When rice is most vulnerable
From active tillering through panicle initiation. N demand peaks between mid-tillering and booting; a shortage in this window caps the maximum yield the crop can reach.How nitrogen deficiency shows in satellite data
- NDRE is the leading indicator. NDRE is sensitive to chlorophyll and leaf N content and responds before visible symptoms are obvious.
- NDVI is also low, but NDVI saturates in dense canopies while NDRE keeps discriminating - use NDRE from tillering onward.
- Pattern is uniform across the field or across whole management zones, not patchy - if it is patchy, suspect salinity, poor soil, or biotic stress instead.
- The whole crop looks pale green from the air; the darker green reference strip (if you leave one) stands out clearly.
Field symptoms
- Uniform pale-green to yellow canopy, oldest leaves first
- Reduced tillering and narrow leaves
- Stunted growth and delayed heading
- Older leaves die back from the tip while younger leaves stay greener (N is mobile in the plant)
- Small panicles and reduced grain filling
Reduce the damage by
- Split N application - avoid applying all N at basal; split into basal, active tillering, and panicle initiation.
- Use a leaf color chart (LCC) or SPAD meter to time top-dressing to actual crop need. This documentation publishes no threshold to read either against — see below.
Leaf colour readings are recorded, not interpreted
The field walk protocol asks a scout to take an LCC or SPAD reading at every stop and record the number. The platform stores that reading and does not turn it into a verdict, because the threshold it would be read against is not settled.Why there is no threshold here yet
Two Malaysian sources give different trigger panels, and neither states the one thing that would make a panel number portable.
Until the panel count and the source conflict are resolved, a leaf colour reading is evidence for the agronomist reading the record, not an input the platform acts on. Recording it is still worth doing: it builds the block history that a later calibration would need.
An LCC reading may not be averaged
An LCC panel number is ordinal. Panel 4 is not twice panel 2, and the steps between panels are not equal, so a mean of panel numbers is arithmetic on a rank and means nothing. Where several stops are summarised, the block carries a distribution — how many stops read at each panel — in the same way a scope spanning several bands carries a distribution rather than a band. See How a band resolves. SPAD is different and may be averaged. The meter returns a continuous chlorophyll index, not a rank. The two are named together throughout this documentation because they answer the same question, but they are not the same kind of number and do not aggregate the same way.- Correct water management - N loss through volatilization and denitrification is very high in flooded rice; incorporate urea into soil and maintain shallow standing water.
- Use deep placement of urea briquettes where available - major reduction in N loss.
- Grow a legume in rotation or as green manure to build background soil N.
Set an alert for early warning
Recommended settings for nitrogen on rice:- NDRE threshold alert - trigger when field-average NDRE falls below your fertile-strip baseline during tillering.
- NDRE zone alert - flag zones that stay one standard deviation below the field mean for two consecutive passes; these are candidates for variable-rate top-dressing.
Related
- Rice Diagnosis
- Create variable-rate prescription maps - turn NDRE zones into an N prescription.
- Set up automated crop alerts