Addition of Leucaena-KX2 mulch in a shaded coffee agroforestry system increases both stable and labile soil C fractions |
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| Authors: | Adel Youkhana Travis Idol |
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| Institution: | Department of Natural Resources and Environmental Management, College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa, 1910 East-West Rd, Sherman Lab 101, Honolulu, HI 96822, USA |
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| Abstract: | Agroforestry systems have the potential to increase sequestration of atmospheric carbon dioxide (CO2) as soil organic carbon (SOC) because of the increased rates of organic matter addition and retention. However, few studies have characterized the relative stability of sequestered SOC in soil. We characterized SOC storage in aggregate size and chemical stability classes to estimate the relative stability of SOC pools after the addition of Leucaena-KX2 pruning residues (mulch) from 2006 to 2008 in a shaded coffee agroforestry system in Hawaii. Soil samples were separated by microaggregate isolation, density flotation and dispersion, and acid hydrolysis, resulting in five distinct fractions that differed in relative stability: coarse particulate organic matter (POM), fine POM, microaggregate-protected POM, silt + clay hydrolyzable soil organic matter (SOM), and silt + clay non-hydrolyzable SOM. With mulch addition, the fine POM fraction increased. There was also a shift in the proportion of SOC to more stable silt + clay fractions. In the absence of mulch there was no significant change in SOC fractions. Given that the turnover time of SOC in silt + clay fractions is on the order of decades to centuries, the potential benefits of active shade management and mulching compensate for the loss of C sequestration in tree biomass from pollarding. |
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| Keywords: | Carbon sequestration Density fractionation Heavy fraction Light fraction Leucaena-KX2 Mulching Particulate organic matter Shade-grown coffee Soil organic carbon Sodium polytungustate |
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