Abstract
Abstract. Tropical agroforestry has an enormous potential to sequester carbon while simultaneously producing agricultural yields and tree products. The amount of soil organic carbon (SOC) sequestered is influenced by the type of the agroforestry system established, the soil and climatic conditions, and management. In this regional-scale study, we utilized a chronosequence approach to investigate how SOC stocks changed when the original forests are converted to agriculture, and then subsequently to four different agroforestry systems (AFSs): home garden, coffee, coconut and mango. In total we established 224 plots in 56 plot clusters across 4 climate zones in southern India. Each plot cluster consisted of four plots: a natural forest reference, an agriculture reference and two of the same AFS types of two ages (30–60 years and > 60 years). The conversion of forest to agriculture resulted in a large loss the original SOC stock (50–61 %) in the top meter of soil depending on the climate zone. The establishment of home garden and coffee AFSs on agriculture land caused SOC stocks to rebound to near forest levels, while in mango and coconut AFSs the SOC stock increased only slightly above the agriculture SOC stock. The most important variable regulating SOC stocks and its changes was tree basal area, possibly indicative of organic matter inputs. Furthermore, climatic variables such as temperature and precipitation, and soil variables such as clay fraction and soil pH were likewise all important regulators of SOC and SOC stock changes. Lastly, we found a strong correlation between tree species diversity in home garden and coffee AFSs and SOC stocks, highlighting possibilities to increase carbon stocks by proper tree species assemblies.
Highlights
Land-use changes in the tropics are responsible for approximately 10 % of the human-induced greenhouse gas emissions and are expected to remain the second largest source of carbon (C) emissions in the near future (Achard et al, 2014)
In this study we investigated how soil organic carbon (SOC) stocks changed when forests are converted to agriculture and subsequently to agroforestry systems in four different climatic zones along a precipitation gradient
While SOC stocks in home garden and coffee agroforestry systems (AFSs) rebounded to near forest levels, the SOC stocks in both coconut and mango AFSs increased only marginally compared to the agricultural reference (Figs. 2 and 3)
Summary
Land-use changes in the tropics are responsible for approximately 10 % of the human-induced greenhouse gas emissions and are expected to remain the second largest source of carbon (C) emissions in the near future (Achard et al, 2014). To reduce carbon emissions from agriculture while simultaneously maintaining agricultural productivity it is necessary to identify and implement simple and cost-effective measures to store and capture carbon In this context agroforestry practices, which integrate trees into agricultural systems, offer a unique opportunity to sequester atmospheric carbon while growing food, diversifying incomes Hombegowda et al.: Soil carbon rebounds in Indian agroforestry systems ple foods), and simultaneously providing numerous environmental benefits These include mitigating soil erosion (Montagnini and Nair, 2004), improving soil structure (Lal, 2007), pumping up nutrients from the subsoil (Das and Chaturvedi, 2008) and sequestering atmospheric carbon (Lal, 2007; Nair et al, 2009). Agroforestry systems (AFSs) have higher soil organic carbon (SOC) sequestration rates than conventional agricultural systems (Nair et al, 2009) as the trees have comparatively higher litter inputs and are capable of inserting carbon deep in the soil with their root systems (Montagnini and Nair, 2004)
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