Agronomy Fact Sheet Series 1994-3
Department of Agronomy and Range Science
University of California, Davis

Instructions for Use of Chlorophyll Meter in Rice

1. Turn on meter and follow the manufacturer's instructions for calibration.
2. Take the most recently fully expanded leaf - the so-called "Y-leaf" - from rice plants representative of those in the sampling area. If the leaf collar is not showing yet, or if you cannot decide whether the leaf is fully expanded, take the next oldest leaf. Avoid leaves that are dark green but which are noticeably pale or chlorotic on the basal portion of the leaf, i.e., the end of the leaf attached to the tiller. Do not pick leaves with discoloration or necrosis caused by insects, disease, toxicities, or non-nitrogen nutrient deficiencies, as these will give false readings. Do not select leaves from very late forming tillers that will not be contributing to yield. Do not sample plants that are standing alone surrounded by open water.
3. Separate the whole leaf from the plant at the base, that is, just above the collar, and within a few seconds, insert it into the meter. Rice leaves quickly roll up after picking and are then difficult to insert into the meter. Therefore, leaves must be read in the field one at a time as they are picked, rather than collected and read later. It is possible, though awkward, to take readings on leaves still attached to the plant.




4. On each leaf, make two readings - at approximately one-third and two-thirds of the distance from the leaf tip to the base. Avoid taking readings in the paler green area that may be present at the basal end of the leaf. During the reading, shade the meter with your body so as to keep direct sunlight from possibly influencing the measured value.
5. Delete any obviously odd (outlier) values using the meter's delete button and either take another reading in a different spot on the same leaf or discard the leaf and pick a new one. Outlier (extreme or odd) values may be caused by positioning of the meter's head over the leaf edge or midrib, on insect bites, or on other discolored areas of the leaf. Rice leaves are so narrow that it usually will not be practical to avoid the midrib of the rice leaf; fortunately, the error caused by taking readings on the midrib is not large.
6. The meter can store up to 30 numbers. Additional readings will be stored by "bumping off" earlier values, beginning with the first one. Therefore, after reading 15 leaves (i.e., after 30 readings), press the meter's AVERAGE button and write in a notebook the displayed value. Fifteen leaves may be adequate for evaluating small areas of a field, but to monitor whole fields, it is suggested that separate readings be collected for individual basins or from areas that are known from experience to differ in N requirement from the rest of the field.
7. Compare the recorded values to critical values shown in the table below. Readings below the critical meter value indicate the possible need for N topdressing. Use this information along with observations of crop growth and other factors to help with this decision. If readings are near the critical value, check again in a week or so.

A handheld chlorophyll meter (Model SPAD 502, Minolta Camera Co., Ltd.) can be used to assess the nitrogen status of rice from maximum tillering to panicle initiation stage of growth. The meter measures the amount of light absorbed by the green pigments, mainly chlorophyll, in rice leaves. Because the amount of chlorophyll is closely related to leaf N content, the meter provides information similar to that provided by conventional leaf sampling and laboratory determination of leaf N content. This information can be useful in deciding whether or not to topdress with N fertilizer.

Advantages of the meter over conventional leaf analysis are the ability to assess plant N status in the field (saving the time required for sample drying and analysis) and the ability to determine N status at many separate locations in a field. The meter has limitations. Before maximum tillering, up to 40-45 days after planting in early maturing cultivars, leaf greenness is not as consistently related to N content as at later stages of development. Critical values have not been as consistent at or before mid-tillering. Also, the meter reading is somewhat more affected by cultivar and stand density than is leaf N content.

Modified: 10 Sep 1998 Comments to jayoung@ucdavis.edu