Gypsum for alkali, leaching for salt — they are not the same job
White crust is salt. Slick hard cap is more sodium.
- High pH, smears wet and sets hard dry, poor emergence — that looks sodic.
- Gypsum is for alkali, not every white crust.
- Salty soil is high EC, pH not always very high; alkali soil is high pH and poor structure.
- Lime is for acid soil; lime on alkali soil makes it more alkali.
- Don’t gypsum an acid soil; don’t high-rate gypsum without an outlet.
- Agricultural gypsum: Follow a soil test. Commonly tens to a hundred-plus kg per mu. Must be tested; pair it with washing salt
- Name what you see before you feed.
- If leaves, roots and the surface disagree, stop.
What you see in the field
High pH, smears wet and sets hard dry, poor emergence — that looks sodic. Gypsum is for alkali, not every white crust.Squat on the whitest, worst strip and scrape the crust. Compare with a neighbour that is still green. White crust plus scorched margins count; wilt without a crust may just be drought. Note whether the ditch actually runs.
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 “Ordinary salty soil”
Salty soil is high EC, pH not always very high; alkali soil is high pH and poor structure.
Looks like “Acid soil treated with lime”
Lime is for acid soil; lime on alkali soil makes it more alkali.
Do this / don’t do that
- 1Compare the worst plants with a neighbour ridge. Photograph whole plant, close-up and soil surface before you add fertiliser.
- 2Match roots, leaves and the soil surface to this guide. If they do not line up, do not copy a bag count.
- 3Use the rate range on this page only as a range. Confirm with a local station and the product label.
Don’t do this first
- Don’t gypsum an acid soil; don’t high-rate gypsum without an outlet.
Rate range
Agricultural gypsum
Follow a soil test. Commonly tens to a hundred-plus kg per mu
Must be tested; pair it with washing salt.
Drainage
Sodium only washes if there is an outlet
No drain, no large rate.
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 High pH, test. Take soil from the bad patch and from a greener neighbour, separately.
Lesson video
2026-03-09 · 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