Effects of Fluorescent Intracanopy Lighting on Cowpea Canopy Productivity and Yield

in HortScience

The planophile (horizontal) leaf presentation of closed cowpea (Vigna unguiculata Walp.) leaf canopies limits PAR absorption from overhead lamps to the top layer of overlapping leaves, resulting in suboptimal canopy photosynthesis and premature senescence and abscission of lower, shaded leaves. Very low crop yield rates have been obtained in growth chamber studies using dense cowpea stands compared to greenhouse and field studies using more widely spaced plants. Nine separate growth compartments were constructed in each of two growth rooms. Eight or sixteen 15-W fluorescent lamps were mounted horizontally or vertically in tiers within each compartment, remote from their ballasts, and which can be switched on or off separately according to different lighting strategies. Mylar sleeves around each tube prevents contacting leaves from overheating. Intracanopy lighting arrangements draw from 0.27 to 0.54 kW of power/m3 of growth volume, compared to 1.18 kW·m–3 for traditional overhead lighting. PPF within compartments varies from 80 to 280 mmol·m–2·s–1, depending on sensor location, lamp arrangement, and lamp number. Each compartment is equipped with a recirculating hydroponic system. One room is operated with overhead plus intracanopy lighting, whereas the other utilizes intracanopy lighting only. Cowpea canopies are being grown under different lighting strategies and compared for growth, yield, productivity, leaf orientation, and individual leaf gas-exchange rates. Electrical power draw and total electrical energy consumption are being compared among treatments.

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