April 2020 - 27

PRODUCTION
Figure 2. Buckets are used to capture applied irrigation water and
leachate. The plant container needs to nest in the opening of the
bucket lid. The mating between the container and lid should not
allow water to enter the bucket. Putty or caulk may need to be
used to exclude the water.
total salinity is less than 1.0, then a leaching
fraction of 0.10 is sufficient. If the water quality is
very poor, you may also want to look at treatment
or blending higher quality water to lower the
salinity. Information regarding this can be found
at the CleanWateR3.org website, from literature
on the topic, or your cooperative Extension agent
or specialist.
When the leaching fraction is greater or
less than optimal, you will need to adjust your
irrigation duration. The closer you are to the
target, the more accurate each adjustment is.
An estimate* of the adjustment to the runtime
can be calculated by:
TA
= t × (LFT - LFM)
Where:
* TA
is the time adjustment
* t is the current duration of the irrigation
* LFT
is the targeted leaching fraction
* LFM is the measured leaching fraction
* *This is a simplified version of the
actual calculation
Figure 3. Drip emitters or spray stakes can be placed directly in a
container. The bottom of the plant container should be raised to allow
excess water to drain.
Calculate the leaching fraction by dividing the
leachate volume by the applied water volume.
Leaching fraction = leachate volume ÷
applied volume
The volume method can provide leaching
fraction values greater than 1.0 or 100% leaching
since the canopy of the planted container can
collect more water than an empty container.
This occurs when plant canopies are greater
diameter or taller than the empty, lined container.
The weight method described below will always
provide a leaching fraction between 0.0 and 1.0.
If using a drip irrigation or spray stakes, a pan
under a raised container and milk or juice jug
can be used to collect leached and applied water
(Figure 3).
MEASURING BY WEIGHT YIELDS
ADDITIONAL INFORMATION
A scale can be used to easily convert weight
in grams to volume when it comes to water
(1 mL = 1 gram). When using the weight
method, first separately weigh: 1) the empty
bucket and 2) the planted container before the
plant needs to be irrigated (Figure 4). Place
the modified bucket lid on the bucket and then
nest the planted container in the the lid. Make
sure that water that lands on the lid will not be
able to drain into the bucket. Place the planted
Figure 4. A scale can be used to
calculate the amount of water
captured. 1 gram of water equals
1 milliliter (mL) and 1 ounce by
weight equals 1 ounce by volume.
Also remember: " A pint is a pound
the world around " and both a pint
and a pound are 16 ounces.
container and bucket in the irrigation area.
Complete an irrigation event and then wait
about an hour to allow all of the water to drain
from the substrate into the bucket. Remove the
irrigated plant from the bucket and reweigh it,
then weigh the bucket with the collected water.
Subtract the pre-irrigation weights from the
corresponding post-irrigation weights. What you
will determine:
1. Water retained by the plant = irrigated
plant - " dry " plant
2. Leachate volume = bucket with water -
empty bucket
3. Applied water volume = water retained by
the plant + leachate volume
4. Leaching fraction = leachate volume ÷
Applied water volume
WHAT THIS INFORMATION TELLS YOU
For most levels of salinity of the production
system (water, fertilizer, substrate), a leaching
fraction of 0.20, an amount equivalent to 20%
of applied water draining from the container, is
necessary to ensure you are applying adequate
amount of water and leaching any excess salts.
If the electrical conductance (EC) of your water,
including nutrients for liquid feed systems, is
greater than 2.0, then a leaching fraction of 0.30
is required to leach the additional salts. If the
OTHER BENEFITS
A benefit of using the bucket method for
plants irrigated by overhead irrigation is that
the leachate represents the amount water that
actually enters the container, and it takes into
consideration both the water that lands directly
on the substrate and the water that is intercepted
by the plant canopy. This is important because
the architecture of the canopy could either direct
the intercepted water into the container (for
example, a vase-shaped plant) or the water could
be shed away from the substrate surface (an
umbrella-shaped canopy with broad leaves, for
example). A simple pruning can have a dramatic
effect and result in a change in the amount of
water applied.
Measuring leachate can be a good tool to
determine if the proper amount of water is applied
at each irrigation to control substrate salinity. It
is quick, inexpensive, easy to do and will provide
the information you need to be a better irrigation
manager. Using the information gathered
can reduce water use, improve nutrient use
efficiency and reduce runoff. For more detailed
information on this method, download the Virginia
Cooperative Extension publication at: www.pubs.
ext.vt.edu/content/dam/pubs_ext_vt_edu/spes/
spes-128/SPES-128.pdf.
Lorence R. Oki is cooperative Extension specialist in
the department of Environmental Horticulture and
co-director of the UC Nursery & Floriculture Alliance
at the University of California-Davis. James S. Owen
is research horticulturist with the US Department of
Agriculture Agricultural Research Service (USDA-ARS).
They can be reached at lroki@ucdavis.edu and jim.
owen@usda.gov, respectively.
GREENHOUSE PRODUCT NEWS 27
http://www.CleanWateR3.org http://www.pubs http://ext.vt.edu/content/dam/pubs_ext_vt_edu/spes/
April 2020

Table of Contents for the Digital Edition of April 2020
