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Unit 6 - Notes

HRT108 7 min read

Unit 6: Field practices in horticultural crop management

1. Importance of Plant Bio-Regulators (PBRs) in Horticulture

Plant Bio-Regulators (PBRs), also known as Plant Growth Regulators (PGRs) or phytohormones, are organic compounds other than nutrients which, in small amounts, modify specific physiological processes in plants.

Classification of PBRs

  1. Growth Promoters: Auxins, Gibberellins (GAs), Cytokinins.
  2. Growth Inhibitors/Retardants: Abscisic Acid (ABA), Ethylene.

Applications and Importance

A. Propagation

  • Rooting of Cuttings: Auxins like IBA (Indole Butyric Acid) and NAA (Naphthalene Acetic Acid) are extensively used to induce root formation in hard-to-root cuttings (e.g., Grapes, Pomegranate).
  • Tissue Culture: The balance between Auxins (rooting) and Cytokinins (shooting) dictates organogenesis in micropropagation.

B. Growth and Size Control

  • Growth Inhibition: Growth retardants like Paclobutrazol are used in mango (cv. Alphonso) to restrict vegetative growth and induce regular flowering.
  • Dwarfing: CCC (Cycocel) is used in ornamental plants to create compact, bushy pot plants.

C. Flowering Management

  • Induction of Flowering: NAA induces flowering in pineapples. Paclobutrazol promotes flowering in mangoes during "off" years.
  • Sex Expression:
    • Gibberellins (GA3): Induce male flowers (staminate) in cucurbits.
    • Ethrel (Ethylene): Induces female flowers (pistillate) in cucumber and pumpkin, thereby increasing yield.
  • Prevention of Flower Drop: 2,4-D (at low concentrations) and NAA prevent pre-harvest fruit drop in citrus and mango.

D. Fruit Set and Development

  • Parthenocarpy (Seedless Fruits): Application of GA3 induces seedlessness in grapes (e.g., Thompson Seedless) and guava.
  • Fruit Size Enlargement: GA3 and Cytokinins increase berry size and loosen clusters in grapes.
  • Thinning: NAA is used to thin excess fruitlets in apples to ensure the remaining fruits achieve optimal size and quality.

E. Ripening and Post-Harvest

  • Ripening: Ethylene (commercial form: Ethrel/Ethephon) is the standard treatment for uniform ripening of bananas, mangoes, and tomatoes.
  • Shelf-life Extension: Cytokinins delay senescence (aging) in leafy vegetables like lettuce and broccoli.
  • Sprout Inhibition: Maleic Hydrazide (MH) prevents sprouting in onions and potatoes during storage.

2. Irrigation Methods: Merits and Demerits

Water management is critical in horticulture due to the high water content of fruits and vegetables (80-95%).

A. Surface Irrigation

Water is applied to the soil surface and moves by gravity.

1. Check Basin / Ring Method (for Orchards)

Water is confined to a basin made around the tree trunk.

  • Merits:
    • Economical and simple layout.
    • Good for young trees.
  • Demerits:
    • High labor requirement for making basins.
    • Hinders use of heavy machinery.
    • Water touches the trunk, increasing risk of collar rot and fungal diseases.

2. Furrow Irrigation

Used for row crops like potato and vegetables.

  • Merits:
    • Suitable for row crops.
    • Reduces crusting of soil surface compared to flooding.
  • Demerits:
    • Not suitable for sandy soils (high infiltration).
    • Salt accumulation on ridge crests.

B. Sub-Surface Irrigation

Water is applied below the ground surface through porous pipes or deep ditches.

  • Merits:
    • Minimal evaporation loss.
    • Surface remains dry (fewer weeds, less fungal disease).
  • Demerits:
    • High installation cost.
    • Risk of clogging in pipes due to roots or soil particles.
    • Salt accumulation in the root zone.

C. Sprinkler (Overhead) Irrigation

Water is sprayed into the air and falls like rain.

  • Merits:
    • Suitable for undulating (uneven) lands where leveling is expensive.
    • Useful for protecting crops from frost (latent heat release).
    • Soluble fertilizers can be applied.
  • Demerits:
    • High evaporative loss in hot/windy climates.
    • Wind distorts distribution pattern.
    • Wet foliage promotes fungal/bacterial diseases (e.g., mildews).
    • High energy requirement for pumps.

D. Drip (Trickle) Irrigation

Water is applied slowly and directly to the root zone through emitters.

  • Merits:
    • Highest Water Use Efficiency (90-95%).
    • Reduced weed growth (inter-row spaces remain dry).
    • Ideal for Fertigation (fertilizer + irrigation).
    • Suitable for saline soils (pushes salts to the wetting front edge).
  • Demerits:
    • High initial investment cost.
    • Emitters clog easily (requires filtration units).
    • Restricted root zone development (roots stay near the dripper).
    • Rodent damage to lateral pipes.

3. Fertility Management in Horticultural Crops

Horticultural crops act as heavy feeders, requiring specific nutrient management strategies involving both manures and fertilizers.

