Diagnosing nodule dysfunction in narrow-leafed lupins
Nitrogen deficiency from nodule dysfunction can be caused by lack of Rhizobia, soil conditions, herbicide toxicity, or molybdenum or cobalt deficiency.
What to look for
- Smaller paler plants, with severity often varying with soil type.
- Plants frequently recover in spring.
- Smaller paler plants with thinner stems and fewer laterals.
- Nodules are reduced or absent.
- If nodules are present they are small, and when split have pale or white, rather than pink interiors.
- Plants frequently recover in warmer weather as plant growth increases and nodules form on laterals.
What else could it be
|Diagnosing waterlogging in narrow-leafed lupins and field peas||One cause of nodulation failure||Waterlogging causes premature plant death if sustained|
|Diagnosing potassium deficiency in narrow-leafed lupins||Smaller pale plants||Nodules present|
Where did it come from?
Possible causes are:
- Lack of suitable rhizobia. This is rare on soils suitable for lupins as lupin rhizobia live freely in all but very alkaline soils. Nodules will be absent. Other causes below tend to result in small white or green nodules.
- Residual herbicides can prune fine roots and reduce nodulation.
- Cold or wet conditions inhibit nodulation formation and function, but plants generally recover when in warm well-drained conditions.
- Molybdenum deficiency that causes scattered affected plants amongst normal ones on acidic sandy soils.
- Rhizobia require cobalt for effective nodule function, but it is not a plant nutrient. Nodulation responses are very rare but have occurred on Swan coastal plain sands.
How can it be monitored?
- Check roots for nodules with a pink interior.
- There is no reliable soil test for molybdenum or cobalt deficiency.
- Use youngest fully-emerged leaf to test for molybdenum. Levels less than 0.005 mg/kg indicate deficiency. Take paired good/poor plant samples when possible.
Page last updated: Thursday, 5 February 2015 - 3:08pm