PARENT SESSION
Friday, August 11, 8:00-11:30 am
COS 105 - Nutrient cycling
Chickasaw, Mezzanine Level, Cook Convention Center
Presiders: D Bryant
Species interactions in cocoa (Theobroma cacao L.) polycultures: diagnosis of nutrient uptake by vector analysis.
Isaac, Marney*,1, Timmer, Vic1, Quashie-Sam, James2, 1 University of Toronto, Toronto, ON, Canada2 Kwame Nkrumah University of Science and Technology, Kumasi, AR, Ghana
ABSTRACT- Enhanced crop biomass production in polyculture presumably results from improved resource status associated with common agroforestry processes, such as increased biomass inputs, nutrient cycling efficiency and facilitative interactions. The search for complementary species in cocoa (Theobroma cacao) polyculture that maximizes resources and reduces interspecific competition is important for increasing agroforestry productivity. We hypothesized that cocoa productivity is enhanced under multi-strata polyculture because of improved resource status such as moisture availability, temperature regimes, light regulation and nutrient availability. This study examined cocoa plant biomass in polyculture under varying shade intensity provided by the distinctive upper-canopy tree structures of Albizia zygia (D.C.) Macbr, a nitrogen fixer, Milicia excelsa (Welw.), a timber species, and Newbouldia laevis (Seem.), a native small stature species, each compared to monoculture cocoa. Cocoa dry matter production increased (from 22.8 to 41.1 Mg ha-1) under full shade polyculture versus monoculture. No significant differences in soil moisture availability and temperature regimes were detected between the two systems. However, as expected, direct light under the monoculture system was greater than the polycultures (P=0.0492). Soil exchangeable K was unchanged or increased under full shade polyculture, while available P decreased and total N status was unaffected. Vector analysis revealed that nutrient uptake by the cocoa plants increased under full shade polyculture (43-80% and 22-45% for N and P, respectively), with K (96-140%) as the most responsive nutrient. Our results suggest that a balance between nutrient supply and shade provision is evidently required, and farmer manipulation of the upper tree canopy is critical for optimal levels of cocoa productivity and sustainability.
Key words: nutrient diagnosis, agroforestry, on-farm research