Diagnosing potassium deficiency in field peas
Field peas have a high potassium (K) requirement, but deficiency has been rare because they are mainly grown on heavy textured soils.
What to look for
- Smaller plants with necrotic spots on older leaves
- Symptoms are worse on lighter soils with less affected plant in patches (livestock manure), or lines (harvest rows).
- The earliest symptom is pale grey necrosis of leaf veins (particularly the midrib) of the second oldest leaf.
- This is followed by older leaf pale to pink necrotic spots, that spread until the leaf shrivels and dies.
- New growth is darker than normal.
What else could it be
|Diagnosing soil acidity in field peas||Older leaf pale necrosis.||Necrotic leaf patches rather than pinkish spots, stunted roots.|
|Diagnosing boron toxicity in field peas||Older leaf pale necrosis.||Marginal necrosis rather than pinkish leaf spots; occurs on heavy alkaline soils.|
|Diagnosing group C herbicide damage in field peas||Older leaf pale necrosis.||Marginal necrosis rather than pinkish leaf spots; occurs soon after emergence.|
|Diagnosing zinc deficiency in field peas||Older leaf pale necrosis.||Marginal necrosis rather than pinkish leaf spots; occurs on heavy alkaline soils.|
Where does it occur?
- Sandy soils and deep grey sandy duplex soils tend to be more susceptible to K deficiency.
- High rates of hay or grain removal can result in K deficiency.
- Top-dressed or banded K fertilisers will correct the deficiency
- Excessive K fertiliser leaching can occur if applied earlier than four weeks after sowing on very sandy soils in high rainfall areas, because roots are not yet sufficiently developed to capture all of the K.
- Potassium chloride can be toxic when drilled with the seed.
- Grain potassium removal (3.4 kg of K per tonne of grain), is a guide to long term K requirements on marginal soils.
How can it be monitored?
- Use whole-top plant test to diagnose suspected potassium deficiency.
- Potassium soil test values have not been established in Western Australia as deficiency was not observed..
Where to go for expert help
+61 (0)8 9690 2174
Page last updated: Wednesday, 13 May 2015 - 4:12pm