Soil Fertility and Plant Nutrition
( HORSS-201 & AGRMI-202 )
UNIT II
Nutrient deficiencies and toxicities: recent diagnostic techniques and ameliorative measures.
Nutrient Deficiencies
Definition: A nutrient deficiency occurs when an essential nutrient is not available in sufficient quantity or a plant-available form, resulting in restricted plant growth, poor yield, and visible symptoms.
Common Deficiency Symptoms
Nutrient Toxicities
Definition: Occurs when a nutrient is present in excessive amounts, leading to toxic effects on plant metabolism and interference with the uptake or function of other nutrients.
Nutrient deficiencies and toxicities in horticultural crops can severely impact growth, yield, and quality. Accurate and timely diagnosis, followed by effective corrective measures, is crucial for sustainable crop production.
Examples of Toxicity Symptoms
- Boron: Marginal leaf burn and chlorosi
- Manganese: Brown spots, crinkled leaves, interference with Fe uptake
- Iron: Bronzing and speckling of leaves
- Aluminium (in acid soils): Root inhibition, phosphorus deficiency-like symptoms
- Sodium/Chloride: Leaf scorching and salt stress
Management of Sodium Toxicity in Soils
- Symptoms: Surface crusting, poor infiltration, stunted plant growth.
- Indicators: ESP >15%, SAR >13.
- Management:
- Apply Gypsum (10–15 t/ha).
- Improve drainage for leaching.
- Use green manure (dhaincha) and organic matter.
- Grow salt-tolerant varieties (e.g., Karnal grass, barley).
- Maintain soil pH ~7 with acid-forming fertilizers.
✅ Toxicity Management of Essential Elements (Quick Revision Table)
Note:
Sodium is technically not essential for most crops.
Aluminum is toxic at low pH, not a nutrient.
🧠 Quick Mnemonic for Toxicity Fixes:
"LIME and LEACH to REACH balance!"
- LIME: Mn, Fe, Cu, Zn, Al toxicities — corrected by raising pH.
- LEACH: B, Na, Cl — toxicities managed by irrigation and leaching.
- REACH: A broader action that includes:
- Use of organic matter (Helps immobilize excess Cu, Zn, Mn)
- Enhance Nutrient buffering and microbial activity
- Aid adsorption of excess metals
- Correct cation imbalance
- Help in chelation and immobilization of toxic elements
Recent Diagnostic Techniques for Nutrient Disorders
Diagnosing nutrient disorders accurately is crucial for effective nutrient management in horticultural crops. Traditional methods are being complemented and enhanced by modern, rapid, and precise diagnostic tools.
1. Visual Diagnosis
- Symptoms include chlorosis (yellowing), necrosis (dead spots), stunted growth, leaf discoloration, and abnormal leaf patterns.
- Deficiency symptoms often appear on specific plant parts depending on nutrient mobility (e.g., older leaves for mobile nutrients like N, P, K; younger leaves for immobile nutrients like Ca, Fe).
- Limitations: Symptoms can be confused with those caused by pests, diseases, or abiotic stresses.
2. Soil Testing
- Involves systematic sampling and laboratory analysis to determine nutrient content, pH, EC, organic carbon and salinity.
- Provides a snapshot of soil nutrient status and guides fertiliser recommendations.
- Limitations: May not capture temporal changes or nutrient interactions; requires expertise for interpretation.
- Methods:
- Olsen’s method (P)
- Ammonium acetate (K)
- DTPA (Fe, Zn, Mn, Cu)
3. Leaf/Tissue Analysis
- Direct assessment of nutrient concentrations in plant tissues, often at specific growth stages.
- More precise than soil testing for diagnosing deficiencies and toxicities before symptoms become visible.
- Best Time: Before flowering or during active vegetative stage.
- Limitations: Results can vary with sampling technique, plant age, and environmental factors.
- Advantages:
- Detects both deficiencies and toxicities.
- Identifies “hidden hunger” (when symptoms are not visible yet).
4. DRIS (Diagnosis and Recommendation Integrated System)
- Developed to overcome limitations of tissue analysis.
- Uses ratios of nutrients rather than absolute values.
- Helps assess nutrient balance and prioritize deficiencies.
- Commonly used in fruit crops like banana, citrus, papaya.
5. CND (Compositional Nutrient Diagnosis)
- An advancement over DRIS.
- Based on multivariate statistical methods.
- Evaluates the entire nutrient balance, considering interactions.
- More reliable in high-value crops like vegetables and ornamentals.
6. Chlorophyll Meters (SPAD Meters)
- Measure relative chlorophyll content (correlated with nitrogen).
- Non-destructive and real-time.
- Helps guide nitrogen top-dressing decisions.
- Example: SPAD-502 meter.
7. Leaf Color Chart (LCC)
- Simple visual tool for assessing N status in crops like rice and vegetables.
- Farmers compare leaf color with chart and decide fertilizer application.
8. Histochemical Methods
- Use of stains to visualize nutrient deficiency/toxicity:
- Fe: Prussian Blue staining using potassium ferrocyanide.
- Zn: Dithizone reagent forms colored complex.
- Advantage: Detects localized deficiency before symptoms appear.
9. Enzymic Methods
- Track changes in enzyme activity:
- Nitrate Reductase: Indicator of nitrogen sufficiency.
- Peroxidase, Catalase: Affected by micronutrient levels.
