Irrigation Systems Used in Greenhouses

Irrigation systems are crucial in greenhouse environments to ensure consistent water supply for healthy plant growth. A well-designed irrigation system maintains the precise amount of water required daily, irrespective of seasonal changes or weather conditions. The choice of system depends on the growing area, crop type, weather, and the operating status of the heating or ventilation system. Proper watering techniques are essential to avoid over-watering or under-watering, which can lead to crop damage or reduced quality.

Types of Irrigation Systems in Greenhouses

1. Overhead Sprinklers
2. Drip Irrigation System
3. Foggers (Mist Spraying)
4. Hand Watering and Perimeter Watering

Rules of Watering in Greenhouses

1. Use a Well-Drained Substrate with Good Structure Ensures proper drainage and aeration. Substrates should retain moisture while maintaining good aeration for optimal root growth. Well-structured substrates prevent waterlogging and enhance plant health.
2. Water Thoroughly Each Time Avoid partial watering; ensure the entire root zone is wetted. Water should flow from the bottom of containers or thoroughly wet bed roots. Supply 10-15% excess water to ensure full saturation and prevent dry spots.
3. Water Just Before Initial Moisture Stress Occurs Over-watering reduces root aeration, leading to poor development. Water should be applied just before signs of moisture stress, which vary by crop. For crops showing no visible symptoms, assess moisture by substrate color, feel, and weight.

1. Overhead Sprinklers

• Suitable for crops that tolerate wet foliage, such as bedding plants and some green plants.
• Setup: A pipe runs along the center of the bed, with riser pipes installed at intervals above crop height. Nozzles at the top of risers either spray a continuous 360° pattern or rotate around a 360° circle.
• Advantages: Simple and cost-effective for crops that do not require dry foliage. Ideal for watering flats of bedding plants or fresh flowers.
• Challenges: Not suitable for crops prone to foliar diseases as wet foliage increases disease risk. Water wastage can occur if trays are not used to catch excess water.

2. Drip Irrigation System Also known as trickle irrigation, it uses small diameter plastic tubes laid beside or under the plants.

• Functionality: Water is delivered directly to the root zone at frequent intervals through emitters along the tubes. Can be used with plastic mulches, row covers, or in open field crop production.
• Advantages:
  • Water Efficiency: 90-95% application efficiency, minimizing water usage.
  • Uniformity: Ensures uniform water and fertilizer distribution.
  • Cost-Effective: Reduces labor and machinery costs.
  • Soil and Nutrient Conservation: Limits soil erosion and nutrient leaching.
  • Optimal Production: Provides consistent moisture, enhancing crop yield and quality.
• Disadvantages: Initial Cost: High setup cost due to equipment like pumps, filters, pressure regulators, and drip tapes. Maintenance: Filters are necessary to prevent clogging of emitters.
• Components of Drip Irrigation:
  • Pump: Ensures consistent water pressure.
  • Main Line and Delivery Pipes: Transport water from the source to the drip tapes.
  • Emitters: Regulate water flow to plants.
  • Control Valves, Filters, and Pressure Regulators: Maintain flow rate and prevent clogging.

3. Foggers (Mist Spraying)

• Purpose: Used for maintaining humidity and cooling the greenhouse environment. Ideal for propagation as it balances humidity and transpiration rates.
• Fog vs. Mist: Fog: Particles less than 50 microns in diameter, typically around 10 microns. Mist: Particles between 50 to 100 microns.
• Functionality: Tiny droplets of fog remain suspended in the air, evaporating gradually. Fog cools the air without wetting the foliage or growing medium, reducing disease risk. Mist particles are heavier and take longer to evaporate, potentially causing foliage wetness.
• Advantages:
  • Temperature Regulation: Lowers air temperature without oversaturating the growing medium.
  • Improved Rooting: Enhances oxygen in the root zone, promoting faster rooting.
  • Uniform Application: Automated systems ensure even distribution of water, fertilizers, or pesticides.
• Components of Fogging System:
  • High-Pressure Pump: Generates 800-1200 psi pressure to create fine droplets.
  • Distribution Piping and Nozzles: Ensure even dispersion above the crop canopy.
  • Anti-Drip Check Valves and Filters: Prevent dripping and clogging of nozzles.
• Challenges:
  • Nozzle Clogging: Caused by chemical deposits or particulate matter.
  • Water Quality: Requires high-quality water or advanced filtration systems.

Comparison of Irrigation Systems

Hand Watering

Hand watering involves manually watering plants using watering cans, hoses, or similar tools. It’s one of the simplest and most direct methods of irrigation, typically used for smaller greenhouse operations or areas where automation is not practical.

Advantages of Hand Watering:

1. Precise Control: Allows growers to control exactly how much water each plant receives, which is beneficial for sensitive plants or small-scale operations.
2. Flexibility: Can be used for various types of plants, from small seedlings to larger, established plants.
3. Low Initial Cost: Requires minimal investment in irrigation infrastructure.
4. No Power Supply Required: It can be done without electricity or complicated plumbing systems, making it a good option for greenhouses with limited resources.

Disadvantages of Hand Watering:

1. Time-Consuming: Watering manually takes time, especially in large greenhouses, and can be labor-intensive.
2. Inconsistent Watering: Without proper care, there might be uneven watering, either overwatering or underwatering, leading to plant stress.
3. Labor Costs: It requires a significant amount of human labor, making it impractical for large-scale operations.
4. Limited Efficiency: Water usage might be inefficient, especially in larger areas where more systematic irrigation methods could save water.

Best Practices for Hand Watering:

• Water early in the morning to prevent fungal growth and reduce evaporation losses.
• Ensure that the water is applied evenly across all plants.
• Use a watering can with a fine nozzle or a hose with an adjustable nozzle to avoid disturbing the soil or over-watering.

Perimeter Watering

Perimeter watering refers to the practice of setting up irrigation around the perimeter (edges) of a greenhouse or garden area. This method is typically used to irrigate the boundary areas and ensure that water is supplied to crops along the edges, often using overhead sprinklers or drip irrigation lines along the edges.

Advantages of Perimeter Watering:

1. Efficient Use of Water: It’s often more water-efficient than hand watering, as it avoids excess water wastage in the central areas of the greenhouse.
2. Automated Control: Often part of a larger automated irrigation system, it can reduce labor costs and time spent on manual watering.
3. Uniform Coverage: Sprinklers or drip systems designed for perimeter watering can ensure even coverage across a wide area.
4. Low Maintenance: Requires minimal upkeep compared to more complex irrigation systems that cover the entire greenhouse.

Disadvantages of Perimeter Watering:

1. Not Suitable for All Crops: This method may not be effective for plants that are located away from the perimeter or in the middle of the greenhouse, where water might not reach.
2. Limited Flexibility: It’s less adaptable for irregularly shaped or multi-tiered planting arrangements.
3. Inconsistent Distribution: If the irrigation system is not properly calibrated, certain areas might receive too much water while others may not get enough.
4. Water Distribution Can Be Limited: While effective on edges, perimeter systems might not be able to reach plants growing in the center of large greenhouses unless designed for better coverage.

Best Practices for Perimeter Watering:

• Combine with Other Systems: For large areas, perimeter watering can be combined with drip irrigation or overhead sprinklers to ensure that all plants receive adequate water.
• Ensure Proper Calibration: Ensure that the system is correctly calibrated to deliver the right amount of water to each section of the greenhouse.
• Regularly Check for Clogging: Drip emitters or sprinkler nozzles can become clogged over time, so they need to be cleaned and maintained regularly.