Nutrient Interactions

Nutrient interactions = effect of one nutrient on uptake, availability, or function of another nutrient.
Types → Synergistic (positive), Antagonistic (negative), Independent.

Synergistic Interactions (Positive effect)

One nutrient improves availability or uptake of another.

• N × P: N application enhances P uptake.
• N × S: Both needed for protein synthesis (S = component of amino acids; N = proteins).
• P × Zn (at optimum level): Improves plant metabolism.
• Ca × B: Required together for cell wall stability, root & meristem growth.
• Mo × N: Mo essential for nitrate reductase and N fixation in legumes.

Antagonistic Interactions (Negative effect)

One nutrient reduces availability or uptake of another.

• P × Zn: High P induces Zn deficiency (common in rice, maize, wheat).
• P × Fe & Mn: High P causes Fe & Mn deficiencies in calcareous/alkaline soils.
• K × Ca & Mg: Excess K suppresses Ca and Mg uptake.
• Ca × B: Excess Ca reduces B uptake.
• Zn × Cu: Excess Zn reduces Cu absorption.
• N × K: Imbalance reduces efficiency of both.

Independent Interactions; No significant effect on each other’s uptake. Example: Mo × Cl – function independently.

4. Special Cases for India (Emerging Issues)

• High P use (DAP, SSP) → induces Zn, Fe, Mn deficiency.
• High K fertilization → leads to Mg deficiency in light soils.
• Excess liming (Ca) → induces B deficiency in acid soils.

Key Exam Pointers (ASRB NET Agronomy):

• Most common antagonism: P × Zn.
• Protein synthesis interaction: N × S.
• Legume nodulation dependency: Mo × N.
• Root & meristem growth: Ca × B.

Diagnostic Techniques

Visual Diagnosis

• Simple & immediate but sometimes misleading.
• Examples:
  • N → yellowing of older leaves
  • Fe → yellowing of young leaves
  • Zn → Khaira disease in rice
  • Mo → Whiptail in cauliflower

Soil Testing

• Measures available nutrient status of soils.
• Common methods:
  • Olsen’s method → P (alkaline soils)
  • Bray’s method → P (acid soils)
  • DTPA extraction → Zn, Fe, Cu, Mn
  • Hot-water method → Boron

Plant Tissue / Leaf Analysis

• Measures nutrient concentration in plant parts.
• Based on critical concentration concept.
  • Example:
    • N → 1.5–5.0%
    • Zn → 20–100 ppm
    • Mo → 0.1–1 ppm

Advanced / Modern Techniques

• SPAD meter: Measures leaf greenness (N status).
• Leaf Colour Chart (LCC): Field tool for N management in rice.
• DRIS (Diagnosis & Recommendation Integrated System): Nutrient balance indices.
• CND (Compositional Nutrient Diagnosis): Multivariate approach for nutrient ratios.
• Remote sensing / spectral imaging: Detect nutrient stress at field scale.

Emerging Nutrient Deficiencies in India

Due to intensive cropping, HYVs, high NPK use, low organic matter, and neglect of secondary & micronutrients, several deficiencies are now widespread:

Secondary Nutrients

• Sulphur (S):
  • Most common secondary deficiency in India.
  • Affects oilseeds, pulses.
  • Deficiency: Uniform chlorosis of younger leaves.
• Calcium (Ca):
  • Deficient in acid soils, high rainfall areas.
  • Deficiency: Death of meristems, blossom end rot (tomato).
• Magnesium (Mg):
  • Deficient in sandy soils, under high K application.
  • Deficiency: Interveinal chlorosis of older leaves.

Micronutrients

• Zinc (Zn):
  • Most widespread micronutrient deficiency in India.
  • Seen in rice, wheat, maize.
  • Deficiency: Khaira disease (rice), rosetting in maize.
  • Cause: High P fertilization, alkaline soils.
• Iron (Fe):
  • Common in calcareous & alkaline soils.
  • Deficiency: Interveinal chlorosis in young leaves.
• Boron (B):
  • Deficiency increasing in acidic soils of NE India, Odisha, WB.
  • Deficiency: Brown heart (beet), hollow stem (cauliflower).
• Molybdenum (Mo):
  • Deficiency in acid soils.
  • Deficiency: Whiptail in cauliflower, poor nodulation in legumes.
• Copper (Cu):
  • Deficiency in sandy soils of Rajasthan, MP.
  • Deficiency: Dieback, exanthema in citrus.

Management Approaches

• Balanced fertilization (N:P:K = 4:2:1).
• Use of fortified fertilizers: Zn-coated urea, S-fortified SSP.
• Foliar sprays for quick correction (ZnSO₄, FeSO₄, Borax, etc.).
• Biofertilizers & organic manures.
• Nano-fertilizers (emerging technology).
• Integrated Nutrient Management (INM).

Key Exam Notes (ASRB NET Agronomy):

• Most widespread micronutrient deficiency in India → Zinc.
• Most common secondary nutrient deficiency → Sulphur.
• Mo deficiency symptom → Whiptail in cauliflower.
• Tools: SPAD (N), LCC (rice), DRIS (nutrient balance).
• Soil test: DTPA for Zn, Fe, Mn, Cu; Hot water for B.