Unit4 - Subjective Questions

Establishing an orchard is a long-term investment. The primary principles revolve heavily around site selection to ensure sustainability and profitability:

• Climate: The choice of fruit crop must match the climatic zone (Tropical, Sub-tropical, or Temperate). Factors include temperature (chilling requirements), rainfall distribution, wind velocity, and light intensity.
• Soil: Most fruit trees prefer deep, well-drained, loamy soil. Factors include pH (usually 6.0–7.5), drainage (to prevent waterlogging), and absence of hardpans.
• Topography: Ideally, land should be level. In hilly areas, the aspect (direction of slope) affects sunlight exposure and frost susceptibility. Slopes greater than 5% require contour planting.
• Water Supply: Availability of a permanent source of irrigation is crucial, especially during dry spells and for young saplings.
• Proximity to Market and Transport: Perishable fruits require quick transport facilities and proximity to cold storage or markets to minimize post-harvest losses.

Square System:
In this system, trees are planted at the four corners of a square. The row-to-row distance is equal to the plant-to-plant distance ().

Advantages:

• It is the simplest and most common method of layout.
• Intercultural operations (ploughing, harrowing) can be done in two directions (cross-cultivation).
• Better supervision of the orchard is possible.

Disadvantages:

• Comparatively less number of trees are accommodated compared to the hexagonal system.
• There is some wastage of land in the center of the squares.

Hexagonal System:
Also known as the Septuple system. Trees are planted at the corners of an equilateral triangle. A seventh tree is placed in the center of the hexagon formed by six trees.

Key Characteristics:

• The perpendicular distance between rows is calculated as or roughly .
• All trees are equidistant from their neighbors.

Population Difference:

• This system accommodates approximately 15% more plants than the square system.
• It is ideal for fertile lands where high-density planting is feasible, but it makes intercultural operations difficult (possible only in three diagonal directions).

Formula Derivation:
For the Square System, the area occupied by a single tree is the square of the spacing distance ().

Where:

• = Number of plants
• Total Area = 1 Hectare =
• Spacing =

Calculation:

1. Calculate area per tree:
2. Apply formula:
   
   
   

Result:
The orchardist requires 100 mango plants.

Definition:
High Density Planting (HDP) is a technique of planting fruit trees closer together than the traditional spacing to achieve a higher population per unit area. It involves using dwarfing rootstocks, growth regulators, and specific pruning methods to control tree size.

Significance:

• Higher Yield: Drastically increases yield per unit area, especially in the early years of the orchard.
• Efficiency: Facilitates mechanization of operations like harvesting, spraying, and pruning.
• Quality: Often results in better fruit quality due to improved light interception in smaller canopies.
• Examples: Meadow orcharding in Guava () or Apple using M9 rootstock.

Training:

• Definition: A practice adopted during the early years of a tree's life to give it a desired shape and strong framework.
• Primary Objective: To build a strong scaffold system capable of bearing a heavy load of fruits in the future and to admit sunlight.
• Timing: Mostly done in the initial 3-5 years.

Pruning:

• Definition: The judicious removal of plant parts (branches, roots, leaves) to influence growth and fruitfulness.
• Primary Objective: To maintain the balance between vegetative growth and reproductive (fruiting) growth, and to remove diseased/dead wood.
• Timing: Performed annually throughout the productive life of the tree.

Central Leader System:

• Structure: The main trunk is allowed to grow vertically indefinitely. Side branches grow at intervals.
• Shape: Resembles a pyramid or Christmas tree.
• Strength: structurally very strong.
• Drawback: The interior of the canopy may become shaded, leading to poor fruiting in the lower center.

Open Center (Vase) System:

• Structure: The main trunk is headed back (cut) at a low height (e.g., 60-75 cm). 3-5 scaffold branches are allowed to grow outwards.
• Shape: Vase or bowl-shaped.
• Strength: Structurally weaker (prone to splitting at the crotch) compared to the central leader.
• Light Penetration: Preferred for light penetration. Sunlight reaches the center of the tree, improving fruit color and ripening.

Modified Leader System:
This system is an intermediate form that combines the best qualities of the Central Leader and Open Center systems.

Method:

1. Initially, the central leader is allowed to grow for 4–5 years to develop side scaffolds.
2. Once a height of 2–3 meters is reached and sufficient scaffold branches are formed, the central leader is headed back (cut off).
3. This prevents the tree from growing too tall while maintaining a strong framework.

Benefits:

• Strong Framework: Like the Central Leader system.
• Light Access: Like the Open Center system (sunlight enters the top).
• Suitability: widely used for commercial fruit crops like Pear, Apple, and Mango.

Heading Back:

• Technique: Cutting a branch back to a bud or a stub, removing only the terminal portion.
• Effect: It breaks apical dominance. This stimulates the sprouting of lateral buds just below the cut, resulting in a bushy, dense growth (vegetative response). It is used to control tree height and induce branching.

Thinning Out:

• Technique: Complete removal of a branch or shoot from its point of origin (at the trunk or parent branch).
• Effect: It does not stimulate excessive vegetative regrowth. Instead, it opens up the canopy, improving light penetration and air circulation. It redirects energy to the remaining branches, often promoting fruitfulness.

Girdling (Ringing):
It is the process of removing a circular strip of bark (phloem) from the trunk or a branch of a tree.

