Nutrient Deficions in plants 

 A Quick  Guide

Symptoms appear first in the oldest leaves:

Nitrogen         : general yellowing; stunting; premature maturity
Magnesium     : patchy yellowing; brilliant colours especially around edge
Potassium       : schorced margins; spots surrounded by pale zones
Phosphorus    : yellowing erect habit; lack lustre look; blue - green, purple colours
Molybdenum  : mottling over whole leaf but little pigmentation; cupping of leaves and distortion of stems
Cobalt            : legumes only, as for nitrogen 
( excess salt  marginal scorching, generally no spotting )  


taken from food from plants by csiro division of soils