Chapter 16

Irrigation Water for Greenhouses

(book excerpts)

A dependable supply of high-quality irrigation water is a vital component for growing plants in a greenhouse since it is one of the largest inputs by volume and is the most broadly applied input. Characteristics of irrigation water that define its quality vary with the source of the water. There are regional differences in water characteristics, based mainly on geology and climate. There may also be great differences in the quality of water available on a local level depending on whether the source is from above ground (rivers and ponds) or from groundwater aquifers with varying geology, and whether the water has been chemically treated as in the case of municipal water. Water quality is very important for containerized plants that live in a small quantity of substrate. Many soilless substrates lack the buffering capacity of soils, and therefore alkaline water supplies have drastic effects on availability of nutrients in organic potting substrates. Poor water quality may lead to excessively high salts and pH extremes in the substrate, and nutritional problems. These problems are greatly magnified when growing plugs and cuttings, because young plants are particularly sensitive to water quality. Furthermore, high concentrations of sediment, iron and bicarbonates plug low volume nozzle orifices. Therefore, greenhouse producers should regularly monitor irrigation water sources for electrical conductivity (EC), pH, and nutrient content. Water quality factors outside the acceptable range do not necessarily mean that the water source cannot be used. There are several water treatment options available to greenhouse operations that can correct many water quality problems. Water treatment can be thought of as a three-dimensional challenge: physical, chemical, and microbial. A combination of physical, chemical and microbial treatment methods is often needed. No single treatment system is best for all greenhouses. The main sources for irrigation water are groundwater from wells, surface water, drainage ponds, rain, and municipal water.

Click on the following topics for more information on irrigation water for greenhouses.

Topics Within This Chapter:

  • Water Quality for Greenhouse Crops
  • Water Quality Target Parameters
  • Electrical Conductivity
  • Units of Measurement of Electrical Conductivity
  • Salinity Effects on Plants
  • EC Meters
  • pH
  • The Importance of pH
  • pH Meters
  • Alkalinity
  • Why Is Water Alkalinity Important?
  • Alkalinty verus pH
  • Units of Measurement of Alkalinity
  • General Guidelines of Upper and Lower Alkalinity Limits
  • Measuring Alkalinty
  • Water Hardness
  • Sodium Adsorption Ratio
  • Macro Elements
  • Micro Elements
  • Water Treatment for Total Dissolved Solids
  • Management Strategies for Controlling Soluble Salts
  • Leaching Fraction
  • Selection of Growing Media
  • Use of Substrate Amendments
  • Irrigation Method
  • Fertility Regime
  • Plant Tolerance
  • Reverse Osmosis
  • Pretreatment Stage
  • Filtering Efficiency
  • Deionization
  • Neutralizing Alkalinity/pH Adjustment
  • Reduce Limestone Added to Potting Media
  • Fertilizer Selection
  • Acid Treatment
  • Types of Acids
  • Pre-Dilution of Acid/Base Concentrates
  • pH Reaction Time
  • Nutrients from Acids
  • Water Treatment for Suspended Solids
  • Centrifugal Sand Separator
  • System Flushing
  • Media Filters
  • Sizing of Sand Media Filters
  • System Flushing
  • Screen Filters
  • Sizing Screen Filters
  • System Flushing
  • Disc Filters
  • System Flushing
  • Disinfestation of Greenhouse Irrigation Water
  • Pre-Filtration
  • Chlorination
  • Chlorine Gas
  • Sodium Hypochlorite
  • Calcium Hypochlorite
  • Factors to Consider with Water Chlorination
  • Chlorine Dioxide
  • Hydrogen Peroxide-Based Materials
  • Copper Ionization
  • Ozonation
  • Ultraviolet (UV) Light Treatment
  • Heat Pasteurization
  • Water Treatment for Specific Ions
  • Boron
  • Calcium and Magnesium
  • Ion Exchange
  • Lime Softening
  • pH Adjustment with Acid
  • Chloride
  • Fluoride
  • Iron and Manganese
  • Depth of Irrigation Intake from Holding Pond
  • Basin Aeration Pump
  • Tank Oxidation
  • Oxidatizing Agents and Oxidizing Filters
  • Water Supply for Greenhouses
  • Greenhouse Water Requirements
  • Water Sources for Greenhouses
  • Groundwater
  • Municipal Water
  • Surface Water
  • Tailwater and Stormwater Runoff