Interspecific competition in a pecan–cotton alleycropping system in the southern United States: Production physiology

A study was conducted on a Red Bay sandy loam soil (Rhodic Paleudult) in Jay, Florida, USA, to investigate how interspecific interactions between pecan (Carya illinoensis K. Koch) and cotton (Gossypium hirsutum L.) would affect cotton leaf morphology and gas exchange and thereby biomass and lint yield. We quantified specific leaf area (SLA), specific leaf nitrogen (SLN), net photosynthesis (A), transpiration, stomatal conductance, and net canopy photosynthetic index (CNPI) from cotton with and without aboveground and belowground interactions. To separate roots of cotton and pecan, polyethylene-lined trenches were installed (barrier treatment) parallel to tree rows in half the number of plots. Results showed that SLA for barrier and nonbarrier plants was 61% and 47% higher, respectively, compared with the monoculture cotton. Monoculture plants exhibited higher CNPI (70.7 mmol m–2 s–1) compared with the barrier (52.7 mmol m–2 s–1) and nonbarrier plants (18.3 mmol m–2 s–1). SLN was similar for both the barrier and nonbarrier plants; however, it was lower than the monoculture. A positive curvilinear relationship between A and SLN was observed, with peak A (28 mmol m–2 s–1) observed between 2.2 and 2.4 mg N m–2. Significant curvilinear relationships between CNPI and aboveground biomass and lint yield were also observed for all treatments. These findings indicate that competitive interactions in alleycropping regulate leaf level traits such as SLA and SLN by altering water and light availability, which in turn exert a profound influence on aboveground biomass and lint yield for cotton plants.