Exchangeable Al
Exchangeable aluminium is the toxic ion in very acid soil. The job is lime and organic matter, not more nitrogen.
- Exchangeable aluminium is the toxic ion in very acid soil.
- Below about pH 5.5 it dissolves and injures root tips.
- Brown, bald tips with few white points, then the top stalls.
- The job is lime and organic matter, not more nitrogen.
How it appears on the sheet
Below about pH 5.5, aluminium dissolves and injures root tips: brown, bald, few white tips. Then the shoot stalls.
A sketch. Do not fertilise from the picture alone.Common units
Exchangeable Al often cmol/kg. It becomes active when pH is low.
How to read the number
Below about pH 5.5, aluminium dissolves and injures root tips: brown, bald, few white tips. Then the top stalls. Southern red-yellow earth, tea, and ammonium-N grain fields show it.
Hunger keeps a root, just thin; aluminium injures the tip. Wash roots before you add fertiliser. The job is lime and organic matter, not more nitrogen. Tea likes acid, not ever-more-acid.
Thresholds only, not a prescription. Rates live in the field guide. This page does not hand you a bag count.
What it looks like in the field
Below about pH 5.5, aluminium dissolves and injures root tips: brown, bald, few white tips. Then the top stalls.
Don’t do this
- Urea on bald roots.
- Liming by hearsay without a pH.
- Hunger keeps a root, just thin; aluminium injures the tip. Wash roots before you add fertiliser.