With potassium deficiency leaf margins of the older leaves turn pale yellow or sometimes bronze. With ongoing deficiency cholorosis spreads over the whole leaves.
Made worst by
Acidic soils (low pH). Sandy or light soils (leaching). Drought conditions. High rainfall (leaching). or heavy irrigation. Heavy clay (illite) soils. Soils with low K reserves. Magnesium rich soils.
Larger leaf area maintaining through season. Shoot growth more vigorous. Fruit load increase/benifit to yield. Fruit are larger with better colour, skin texture and flavouring (more acidity). Level of vitamin C increases.