Fertilizer Recommendation Concepts: STCR / RTNM / IPNS / IPNS–STCR

1. STCR – Soil Test Crop Response Approach

STCR is a scientific and quantitative fertilizer recommendation approach developed by ICAR to prescribe fertilizer doses for achieving a pre-determined (targeted) crop yield.
It is based on soil test values, crop nutrient requirement, soil nutrient contribution, and fertilizer use efficiency.

Principle: Crop yield is a function of nutrient supply from soil and fertilizer.

The approach considers:

• Nutrient requirement per unit yield
• Contribution of nutrients from soil
• Contribution (efficiency) of applied fertilizers

STCR Formula: F = (NR×T−CS×S) / CF

Merits

• Highly scientific and yield-oriented
• Avoids under- and over-fertilization
• Improves fertilizer use efficiency and profitability
• Recommended by ICAR for major field crops

Limitations

• Requires reliable soil testing facilities
• Crop- and location-specific calibration needed
• Slightly complex for direct farmer adoption
• Needs periodic updating with new varieties

2. RTNM – Real Time Nutrient Management

RTNM is a dynamic, in-season nutrient management approach in which fertilizer application—mainly nitrogen—is adjusted according to real-time crop demand and field conditions.

Definition: RTNM involves real-time adjustment of fertilizer doses based on plant indicators, crop growth stage, and environmental conditions.

Key Tools

• Leaf Colour Chart (LCC)
• SPAD (chlorophyll) meter
• NDVI sensors
• Visual crop observations

Features

• Focuses mainly on nitrogen management
• Demand-driven and field-specific
• Widely adopted in rice cultivation

Merits 

• Prevents excess nitrogen application
• Reduces N losses (leaching, volatilization)
• Improves nutrient use efficiency (NUE)
• Simple and farmer-friendly (especially LCC)

Limitations 

• Mostly limited to nitrogen
• Influenced by light, crop variety, and growth stage
• Does not assess long-term soil fertility

3. IPNS – Integrated Plant Nutrient Supply System

Meaning

IPNS emphasizes balanced nutrient supply through integration of:

• Chemical fertilizers
• Organic manures
• Biofertilizers
• Crop residues

Definition: IPNS is a holistic approach to nutrient management that ensures crop nutrition while maintaining soil fertility using all available nutrient sources.

Components of IPNS

1. Chemical fertilizers
2. Organic manures (FYM, compost, green manure)
3. Biofertilizers
4. Crop residue recycling

Objectives of IPNS

• Improve soil health
• Reduce chemical fertilizer dependence
• Enhance nutrient cycling
• Promote sustainable agriculture

Merits of IPNS

• Improves soil physical, chemical & biological properties
• Enhances NUE
• Environment-friendly
• Long-term soil fertility

Limitations of IPNS

• Nutrient release from organics is slow
• Bulky organic inputs
• Difficult nutrient quantification
• Requires good management

4. IPNS–STCR – Integrated Plant Nutrient Supply with STCR

Meaning: IPNS-STCR is an advanced fertilizer recommendation approach combining:

• STCR (quantitative precision)
• IPNS (sustainability)

Definition: IPNS-STCR is a fertilizer recommendation system that integrates soil test–based targeted yield approach with nutrient contribution from organic and biological sources.

Concept: Total nutrient requirement =

• Soil contribution
• Fertilizer contribution
• Organic manure contribution

Modified STCR Equation (IPNS–STCR): F = (NR×T−CS×S−CO×O) / CF

Where:

• CO = Contribution from organic sources
• O = Organic nutrient content

Advantages of IPNS–STCR

• Most precise and sustainable approach
• Reduces chemical fertilizer requirement
• Improves soil health
• Enhances long-term productivity
• Strongly recommended by ICAR

Limitations

• Needs accurate estimation of organic nutrient contribution
• Requires technical support
• Limited field-level adoption

Comparative Summary