It is often quite difficult to identify a deficiency or toxicity symptom in the field because they never really occur as a single element deficiency or toxicity. Each of the elements are inter dependent and they influence each other within certain ratio’s. One would find for instance that phosphorus toxicity, is expressed as either a zinc or copper deficiency because of the suppressing effect phosphorus has on the uptake of these two elements.

The tables below provide a basic summary of the effects of deficiencies or toxicities on most vegetable crops with the emphasis on lettuce. The table should be used as a basic reference point from where one would develop further theories of what is wrong with the plant.

Some of the deficiency and toxicity symptoms of micro elements found in lettuce are provided in the second table.

A summary of the effects of toxicities and deficiencies of five macro elements.
NitrogenLight green leaves
Lower leaves yellow
Stalks short & slender
Older leaves affected first
Younger leaves remain green
No head forms with severe deficiency
Has very dens root system
Leaves very dark green
Restricted root system
Ammonia: necrotic leaves leaving only the veins green
Leaves are small and resemble spinach in form
PhosphorusStunted abnormal dark green
No specific symptoms to identify
Purple pigmentation under leaves
No necrosis tissue
Yellowing of older leaves
Older leaf tips become yellow
Leaf abscission develops
Copper & zinc deficiency are more likely to appear
Iron precipitates in water especially at low pH
PotassiumWeak plant
No resistance to water stress
Sodium replaces K on short term
Older leaves first
Chlorosis at leaf tips and between veins
Growth is stunted
Small leaves
Leaves are less crinkled
Purple leaf margins
Induces a deficiency symptom of other elements.
CalciumGrowth severely stunted
Leaf have open rosette growth
Interveinal white spots near margins of mature leaves
Leaves more crinkled than normal
Plant growth is also flat
Older leaves curl downwards
Leaves are brittle
Chlorosis and later necrosis in leaf margins
Could be induced by high potassium
Hardly ever shown as Ca toxicity
Rather expresses in terms of Fe, K or Mg effects
MagnesiumVery mobile element
Symptoms first in younger leaves
Symptoms fist as interveinal chlorosis
Moderate deficiency – overall plant colour is light green
Leaves have mottled appearance
Plants are smaller
Margins curl upwards
Yellow spots in interveinal areas
Green margin even in severe cases
Induced by high potassium, calcium, ammonium or low pH
Marginal scorching
Dark green leaves
Very rare
SulphurS and N are closely related in metabolism
Symptoms are closely related to N
Deficiencies are rare
Plants stunted and woody
Heart of plant light green
Leaves are thicker
Anthocyanin discolouration on leaf edges
Plants are tolerant of high sulphur
Symptoms do not show up to 600ppm in solution
Plants feel hard
Leaves bluish green
Extreme cases leaf margins brown
High S content limits Ca uptake
Induces Mo deficiency
A summary of the effects of deficiencies and toxicities of six micro elements found in lettuce. Micro elements are found and consumed in small quantities but their effect can sometimes be more devastating and prominent than macro elements. We mostly focus on the macro elements in nutrition, ignoring the importance of micro elements and keeping their levels optimally.
IronInfluences new growth
Interveinal chlorosis of young leaves
Whole plant is light green
Growth is stunted and stops
Check excessive manganese
Veins remain green initially
Fe deficiency is usually induced
Low oxygen content can induce Fe deficiency
Leaves are less crinkled
Check for anthocyanin discolouration in young leaves
Very rare phenomenon
Spotting of leaves initially
Total browning of leaf later
BoronImmobile in plant
Restricted root growth
Plant darker than normal
Young leaves hard and rounded
Brown spots at growth points
Growth point dies with severe deficiency
Poor root development
Plants have dwarf appearance
Can be confused with tip burn
Leaves appear scorched at margins
Necrotic spots feels papery
Symptoms in older leaves first
Toxicity in older leaves first
Leaf margins turn yellow, cup downward
ManganeseRelative immobile in plant
Entire plant light green to yellow
Young leaves are smoother
Overall pale appearance
Older leaves may become chlorotic
Veins always remain green vs. Fe where the become pale to white
Leaves show marginal chlorosis
Spots on older leaf margins
Spots coalesce from margin inwards
Older leaves may die
Young leaves are stunted
Heads are loose
ZincCareful with P fertilizer
Induced by P fertilization
Upper internodes remain short
Rosette appearance (like a Rose)
Growth stunted
Leaf margins show necrotic spots
Can be mistaken for chemical scorch
Older leaves first
Plant has brown-green colour
Growth stunted
Middle leaves red-brown spots
No head forms with acute toxicity
Leaves are long and narrow
Older leaves yellow and die
CopperLeaves become elongated and cupped
Interveinal chlorotic blotches
Plant remains small
Leaf margins turn up
Chlorosis along edges
Leaves wilt at a later stage
No heads form
Expresses as Fe chlorosis
MolybdenumPale distorted very narrow leaves
Interveinal yellowing
Plants are stunted
Leaf wither from margins and tip
Necrotic spots appear and coalesce
Symptoms progress from old to young leaves
Root growth stunted
Plants can collapse entirely