Unit6 - Subjective Questions

Fertilizer recommendation approaches are broadly classified into qualitative and quantitative methods to ensure optimal crop yields.

1. Generalized or Blanket Recommendation:

• Based on multi-locational field trials.
• Does not consider specific soil variability.
• Suitable for areas where soil testing is not available.

2. Soil Test Based Recommendation (STL):

• Fertilizer rates are adjusted based on the available nutrient status of the soil (Low, Medium, High).

3. Soil Test Crop Response (STCR):

• A quantitative approach connecting soil test values, fertilizer doses, and crop yield.
• Based on the 'Targeted Yield' concept.

4. Critical Level Approach:

• Identifies the nutrient concentration in the plant or soil below which the crop will respond to fertilizer application.

5. Site-Specific Nutrient Management (SSNM):

• Dynamic adjustment of nutrients based on spatial and temporal variability using tools like STCR, omission plots, or crop sensors.

Broadcasting:

• Method: Spreading fertilizer uniformly over the entire field.
• Suitability: Suitable for crops with dense stands (e.g., wheat, pastures) and for applying large quantities of fertilizers like Potash or Lime.
• Drawback: High fixation of Phosphorus due to maximum soil contact; weed growth is stimulated.

Localized Placement:

• Method: Application of fertilizer in bands or pockets near the seed or plant row.
• Suitability: Best for crops sown in wide rows (e.g., maize, cotton) and for phosphatic fertilizers to reduce fixation.
• Advantage: High nutrient use efficiency due to reduced soil-fertilizer contact and easy accessibility to roots; less weed competition.

Concept:
Foliar application involves dissolving fertilizers in water and spraying them directly onto the crop foliage. It relies on the absorption of nutrients through stomata and leaf cuticle.

Advantages:

1. Rapid Correction: Best for quick recovery from deficiency symptoms (e.g., Iron chlorosis).
2. Micronutrients: Highly efficient for applying small quantities of micronutrients (Fe, Mn, Zn, Cu) which might get fixed in the soil.
3. Stress Conditions: Useful when root activity is restricted due to drought, waterlogging, or salinity.
4. Economy: Reduces total quantity of fertilizer required compared to soil application for certain nutrients.

Limitations: Concentration must be low to avoid leaf scorching (burning).

1. Rain-fed Conditions:

• Moisture Availability: The most critical limiting factor. Low moisture restricts nutrient diffusion and mass flow to roots.
• Timing: Fertilizers must be applied at sowing or when soil moisture is adequate. Top dressing is risky if rains fail.
• Placement: Deep placement is crucial to place nutrients in the moist zone.
• Losses: Volatilization losses of Nitrogen (urea) are high if applied on dry surface soil.

2. Irrigated Conditions:

• Leaching: Excessive irrigation leads to leaching of Nitrate () and Potassium, reducing NUE.
• Waterlogging: Can cause denitrification (conversion of nitrate to gas) in submerged conditions (e.g., paddy).
• Intensity of Cropping: High cropping intensity mines soil nutrients faster, requiring balanced fertilization to maintain NUE.
• Fertigation: Irrigation allows for fertigation, which significantly enhances NUE by delivering water and nutrients simultaneously.

1. Agronomic Efficiency (AE):
It represents the amount of yield increase per unit of fertilizer nutrient applied. It reflects the economic return.

Where:

• = Yield in fertilized plot (kg/ha)
• = Yield in control/unfertilized plot (kg/ha)
• = Quantity of fertilizer nutrient applied (kg/ha)

2. Recovery Efficiency (RE):
It represents the percentage of applied nutrient that is absorbed/taken up by the crop.

Where:

• = Nutrient uptake by fertilized crop (kg/ha)
• = Nutrient uptake by control crop (kg/ha)
• = Fertilizer applied (kg/ha)

The STCR approach, established by Ramamoorthy et al., assumes a linear relationship between crop yield and nutrient uptake. It formulates fertilizer doses based on three parameters:

1. Nutrient Requirement (NR): Amount of nutrient required to produce one quintal (or ton) of grain.
2. Contribution from Soil (CS): The percentage of soil available nutrient utilized by the crop.
3. Contribution from Fertilizer (CF): The percentage of applied fertilizer nutrient utilized by the crop.

Basic Equation Derivation:
The total nutrient uptake () required for a targeted yield () is derived from soil () and fertilizer ().

Also, uptake is the sum of contributions from soil and fertilizer:

Where is the Soil Test Value.

Equating the two:

Solving for Fertilizer Dose ():

This formula allows for calculating the exact fertilizer dose required to achieve a specific yield target based on soil testing.

