Fertilizer consumption in India has increased significantly in recent years. However, this increase has not translated to a proportional rise in crop productivity due to deficiencies in secondary and micronutrients and declining soil fertility. With the target of producing 300 MT of food grains by 2025, enhancing crop productivity is critical, given the limited scope for expanding cultivated land. This underscores the importance of developing fertilizer best management practices to address nutrient deficiencies and improve fertilizer use efficiency.
Secondary Nutrients for Enhancing Nutrient Use Efficiency and Yield
Secondary nutrients such as Calcium (Ca), Magnesium (Mg), and Sulphur (S) are as essential for plant nutrition as primary nutrients. While required in smaller quantities, these nutrients play a crucial role in optimizing crop yields.
1. Calcium (Ca)
Role:
- Absorbed as Ca²⁺ ions, calcium improves nutrient absorption and translocation in plants.
- Activates growth-regulating enzymes and contributes to cell wall formation and division.
- Prevents toxic effects of aluminum and manganese in acidic soils by neutralizing their impact.
Symptoms of Calcium Deficiency:
- Death of terminal buds and root tips.
- Premature shedding of blossoms and buds.
- Weak stems and discolored, water-soaked areas on fruits (e.g., blossom-end rot in tomatoes, bitter pit in apples).
Recommendations:
- Foliar Spray: 1% calcium nitrate.
- Specific Crops:
- Grapes: Chelated EDTA calcium (0.2%) + Boric acid (0.1%) during early berry development.
- Tomato: Soil application of calcium sulfate (1-2 kg/acre); Foliar application of calcium chloride (0.5%).
- Flowers (e.g., roses, carnations): Use calcium nitrate.
Sources of Calcium Fertilizers:
| Source | Calcium Content (%) |
|---|---|
| Gypsum | 23.3 |
| Calcium nitrate | 19.4 |
| Calcium chloride | 15.0 |
| SSP (Single Super Phosphate) | 20.0 |
2. Magnesium (Mg)
Role:
- Absorbed as Mg²⁺ ions, magnesium is vital for photosynthesis as it is a core component of the chlorophyll molecule.
- Activates plant enzymes required for growth and helps balance the high potassium levels from fertilizers.
Symptoms of Magnesium Deficiency:
- Interveinal chlorosis in older leaves.
- Leaf curling along margins.
- Marginal yellowing along the midrib.
Recommendations:
- Soil Application: Magnesium sulfate or magnesium chloride (20 kg/ha for cotton).
- Foliar Spray: Magnesium sulfate (1%).
Sources of Magnesium Fertilizers:
| Source | Magnesium Content (%) |
|---|---|
| Magnesium sulfate | 9-20 |
| Dolomite | 20 (as MgCO3) |
| Potassium magnesium sulfate | 11 |
| Magnesium nitrate | 16 |
3. Sulphur (S)
Role:
- Absorbed as sulfate (SO4²⁻), sulfur is crucial for amino acid and protein synthesis.
- Plays a role in photosynthesis, nitrogen fixation, and the nitrate-reduction process.
- Essential for winter hardiness in crops and healthy growth in legumes.
Symptoms of Sulphur Deficiency:
- Retarded growth and delayed maturity.
- Yellowing of young leaves (immobile in plants).
- Stunted plants with general yellowing similar to nitrogen deficiency.
Recommendations:
- Foliar Spray: 1% potassium sulfate (K2SO4), applied twice at fortnightly intervals.
- Soil Application: Elemental sulfur or gypsum (100 kg/acre).
- Fertilizer Options: Ammonium sulfate, single super phosphate (SSP), potassium sulfate, or sulfur-containing fertilizers.
Sources of Sulphur Fertilizers:
| Source | Sulphur Content (%) |
|---|---|
| Elemental sulfur | 90 |
| Ammonium sulfate | 23 |
| Single super phosphate (SSP) | 11 |
| Potassium sulfate | 17.5 |
| Gypsum | 18.6 |
Recommendations for Specific Crops
- Calcium:
- Grapes: Foliar spray of EDTA calcium (0.2%) with boric acid (0.1%) reduces berry cracking.
- Tapioca: Apply 25 kg zinc sulfate, 20 kg gypsum, and 10 kg borax per hectare.
- Magnesium:
- Cotton: Soil application of magnesium sulfate (20 kg/ha); foliar spray at 1% concentration.
- Sulphur:
- Foliar spray of potassium sulfate (1%) at fortnightly intervals for sulfur deficiency.
Conclusion
Secondary nutrients play a critical role in enhancing crop yields, ensuring nutrient use efficiency, and improving soil fertility. While they are often present in sufficient quantities, deficiencies in certain soils can significantly impact crop productivity. Timely soil tests and corrective applications of calcium, magnesium, and sulfur can prevent yield losses and enhance crop performance.
Dr. P. Malathi, Dr. K. M. Sellamuthu, Department of Soil Science & Agricultural Chemistry, Tamil Nadu Agricultural University, Coimbatore – 641 003.
