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  • From: "Lawrence F. London, Jr." <lflj@bellsouth.net>
  • To: permaculture <permaculture@lists.ibiblio.org>
  • Subject: [permaculture] Fwd: The Overstory #249: Wick Irrigation for Tree Establishment
  • Date: Fri, 21 Sep 2012 00:26:55 -0400

-------- Original Message --------
Subject: The Overstory #249: Wick Irrigation for Tree Establishment
Date: Wed, 19 Sep 2012 19:30:38 -0600
From: The Overstory <overstory@agroforestry.net>

The Overstory #249: Wick Irrigation for Tree Establishment
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Wick irrigation can greatly increase water use efficiency, which is
especially needed in regions with severe water scarcity. In this photo,
different wicking materials are evaluated for capillary rise, gravity
flow and wetting rates.

------------------------------------------------------------------------

**/The Overstory/* #249/
/*

*Wick Irrigation for Tree Establishment*

by David A. Bainbridge

September 17, 2012

The world’s 500 million resource-limited farmers are facing ever more
difficult challenges in growing sufficient food and products for sale
with inadequate water supplies (Hazell et al., 2007). These farmers face
difficulties in locations where the climate is moderate but rainfall is
seasonal, and endure far more severe problems in arid and semi-arid
regions where rainfall is scarce and unpredictable. Climate change,
including increased climate variability, is expected to worsen the
problems these farmers and gardeners face by raising the temperature and
reducing rainfall. The severe 2011-12 drought in Mexico illustrates what
we may expect in the future (Figure 1, NOAA, 2012). The global maps of
predicted chances are equally daunting.


*Figure 1. Mexico drought – a view of the future.*

These small farmers urgently need to increase water use efficiency.
Despite the need for low cost, simple, improved irrigation systems that
could increase yields, scientific research and international development
programs have largely neglected this challenge. This is primarily due to
the lack of money in these resource-limited communities. Even with
increased water use efficiency, many farmers will still struggle to meet
their basic food needs. Deep pipe (Bainbridge, 2006), buried clay pot
(Bainbridge, 2001) and other traditional systems work well but are often
too expensive.

Wick irrigation is a low cost alternative that may help many of these
small farmers. A wettable fabric or rope is used to carry water from a
reservoir or pipe to the roots of the plant. In its simplest form it can
be done with rags and recycled bottles at almost no cost. Cotton wicks
were traditionally used in conjunction with buried clay pot irrigation
in India (Mari Gowda, 1974). The wicks help move the water further from
the clay pot to encourage greater root development (Bainbridge, 2002).
Subsequent tests and research have demonstrated the value of wicks for
irrigation even in very severe environments. These wicks can be gravity
flow down (fast), capillary flow up (slow), or a hybrid (Figure 2).


*Figure 2. Wick styles – capillary, gravity, hybrid. Figure 3.
Travertine capillary wick installation*

Capillary mats are now widely used in greenhouses and plant propagation
(Neal and Henley, 1992). Wicks have also been used for watering plants
in containers for decades (Editor, 1955). A well-developed wick system
for irrigating window boxes is also sold in commercial kits (e.g.,
Wickinator™ and Groasis Waterboxx) (Editor, 2010).

Wicks for field use are less well studied. To explore their potential
for agroforestry, trials of wick irrigated tree seedlings were conducted
in the greenhouse at University of California, Riverside. The 6 mm nylon
wick was threaded through the bottom of the plant container with
capillary rise providing water from a reservoir below. A very young palo
verde (Parkinsonia floridum) seedling about 8 cm tall in 16 grit silica
sand was growing and exhibited no sign of water stress after one month
with water consumption of just 20-30 ml/day in a very dry greenhouse
environment. This result is promising for agroforestry and environmental
restoration.

An initial field test was installed on a very dry, east facing slope at
a borrow pit restoration site in California’s Coachella Valley in 1988.
This site has an average rainfall of just 6.7 cm (2.6”) and pan
evaporation of 267.5 cm (105”). The tree seedlings were fed by 5 mm
cotton capillary wicking from a 2 liter bottle with the wick rising from
the reservoir through a plastic tube with the exposed end of the wick
placed with the seedling roots (Figure 3). The water moved by capillary
action and wicking up and across the arched tubing to the seedling.
Prosopis glandulosa (mesquite) seedlings with wicks grew and survived
better than surface watered plant receiving more water, although
algae/mold/scum built up on the wicks and appeared to reduce water transfer.

The next test used capillary nylon wicks wetted from below by a buried
pipe on a landscape restoration project along highway 86 also in
Coachella Valley. Here the wicks were wetted by a buried 10 cm diameter
pipe reservoir that was refilled periodically (Figure 4). The 8 mm nylon
wicks worked better than cotton, but the small wicks and capillary rise
did not promote growth and survival as well as buried clay pot, porous
capsule or deep pipe irrigation (Bainbridge, 2002).

