Applied Agricultural Science: Germination and Establishment

The Germination Process

  • Imbibition: The essential process of taking water into the seed to initiate germination.

  • Moisture Requirements: Cereal seeds require 18%18\% moisture to begin germination, while oilseed rape requires 40%40\%.

  • Hormonal Control:

    • Abscisic acid (ABA): Suppresses germination and enforces dormancy; inactivated by oxidation (requires oxygen).

    • Gibberellin (GA): Promotes germination.

  • Enzymatic Activity: Starch is broken down into sugars by enzymes (α\alpha-amylase, β\beta-glucanase, lipase, proteases).

  • Mechanism: GA\text{GA} is synthesized in the scutellum and embryo, moving to the aleurone layer to induce α\alpha-amylase production, which converts endosperm starch to sugars for respiration and growth.

Seed Vigour and Dormancy

  • Dormancy: The failure of living seeds to germinate in favorable conditions (water, warmth, oxygen), depending on the dominance of inhibitors (ABA\text{ABA}) over promoters (GA\text{GA}).

  • Seed Vigour: The ability of a seed to survive and grow uniformly in non-optimal conditions.

  • Factors Affecting Vigour: Reduced by long storage periods, small grain size, and certain fungicide or insecticide seed treatments.

Factors Influencing Establishment

  • Temperature: The germination range for cereals is 4−37∘C4 - 37^{\circ}C with an optimum of 20−24∘C20 - 24^{\circ}C. Winter wheat and barley require 150∘C150^{\circ}C days (thermal time) from sowing to emergence.

  • Oxygen: Critical for respiration using carbohydrate reserves; waterlogging causes hypoxic (low oxygen) or anoxic (no oxygen) conditions that impede growth.

  • Drilling Date: Later drilling (e.g., November vs. September) increases the time to reach thermal time requirements and significantly reduces establishment rates.

  • Drilling Depth:

    • Optimum: 30−60 mm30 - 60\,mm.

    • Too Deep: Seed reserves are exhausted before the seedling reaches sunlight (emergence).

    • Too Shallow (<10\,mm): Increased risk of drying and pest damage.

    • Herbicides: Most pre-emergence herbicides require a minimum depth of 30 mm30\,mm to avoid crop damage.

  • Soil Texture:

    • Sands: Provide better soil-to-seed contact and lower resistance for root/shoot growth.

    • Clays: Difficult to prepare; high risk of waterlogging and coleoptile impedance.

  • Management Tools: Cambridge Rolls are used to improve soil-to-seed contact, reduce moisture loss, and minimize slug damage.