Tropentag, September 20 - 22, 2017 in Bonn "Future Agriculture: Social-ecological transitions and bio-cultural shifts"

Rubber Cultivation Weakened the Soil Methane Sink Function Compared to Natural Forest

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

Abstract

The impact of transforming natural forest into rubber plantations on soil function as CH₄ sink has not been well understood, especially on the seasonal dynamic and changes in underlying soil processes. Aimed to understand how this land use conversion changes the soil CH₄ sink, we conducted measurements in both natural forests and rubber plantations in Xishuangbanna, SW China. Temporal dynamic of soil surface CH₄ flux, CH₄ concentration and isotope signature of ¹³CH₄ in the soil profile at 5, 10, 30 and 70 cm depth were measured at representative time in dry and rainy season.
CH₄ uptake by soils in rubber plantations was only 41.8% of uptake by forest soils, with annual CH₄ cumulative flux of -2.41±0.28 and -1.01±0.23 kg C ha^-1yr^-1 for forests and rubber plantations respectively. The CH₄ oxidation was stronger in dry season than in rainy season, mainly explained by changes in soil moisture. From dry season to rainy season, CH₄ flux shifted to weak consumption in forest and young rubber plantation, or even towards emission in older rubber plantations; CH₄ concentration increased in all four depths with higher increment in older rubber plantations. The enrichment of soil CH₄ by ¹³CH₄ was higher in forest than in rubber plantations. The decrement of delta ¹³CH₄ from dry to rainy season in both land uses indicated the increased CH₄ production in rainy season, while the flux showed the net consumption. The CH₄ turnover rate suggested that the surface 0-5 cm soil was the most active layer responsible for CH₄ oxidation.
Conversion the forest into rubber plantation weakened soil CH₄ sink function. Seasonal change of CH₄ flux and ¹³CH₄ enrichment was larger under rainforest than rubber plantations, indicating modified soil water regime under rubber. Converting forest into rubber plantations and rubber cultivation may have profound impact on greenhouse gas emission from soil.

Keywords: Land use change, methane sink, rubber plantation, tropical soil

Contact Address: Rong Lang, University of Hohenheim, Inst. of Agricultural Sciences in the Tropics (Hans-Ruthenberg-Institute)
current address: 132 Lanhei Road Heilongtan, 650201 Kunming, China, e-mail: langrongmail.kib.ac.cn