Crop Water Requirements

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 Crop water requirements are important for planning dugout size and/or obtaining water permits for drawing water from a creek or river. When calculating the water requirements of crops, keep a few things in mind.

Solar radiation
This is the major factor in estimating water requirements. The higher the solar radiation, the higher the evapo-transpiration from plant surfaces will be. In the winter water loss due to transpiration from leaves is less than that of summer light conditions. If artificial lights are used in winter, as is done in case of roses, then the winter water usage will be higher. This also means the amount of water will vary from spring through to fall.

Solar radiation is measured by a solarimeter, which is located outside the greenhouse. The readings, which are in joules/cm² or kilojoules/m² can be fed into the environmental control computer for greenhouses so equipped. The computer should be programmed for each 100 joules/cm², plants should receive between 150 to 200 ml/m² of greenhouse space. Cucumbers grown at a density of 1.25 plants/m², will receive between 150 to 200 ml of water for each 100 joules of light energy. The growers know the volume of drippers/hour and are able to deliver the required amount of water accordingly.

Growers who don't have access to computers use visual tools to water the plants. Over a period of time growers gain experience with water management and some of the figures are as follows:

  • Floricultural crops generally are estimated to be around 400 L/m²/year
  • Peppers, tomatoes and cucumbers are estimated to be around 700 to 800 L/m²/year.
Stage of plant growth
Younger plants require less water when compared to a fully grown, mature crops.

Leaching requirements
Growers using sawdust as a growing medium may use up to 50% of the water for leaching purposes. The amount of leachate is adjusted according to sunlight. A study has been completed at CDCN where low volume drippers were used to irrigate a cucumber crop. Two liters of water was delivered in 4 hours which was compared to the same amount of water delivered in 40 minutes. The leaching of water from root zone was around 7% in the first case as compared to 33% in the second. Two growers are currently using this slow water delivery system to grow roses.

Other uses of water
When calculating water requirements of greenhouses, also keep in mind the water used for misting, fogging or washing the vegetables.

M. Mirza and M. Younus, CDCN
Greenhouse Coverings - December 1999
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For more information about the content of this document, contact Shelley Barkley.
This information published to the web on July 3, 2002.
Last Reviewed/Revised on June 19, 2010.