Leaching Fraction Explained

In case you missed the class on container irrigation we had this week, learning about how to conduct a leaching fraction is a great tool to get to know.  This super-simple method will give you the confidence to irrigate effectively to reduce excess pumping, reduce the amount of fertilizer needed to grow a plant, reduce pesticide use and grow quality plants.   It will also give you an accurate amount of time to tell people to run the irrigation system depending upon the changes in weather, season, plant size, etc.
A leaching fraction is simply the amount of water that leaves the container after you run irrigation divided by the total amount of water that was applied and captured by the container during irrigation.  The last number is arrived at by subtracting the weight of a dry plant before irrigation from a wet plant after irrigation.  This simple equation creates a number, the leaching fraction.  When multiplied by 100 will give a percent.  The Water Quality/Quantity Best Management Practices for Florida Nurseries manual states that the leaching fraction percent should be 10-15%.  If the number is extremely low say 0-5% you may be under-watering plants.  If the number is higher than you are over-watering plants.  You can easily do this with buckets attached underneath the pots you are growing, randomly scattered in your field.  This can be easily done for small annual containers to large containers with a slight modification on catching the leachate.  For more information here is a video that can be found in the BMP Manual  http://www.freshfromflorida.com/Media/Files/Agricultural-Water-Policy-Files/Best-Management-Practices/Nursery-Videos/Video-8-Leaching-Fraction  If you would like to see the rest of the Florida Nursery manual here is a link to that  http://www.freshfromflorida.com/content/download/37570/848371/NurseryBMP.pdf  If you would like help setting up a leaching fraction and interpreting the results, contact Shawn at UF/IFAS Extension Hillsborough/Polk County ststeed@ufl.edu for a nursery visit.