A. Essential Nutrients

  • Primary (Macro): Nitrogen (N - vegetative growth), Phosphorus (P - root development), Potassium (K - fruit quality/disease resistance).
  • Secondary: Calcium, Magnesium, Sulfur.
  • Micro: Zinc, Boron (crucial for pollen germination/fruit set), Iron, Manganese, Copper, Molybdenum.

B. Manures (Organic Sources)

Manures are plant and animal wastes used as sources of plant nutrients. They are bulky with low nutrient analysis.

Types of Manures:

  1. Bulky Organic Manures:

    • Farm Yard Manure (FYM): Decomposed mixture of dung and urine of farm animals along with litter. Contains approx 0.5% N, 0.2% P, 0.5% K.
    • Compost: Prepared by decomposing plant residues. Vermicompost (using earthworms) is richer in nutrients and growth-promoting substances.
    • Green Manure: Growing crops like Sunnhemp or Dhaincha and ploughing them into the soil to add organic matter and Nitrogen.

  2. Concentrated Organic Manures:

    • Oil Cakes: Residue after oil extraction (e.g., Neem cake, Groundnut cake). High N content; Neem cake also acts as a nitrification inhibitor and repels nematodes.
    • Bone Meal: Rich source of Phosphorus and Calcium.

Importance of Manures:

  • Improves soil physical properties (structure, aeration).
  • Increases Water Holding Capacity (WHC).
  • Provides food for soil microorganisms.
  • Micronutrients are supplied naturally.

C. Fertilizers (Inorganic Sources)

Industrially manufactured chemicals containing higher nutrient percentages.

  1. Nitrogenous: Urea (46% N), Ammonium Sulfate (good for tea/acid-loving crops), Calcium Ammonium Nitrate (CAN).
  2. Phosphatic: Single Super Phosphate (SSP - also supplies S and Ca), Di-ammonium Phosphate (DAP).
  3. Potassic: Muriate of Potash (MOP - cheaper, high Cl), Sulfate of Potash (SOP - better for quality, used in potato/tobacco).
  4. Micronutrient Fertilizers: Zinc Sulfate, Borax, Ferrous Sulfate.

D. Bio-fertilizers

Microbial preparations containing living cells.

  • Nitrogen Fixers: Rhizobium (legumes like peas/beans), Azotobacter (non-legumes).
  • Phosphate Solubilizers: PSB (Phosphobacteria) makes insoluble soil phosphorus available to plants.
  • VAM (Vesicular Arbuscular Mycorrhiza): Mobilizes Phosphorus and water; crucial for fruit trees like papaya and citrus.

4. Different Methods of Fertilizer Application

The efficiency of fertilizer use depends significantly on the method of application.

A. Application to Soil (Solid Form)

1. Broadcasting

Spreading fertilizer uniformly over the entire field.

  • Basal Dressing: Applied before sowing/planting during land preparation.
  • Top Dressing: Applied to the standing crop.
  • Disadvantage: High loss of Nitrogen through volatilization; Phosphorus fixation makes P unavailable.

2. Placement

Placing fertilizers in the soil at a specific location.

  • Plough-sole placement: Placing fertilizer in the furrow during ploughing.
  • Deep placement: Essential for ammoniacal nitrogen fertilizers in paddy fields to prevent denitrification.

3. Localized Placement

  • Drilling: Sowing seed and fertilizer together (but separated by soil) using seed-cum-fertilizer drills.
  • Band Placement: Applying fertilizer in bands to one or both sides of the crop row (common in potato).
  • Ring/Basin Placement: Most common in fruit trees. A trench is dug along the periphery of the tree canopy (drip line) where feeder roots are concentrated, fertilizer is applied, and covered with soil.

B. Application in Liquid Form

1. Starter Solutions

Dissolving N-P-K in water and applying it to the roots of vegetable seedlings (tomato, chili, cauliflower) at the time of transplanting. Helps establish roots quickly and overcome transplanting shock.

2. Foliar Application

Spraying dilute fertilizer solutions directly onto leaves.

  • Usage: Best for Micronutrients (Fe, Zn, B) and Urea.
  • Advantages: Rapid correction of deficiencies; useful when soil conditions (high pH) fix nutrients.
  • Disadvantages: Risk of leaf scorching (burning) if concentration is too high; cannot supply bulk macronutrients.

3. Fertigation

Application of water-soluble fertilizers through the irrigation system (mainly Drip).

  • Mechanism: Fertilizer tank or Venturi injector sucks fertilizer solution into the main water line.
  • Advantages:
    • Nutrients applied directly to the active root zone.
    • Precise control over quantity and timing.
    • Saves labor.
    • Increases Fertilizer Use Efficiency (FUE) significantly (up to 80-90%).

4. Tree Injection / Trunk Feeding

Injecting nutrients directly into the trunk of trees.

  • Used for correcting severe micronutrient deficiencies (e.g., Iron chlorosis) in large trees like coconut or mango where soil application is ineffective due to depth or fixation.
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