Carbon sequestration in sub-tropical soils under rubber plantations in north-east India Debasis Mandal and K. R. Islam Indian Rubber Research Institute, Tripura, and University South Centers, USA Widespread deforestation for fuelwood, timber and forage is an on-going process in the south-east Asian countries (Islam et al 1999). Deforestation transfers C directly to the atmosphere, and affects the mechanism to hold C in soil (Chambers et al. 2001). Rubber plantations were raised as a secondary forest in the Indian state of Tripura since 1975 to improve degraded lands, generate income for locals, and meet increasing demand for rubber. [...]... Standing biomass, biomass C content, and annual litter-fall of rubber plants quadratically and significantly increased Greater accumulation litter-fall on the surface linearly and significantly decreased soil compaction The beneficial effects of litter-fall on decreasing compaction was greatest on surface soil Conclusions…… The COX stock increased linearly in surface soil compared to a non-linear increase... 0.2 0.0 0 10 20 Years after plantation 30 2 0-15 cm: y = 2.23 - 0.028*X r2=0.99*** -1 CT sequestration (Mg ha yr ) 3.0 15-30 cm: y = 2.49 - 0.12*X + 0.002*X2 r2=0.98*** -1 2.5 2.0 1.5 1.0 0.5 0.0 0 10 20 Years after plantation 30 Table 4: Profile-wise C sequestration rates in soils under different ages of rubber plantations Plantation COx CNOx CT Age (year) _ (Mg ha-1 y-1)... surface soil Conclusions…… The COX stock increased linearly in surface soil compared to a non-linear increase in subsurface soil However, both CNOX and CT stocks increased quadratically over time Summing the C content over soil depth, the profile-wise accumulation of various C fractions increased non-linearly over time Thanks ...Results and Discussion Table 1: Standing biomass of different ages of rubber plantations _ Plantation Shoot Root Total age (year) biomass (Mg ha-1) _ 0 (initial) 16.8c 4.2d 21.0c 5 29.3c 13.6c 42.3c 10 121.3b 26.6b 145.9b 15 156.0ab 29.4ab 185.5ab 20 160.4ab 32.4a 193.4a 25... of different ages of rubber plantations _ Plantation Shoot Root Total Age (year) _ biomass C (Mg ha-1) _ 0 7.2b 1.9d 9.1b 5 12.6b 5.7c 18.4b 10 52.3a 11.1b 63.3a 15 67.1a 13.2ab 80.3a 20 69.2a 14.5a 83.7a 25 69.2a 14.3a 83.5a 30 69.5a 13.3a 82.9a _ 19.7 3.2 20.9 LSDP>0.05 Litter-fall (Mg ha-1 yr-1) 8 6 Biomass Carbon 4 2 0 0 10 20... r2=0.37ns 0 CT = 84.35 + 60.2*(1-exp(-0.076*X, r2=0.85** 0 10 20 30 Years after plantation 1200 -1 -1 Cox sequestration (kg ha yr ) 1400 1000 800 600 400 0-15 cm: y = 872.8 - 2.33*X 2 r =0.99*** 200 15-30 cm: y = 1354.2 - 56.4*X + 0.84*X 2 r =0.98*** 2 0 0 10 20 Years after plantation 30 -1 -1 CNox sequestration (Mg ha yr ) 1.4 0-15 cm : y = 1.36 - 0.026*X 2 r =0.99*** 15-30 cm : y = 1.13 - 0.06*X + 0.001*X . Carbon sequestration in sub-tropical soils under rubber plantations in north-east India Debasis Mandal and K. R. Islam Indian Rubber Research Institute, Tripura, and University. 2001). Rubber plantations were raised as a secondary forest in the Indian state of Tripura since 1975 to improve degraded lands, generate income for locals, and meet increasing demand for rubber. . degraded sub-tropical forest lands in Tripura, India. Materials and methods Site: 10,412 ha of rubber plantations of different ages at Kunjaban, Agartala, NE India Soil Ultisol Texture Clay loam Porosity