Given Data:

• Target Yield () = 50 q/ha
• Nutrient Requirement () for N = 2.0 kg/q
• Soil Test Value () for N = 150 kg/ha
• Contribution from Soil () = 20%
• Contribution from Fertilizer () = 40%

Formula:

Calculation:

1. Total N Required:
   

2. N supplied by Soil:
   

3. N needed from Fertilizer:
   

4. Fertilizer Dose (accounting for efficiency):
   

Answer: The required Nitrogen fertilizer dose is 175 kg N/ha.

Definition:
Real-Time Nutrient Management (RTNM) involves adjusting fertilizer application, particularly Nitrogen, during the crop growth season based on the actual status of the crop, rather than relying solely on pre-season soil tests. It synchronizes nutrient supply with crop demand.

Tools for RTNM:

1. Leaf Color Chart (LCC):

   • A simple, low-cost plastic scale with shades of green.
   • Farmers compare leaf color to the chart; if the color is lighter than a critical value, N fertilizer is applied.
   • Widely used in Rice and Maize.

2. SPAD Meter (Chlorophyll Meter):

   • An electronic device that measures the chlorophyll content (greenness) of leaves non-destructively.
   • Provides a precise numerical value.

3. Optical Sensors (e.g., GreenSeeker):

   • Measures Normalized Difference Vegetation Index (NDVI) to assess crop vigor and biomass.
   • Used in variable rate technology (VRT) applicators to apply fertilizer on the go.

The Leaf Color Chart (LCC) is a decision support tool used to optimize Nitrogen application in rice.

Methodology:

1. Timing: Readings are usually started 14 days after transplanting (DAT) or 21 days after sowing (DAS) and taken every 7–10 days.
2. Sampling: Select 10 healthy, fully expanded leaves from random plants in the field.
3. Measurement: Place the leaf on the chart and compare its color with the panels (usually numbered 1 to 6).
   • Do this in the shade of the body to avoid direct sunlight reflection.
4. Decision Rule:
   • Determine the average score of the 10 leaves.
   • If the average color is below the Critical Value (usually 3 for low-yielding varieties and 4 for high-yielding/hybrids), Nitrogen fertilizer needs to be applied immediately.

Benefits: Prevents over-application of Urea, reduces cost, and minimizes lodging and pest incidence.

Definition:
Integrated Plant Nutrient Supply (IPNS) system is the combined application of chemical fertilizers, organic manures, and bio-fertilizers in a balanced manner. The goal is to maintain soil fertility, optimize crop yield, and minimize environmental degradation by utilizing all available nutrient sources.

Main Components:

1. Chemical Fertilizers: Provide readily available nutrients (N, P, K) to meet immediate crop demand.
2. Organic Manures:
   • Bulky: Farm Yard Manure (FYM), Compost, Vermicompost.
   • Concentrated: Oil cakes, poultry manure.
   • Improve soil physical properties and supply micronutrients.
3. Bio-fertilizers:
   • Nitrogen fixers (Rhizobium, Azotobacter).
   • Phosphorus solubilizers (PSB).
   • Mycorrhizae (VAM) for mobilizing nutrients.
4. Green Manures: Leguminous crops (e.g., Sesbania, Crotalaria) incorporated into the soil to add organic matter and N.
5. Crop Residues: Incorporation of straw or stubble.

1. Sustained Productivity: IPNS maintains soil health, preventing the yield plateau often observed with continuous chemical farming.
2. Soil Physical Health: Organic components improve soil structure, water holding capacity, and aeration, which chemicals cannot do.
3. Nutrient Availability: Organic matter acts as a slow-release source and chelating agent, reducing fixation of nutrients like P and preventing leaching of N.
4. Microbial Activity: Enhances soil biological activity and biodiversity (earthworms, beneficial microbes).
5. Environmental Safety: Reduces nitrate pollution of groundwater and eutrophication by improving nutrient use efficiency.
6. Cost Efficiency: Reduces the dependency on expensive chemical fertilizers by substituting them with locally available organic wastes and bio-fertilizers.

Concept:
Fertigation is the precise application of water-soluble fertilizers, soil amendments, or other water-soluble products through an irrigation system (Drip or Sprinkler).

Benefits:

1. High Efficiency: Nutrients are applied directly to the active root zone, leading to Nutrient Use Efficiency (NUE) as high as 90%.
2. Timing: Nutrients can be applied exactly when the crop needs them (split application) during critical growth stages.
3. Reduced Losses: Minimizes volatilization and leaching losses compared to broadcasting.
4. Resource Saving: Saves labor and energy required for separate fertilizer application.
5. Micronutrients: Even distribution of micronutrients is possible, which is difficult with solid application.

