Techniques for using rice leaf color comparison chart

Rice leaf color chart helps decide when to add nitrogen, avoid fertilizing based on emotion. The correct way is to take about 20 representative leaves, compare the colors in the morning and use a threshold of 3 or 4 depending on the variety.

Summary: Fertilizing nitrogen according to field color with the naked eye is easy to make mistakes. A dark green field is not necessarily good, a slightly pale field is not necessarily lacking in fertilizer. The rice leaf color chart helps growers check nitrogen needs based on actual leaf color, thereby reducing over-fertilization, reducing pests and saving costs.

Applies to: paddy fields are growing, especially the tillering stage before tillering.
Duration: 15-20 minutes per field if sampled properly.
Difficulty level: Basic. The important thing is to choose the right leaves and compare the color with the right light.
Estimated additional costs: Very low; Just need a color chart and notes.

What is the rice leaf color chart used for

The rice leaf color chart is a tool to help determine whether the rice plant is lacking or having enough nitrogen. The darker the green rice leaves, the more protein they usually have, but if you only look at them with the naked eye, they will be easily affected by sunlight, cloud shade, rice variety and the observer's habits.

Use the color comparison chart to help:

Fertilize nitrogen according to plant needs.
Avoid over-fertilizing, which makes the rice soft and easy to fall.
Reduce the risk of rice blast, brown planthoppers and pests due to fields being too green.
Save fertilizer costs.
Fields ripen more evenly.

This table does not completely replace experience, but gives experience a more specific measurement point.

The best time to compare colors

The suitable time is 8:30-9:30 am. At this time the light is clear enough, but not too harsh like at noon.

When comparing colors:

Stand with your back to the sun.
Use your body to block direct light from the leaves.
Do not compare colors when the weather is too dark, rainy or sunny.
Do not fertilize immediately after fertilizing or spraying chemicals to wet leaves.

The wrong light makes the leaves look different. This is a common error that causes inaccurate results.

Select leaves to compare color

Do not take old leaves, diseased leaves or low lying leaves. The leaf to choose is the highest fully opened leaf on the rice bush, fully developed and healthy.

How to get sample:

Walk diagonally or in a W shape in the field.
Choose 5 representative points.
Each point takes about 4 cards.
A total of about 20 leaves per field.

Don't just take leaves from the banks, because the banks are often different from the middle of the field. Don't just take the best or worst rice, unless you want to test an unusual area in particular.

How to place leaves on the color comparison board

When comparing, place the leaf from one-third to two-fifths from the tip of the leaf on the palette. This is the leaf section for more stable and representative color.

How to do:

Place the leaves close to the color palette.
Quick comparison with colored cells.
Record the most recent color level.
Do this one at a time for about 20 leaves.
Average the results.

Don't look at one leaf for too long because your eyes can easily lose color perception. Color comparison needs to be fast, even and under the same lighting conditions.

Choose color threshold according to rice variety

After getting the average color, compare the threshold to decide whether to fertilize with nitrogen or not.

Varietal group	Reference color threshold	How to understand
Slow response variety, light green leaves	3	An average of 3 or less means there may be protein deficiency
Quick response variety, dark green leaves	4	An average of 4 or less may require additional fertilization

If the average color is less than or equal to the threshold, the field shows signs of nitrogen deficiency and can be supplemented as recommended. If the average color is higher than the threshold, there is no need to add nitrogen.

The specific amount of protein is usually printed on the back of the color chart. These instructions should be followed, combined with field conditions, soil type and growth stage.

Example of how to read results

Suppose the field uses light green leaf varieties, the threshold is 3. After comparing 20 leaves, the average color is about 2.8. This result is lower than the threshold, more nitrogen can be applied.

If the field uses a dark green variety, the threshold is 4. If the average color is 4.3, you should not fertilize more, even though the field does not appear to be too green. Adding more fertilizer at this time can easily cause excess nitrogen.

The key point is not to use the same threshold for all breeds. There are varieties whose natural leaf color is already light, and there are varieties whose leaves become dark green quickly after nitrogen fertilization.

Combined with field observation

The color chart shows nitrogen needs, but you still need to look at the overall field:

Is the sowing density thick or sparse?
What stage is rice in?
Does the field have pests or diseases?
Alum soil, light soil or alluvial soil.
How much fertilizer was applied before?
The weather is stable sunshine or prolonged rain.

If the field is suffering from severe blast or brown planthopper disease, do not rush to apply nitrogen just because the leaf color is low. The cause needs to be treated first, because adding nitrogen can make the disease worse.

Checklist uses color comparison table

[ ] Check colors at 8:30-9:30 am.
[ ] Stand with your back to the sun.
[ ] Get about 20 leaves from 5 spots in the field.
[ ] Choose the highest fully opened leaf.
[ ] Place the segment 1/3 to 2/5 from the tip of the leaf on the board.
[ ] Record each result and calculate the average.
[ ] Use a threshold of 3 or 4 depending on the variety.
[ ] Only apply nitrogen when the average color is equal to or lower than the threshold.

Common mistakes

Compare color in strong sunlight: leaf color is brighter than reality, easy to misjudge.

Taking leaves from the edge: results are not representative of the whole field.

Choose old or diseased leaves: leaf color does not accurately reflect nitrogen needs.

Use one threshold for all varieties: light green and dark green varieties respond differently.

Nitrogen fertilization even though the color has exceeded the threshold: beautiful green fields at first but susceptible to pests, falling and uneven ripening.