Canopy light interception assessment – from DC20

Within the manual Protocols for experimental plot sampling, handling and processing of cereals in field experiments(external link) by G.J. Rebetzke (, A. van Herwaarden, B. Biddulph, C. Moeller, R. Richards, A. Rattey and K. Chenu.

Interception of incident light is important for crop growth. Sunfleck ceptometers such as those developed by Decagon® (Fig. 11a) allow measurement of sunlight (particularly the photosynthetically active component) below the canopy.


  1. Ceptometers have two components: a master box which records and stores light readings; and a light-integrating probe containing the light sensors (Fig. 11a).
  2. On the day of sampling try and ensure there will be no clouds during the time of measurement. Restrict measurements to when the sun is highest in the sky (i.e. between 1000 and 1400h)
  3. Prior to measurement, clean the probe of any soil, and reset the computer to commence recording/storing of readings.
  4. To measure, hold the probe parallel to the ground and above the canopy of the first plot to record incident sunlight. Kneel perpendicular (at 90�) to the first plot and move the probe along the ground toward the centre of the plot until the probe is completely covered by the canopy. Be sure that the probe is sitting on the soil surface and not lying on top of any plant leaves. Record value. Repeat at an angle of 45� to the left of the first measurement and then repeat at 45� to the right of the first measurement (Fig. 11b).
  5. Follow this procedure for each plot. However, be sure to include a measure of sunlight above the canopy for every 20 plots (to track incident light changes).
  6. Light interception (%) = 100* [1-(avg below canopy scores � avg above canopy scores)]Alternatively, solarimeter tubes can be installed above and below the canopy to measure light interception continuously, over time (Fig. 11c,d). The inconvenience here is that these sensors have to be linked to a data logger and are typically used for a limited number of key plots.
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Figure 11. (a) A sunfleck ceptometer that can be placed inside a plot to measure sunlight transmitted through the canopy; (b) Schematic showing the three relative positions of the ceptometer probe into a plot; (c) Linear PAR sensors (Solems SA, Palaiseau, France) at ground level; and (d) above a maize canopy.

Other resources

Appendix 1.(external link) Text description of phenological scale, Zadoks decimal code (DC).
Appendix 2.(external link) Picture description of phenological scale, Zadoks decimal code (DC).
Zadoks JC, Chang TT, Konzak CF (1974) A decimal code for the growth stages of cereals. Weed Research 14(6),415-421. doi: 10.1111/j.1365-3180.1974.tb01084.x

Notes and troubleshooting tips


Download complete manual: Protocols for cereal field experiments_Nov2012.pdf

Health, safety & hazardous waste disposal considerations


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