Competitive interactions in a pecan (Carya illinoinensis K. Koch)-cotton (Gossypium hirsutum L.) alleycropping system in the southern United States

A research project was conducted at the West Florida Research and Education Center Research Farm of the University of Florida (Jay, Florida) to examine the competitive interactions involving light in a pecan-cotton alleycropping system. Polyethylene root barriers were used to prevent belowground interaction between pecan and cotton in half the numbers of test plots.;Light distribution (interception and absorption) was greatly affected by leaf area index of both pecan and cotton. Interspecific competition resulted in varying leaf morphology (e.g., specific leaf area) resulting in variations in canopy net photosynthesis (Pnet). Eliminating belowground competition via the barrier treatment resulted in a tri-fold increase in Pnet over the non-barrier and was comparable to the Pnet in monoculture. Despite 50% shading in the alleys, the barrier treatment had similar biomass to that of monoculture. Although cotton yield was similar for the monoculture and barrier treatments during the first year of the study, a slight decrease was noted in cotton yield in the barrier treatment in the second year. Biomass and lint yield always remained lower in the non-barrier treatment compared to the other two treatments.;Cotton root morphology was also affected by interspecific competition. Shading resulted in the allocation of more carbon to the aboveground components at the expense of the root systems, resulting in lower root:shoot ratio compared to the monoculture. Plants in the non-barrier treatment exhibited 25% and 33% reduction in total root length compared to barrier and monoculture, respectively. Similar reduction in root length density was observed in comparison to the other two treatments. Results also revealed significant curvilinear relationships between root length and root biomass regardless of treatment, but the magnitude of relationship varied, with non-barrier plants producing significantly lower root length compared to the barrier and monoculture for the same amount of carbon.;Results of simulation modeling indicated that the CROPGR4-cotton model can be used to predict cotton biomass under varying light levels. Correlation analyses indicated a significant relationship between measured and simulated aboveground biomass (R2 = 0.95 and R2 = 0.92, respectively for 2001 and 2002).;Results from this study can be used to improve system design and management techniques of pecan-cotton and similar alleycropping systems in the temperate region.