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20171
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Subject: Agroforestry × Author: Delphy Rocha × Author: KAU × End date: 2019 × Type: Thesis ×
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    ThesisItemOpen Access
    Fine root dynamics and associated carbon and nutrient flux in 12 year old acacia mangium at varying stand densities
    (Department of Silviculture and Agroforestry, College of Forestry, Vellanikkara, 2017) Delphy Rocha; KAU; Kunhamu, T K
    Fine root production has been estimated to account for up to 33% of global annual Net Primary Production, NPP (Gill and Jackson, 2000). Thus, fine root turnover has important implications for individual plant growth, plant interactions, and below-ground carbon and nutrient cycling. Direct and indirect methods for measuring fine root production and turnover in 12 year old Acacia mangium Willd. at varying stand densities were studied. Fine root production estimated ranged from 3.8 - 5.75 Mg ha-1 with a turnover of 4 yr-1. It was estimated that through fine root decomposition about 1.36-2.39 Mg C ha-1, 34.56- 102.52 kg N ha-1, 1.46-3.3 kg P ha-1 and 19.94-33.60 kg K ha-1 is released to soil. Even though fine root constitutes only 1.7-2.14% of the total tree biomass its contribution to the system productivity is very high. Attempts were also made to relate fine root production with various growth variables and in general most of the variables (DBH, basal area per tree, volume per tree, aboveground biomass per tree and leaf area per tree) gave good correlation (R>8**) with fine root production when considered on per tree basis. Average annual litter production was estimated to a range of 9.99-11.69 Mg ha-1. Interestingly, annual litter production had a high correlation (R=0.9**) with fine root production. Through litter decomposition, 1.4-2.07 Mg C ha-1, 36-48 kg N ha-1, 1- 4 kg P ha-1 and 3-6 kg K ha-1 is released to the soil. Total soil carbon stock up to 1m soil depth was estimated and it was significantly different across different density regimes. Invariably the SOC concentration was relatively lower in treeless plot compared with A. mangium at different density regimes. Soil C sequestration was 15.96 - 34.58 Mg C ha-1 and the nutrient content of soil estimated as 2343.811-948 kg N ha-1, 13.12-21.92 kg P ha-1, 313.52-261.25 kg K ha-1. Total system C content estimates in the ranges from 148.93 -263.79 Mgha-1. So Density manipulation plays a significant role on productivity in 12 year old A. mangium. Hence, management objectives should be based on assessment of their impact on various productivity attributes