Response of Crops to Nutrient Imbalances

What is nutrient imbalance?

• When a plant does not get nutrients in the right amount.
• It may be:
  1. Deficiency – too little nutrient.
  2. Toxicity – too much nutrient.
  3. Wrong proportion – one nutrient affects the availability of another.

How do crops respond?

1) Morphological (visible changes)

• Plant becomes stunted / small.
• Poor tillering in cereals.
• Roots do not grow well.
• Leaves change color (yellow, purple, necrosis, scorching).
• Flowers and fruits drop.
• Special disorders:
  • Whiptail in cauliflower (Mo deficiency).
  • Blossom-end rot in tomato (Ca deficiency).
  • Khaira disease in rice (Zn deficiency).

2) Physiological (inside plant functions)

• Photosynthesis reduces (less chlorophyll).
• Enzymes stop working properly (Mo needed for nitrate reductase, Fe for chlorophyll).
• Nodulation in legumes fails if Mo, Fe, P are deficient.
• Poor nutrient transport inside plant.
• Membranes and cell walls weaken (Ca, B important here).

3) Biochemical

• Plants make anthocyanin pigment (purple color) in P deficiency.
• Organic acids secreted by roots (P deficiency).
• Protein quality changes if S or N is deficient.

Where deficiency shows first?

• Mobile nutrients (move inside plant): N, P, K, Mg, Mo → Symptoms appear on older leaves first.
• Immobile nutrients (cannot move): Ca, S, Fe, Zn, Cu, B, Mn → Symptoms appear on young leaves / new parts first.

Examples of Nutrient Deficiency Symptoms

Nutrient Interactions (important facts)

• Excess P → Zn deficiency.
• Excess K → Mg deficiency.
• N and S work together (for protein quality).
• Ca and B are linked (both needed for cell wall and fruit quality).

Crop-Specific Sensitivity

• Rice → Zn deficiency (Khaira), Fe toxicity in waterlogged soils.
• Wheat → Zn and S deficiency.
• Maize → P deficiency (purple leaves).
• Mustard & oilseeds → S deficiency (low oil %).
• Pulses → Mo and Fe deficiency (poor nodulation).
• Tomato → Ca deficiency (blossom-end rot).
• Cauliflower → Mo deficiency (whiptail).
• Apple → Ca deficiency (bitter pit).
• Citrus → Fe, Zn, Mn chlorosis.

Effect on Plants

General Effects of Deficiency

• Growth slows down → small plants, fewer tillers, fewer leaves.
• Leaves show patterns → yellowing (chlorosis), browning (necrosis), purpling, or striping.
• Roots → become weak, less branched, shallow.
• Flowers & fruits → drop early, poor seed set, low quality.

General Effects of Excess (Toxicity)

• Leaf burn / necrosis (too much salts).
• Nutrient antagonism → excess of one blocks another (e.g., excess K → Mg deficiency).
• Delayed maturity (too much nitrogen).
• Soil acidification → excess ammonium fertilizers.
• Salinity & osmotic stress → too much soluble nutrients/salts.

Specific Nutrient Imbalance Effects

• Nitrogen (N) Deficiency: pale yellow old leaves, poor tillering. Excess: lush green plants, soft stems, more pest/disease attack.
• Phosphorus (P) Deficiency: purple leaves, late flowering. Excess: induces Zn deficiency.
• Potassium (K) Deficiency: yellow/brown leaf edges, poor grain filling. Excess: suppresses Mg and Ca.
• Calcium (Ca); Deficiency: tip death, blossom-end rot (tomato). Fruits become soft → poor storage.
• Magnesium (Mg); Deficiency: yellow stripes between veins (old leaves).
• Sulphur (S); Deficiency: pale young leaves, thin stems, low oil content.
• Zinc (Zn); Deficiency: Khaira disease (rice), little leaf (cotton). Excess: Fe deficiency.
• Iron (Fe); Deficiency: yellowing of young leaves with green veins. Excess: bronzing in rice under waterlogging.
• Boron (B); Deficiency: hollow stem, fruit cracking, poor pollination.
• Molybdenum (Mo); Deficiency: whiptail in cauliflower, poor nodulation in legumes.
• Copper (Cu); Deficiency: dieback in citrus, pale young leaves.
• Manganese (Mn); Deficiency: grey speck in oats, mottling in sugarcane. Excess: small necrotic brown spots in leaves.

Stage-wise Sensitivity

• Early growth stage → P, N, Zn deficiencies show first.
• Flowering stage → B, Ca, Mo deficiencies affect pollination & fruit set.
• Grain filling stage → K, N, S deficiencies reduce yield & quality.

Quality Effects

• N & S → protein/oil content.
• K → sugar, starch, fruit storage.
• Ca & B → fruit firmness, storage life.
• Zn & Fe → grain size, human nutrition value.

Key Memory Aids

• Purple leaves → P deficiency.
• Khaira disease in rice → Zn deficiency.
• Whiptail in cauliflower → Mo deficiency.
• Blossom-end rot in tomato → Ca deficiency.
• Bitter pit in apple → Ca deficiency.
• Grey speck in oats → Mn deficiency.
• Hidden hunger → no visible symptoms but yield loss.
• Luxury consumption → excess uptake without yield benefit (common in K).
• Critical nutrient concept → minimum concentration below which yield drops sharply.