were evaluated: 7.62 m × 7.62 m, 7.0 m × 7.0 m, 6.0 m × 6.0 m, 5.4 m × 5.4 m,
and 4.8 m × 3.9 m. AGB was estimated using a DBH-based allometric equation, while
BGB was derived using the IPCC (2019) Tier 2 root-to-shoot ratio model. TEC was
calculated as the sum of biomass carbon and SOC. Data were analyzed using ANOVA
followed by Tukey’s HSD test at p < 0.05. Results showed a significant effect of planting
density on carbon sequestration. TEC increased progressively with higher planting
density, from 51.0 Mg C ha⁻¹ at 7.62 m × 7.62 m spacing to 67.0 Mg C ha⁻¹ at 4.8 m ×
3.9 m spacing, while intermediate spacings recorded 54.5, 58.5, and 62.5 Mg C ha⁻¹,
respectively. Similar increasing trends were observed for AGB, BGB, and SOC. The
findings demonstrate that closer planting densities significantly enhance carbon
sequestration potential in dry zone cashew agroforestry systems and provide a
scientific basis for climate-smart plantation management.
