title: Enhancement of lettuce yield by manipulation of light and nitrogen nutrition.
abstract: Several levels of photosynthetic photon flux density (PPFD) were tested for effects on growth of 4 cultivars of lettuce (Lactuca sativa L.) under controlled-environment conditions. Growth of 'Salad Bowl', 'Bibb', and 'Ruby' was greater at 932 micromoles s-1 m-2 than at < or = 644 micromoles s-1 m-2 under a 16-hour photoperiod. Thirty mM NO3- or 5 mM NH4+ + 25 mM NO3- increased leaf dry weight while reducing leaf chlorosis in 'Salad Bowl' and 'Grand Rapids' relative to that with 15 mM NO3-, and reduced leaf purpling in 'Bibb' and 'Ruby' with little or no effect on yield. Continuous illumination with 455 or 918 micromoles s-1 m-2 stimulated yield of 'Salad Bowl' and 'Bibb' when 30 mM N as NH4+ + NO3- was used relative to that with 15 mM NO3-.
authors.affiliation: Department of Horticulture, Purdue University, West Lafayette, IN 47907, USA.
authors.forename: S L
authors.initials: SL
authors.lastname: Knight
authors.forename: C A
authors.initials: CA
authors.lastname: Mitchell
mesh_terms: D003470:Culture Media; D004780:Environment, Controlled; D018545:Lactuca / Q000254:growth & development* / Q000378:metabolism / Q000528:radiation effects; D008027:Light; D009566:Nitrates / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D010775:Photic Stimulation; D017785:Photons; D017440:Photoperiod; D010788:Photosynthesis; D018515:Plant Leaves / Q000254:growth & development* / Q000378:metabolism / Q000528:radiation effects; D000644:Quaternary Ammonium Compounds / Q000378:metabolism
chemical_list: D003470:Culture Media; D009566:Nitrates; D000644:Quaternary Ammonium Compounds; D009584:Nitrogen