From forest to cropland and pasture systems: a critical review of soil organic carbon stocks changes in Amazonia.
The impact of deforestation on soil organic carbon (SOC) stocks is important in the context of climate change and agricultural soil use. Trends of SOC stock changes after agroecosystem establishment vary according to the spatial scale considered, and factors explaining these trends may differ sometimes according to meta-analyses. We have reviewed the knowledge about changes in SOC stocks in Amazonia after the establishment of pasture or cropland, sought relationships between observed changes and soil, climatic variables and management practices, and synthesized the δ13C measured in pastures. Our dataset consisted of 21 studies mostly synchronic, across 52 sites (Brazil, Colombia, French Guiana, Suriname), totalling 70 forest-agroecosystem comparisons. We found that pastures (n = 52, mean age = 17.6 years) had slightly higher SOC stocks than forest (+6.8 ± 3.1 %), whereas croplands (n = 18, mean age = 8.7 years) had lower SOC stocks than forest (-8.5 ± 2.9 %). Annual precipitation and SOC stocks under forest had no effect on the SOC changes in the agroecosystems. For croplands, we found a lower SOC loss than other meta-analyses, but the short time period after deforestation here could have reduced this loss. There was no clear effect of tillage on the SOC response. Management of pastures, whether they were degraded/nominal/improved, had no significant effect on SOC response. δ13C measurements on 16 pasture chronosequences showed that decay of forest-derived SOC was variable, whereas pasture-derived SOC was less so and was characterized by an accumulation plateau of 20 Mg SOC ha-1after 20 years. The large uncertainties in SOC response observed could be derived from the chronosequence approach, sensitive to natural soil variability and to human management practices. This study emphasizes the need for diachronic and long-term studies, associated with better knowledge of agroecosystem management.
Centre Technique Interprofessionnel des Oléagineux et du Chanvre (CETIOM), Etablissement Public Local d'Enseignement et de Formation Professionnelle Agricole (EPLEFPA) de la Guyane, Savane Matiti, BP 53, 97 355, Macouria, Guyane française, France.|IRD (Institut de Recherche pour le Développement), UMR 210 Eco&Sols, Campus SupAgro, bât. 12, 2 place Viala, 34060, Montpellier Cedex 02, France.
Kenji
K
Fujisaki
Centre Technique Interprofessionnel des Oléagineux et du Chanvre (CETIOM), Etablissement Public Local d'Enseignement et de Formation Professionnelle Agricole (EPLEFPA) de la Guyane, Savane Matiti, BP 53, 97 355, Macouria, Guyane française, France.
Anne-Sophie
AS
Perrin
IRD (Institut de Recherche pour le Développement), UMR 242 iEES Paris, 32 av. H. Varagnat, 93143, Bondy Cedex, France.
Thierry
T
Desjardins
IRD (Institut de Recherche pour le Développement), UMR 210 Eco&Sols, Campus SupAgro, bât. 12, 2 place Viala, 34060, Montpellier Cedex 02, France.
Martial
M
Bernoux
EMBRAPA Cerrados, Cx Postal 08223, CEP 73310-970, Planaltina, DF, Brazil.
Luiz Carlos
LC
Balbino
IRD (Institut de Recherche pour le Développement), UMR 210 Eco&Sols, Campus SupAgro, bât. 12, 2 place Viala, 34060, Montpellier Cedex 02, France.
Michel
M
Brossard
annual crop; carbon storage; chronosequence; deforestation; grassland; humid tropics; rainforest; soil organic matter; soil tillage; δ13C