- Use in lab-based precision diagnosis.
10. Spectral Reflectance & Remote Sensing
- Use of drones, satellites, or handheld devices to capture leaf/canopy reflectance.
- Assesses nutrient status, deficiencies, and crop health.
- Enables precision nutrient management.
11. Ion-Selective Electrodes & Portable Kits
- Measure specific ion concentrations (e.g., nitrate, potassium) in soil or sap.
- Rapid, field-friendly, and used for on-the-spot decision-making.
12. Image Processing and AI-Based Apps
- Smartphone apps using AI & image recognition to detect nutrient deficiencies based on leaf symptoms.
- Useful for farmers in remote areas.
- Example: Plantix app, IFFCO Kisan app.
13. Near Infrared Spectroscopy (NIRS)
- Non-destructive, fast technique using near-infrared light.
- Estimates nutrient and moisture levels in leaves and fruits.
- Gaining popularity in post-harvest and quality control too.
14. ICLeaf: Uses X-ray Fluorescence (XRF) and Near Infrared Spectroscopy (NIS) for rapid, non-destructive leaf analysis, enhanced by machine learning for real-time nutrient recommendations.
Ameliorative Measures
I. Ameliorative Measures for Nutrient Deficiencies
A. Soil Application
- Apply deficient nutrients in recommended doses based on soil/leaf analysis (e.g., Urea, DAP for N & P, MOP, SOP & KCl for K).
- Use gypsum or elemental sulfur for sulfur deficiency and calcium chloride for Ca deficiency.
- Time and method of application matter (e.g., split application for N).
B. Foliar Sprays
- Rapid correction for acute deficiencies, especially for micronutrients.
- Examples:
- 1% urea spray for N deficiency
- 2% DAP spray for P deficiency
- 1% KCl spray for K deficiency
- 0.5% solutions for Ca, S, and Mg deficiencies
- ZnSO₄ @ 0.5%
- FeSO₄ or Fe-EDTA @ 0.5%
- Boric acid @ 0.2%
C. Variable Rate Fertilization: Use productivity mapping and remote sensing to apply fertilizers only where needed, improving efficiency and sustainability.
D. pH Management
- Adjust soil pH to enhance nutrient availability (e.g., liming acidic soils, adding sulfur to alkaline soils).
- Lime application in acidic soils to improve Ca, Mg availability and reduce Al toxicity.
- Elemental sulfur or acid-forming fertilizers in alkaline soils to improve micronutrient availability.
E. Integrated Nutrient Management
- Combine organic, inorganic and biological sources, crop rotation, and green manures to maintain balanced fertility and prevent deficiencies/toxicities.
- Sustainable and environment-friendly approach.
F. Use of Biofertilizers
- Encourage nutrient mobilization and fixation.
- Azotobacter, Azospirillum (for N fixation)
- PSB – Phosphate Solubilizing Bacteria
- VAM fungi – Enhance uptake of P, Zn
G. Organic Amendments
- Improve soil structure, CEC, and microbial activity.
- FYM, compost, green manure
- Enrich with nutrients for slow-release effect.
Zinc Deficiency
- Symptoms: Short internodes, little leaf, rosetting, white bud in maize.
- Crops affected: Maize, wheat, rice.
- Amelioration: 25 kg ZnSO₄/ha every 2–3 years + 0.5% foliar spray during early stages.
Iron Deficiency
- Symptoms: Interveinal chlorosis, especially in young leaves.
- Common in: Calcareous or alkaline soils.
- Amelioration: FeSO₄ (25 kg/ha) or chelated iron spray (Fe-EDTA @ 0.5%)
II. Ameliorative Measures for Nutrient Toxicities
1. Leaching
- In areas with excess salts or soluble toxic elements.
- Requires good-quality irrigation water.
- Helps in removing excess boron, chloride, sodium.
2. pH Correction
- Alkaline soils: Improve micronutrient availability (e.g., Fe, Zn) by lowering pH with elemental sulfur or organic matter.
- Acidic soils: Raise pH using lime, which also precipitates toxic Al and Mn.
3. Use of Gypsum
- For sodic soils, gypsum provides calcium which replaces sodium on soil colloids.
- Helps in reclaiming alkali soils.
4. Crop and Variety Selection
- Choose varieties tolerant to specific toxicities.
- E.g., rice varieties tolerant to Fe toxicity or Al stress.
5. Addition of Organic Matter
- Binds toxic elements and improves soil buffering.
- Increases microbial activity that can detoxify or immobilize harmful elements.
6. Use of Chelates
- Chelated forms of micronutrients (like Fe-EDTA) are more stable and available in problematic soils
- Reduce risk of toxicity and ensure controlled nutrient release.
III. Preventive Approaches
- Balanced fertilization based on soil test.
- Proper irrigation management to avoid salt build-up.
- Crop rotation and intercropping to maintain soil health.
- Regular monitoring using tools like SPAD, LCC, and remote sensing.
- Key Points
- Early and accurate diagnosis is vital; integrate visual, chemical, and advanced techniques for the best results.
- Prompt, targeted ameliorative measures can restore plant health and optimise yields.
- Precision agriculture tools and integrated nutrient management are essential for sustainable horticulture.
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Tags:
AGRMI-202
HORSS-201
MSc (Ag) Agronomy 1st Year
MSc (Ag) Horticulture 1st Year
Soil Fertility and Plant Nutrition