Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/10/2009
Publication Date: 1/13/2010
Citation: Gama-Rodrigues, E.F., Ramachandran, N.P., Nair, V.D., Gama-Rodrigues, A.C., Baligar, V.C., Machado, R.C. 2010. Carbon storage in soil-size fractions under two cacao agroforestry systems in Bahia, Brazil. Agriculture, Ecosystems and Environment. 45:274-283. Interpretive Summary: Agroforestry systems used for cacao production also play an important role in improving soil fertility by storing a large amount of organic carbon in the soil. A field experiment was undertaken in Bahia, Brazil, to evaluate different cacao management systems on soil organic carbon content. Surface soil samples were collected from two cacao agroforestry systems (30-year-old cacao trees shaded by native rainforest trees and 30 years-old cacao tress shaded by non-native trees) and from a native rainforest. In both cacao-agroforestry systems, the organic carbon in soil was higher than in the native rainforest soils. These results demonstrate that agroforestry systems used to produce cacao are more efficient at storing organic carbon than native rainforests. These findings are important for improving the utilization of native rainforests and will be useful to scientists, extension personnel and government planners to develop farming systems that are economically viable and environmentally safe.
Technical Abstract: Shaded-perennial agroforestry systems contain relatively higher quantities of soil carbon (C) because of continuous deposition of plant residues; however, the amount of C sequestered in the soil will vary depending on the turnover time and the extent of physical protection of different soil organic matter fractions. The objective of this study was to characterize soil organic C (SOC) pools in relation to various soil aggregate-size classes in different soil layers up to one meter depth in cacao (Theobroma cacao) agroforestry systems (AFS) in Bahia, Brazil. Soil samples were collected from four depth classes (0 – 10, 10 – 30, 30 – 60, and 60 – 100 cm) under three land-use systems in reddish-yellow Oxisols; the land-use systems were: (1) a 30-year-old stand of cacao under natural forest (cacao cabruca), (2) a 30-year-old stand of cacao with Erythrina glauca as shade trees (cacao + erythrina), and (3) an adjacent natural forest. The soil sample from each depth was separated by wet sieving into three aggregate-size classes (> 250 µm, 250 – 53 µm, and < 53 µm). The organic C stock in the 0 – 100 cm soil layer did not vary among different systems (mean: 302 Mg ha-1); however, in the 0 – 30 cm layer, it was in the order: cacao cabruca > cacao + erythrina > natural forest (154, 118, and 84 Mg ha-1, respectively). On average, 73 % of SOC content was in the largest (macro-sized) fraction (2000 – 250 µm), 19 % in the micro-sized fraction (250 – 53 µm) and 7 % in the silt-and-clay-sized fraction (< 53 µm) in the 0-100 cm layer. Seventy percent of SOC in cacao AFS are located inside the macroaggregates, representing well-protected form of C. The results suggest the important role of cacao AFS in environmental protection by mitigating GHG emission through storage of high amounts of well-protected organic C in the soils.