Precision in Top Dressing

Definition

Precision top dressing refers to applying fertilizers (mainly nitrogen) at the right time, in the right quantity, at the right place, and in the right form, based on crop demand, growth stage, and soil nutrient availability.
It is guided by the 4R Nutrient Stewardship Principle:

• Right Source – using suitable fertilizers (urea, ammonium sulfate, calcium ammonium nitrate)
• Right Rate – applying the correct quantity based on soil tests and crop requirements
• Right Time – applying at critical crop growth stages
• Right Place – band placement, side dressing, or fertigation rather than broadcasting

Objectives of Precision Top Dressing

• Maximize nitrogen use efficiency (NUE).
• Ensure nutrient availability during critical growth stages.
• Reduce losses due to volatilization, leaching, or denitrification.
• Enhance crop yield and quality.

Timing of Top Dressing

Critical growth stages for top dressing differ among crops:

Fact: Split N application can increase crop yields by 10–20% and reduce N loss by 15–25%.

Placement Methods

Precision top dressing focuses on placing fertilizer near the plant roots to improve uptake efficiency:

• Band Placement / Side Dressing – Urea or other N fertilizers placed 5–10 cm away from crop row, 7–10 cm deep.
• Fertigation – Fertilizer applied through drip irrigation for even distribution and minimum loss.
• Urea Super Granules (USG) – 2–5 g granules placed near root zone in rice fields to reduce N volatilization by 50%.
• Foliar Top Dressing (small N doses) – In crops with short growth duration or when soil application is not effective.

Tools and Techniques

• Leaf Color Chart (LCC) – Measures leaf greenness to determine N requirement in rice/wheat.
• SPAD Chlorophyll Meter – Real-time estimation of leaf N status.
• Drone-based application – Ensures uniform and precise distribution over large fields.
• Soil Testing & Sensor-based recommendations – Guides exact dose for each plot.

Fact: LCC-guided N application saves 15–25% urea without reducing yield in rice.

Advantages

• Increases crop yield by providing N during critical stages.
• Improves N use efficiency (NUE) – reduces losses to the environment.
• Reduces production cost by avoiding over-application.
• Reduces risk of lodging in cereals by preventing excess N at early stages.
• Compatible with precision farming technologies (LCC, SPAD, drones, fertigation).

Limitations

• Requires skilled labor to determine timing and dose.
• Needs monitoring tools (LCC/SPAD), which may not be available to all farmers.
• Uneven application in large fields if manual methods are used.
• Not suitable for extremely water-stressed fields where fertilizer uptake is limited.

Key Facts

• USG in transplanted rice fields improves NUE by 15–20% compared to broadcasting.
• Split N application in wheat can increase grain yield by 15–20% and protein content by 1–2%.
• Precision top dressing is a major component of Integrated Nutrient Management (INM).

Precision in Foliar Application

Definition

• Foliar application is the process of spraying nutrients directly on the leaves of crops, allowing plants to absorb nutrients through the leaf cuticle and stomata.
• Precision foliar application means delivering the right nutrient, at the right concentration, at the right time, and in the right manner, based on crop growth stage and nutrient requirement. It ensures maximum efficiency, minimal waste, and targeted correction of nutrient deficiencies.

Rationale for Foliar Application

• Rapid Correction of Nutrient Deficiency: Leaves absorb nutrients quickly, which is crucial for short-duration deficiencies.
• Avoid Soil Constraints: Useful in soils with poor nutrient availability, high pH (iron, zinc), or waterlogging where roots cannot absorb efficiently.
• Precision Nutrient Supply: Allows targeted application in critical growth stages for yield and quality improvement.

Fact: Foliar application of Zn and Fe in cereals can increase grain yield by 8–15% in deficient soils.

Nutrients Commonly Applied Foliar

Timing for Precision Foliar Application

Critical stages for nutrient spraying:

Fact: Foliar urea application in wheat at booting stage can increase yield by 10–12%.

Methods of Foliar Application

1. Hand Sprayers / Knapsack Sprayers: Common in small fields.
2. Power Sprayers / Tractor-mounted Sprayers: For medium to large fields.
3. Mist or Foggers: Provides uniform droplet distribution for sensitive crops.
4. Drone Spraying / UAVs: High precision, covers large fields with minimal labor.

Important: Uniform droplet size and coverage are essential for effective absorption and minimal runoff.

Advantages of Precision Foliar Application

• Rapid correction of nutrient deficiencies.
• Efficient use of nutrients with lower doses compared to soil application.
• Can be used in soils where nutrients are unavailable to roots (high pH, alkaline, or waterlogged soils).
• Improves crop yield, quality, and nutrient content.
• Reduces environmental pollution from excess fertilizer application.