Soil fertility and Theobroma cacao growth and productivity under commonly intercropped shade-tree species in Sulawesi, I
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Soil fertility and Theobroma cacao growth and productivity under commonly intercropped shade-tree species in Sulawesi, Indonesia Ariani C. Wartenberg & Wilma J. Blaser & James M. Roshetko & Meine Van Noordwijk & Johan Six Received: 16 July 2018 / Accepted: 18 December 2018 # Springer Nature Switzerland AG 2019
Abstract Background and aims Trade-offs between ecological benefits and potential yield and growth reductions associated with the inclusion of shade trees in cocoa agroforests remain poorly understood. In this study we investigate interactions between shade and cocoa trees in cocoa agroforests in terms of soil fertility and cocoa productivity. Methods We quantified the effects of individual shade trees from 11 commonly intercropped species on cocoa growth (aboveground biomass) and yield and soil fertility indicators (total soil carbon, nitrogen, phosphorus contents and soil aggregation) at field sites in Southeast Sulawesi, Indonesia. Results Shade trees had a net positive effect on soil fertility in cocoa agroforests, with a 6% increase in soil carbon, a 4% in soil nitrogen and a 24% increase in mean weight diameter (used as an indicator for median soil aggregate size), under
shade tree canopies compared to open areas. We found that shade trees had a net negative effect on cocoa tree growth and no net effect on cocoa yields. We were not able to link costs versus benefits with specific shade tree traits, but nevertheless observed significant differences between shade tree species. G. sepium (gliricidia) had significantly positive effects on yields, soil carbon and aggregation. N. lappaceum (rambutan) and D. zibethinus (durian) had significantly positive effects on soil carbon and nitrogen contents and on aggregation, but not on yields. Conclusions Our findings confirm the potential for soil improvements under shade trees and suggest that the inclusion of individual shade trees does not always constitute a direct trade-off for farmers in terms of yield losses.
Responsible Editor: Remi Cardinael.
Abbreviations AGB Above-ground biomass C Carbon LM Large macroaggregates m Microaggregates MWD Mean weight diameter N Nitrogen P Phosphorus sM small macroaggregates s+c silt & clay particles SOM Soil organic matter
: W. J. Blaser : J. Six
A. C. Wartenberg Department of Environmental Systems Science, ETH Zürich, Zurich, Switzerland A. C. Wartenberg (*) Department of Environmental Science, Policy & Management, Mulford Hall, UC, Berkeley, CA 94720, USA e-mail: [email protected] J. M. Roshetko : M. Van Noordwijk World Agroforestry Centre, ICRAF Southeast Asia Regional Office, Bogor, Indonesia
Keywords Agroforestry . Soil fertility . Yields . Theobroma cacao . Shade trees
Plant Soil
Introduction On a global scale, smallholder Theobroma cacao (cocoa) cultivation systems are facing increasing production pressures related to factors such as soil degradation or pest and disease outbreaks (Vaast and Somarriba 2014). The inclusion of shade trees in cocoa agroforests has been heralded as a solu
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