Goal: To measure compaction of paper-wrapped substrates, including Ellepot® and Fertiss®.
Substrate compaction reduces air porosity in the mix, which can lead to reduced root growth and slow drying. Moderate compaction helps the pot hold together during growing and shipping, and can improve distribution of water through the substrate.
Step 1. Requirements
Step 2. Irrigate to container capacity
After manufacturing the pots, bring the substrate to container capacity by passing through a water tunnel for 3 to 4 times or using a fine mist nozzle by top irrigation, or subirrigating.
Allow to drain for 30 seconds.
Step 3. Set the digital force gauge
Step 4. Measure compaction
Measure the stabilized pot by slowly pushing the 1-inch adapter disc downward by 3/8-in (1 cm) from the top of the pot, and take the reading on the LCD display (k).
Step 5. Calculate substrate compaction
Compaction (g/cm2) equals the reading on the meter (k) divided by 5.07.
For example, 1520 g on the meter equals 300 g/cm2. If a different sized adapter disc is used (other than 1-inch diameter), with radius r, divide the meter reading k by πr2.
For companies that manufacture a large volume of pots with the same substrate, another approach is to air-dry a tray of pots over a period of days, and then weigh the tray.
This 'bulk density' is another compaction measurement that should be consistent over time.
For more information: Contact authors Jinsheng Huang and Paul Fisher of University of Florida IFAS Extension. Thanks to our Floriculture Research Alliance at University of Florida sponsors including A.M.A. Plastics, Blackmore Co., Everris, Fafard et Frères Ltd (Canada), Fine Americas, Greencare Fertilizers, Pindstrup, Premier Tech Horticulture, Quality Analytical Laboratories, Sun Gro Horticulture, and leading young plant growers. August 23 2014.