African Journal of
Agricultural Research

  • Abbreviation: Afr. J. Agric. Res.
  • Language: English
  • ISSN: 1991-637X
  • DOI: 10.5897/AJAR
  • Start Year: 2006
  • Published Articles: 6574

Full Length Research Paper

Determination of optimum dose and frequency of application of free-living diazotrophs (FLD) on lettuce

M. H. Kifle1* and M. D. Laing
Discipline of Plant Pathology, School of Agricultural Science and Agribusiness, University of KwaZulu-Natal, Private Bag X01, Scottsville 3209, Pietermaritzburg, South Africa.
Email: [email protected]

  •  Accepted: 20 October 2010
  •  Published: 04 February 2011



Free-living diazotrophic isolates L1 (Bacillus cereus Frankland) and Br2 (Bacillus subtilisEhrenberg Cohn) were evaluated in greenhouse trials for their optimum dose and frequency of application on seedlings of a single lettuce variety (Great Lakes) in a composted pine bark medium. Bacterial isolates were grown in Burke’s broth and were applied as a drench at four different doses (105, 106, 107 and 108 colony forming units (cfu) ml-1) and at different frequencies of application (1, 7, 14 and 21 days). Two months later, wet weight, dry weight and plant N levels were measured. Lettuce growth and plant N level responded positively to both bacterial isolates inoculated at 106cfuml-1 weekly and fortnightly. Isolate Br2 inoculated at 106cfuml-1 fixed 32.4% plant N when applied weekly and 26.7% when applied every two weeks. Isolate L1, at the same dose, applied weekly or every two weeks, fixed 27.7 and 29.1% of plant N requirement, respectively. The lettuce seedlings responded less well to a higher dose at 108cfu ml-1 of either isolate applied weekly and every two weeks. The response to dosage depended on frequency of application. Doses of 10cfu ml-1 of both isolates applied weekly or every two weeks had the best effect on lettuce seedling growth and plant N.


Key words: Free-living diazotrophs, lettuce, optimum dosage, frequency of application.