Heat unit-based crop coefficient for grapefruit trees

E. C. Martin, A. K. Hla, P. M. Waller, D. C. Slack

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


The onset and rate of sap moving up the branches of grapefruit (Citrus paradisi Macfadyen) trees were monitored hourly using portable sap flow sensors at Waddell, Arizona. Hourly reference evapotranspiration (ETo) estimates were calculated using data from a nearby weather station. Crop water use was estimated from soil moisture measurements using a neutron probe. These data were used to first delineate the upper and lower temperature threshold values for the determination of heat units. A heat unit-based crop coefficient was then derived from a correlation of the crop coefficient with heat units over a crop year. The heat unit-based crop coefficient was found to be similar to crop coefficients derived by other researchers.

Original languageEnglish (US)
Pages (from-to)485-489
Number of pages5
JournalApplied Engineering in Agriculture
Issue number4
StatePublished - Jul 1997


  • Citrus
  • Crop water use
  • Growing degree days
  • Sap flow
  • Threshold temperature

ASJC Scopus subject areas

  • General Engineering


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