NDVI Values Explained: What Is Normal for Wheat, Rice, Cotton and Maize?
“Is this NDVI good for my crop?” needs more context than a single number. Start with the observation date, growth stage, amount of visible soil and quality of the image. Then compare areas within the same field. A value that accompanies sparse young plants can also occur after harvest or in a damaged mature crop; the number alone cannot distinguish them.
Start with the same-field comparison
Keep the field boundary consistent between observations. Identify a comparison area with a similar variety, sowing date, irrigation history and soil setting. Note whether the difference persists, but do not postpone a necessary inspection just to obtain another image. Clouds, shadows and recent operations can change the apparent pattern.
The summary on ndvi.us is estimated by matching rendered image colours to palette values. It is not a direct export of all native reflectance pixels. Read the methodology before using small numerical differences to compare dates.
Wheat: separate establishment from maturity
During establishment, exposed soil contributes strongly to the observation. Look for differences in stand and coverage, then inspect for uneven emergence. During vegetative growth, a lower-value zone is a reason to compare plants and soil with another area, not proof of nitrogen deficiency. Near maturity, declining greenness may be part of normal senescence. Record the actual crop stage rather than relying only on days since sowing.
Field check: compare plant density, tillering, leaf appearance, soil moisture and recent operations. If a nutrient issue is suspected, use local agronomic assessment and suitable measurements before selecting a rate.
Rice: consider water and canopy cover
Flooded or recently transplanted rice can have a low vegetation signal because the sensor sees water between plants. As canopy cover changes, the proportion of water and soil visible to the sensor also changes. A low value early in the crop does not by itself indicate failed establishment. During dense growth, NDVI becomes less sensitive to additional leaf area.
Field check: compare stand, water depth, growth stage, weeds and visible symptoms in both locations. Check whether a patch coincides with a low point or uneven establishment before deciding what it means.
Cotton: check crop structure and weeds
Wide rows can expose substantial soil early in the season. Later, high greenness does not establish boll number, boll quality or final yield. Green weeds can also contribute to the signal. A change after a planned field operation should be interpreted alongside that operation and the crop stage.
Field check: compare crop cover, weed cover, plant development and visible symptoms. Inspect leaves and plants directly if disease or pest pressure is suspected; an NDVI pattern cannot name the pest or pathogen.
Maize: remember dense-canopy saturation
A dense maize canopy can produce similar high NDVI values across areas that still differ in condition. Small differences at this stage may be difficult to interpret. Earlier observations can provide useful context about establishment, but they cannot substitute for current field observations.
Field check: compare plant population, development stage, leaf symptoms and soil conditions. Consider recent weather and irrigation. Do not convert an NDVI difference into a fertiliser recommendation without a locally appropriate assessment.
Why this guide does not prescribe a universal “normal” range
Variety, planting density, field size, soil background, processing method, illumination and crop stage all affect interpretation. The app's crop-stage ranges are illustrative references, not locally calibrated action thresholds. There is no single number on this page that authorises treatment.
A repeatable field record
- Record the field name, crop, stage and satellite date.
- Mark an area of concern and a comparison area.
- Record image-quality concerns and relevant field operations.
- Inspect both locations and write down observations separately from possible causes.
- Decide whether more evidence or local agronomic advice is needed.
- Revisit the same locations and compare another suitable observation when available.
Use the field checklist to keep these steps together. The aim is to make the next inspection more focused and better documented, not to replace it.
Interpretation and references
The map is a scouting aid. Displayed summaries are colour-derived estimates; cloud and shadow may remain after scene filtering. Check how ndvi.us works, and use the field checklist to record observations. Examples and suggested workflows are not verified field trials or guarantees of savings.