A study was conducted in northwest Florida, USA, to investigate root development and morphology of cotton (Gossypium hirsutum L.) under pecan (Carya illinoensis K. Koch) trees in an alleycropping experiment. Root:shoot ratio, root biomass, total root length and root length density were examined under three treatments: (1) barrier (separating belowground interspecific competition by trenching to a depth of 120 cm and installing polyethylene barrier), (2) non-barrier (root systems were free to interact), and (3) monoculture of cotton (without above and belowground interspecific competition with trees). Results indicated that plants in the barrier and non-barrier treatments had lower root:shoot ratios compared to the monoculture treatment. Belowground competition for resources between pecan and cotton in the non-barrier treatment resulted in 25 and 33% reduction of total root length (359 cm) when compared to that of the barrier (477 cm) and monoculture (539 cm) treatments, respectively. The non-barrier plants also exhibited the lowest root length density. Specific root length was highest for the monoculture (179 cm g-1) and lowest for the non-barrier treatment (146 cm g-1) with the barrier treatment being intermediate (165 cm g-1). Interspecific competition with pecan significantly altered root development and morphology of cotton plants. Research in agroforestry should take into account the developmental differences in root systems of the associated crop species so that better models incorporating nutrient and water uptake can be developed.
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Acknowledgments Special thanks are extended to Dr Johannes Scholberg for allowing us to use the Winrhizo equipment and program; Corey Cherr for the technical help in using the Winrhizo; Jeremy Monnot, D. Hatfield and J. Nelson for assistance in field and laboratory. This study was funded by the Center of Subtropical Agroforestry (CSTAF) at the University of Florida through USDA-CSREES grant 00-52103-9702, and also by the USDA Southern Region Sustainable Agriculture Research and Education (SARE) program (# LS02-136).
- Root length density
- Root-shoot ratio
- Specific root length