LAI AccuPAR LP-80 Ceptometer
In use from 2013-05-17
Leaf Area Index (LAI) is an important measurement because many models use LAI as an index of canopy biomass and hence aboveground production.
A Licor LAI-2000 has been used for LAI measurements so far. This has a point sensor. Measurements are made at paired locations on each of the four sides of the plots in Block 1. These points are designated by treatment (e.g., G1), compass direction facing from the plot looking outward (i.e., N, E, S or W), and location 1 or 2. Hence an example would be “G7 NP1” for point 1 on the north side of treatment G7.
A flag is placed at each measurement point at the beginning of the growing season. Measurements are made close to the flag throughout the growing season at two-week intervals, starting as soon as there is sufficient biomass that attenuates light. Where crops are in rows (corn, soybean) or grow in clusters (Miscanthus, switchgrass), measurements have been made near the base of the plant. In the case of the poplars, where the sun may shine in from the side, measurements are made in the shadows of tree trunks.
Measurements are made as early in the day as possible (i.e., dawn) so that light is diffuse, although by the time they are completed sunlight strikes the plots.
Direct comparisons of the ceptometer and the LAI-2000 were made in 2012 and 2013. The ceptometer was used every 2 weeks, and every 4 weeks, simultaneous measurements were made with the LAI-2000. These comparisons included across-row as well as along-row measurements for corn and soybean. For along-row measurements, the ceptometer sensor array was placed at such an angle that it crossed the space between rows, but did not cross a row.
For 2014-2017, LAI measurements are made with a ceptometer only. The concurrent point/ceptometer measurements may be used to convert previous point measurements to ceptometer measurements.
1) Power it on. Be sure the sensor surface is clean and dry. Handle with care as it is a delicate instrument.
2) Make an ambient light measurement above or just outside the canopy by pressing the Up arrow once.
3) Place the sensor at ground level oriented from north to south. If the crops are in rows place it close to the base of the plants.
4) Press the Down arrow once to make the below-canopy measurement. LAI is automatically calculated, taking account of the preceding above-canopy measurement.
5) Press Enter and select Annotate from the listed options (Save, Annotate, or Discard). Name the data using the naming system described above. Press Enter again.
6) To make another measurement one must repeat steps 2-6 above.
Downloading the data:
1) Connect the RS-232 cable provided in the ceptometer case to the instrument and to the KEYSPAN 9-pin to USB cable attached to GPRPC26. Turn on the ceptometer.
2) On GPRPC26 computer, select HyperTerminal from the Start menu.
3) Once opened a “Connection Description” box automatically opens prompting the user to create and name a new connection. Click Cancel and instead choose File-Open and select Ceptometer.
4) Choose Transfer-Capture Text. Then you can either directly enter the location where you want the ceptometer data saved or browse to find a location.
5) On the ceptometer, push MENU twice. The display should show Data at the top with View, Download and Erase listed below. Use the down arrow to scroll to Download and push ENTER. Stored data will start downloading both in the HyperTerminal screen on PC26 and in the location you specified. The ceptometer display will show Downloading, Please wait… and will stop when all data has been downloaded.
6) Data will be saved as a text file.
7) Once download is complete, the ceptometer can be disconnected and turned off. HyperTerminal can be disconnected.
Date modified: Thursday, Apr 11 2019