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
Paddock
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).
Plant
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.
Where does it occur?
Soil type
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.
Management strategies
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?
Tissue test
Soil test
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..
