Intracanopy lighting influences radiation capture, productivity, and leaf senescence in cowpea canopies

Traditional overhead lighting of dense crop stands in controlled environmen ts favors development of upper Leaf layers to maximize interception of ligh t incident at the top of the foliar canopy, The resultant mutual shading of lower leaves in the understory of the canopy can severely limit productivi ty and yield of planophile crops. Intracanopy lighting alleviated the effec ts of mutual shading in dense, vegetative stands of cowpea [ Vigna unguicul ata (L.) Walp ssp, unguiculata] growing in a controlled environment by sust aining irradiance within the understory throughout development of this edib le-foliage crop. For an overhead lighting system, photosynthetic photon flu x (PPF) in the understory was reduced to 1% of its initial value by 35 days of growth, PPF in an intracanopy-lighted stand remained within 30 mu mol(. )m(-2.)s(-1) of initial values throughout the 50-day cropping period. Spect ral distribution of radiation within the intracanopy-lighted stand also rem ained relatively constant throughout canopy development. In the overhead-li ghted stand, violet and blue radiation in the understory decreased as much as 60% from initial values. Stability of the radiation environment within t he intracanopy-lighted stand delayed leaf senescence 27 days beyond when in terior leaves of the overhead-lighted canopy began to turn yellow on day 16 . The intracanopy-lighted stand produced twice as much edible biomass per u nit electrical energy consumed by lamps as for the overhead-lighted system. The treatment differences were due to the continuous presence of understor y irradiation when using intracanopy lighting but not when using overhead l ighting, and they underscore the importance of the entire foliar canopy in realizing the full productivity potential of dense crop stands in controlle d environments.