Abstract
Soil plays a pivotal role in global carbon stocks and climate change due to green house gasses. Atmospheric CO2 could be sequestered in soils by converting degraded lands into rubber plantations and by adopting better agro-management practices in existing rubber plantations. This study reviews the information available on soil organic carbon (SOC) stocks in rubber growing soils of Sri Lanka and strategies to increase carbon sequestration in rubber plantations. To date, data generated under the SRICANSOL project were the only available information to estimate SOC stocks down to 1 m depth in rubber growing areas in Sri Lanka. Calculations made using that data set revealed that the mean SOC stocks in rubber growing soils of Wet, Intermediate and Dry Zone were 105, 85 and 78 Mg ha-1, respectively. In mature rubber plantations, SOC stocks had ranged from 40 to 133 Mg ha-1 and this as a proportion of ecosystem C stock could be varied from 25 to 65% depending on the soil depth, type, and agro-management practices. Establishment of rubber based agro-forestry systems using perennial crops that incorporate large quantities of organic matter into soil (e.g. cocoa, banana) is the best land use option to sequester atmospheric CO2 in rubber growing soils. Erosion control by establishing a good Mucuna bracteata ground cover since land preparation, establishment of deep rooted vetivar grass or gliricidia as hedgerows and mulching with their loppings, return part of the fuelwood back into rubber field as biochar, adopting favourable agricultural practices that increase growth of the rubber plants were among the key strategies to increase SOC stocks in rubber plantations. The information generated here could be useful when drafting a project design document when tapping into carbon markets.
Highlights
World soils represent the largest terrestrial pool of organic carbon, about1530 Pg compared with about 760 Pg in atmosphere and 560 Pg in land biota (Lal, 2004)
In dry and cold southwest China, Yang et al (2005) observed about 15 Mg of more C ha-1 in the top 40 cm soils in 15-30 year rubber plantations established on former arable lands when compared with those of nearby arable lands. These findings suggests that, conversion of lands used for shifting cultivation in the Dry Zone of Sri Lanka into permanent rubber based agroforestry systems is likely to increase soil organic carbon (SOC) stocks
A comprehensive data set was available under the SRICANSOL project, a twinning project between the Soil Science Society of Sri Lanka and Canadian Soil Science Society, that could be used to calculate the SOC stock down to 1m depth
Summary
World soils represent the largest terrestrial pool of organic carbon, about1530 Pg compared with about 760 Pg in atmosphere and 560 Pg in land biota (Lal, 2004). A comprehensive data set with all information required to estimate total SOC stocks down to 1m depth was available from the SRICANSOL project, a twinning project by the Soil Science Society of Sri Lanka and Canadian Soil Science Society initiated in 1995 and completed in 2009 in 3 phases (Senarath, Dassanayake & Mapa, 1997; Dassanayake, de Silva & Mapa, 2003; Dassanayake et al, 2005). Under this project soils of Sri Lanka were classified into series level
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