Physiological Basis:

• Phloem Interruption: The bark contains phloem vessels which transport photosynthates (sugars) from leaves down to the roots.
• Accumulation: By cutting the phloem, carbohydrates accumulate above the girdle (in the branches/leaves) because they cannot move down.
• C:N Ratio: This increases the Carbon:Nitrogen (C:N) ratio in the upper parts of the tree.
• Result: High carbohydrate accumulation promotes flower bud differentiation, earlier fruiting, and larger fruit size (e.g., in Grapes and Mango). Note: The cut should not be too wide to allow healing, otherwise roots will starve and the tree may die.

Both are minor pruning techniques used to influence bud activity by manipulating auxin and carbohydrate flow.

Notching:

• Action: Making a small cut or removing a wedge of bark above a dormant bud.
• Physiology: This checks the downward flow of auxins (which suppress lateral buds) and accumulates carbohydrates near the bud.
• Result: It forces the dormant bud to sprout into vegetative growth.

Nicking:

• Action: Making a notch or cut below a bud.
• Physiology: This obstructs the supply of carbohydrates/nutrients from leaves/roots to the bud.
• Result: It prevents the bud from sprouting vegetatively and often encourages the formation of fruit buds (due to carbohydrate accumulation in the shoot above the nick).

Importance:
Orchards decline in productivity after a certain age due to dense canopies, dead wood, pest infestation, and lack of sunlight. Rejuvenation restores productivity without the cost and time of replanting a new orchard.

Process:

1. Heading Back: Main branches are cut back severely (usually to a height of 2–3 meters) to the main trunk or primary scaffolds. This is typically done during the dormant season or before the rainy season.
2. Paste Application: Cut ends are treated with fungicides (e.g., Copper Oxychloride) to prevent infection.
3. New Growth: Latent buds sprout and produce vigorous new shoots.
4. Selection: Only healthy, well-positioned shoots are retained to form a new canopy; others are thinned out.
5. Cultural Care: Intensive manuring, watering, and pest management are required to support the rapid regrowth.

Definition:
Top working is a technique used to change the variety of an established tree. It involves grafting scions of a superior or desired variety onto the limbs of an existing tree (stock). It is often used to convert inferior seedling trees into superior commercial cultivars.

Common Methods:

1. Cleft Grafting: Used for thicker branches; the stock branch is split, and wedge-shaped scions are inserted.
2. Bark Grafting: Scions are inserted between the bark and wood of the stock; done when bark slips easily (active growth).
3. Patch Budding / Shield Budding: Used on younger regrowth after heading back the old tree.
4. Veneer Grafting: Common in Mango top working.

Frame Working:
In frame working, the main skeletal structure (frame) of the tree is retained. Only the smaller laterals and fruiting branches are replaced by grafting scions of the new variety. This requires inserting a large number of grafts (sometimes hundreds) all over the existing frame.

Difference from Top Working:

• Structure: Top working involves cutting back the main large limbs (severe pruning) and grafting near the trunk. Frame working keeps the full spread of the tree.
• Fruiting Time: Frame worked trees return to fruiting much faster (often within 2 years) because the large skeleton is already present.
• Labor: Frame working is much more labor-intensive and costly due to the high number of grafts required compared to top working.

The main objectives of pruning are:

1. Balance: To maintain a physiological balance between vegetative growth and cropping (fruit production).
2. Sanitation: To remove dead, diseased, crisscross, and broken branches.
3. Light & Air: To open the canopy to ensure sunlight reaches the center, improving fruit color and reducing fungal diseases.
4. Size Control: To keep the tree at a manageable height for spraying and harvesting.
5. Quality: To improve the size and quality of the fruit by thinning out excess crop load (regulating the crop).
6. Rejuvenation: To invigorate old or stagnant trees.

Cluster Planting:
This is a system where a group of 2–4 trees is planted very close together at a single spot (or pit), effectively acting as a single unit in the larger field layout.

Usage:

• Rootstock Utilization: Often used when rootstocks are dwarfing, allowing multiple stems to occupy the space of one standard tree.
• Pollination: It is sometimes used to ensure proximity of pollinizer varieties (e.g., planting a pollinizer tree in the same hole as the main variety in walnuts or pistachios).
• High Density: It is a variation of high-density planting to maximize land use.

Root Pruning:
This involves cutting a portion of the root system of a tree, usually by digging a trench around the drip line or using a sharp spade.

Objectives:

1. Growth Restriction: It reduces the water and nutrient uptake, checking excessive vegetative growth (dwarfing effect).
2. Flowering Induction: By creating stress and checking vegetative growth, it promotes the accumulation of carbohydrates, leading to flower bud formation (C:N ratio theory).
3. Transplanting: It is done periodically in nurseries to encourage a compact, fibrous root ball before transplanting large trees.

Given:

• Area = 1 Hectare =
• HDP Spacing =
• Standard Spacing =

Calculation for HDP:

Calculation for Standard:

Comparison:
The High Density Planting accommodates 2,500 plants, which is approximately 16 times the population of the standard planting (156 plants). This significantly increases early yield potential.

Double Hedge Row System:
This is a high-density planting system often used in crops like Pineapple or intensive apple orchards.

Structure:

• Two rows of plants are planted very close to each other (e.g., apart) to form a "double hedge."
• A wider alley (walking space) is left between one pair of double rows and the next pair to facilitate management and harvesting.

Advantages:

• Population: Accommodates a very high number of plants per unit area.
• Support: Plants in the double row can support each other or share a trellis system.
• Management: The wide alleys allow machinery or labor to access the dense rows efficiently.