Early growth and nutritional response to resource competition in cocoa-shade intercropped systems |
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Authors: | M E Isaac F Ulzen-Appiah V R Timmer S J Quashie-Sam |
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Institution: | (1) Faculty of Forestry, University of Toronto, 33 Willcocks St., Earth Science Centre, Toronto, M5S 3B3, Canada;(2) Faculty of Renewable Natural Resources, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana |
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Abstract: | Intercropping is often promoted for effective mutualism between species, thus compensating for external inputs. However, for
optimal farm design resulting in superior production and nutrition, an accurate assessment of plant inter- and intra-specific
competition is required. In predominant shade tree-cocoa (Theobroma cacao) systems, inconclusive evidence remains on species interactions, limitations to resource availability and subsequent growth
and nutritional response, particularly in early growth. We examined cocoa biomass and foliar nutrition as well as nutrient
supply through rates of decomposition and N mineralization after 1-year growth. Our approach employed fertilization and mixed
planting treatments in an additive design of cocoa in monoculture (control), under artificial shade, and intercropped under
two separate shade species (Terminalia superba and Newbouldia laevis). Intercropping had no effect on cocoa biomass production in comparison to monoculture cocoa. However, artificial shading
stimulated foliage and root production both with and without fertilization, suggesting strong effects of light regulation
on growth in the absence of belowground competition. Nutritionally, intercropping suppressed K uptake in cocoa foliage as
K concentration was reduced by 20–25%, signifying dilution of this nutrient, presumably due to interspecific competition for
mobile elements. Foliar N content under N. laevis was raised, where N concentration kept up with growth under this intercropped species. Intercropping also delayed decomposition
rates, suggesting slower but sustained release of available nutrients into the topsoil. Cocoa under artificial shade, both
with and without fertilization, exhibited the greatest nutrient responses as compared to unfertilized monoculture cocoa, where
P uptake was stimulated most (175 and 112%), followed by K (69 and 71%), and then N (54 and 42%). Intercropping with shade
trees failed to increase cocoa biomass, however, nutrient uptake was sustained for N and P, suggesting low interspecific competition.
When fertilizers are undesirable or unavailable, intercropping of appropriately selected shade trees will not competitively
suppress early growth of cocoa but will improve light regulation and nutritional status of cocoa saplings. |
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Keywords: | Agroforestry Ghana Leaf decomposition Mineralization Theobroma cacao Vector analysis |
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