Bulky Organic Manures:

• Nutrient Content: Low concentration of nutrients per unit weight (e.g., NPK in trace amounts).
• Volume: Required in large quantities (tons/ha).
• Main Function: Primarily improve soil physical structure, organic carbon, and water holding capacity.
• Examples: Farm Yard Manure (FYM), Compost, Green Manure.

Concentrated Organic Manures:

• Nutrient Content: High concentration of major plant nutrients compared to bulky manures.
• Volume: Required in smaller quantities.
• Main Function: Acts as a significant source of N, P, and K for crop nutrition.
• Examples: Oil cakes (Groundnut cake, Neem cake), Fish meal, Blood meal, Guano.

Definition:
Soil Carbon Sequestration is the process of transferring atmospheric carbon dioxide () into the soil through crop residues and other organic solids, and storing it securely as soil organic carbon (SOC) so it is not immediately re-emitted.

Context in Nutrient Management:

• Positive Feedback: Proper nutrient management (IPNS) increases crop biomass production (roots and shoots).
• Residue Return: Higher biomass leads to more crop residues returning to the soil.
• Humus Formation: Adequate Nitrogen and Sulfur are required to convert this carbon into stable humus (sequestered carbon). If nutrients are limiting, microbes decompose organic matter completely into rather than stabilizing it in the soil.

Carbon Trading Concept:
Carbon trading allows entities that reduce carbon emissions or sequester carbon to sell 'carbon credits' to emitters. In agriculture, farmers can earn credits by sequestering carbon in the soil.

Influence of Nutrient Management:

1. IPNS: Adopting Integrated Plant Nutrient Supply increases Soil Organic Carbon (SOC) stocks. This measurable increase can be monetized as carbon credits.
2. Reduced Emissions: Precise nutrient management (e.g., using urease inhibitors or proper placement) reduces Nitrous Oxide () emissions. Since is a potent greenhouse gas (300x more potent than ), reducing it generates significant carbon credits.
3. Conservation Agriculture: Combining zero-tillage with proper fertilization retains residues, sequestering more carbon and making the farm eligible for carbon markets.

Formula:

Where:

• = Total yield of the harvested portion of the crop (kg/ha)
• = Amount of fertilizer nutrient applied (kg/ha)

Significance:

1. Broad Indicator: It is the simplest measure of nutrient use efficiency.
2. Farmer's Perspective: It answers the question, "How much grain do I get for every kg of fertilizer applied?"
3. Input Efficiency: It integrates the inherent soil nutrient supply and the applied fertilizer efficiency. A very high PFP might indicate soil mining (using soil reserves), while a low PFP indicates poor management or limiting factors.

Concept:
Balanced fertilization implies the supply of all essential nutrients (Primary, Secondary, and Micronutrients) in the right proportion and adequate quantity suited for the specific crop and soil conditions. It is not just applying NPK, but applying them in a specific ratio (e.g., 4:2:1 for cereals) and correcting specific deficiencies like Zinc or Sulphur.

Importance:

1. Liebig's Law of Minimum: Yield is limited by the nutrient in shortest supply. Adding more N will not help if P is limiting.
2. Synergism: Balanced nutrients promote positive interactions (e.g., K improves N utilization).
3. Crop Quality: Improves protein content, grain size, and shelf life.
4. Disease Resistance: Potassium and micronutrients enhance the plant's immune system.
5. Soil Health: Prevents soil mining of specific nutrients.

Description:
The Omission Plot Technique is a diagnostic tool used to determine the indigenous nutrient supplying capacity of the soil and the crop's response to specific nutrients.

Method:
Several plots are established:

1. NPK Plot: Receives ample N, P, and K.
2. -N Plot (N omission): Receives ample P and K, but no N.
3. -P Plot (P omission): Receives ample N and K, but no P.
4. -K Plot (K omission): Receives ample N and P, but no K.

Analysis:

• The yield in the -N plot represents the soil's capacity to supply Nitrogen.
• The difference between the NPK plot yield and the -N plot yield represents the yield gap that must be filled by fertilizer Nitrogen.
• This method forms the basis for SSNM (Site-Specific Nutrient Management).

Definition:
Slow-release or Controlled-release fertilizers are formulations designed to release nutrients gradually over an extended period, matching the crop's uptake pattern.

Mechanisms:

• Coating: Sulphur Coated Urea (SCU), Polymer Coated Urea, Neem Coated Urea (NCU).
• Chemical Structure: Urea-formaldehydes (low solubility).

Improvement in Management:

1. Reduced Losses: Drastically reduces leaching (nitrates) and volatilization (ammonia) losses.
2. Labor Saving: Reduces the need for multiple split applications (top dressing).
3. Steady Supply: Provides a continuous supply of N throughout the growth cycle, preventing 'luxury consumption' followed by starvation.
4. NUE: Significantly increases Nitrogen Use Efficiency.