Rusty-water paddies: ferrous iron poisoning
An oil film and rusty water are not a nitrogen shortage.
- Rusty water, sometimes an oil film, rice yellow and stalled, roots black.
- Not a dryland maize story.
- Nitrogen shortage still has white roots; ferrous toxicity has black roots and rusty water.
- Waterlogging is no air; rusty-water fields often stack acid and ferrous iron.
- Don’t treat rusty water as nitrogen hunger; don’t keep deep water without an airing.
- Dry the field: Follow the growth stage and the station. Let the roots breathe
- Name what you see before you feed.
- If leaves, roots and the surface disagree, stop.
What you see in the field
Rusty water, sometimes an oil film, rice yellow and stalled, roots black. Not a dryland maize story.Walk the worst strip. Pull one plant, rinse the roots at the ditch without rubbing the tips, and read white tips versus brown bald ones. A rusty film on water is extra, not required. Grain land and tea do not share a pH target.
Tap to enlarge. The caption says what to photograph. Missing field photos are marked as to-be-added.
Why it looks like this
The field looks like this because the root cannot take water or nutrients the usual way. Fix the soil condition first — drainage, salt, acidity, compaction or a salt of fertiliser — then a thin feed. Rates live in the range on this page; confirm with a local station and the label.
Easy to mix up
Looks like “Nitrogen shortage”
Nitrogen shortage still has white roots; ferrous toxicity has black roots and rusty water.
Looks like “Ordinary waterlogging”
Waterlogging is no air; rusty-water fields often stack acid and ferrous iron.
Do this / don’t do that
- 1Rusty water, sometimes an oil film, rice yellow and stalled, roots black. Not a dryland maize story.
- 2Drain and expose soil for air. Test pH. If acid, lime a little per the acid guide. Thin feed only after new roots.
- 3Don’t treat rusty water as nitrogen hunger. Use the range on this page only as a range. Confirm with a local station and the product label.
Don’t do this first
- Don’t treat rusty water as nitrogen hunger; don’t keep deep water without an airing.
Rate range
Dry the field
Follow the growth stage and the station
Let the roots breathe.
A drain
Ditches inside the field must connect
Rusty water must have a way out.
These are ranges. Confirm with your local extension station and the product label.
How soon after a spray or a feed it showed
A 1–3 day burst looks more like spray injury / fertiliser burn.
When you see Rusty water, test. Take soil from the bad patch and from a greener neighbour, separately.
Lesson video
2026-03-06 · Li Zeyu · For learning. Serious damage: local agronomist or a soil test.
For learning only. Fertiliser and pesticide decisions need a local agronomist and a soil test.
Not sure? Photograph the field to identify the problem