Abstract
AbstractIncreasing soil organic carbon (SOC) in agroecosystems is necessary to mitigate climate change and soil degradation. Management practices designed to reach this goal call for a deeper understanding of the processes and drivers of soil carbon input stabilization. We identified main drivers of SOC stabilization in oil palm plantations using the well‐defined spatial patterns of nutrients and litter application resulting from the usual management scheme. The stabilization of oil palm‐derived SOC (OP‐SOC) was quantified by δ13C from a shift of C4 (savanna) to C3 (oil palm) vegetations. Soil organic carbon stocks under frond piles were 20% and 22% higher compared with harvest paths and interzones, respectively. Fertilization and frond stacking did not influence the decomposition of savanna‐derived SOC. Depending on management zones, net OP‐SOC stabilization equalled 16–27% of the fine root biomass accumulated for 9 years. This fraction was similar between frond piles and litter‐free interzones, where mineral NPK fertilization is identical, indicating that carbon inputs from dead fronds did not stabilize in SOC. A path analysis confirmed that the OP‐SOC distribution was largely explained by the distribution of oil palm fine roots, which itself depended on management practices. SOC mineralization was proportional to SOC content and was independent on phosphorus availability. We conclude that SOC stabilization was driven by C inputs from fine roots and was independent of alteration of SOC mineralization due to management. Practices favouring root growth of oil palms would increase carbon sequestration in soils without necessarily relying on the limited supply of organic residues.
Highlights
Soil organic carbon (SOC) depletion in agroecosystems is a major source of greenhouse gas emissions, resulting in losses of soil fertility and ecosystem stability (Amundson et al, 2015).Policymakers have recently acknowledged the promotion of soil C sequestration in agroecosystems as a promising strategy to simultaneously mitigate climate change and enhance food security (Lal, 2016)
The specific aims of the study are to i) quantify the new oil palm-derived (C3 signature) and the old savanna-derived soil organic carbon (SOC) stocks (C4) in a mature oil palm plantation established on native savanna grassland, ii) assess oil palm root development and its impact on SOC accumulation with plantation age, iii) determine the impacts of management practices on root development and soil microbial activity and iv) identify the main factors driving SOC stabilization
Soil organic C stocks strongly varied depending on the management zones of the plantation
Summary
Soil organic carbon (SOC) depletion in agroecosystems is a major source of greenhouse gas emissions, resulting in losses of soil fertility and ecosystem stability (Amundson et al, 2015).Policymakers have recently acknowledged the promotion of soil C sequestration in agroecosystems as a promising strategy to simultaneously mitigate climate change and enhance food security (Lal, 2016). Management practices favouring soil C sequestration lead to highly variable outcomes, calling for a deeper understanding of processes and factors controlling C stabilization, especially after land-use changes (Ghimire, Lamichhane, Acharya, Bista, & Sainju, 2017; Haddaway et al, 2017). This is needed in regions that are undergoing rapid and substantial land degradation following conversion from largely forested landscapes to intensive agricultural systems, as has been the case in tropical landscapes dominated by oil palm (Elaeis guineensis) plantations. Nutrient application modifies the stoichiometry of organic matter inputs and of soil organic matter, which in turn affects microbial processes controlling SOC stabilization
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