Part3Lecture3-4 - Water Management There are four main...

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16 Water Management There are four main topics to be addressed regarding water management. The first topic is the timing of the irrigation. In other words, how dry or moist should the medium be, or at what frequency or time interval should water be applied? The second topic is the volume of water to be applied at any one irrigation. What amount of water is needed to moisten the root medium? Is leaching necessary? The third topic is the importance of the temperature of the irrigation water. The fourth and final topic is the method of application . What is the most efficient and economical way to get water to all the plants? Timing In many commercial greenhouses the approach to water management is, when in doubt, water! While this may not be harmful to soil aeration in porous, peat-based media, it may lead to unnecessary water use and runoff. Watering only when needed will 1) reduce water use and runoff, 2) save labor costs and time, and 3) improve the post production survival or quality of many floriculture crops. There are six main methods of determining when to water greenhouse crops: Plant appearance Weight or gravimetric determinations Timed application Media water potential or moisture tension Vapor pressure deficit (VPD) Light or radiant energy measurements Pushing a finger into the root medium or looking at the color of the medium are not among the methods listed. Frequent skin contact with the root medium is generally discouraged due to the potential presence of pest control chemicals. Medium appearance is not acceptable because peat-based media may seem moist, but the water actually available to the plants may be limited. Let’s briefly discuss the six methods of determining when to water. Plant appearance - Recommendations have been made to water when stress or wilting occurs, or just before wilting is noted. While allowing plants to dry thoroughly between irrigations is an important goal, it is not appropriate to allow all crops to go to wilting before irrigation. Depending on the uniformity of drying of plants on the bench, it is possible that allowing a few, 5 percent, of the plants that dry the fastest to wilt will provide an acceptable indicator of when to irrigate the majority of the crop. Weight or gravimetric determinations - Perhaps the most common method of determining the need for water is for the grower to check the weight of individual plants
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17 or pots. Representative plants are taken off the bench manually and put on a scale. By checking the weight, a decision can be made to irrigate when a certain amount or percent of the available water is lost. Using a scale can help growers schedule irrigations more efficiently, especially new growers who are worried about letting plants get too dry. There are five steps in using weight to determine when to irrigate:
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Part3Lecture3-4 - Water Management There are four main...

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