Taking Chlorophyll Meter Readings of Corn Leaves
Chlorophyll meter readings of the field are taken and compared to the average readings from the high N reference area.
The field being tested should have received no fertilizer N beyond a normal amount of starter N and the N applied to the high N reference area.
The manual provided with the chlorophyll meter gives detailed instructions for operating the meter.
Below is a brief explanation of how to use the meter to take leaf readings for the early-season chlorophyll meter test:
1. Internal calibration of the meter is necessary when the meter is switched on. To calibrate the meter, turn on the meter.
CAL will appear in the window. With no sample in the sample slot, press the measuring head down. The meter will beep when the calibration is complete.
The display will now show N = O. (N is the sample number.) If the display flashes CAL and beeps, the calibration was not performed correctly (probably because the sample head was not closed completely).
Repeat the procedure. If the meter beeps and EU appears at the top of the display, the top and bottom windows of the measuring head may be dirty. Wipe them clean and repeat the procedure.
2. To take a leaf reading, place the leaf in the slot of the meter head. Use the center line on the measuring head to align the measuring head window and the spot on the leaf to be read.
When the head is closed on the leaf, the meter will beep, a digital reading will appear on the display, and the reading will be stored in the meter. Sometimes the meter will beep and not give a reading.
When this happens, try changing the alignment slightly before closing the head again.
Chlorophyll meter readings of corn leaves are affected by the part of the leaf and the position of the leaf on the plant that is sampled.
Therefore, it is necessary to standardize which part of the corn plant is read with the chlorophy11 meter.
For this test, chlorophyll meter readings should always be done on leaf five of the plants being tested.
The reading is done at a point on the leaf approximately 1/2 inch from the edge of the leaf and at a point 3/4 of the leaf length from the leaf base .
Do not take readings on the leaf midrib or too close to the edge.
Pick representative plants in the field for meter readings.
Care should be taken to avoid any unusual or damaged parts of the leaf when doing meter readings.
Plants chosen should be relatively evenly spaced rather than separate from others or in a cluster.
Use your body to shield the meter from direct sunlight.
Wet leaves may be read if beaded water is shaken or rubbed off before inserting the leaf in the meter. 3. Occasionally you may get readings that are very different from others in the field or that do not seem correct to you
. These can be deleted by pressing the 1 DATA DELETE button , which will remove the last reading.
Be careful not to press the ALL DATA CLEAR button because this will remove all readings taken to that point. If you want to look over all of your readings at any time, use the DATA RECALL button to scan the readings that you have taken. During the scan you may use the DELETE button to remove a reading and then replace it by taking another reading.
4. The chlorophyll meter will store up to 30 readings.
At any point, pressing the AVERAGE button will display the average of the readings taken.
When you are ready to begin a new set of readings, press the ALL DATA CLEAR button to delete all the readings currently saved.
Picture of chlorophyll meter showing function buttons, display screen, and meter head
Once the operator has become familiar with the meter operation and leaf stage identification, readings can be done very quickly. Since the meter will store up to 30 readings in memory and then calculate an average reading, at least 30 readings should be done. If a field is very variable, more readings may be necessary for an accurate field average, or to determine if several different N rates would be appropriate for the field. At least 25 to 30 readings should be taken of plants in the high N reference sections.