Chapter 11

Irrigation Water for Greenhouses

Water Supply for Greenhouses

A sufficient supply of high quality water is extremely important for the production of greenhouse operations. An adequate water supply is needed for irrigation of crops, pesticide application, evaporative cooling (if applicable), growing media preparation, and cleanup. The main sources of water for greenhouse operations are groundwater from wells, surface water, drainage ponds, rain, and municipal water.

Greenhouse Water Requirements

Greenhouse water requirements depend on the crops grown, weather conditions, time of year among other variables. The design for the water supply needs to be made for the peak use time of the year. The following factors have an influence on the amount of water needed for greenhouses:

Quantity of Water Required for Greenhouse Operations

As mentioned greenhouse water requirements for crops depends on many factors, such as climate, type of growing structure, type of irrigation system, growing medium, plant characteristics among other factors. Therefore, it is difficult to estimate the amount of water that a greenhouse will require. Remember that a greenhouse needs water for operational requirements other than irrigating crops. For example, mixing growing media; cleaning containers, structures, and equipment; and staff personal water needs all increase water use.

Water Sources for Greenhouses

The main sources for water for greenhouse operations are groundwater from wells, surface water, drainage ponds, rain water, municipal water, and recycled tailwater from runoff.

Groundwater Wells

Drilled wells are a clean source of water for many greenhouse operations. Groundwater is removed from the ground by drilling a well into a water bearing strata (or aquifer) and installing a pump to lift the water from the well (See Figure 11.13). The flow of water from a well depends on the permeability and size of the aquifer, its recharge area and the amount of rainfall.

Surface Water

Surface water includes streams, rivers, lakes, and ponds which are dependent on runoff from adjacent land or from ground water springs. These are dependent on rainfall rates that vary from year to year. Surface water is subject to contamination from sources such as sediment, chemicals and plant growth. High levels of particles can reduce the life of pumps and clog irrigation systems and multiple filters may be required

Drainage Ponds

Drainage ponds are usually a combination of rain water and run-off. Drainage ponds are formed by constructing a dam across a gully or small valley that enters the stream. Drainage ponds commonly contain fertilizers or other agricultural chemicals. Because of the size and lack of aeration, biological conditions such as algal growth may be a concern.

Rain Water

Rain water can be collected from greenhouses or building roofs without contacting the ground and held in a concrete cistern, fiberglass or polyethylene tank, water silo or other holding tank (See Figure 11.14). Concrete or plastic tanks can be used but are usually limited to about 15,000 gallons. Corrugated steel tanks can be built to almost any capacity as they are delivered in preformed panels and assembled on site. A basic system consists of a storage tank, roof washer, inflow pipes, overflow pipes and a diverter to redirect the excess water when the tank is full. It is clean except for any debris that gets into the system.

Municipal Water

Municipal water includes water supplied by city, county or municipality. The cost and quality are typically high since much of the water is for residential use and drinking water and is treated. For small greenhouse operations of high value crops, using municipal water may be less than the cost of installing and operating pumps for an irrigation system.

Recycled Tailwater

In many areas of the country, greenhouse operations have begun recycling tailwater runoff from their facilities. “Tailwater” is runoff created by excess irrigation or purposeful leaching from containers. It has the potential to be collected and reused, though treatment may be necessary. It is synonymous in this use with irrigation runoff.

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