Abstract
The agricultural landscape of French Guiana (Amazonia) is expected to undergo substantial change as a result of rapid population growth in the region. Such changes in the landscape will lead to the conversion of tropical forests into land destined for agricultural use. Little information is available on the effect of different agricultural systems on greenhouse gas (GHG) emissions in French Guiana. For our experiment, two hectares of forest were cleared, without the use of fire, at the Combi experimental site (sandy-clayey Ferralsol) at the end of 2008. After one year with legume and grass cover, the site was modified to include the following three fertilized agricultural systems: (1) Grassland (Brachiaria ruziziensis, mowed), (2) cropland (maize/soybean rotation) with disc tillage, and (3) cropland (maize/soybean rotation) with no-tillage in direct seeding. Soil N2O, CH4, and CO2 fluxes were measured with dark chambers from May 2011 to November 2014. Our results show that grassland was a significantly lower emitter of N2O but a significantly higher emitter of CH4 compared to the two cropland systems studied. We did not observe significant differences between the two cropland systems for N2O and CH4 fluxes. Measurements of the net ecosystem CO2 exchange would be useful to better compare the role of different agricultural systems as a source of GHGs.
Highlights
French Guiana is an overseas region of France located in Amazonia, South America.The demographic growth in French Guiana is rapid: The population, 259,865 inhabitants in 2015 [1], is expected to reach 574,000 inhabitants by 2040 [2]
Because aboveground biomass and soil organic C stocks did not differ between the two cropland systems, whereas CO2 emissions were significantly higher in the disc tillage (DT) system, we hypothesize that our results might partly overestimate the mean CO2 fluxes from the DT system soil
Our results show that mowed grassland (Brachiaria ruziziensis) was a significantly lower nitrous oxide (N2 O) emitter but a significantly higher CH4 emitter than both of the cropland systems studied
Summary
French Guiana is an overseas region of France located in Amazonia, South America. The demographic growth in French Guiana is rapid: The population, 259,865 inhabitants in 2015 [1], is expected to reach 574,000 inhabitants by 2040 [2]. Tropical forest covers more than 90% of the land surface in French Guiana [3]. The population growth has led to urban and agricultural expansion to the detriment of forests. 2019, 3, 29 of 3300 ha per year, and the deforested land was mainly converted into cropped areas for subsistence farming or family/small-scale farming and for infrastructure development [4]. As is common in other tropical humid regions, slash-and-burn practices are widely used by French Guianese farmers [5,6]
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