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Tropentag, September 17 - 19, 2018 in Ghent

"Global food security and food safety: The role of universities"

Land Use Change Impact on Soil Organic Carbon: Insights from Isotopic Signature in Soil Profiles

Rong Lang1, Sergey Blagodatskiy1, Jianchu Xu2, Georg Cadisch1

1University of Hohenheim, Inst. of Agric. Sci. in the Tropics (Hans-Ruthenberg-Institute), Germany
2World Agroforestry Centre (ICRAF), East and Central Asia, China


Soil is the largest carbon pool in terrestrial ecosystems, being the natural capital necessary to maintain soil fertility and food security. Land use changes in the tropics have been a large source of anthropogenic greenhouse gas emission and a threat for soil fertility loss due to intensive agricultural usage. Rubber expansion at the expense of tropical forest and shifting agriculture in Southeast Asia is one of those cases. Comparing soils under forest, rubber plantations and agricultural fields using so called “space substitute time” approach helps to assess the land use change impact on soil carbon stock. Isotopic signature of organic carbon in the soil profiles was analyzed, aimed to assess the land use change impact and validity of applied method for comparing selected forest and land converted to rubber plantation.
We selected 3 group of sites in Xishuangbanna, Southwest China, each contained one forest plot and two (or three) rubber plots at different age, and sampled soils at 6 depths up to 90 cm with 15 cm sampling interval. The soil organic carbon content and stable isotope ratio of carbon- δ13C was determined for litter and soil samples.
Forest and rubber plantation had similar δ13C value in the litter, confirming that forest was dominated by C3 plants. The δ13C of soil increased with depth and stabilised below 30cm, but its profile distribution distinctly differed between land uses and between sites. On two sites of three, δ13C in the forest subsoil below 30 cm were -23.3~-23.6 and -24.4~-24.6, which were lower than corresponding values in rubber subsoil, suggesting that C4 crop, like maize or cassava preceded rubber plantation. In contrast, δ13C in forest and rubber subsoil was higher at the third site (-21.5±0.1), as compared to δ13C in forest subsoil from two sites mentioned above, indicating the previous cultivation of C4 crop in both forest and rubber plantation on the third site.
In conclusion, “space substitute time” method should be cautiously used in assessing land use change impact, adding historical land use information derived from δ13C signature in soil profiles can improve the validity of comparison.

Keywords: Delta 13C, forest, land use change, rubber plantation, soil organic carbon

Contact Address: Rong Lang, University of Hohenheim, Inst. of Agric. Sci. in the Tropics (Hans-Ruthenberg-Institute), Garbenstraße 13, 70599 Stuttgart, Germany, e-mail: langrong@mail.kib.ac.cn

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