🌦️ Types of Protected Structures — Greenhouse Polyhouse Net House

This lesson builds core elective concepts in BSc Agriculture with practical applications and exam-oriented clarity.

---

Types of Protected Structures — Greenhouse Polyhouse Net House

Overview of Protected Structures

Protected structures vary widely in design, cost, and level of environmental control. The choice of structure depends on the crop to be grown, the climatic zone, available budget, and the desired degree of climate modification.

Greenhouse (Glasshouse)

A greenhouse is a framed structure covered with transparent or translucent material (glass or rigid polycarbonate sheets) that permits solar radiation to enter while trapping heat inside. Greenhouses offer the highest level of environmental control.

• Frame materials: Galvanized iron (GI) pipes, aluminum, or steel
• Covering: Tempered glass, polycarbonate sheets, or acrylic panels
• Temperature range: Maintained between 15 to 30 degrees Celsius using heating and cooling systems
• Types by shape: Quonset, gothic arch, ridge and furrow, sawtooth, and even-span

Polyhouse

A polyhouse is a greenhouse covered with polyethylene film instead of glass. It is the most widely used protected structure in India due to its lower cost.

Feature	Naturally Ventilated Polyhouse	Fan-and-Pad (Hi-Tech) Polyhouse
Ventilation	Roof and side vents	Exhaust fans + evaporative cooling pads
Cost per sqm	Rs 800 to 1200	Rs 2500 to 4000
Temperature control	Partial (5 to 8 degrees reduction)	Precise (within 2 to 3 degrees of set point)
Suited crops	Vegetables, flowers	High-value crops, seedlings, tissue culture

Net House (Shade House)

A net house is an open structure covered with shade nets of varying mesh density. It provides protection from excessive sunlight, wind, hail, and certain insects.

• Shade percentages: 25%, 35%, 50%, 75%, and 90% shade nets available
• Colors: Green, black, white, and red nets (color affects light spectrum)
• Applications: Nursery raising, leafy vegetable production, orchid cultivation, hardening of tissue-cultured plants

Other Protected Structures

• Walk-in tunnels: Low-cost arched structures covered with polyethylene, suitable for small-scale farmers growing leafy vegetables and strawberries
• Plastic mulch and row covers: Ground-level protection that conserves moisture, suppresses weeds, and moderates root-zone temperature
• Rain shelters: Open-sided structures with only a plastic roof to protect crops from excessive rainfall (used widely in tomato and grape cultivation)
• Insect-proof net houses: Fine mesh (40 to 50 mesh) structures that prevent whitefly, thrips, and aphid entry, reducing virus transmission

Selection Criteria

When choosing a structure, consider:

• Climatic zone: Tropical, subtropical, temperate, or arid
• Target crop and its environmental requirements
• Budget and availability of government subsidies
• Market proximity and logistics for perishable produce
• Water and electricity availability at the site

---

Summary Cheat Sheet

Topic	Key takeaway
Main focus	Types of Protected Structures — Greenhouse Polyhouse Net House.
Section context	Revise this lesson with the rest of Structure & Environment Control for stronger conceptual continuity.