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, type of growing structure, type of irrigation system, growing medium, type of plants grown 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 evaporative cooling. Water used for evaporative cooling during the summer months can dramatically increase the total water use. Under “optimum” evaporative conditions, a greenhouse pad and fan cooling system will use as much as 0.045 gallons (0.17 L) per 1,000 cubic feet per minute (cfm) (472 L/sec) of fan capacity.
Groundwater
Groundwater can also be considered as a source of irrigation water. During dry seasons wells tend to have a higher mineral concentration compared to rainy seasons. 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. The flow of water from a well depends on the permeability and size of the aquifer, its recharge area, and the amount of rainfall. A well in one location may provide a very low yield, while another area, may provide a high-water yield.
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 a groundwater well.
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
Tailwater and Rainwater Runoff
In many areas of the country, producers have begun recycling tailwater and stormwater runoff from their greenhouse facilities. This process can save money, especially for larger operations, since fertilizers in the runoff are re-utilized. However, runoff water may contain pesticide residues and nitrates. Phytotoxicity problems may result when recycled water contains either pesticides with medium to high water solubilities or one pesticide is extensively used, and the recycled water is applied to plants sensitive to that pesticide. Other drawbacks of recycling include the need for adequate infrastructure to collect, capture and treat irrigation water runoff. However, in areas such as California, recycling of tailwater has been practiced since the 1970s.
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