Exchangeable sodium
Alkali is sodium, not every white crust.
Also called: Ex-Na, exchangeable Na
Speed
- Exchangeable sodium is the alkali question.
- White crust is salt. High Na is sodicity.
- Read it with CEC.
- Don’t gypsum every white crust.
How it appears on the sheet
The sheet says exchangeable sodium or Ex-Na, often cmol/kg. Not the same cell as total salt or EC.
A sketch. Do not fertilise from the picture alone.Common units
Exchangeable Na often cmol/kg; ESP is usually %.
Soil:water ratio · ESP needs CEC too. A high Na with a high CEC is a different percentage.
How to read the number
Sodium breaks crumbs. Gypsum is not for every white crust — only when Na is high and calcium is relatively low.
Rates live in the saline-alkali guide.
Thresholds only, not a prescription. Rates live in the field guide. This page does not hand you a bag count.
| Cell | Low | Mid | High |
|---|---|---|---|
| Exchangeable Na (sketch) | Few seats, not the alkali driver | Read as a percentage of CEC | Poor structure; drain before gypsum |
Regional classes differ. This table is a comparison, not a prescription.
What it looks like in the field
Slick, sticky, poor structure, not always a thick crust — often sodium.
Don’t do this
- Don’t mix Na with total salt.
- Don’t gypsum every crust.
- No drain, no flood.