Estimation of the total carbon sequestration potential of coconut-gliricidia mixed cropping systems in Sri Lanka

Abstract

Offsetting carbon footprints by sequestering carbon through plant biomasses has become a key concern under modern thinking on climate change mitigation. This study aimed to estimate the carbon sequestration capacities of coconut-based gliricidia mixed cropping systems in Sri Lanka and, importantly, to develop an allometric model for non-destructive estimation of carbon. Five major coconut age groups and four major gliricidia age groups were selected to estimate the total carbon stock. The age groups of coconut considered were 10, 20, 30, 40, and 50 years, with corresponding carbon stocks of 22.59, 34.99, 53.13, 63.40, and 66.03 Mg[C]ha^-1, respectively. In gliricidia stands, carbon stocks were 25.53, 46.16, 83.83, and 106.09 Mg[C]ha^-1, respectively, for age groups of 5, 10, 15, and 20 years. It is recommended that gliricidia be introduced as an intercrop in coconut plantations 20 years after the establishment of the latter. For this study, a 30-year-old coconut plantation with a 10-year-old gliricidia intercrop, along with its associated ground cover vegetation and soil carbon stock, were considered the benchmark agroforestry system. In the 30-year-old coconut monocropping system, the total carbon stock was 67.76 Mg[C]ha^-1, which consisted of uniform coconut, 1.24 Mg[C]ha^-1 from ground cover vegetation and 13.39 Mg[C]ha^-1 from the soil carbon stock at a depth of 30 cm. The overall carbon sequestration rate for this monocropping system was 2.25 Mg[C]ha^-1yr^-1 and abated CO₂ in 8.23 Mg[CO₂]ha^-1yr^-1. In the 30-year-old coconut and 10-year-old gliricidia mixed cropping system, the total carbon stock was 114.83 Mg[C]ha^-1, which consisted of uniform coconut and Gliricidia, 1.05 Mg[C]ha^-1 from ground cover plants, and 14.49 Mg[C]ha^-1 from soil carbon stock at a depth of 30 cm. Compared to the coconut monocropping system, the coconut-gliricidia mixed cropping system had a higher carbon sequestration rate of 6.84 Mg[C]ha^-1yr^-1 and abated CO₂ in 25.03 Mg[CO₂]ha^-1yr^-1, which are around three times higher than the monoculture system.

Keywords

Carbon sequestration / carbon stock / climate change mitigation / monocropping systems / non-destructive estimation

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