Assessing carbon storage and sequestration potential in a five year rubber-based agroforestry system with intercrops of plantain and cassava In South-South Nigeria

Abstract

This study was designed to assess the total carbon (C) storage and sequestration potential of a Sole Rubber plantation and a Rubber-based agroforestry (RAF) system, considering the interactions between rubber trees and the intercropped Cassava (Manihot esculenta) and Plantain (Musa paradisiaca) after five years of cultivation. A comprehensive field study was conducted in 2025 to assess the carbon stock in aboveground and belowground biomass, as well as soil organic carbon concentrations at the Rubber Research Institute of
Nigeria’s Experimental plot. Sampling plots of 30 m x 30 m were laid out using a randomized complete block design (RCBD) with 3 replications within the rubber-based system. The treatments included: the Sole crop rubber; Rubber + plantain intercrop; and Rubber + Cassava intercrop. A non-destructive method was employed for biomass measurement. Mean tree height and diameter at breast height (DBH) were recorded and the best fit allometric regression model was used to estimate aboveground biomass (AGB). To estimate
Aboveground biomass, the model developed by Ketterings et al., 2001 (AGB=aDb (0.066D2.59) was used, as it demonstrated the highest modeling efficiency. Soil organic carbon (SOC) was assessed across three soil depths (0–15 cm, 15–30 cm, 30–45 cm) using descriptive statistics, one-way ANOVA, Duncan Multiple Range Test (DMRT) and regression analyses. The result showed that the rubber-based agroforestry system intercropped with plantain recorded the highest value with a total biomass of 1954.89 t ha^-1 , total carbon stock of 918.80 t ha^-1 and total carbon sequestration potential of 3371.99 t C t ha^-1 yr1 . This was followed by Rubber Intercropped with cassava, which recorded a total biomass of 1537.66 t ha^-1 , total carbon stock of 722.70 t ha1 and total carbon sequestration potential of 2652.32 t ha-1yr1 . The least total biomass was observed in the sole Rubber plantation with a total biomass of 1110 t ha-1 , total carbon stock of 521.7 t ha^-1 and total carbon sequestration potential of 1914.6 t ha^-1yr1 . Soil Organic Carbon patterns within the rubber-based agroforestry system differed significantly among depths (F = 9.84, p = 0.0127), with 0 – 15 cm >30 - 45 cm ≥ 15 - 30 cm (DMRT). Land use effects were depth-dependent: at 0 - 15 cm, forest > rubber (F = 432.0, p = 0.0023), whereas differences at 15 - 30 cm and 30 - 45 cm were not significant (p > 0.05). The exploratory regression suggested increasing C stock with stand age (slope = 0.713 t C ha⁻¹ yr⁻¹; R² = 0.814; p = 0.0139). These results indicate that rubber-based agroforestry systems enhance carbon storage compared to sole rubber plantations. The synergistic interactions between rubber trees and intercropped arable crops foster a more resilient and sustainable agroecosystem. These findings underscore the critical role of rubber-based agroforestry in climate change mitigation and offer valuable insights for shaping policies aimed at both adaptation and mitigation. Overall, the study highlights the importance of diverse and integrated land-use
practices in promoting carbon sequestration and sustainable land management.