To better understand wick irrigation, a series of lab tests have been
done using water with dilute food coloring to evaluate capillary rise,
gravity flow and wetting rates in wick materials (Figure 5). These
showed significant differences in capillary rise depending on material
and weave. Most materials tested achieved a capillary rise of at least
25 cm and some passed 50 cm. The 11 mm (7/16”) detergent washed solid
braid nylon exhibited the best capillary rise, reaching 25 cm in 100
minutes and 55 cm in 20 hours. Other wicks including polyester yarn and
11 mm double braid polyester rope performed almost as well. Gravity flow
rates also vary widely but are generally related to capillary rise. With
new 11 mm solid braided nylon rope washed once with hot water and
detergent (to remove lubricants used in weaving) the mean flow rate of
gravity wicks in a snug fitting plastic tube was 0.6 ml/second (n=11).
With a hose clamp tightened one turn past snug the mean flow dropped to
0.2 ml/second and the clamp could easily be tightened enough to stop the
flow. Flow studies showed that water in an 11 mm unconstricted gravity
nylon wick would reach 4 meters down a vertical wick in 15 minutes.

*Figure 4. Capillary wick from buried pipe*

*Figure 5. Capillary rise comparison*

With a better understanding of the opportunities for wick irrigation, a
group of five barely alive (plant health rating 2 on a scale of
0=dead–5=excellent) orphan mesquite seedlings left over from field
projects were pruned and planted near the Salton Sea in California’s low
desert in 2009. The wicks used in this trial were 50 cm (20”) long made
with 11 mm washed solid braid nylon rope with 8 liter (2 gallon)
reservoirs (Figure 6). Thread to barb fittings were screwed and glued
into a hole drilled in the bottom of the reservoir to attach clear 12 mm
(1/2”) inside diameter vinyl tubing. A hose clamp near the end of the
plastic tubing was used to adjust the flow to the fully buried wick. All
planted mesquite seedlings received a tree shelter (Bainbridge, 1994).
Reservoirs were refilled when possible, about every 30 days for the
start of the first growing season, or about 250 ml/day. All plants
revived well. After 631 days the mean plant health rating of the
survivors was 3.6 out of 4. As the polyethylene 8 liter bottles broke
down in the sun after more than a year, they were replaced with recycled
20 l containers made with PETE. These were filled twice the second year.
After receiving a total of less than 120 liters of water and less than
7.5 cm of rain, all remained alive and well after three years. Previous
irrigation studies in this area would suggest survival rates of 0-2%
with surface irrigation, 25% with drip, and 80-90% with buried clay pots
or deep pipes. Wicks appear to be as good as the best and use less water
and cost less to install.

Wick irrigation has been demonstrated to work well and should be
considered for field planting of trees and shrubs in agroforestry system
establishment and environmental restoration. It can provide critically
needed water while plants get established in micro catchments or runoff
watering systems (Cohen, 2002; Evenari et al., 1982). It seems unlikely
that one wick would be able to provide enough water to maintain a larger
shrub or tree (1 m tall or more depending on water demand). Future tests
will help clarify this and should suggest how many wicks might be needed
for larger plants and trees of differing species. Wicks may also be used
to help reduce the vulnerability of drip systems to clogging and
blockage (Figure 7).

*Figure 6. Mesquite gravity wick details*

*Figure 7. Wick slid over drip tubing*

The rapid flow rates in gravity wicks also offer a great opportunity for
establishing trees where groundwater is within 5 meters of the surface.
A hole can be drilled to groundwater using a hand or powered auger and a
wick can be pushed down to the water table. The gravity feed from above
will enable the root to extend downward to reach the capillary rise from
the water table (Figure 8). This could make it possible to grow trees in
areas where the roots would otherwise fail to reach groundwater. In hot
climates this could be rapid for some species. Under favorable
conditions mesquite roots can grow rapidly, up to 4 mm/hour (Cannon,
1917). If the groundwater rise in the wick is 1 m, and the roots grow
just 1 mm an hour they could reach groundwater in about two weeks.
Without the wicks, developing this ground water connection can take
several years (pers. obs.).

Wicks may also prove useful in planting cuttings and poles. A wick (for
cuttings) or several wicks (for pole planting) could be loosely tied to
the cutting to provide moisture for root establishment. The wick could
again be extended to groundwater to improve long-term survival.

Wicks are robust, low cost and offer a long refill interval. This can
make them a good candidate for agroforestry in many areas of the world.
With global climate change increasing the challenges of developing
sustainable agro-ecosystems, wick irrigation may be a valuable addition
to the tool kit of small scale irrigation systems (deep pipe, clay pot,
porous pipe and porous capsule) suited for small, resource-limited
farmers. It can help with the key challenges of establishing needed
trees and conserving water (Chambers et al., 1991).

Additional research on wick material and wick preparation is well suited
for school and university class projects. Demonstration projects are
urgently needed (Bainbridge, 2012). Tests of wicks in different
configurations for gardens and greenhouses are also needed.

*Wicks for starting trees or shrubs*

Tree or shrub wicks can be made with nothing more than a larger plastic
bottle or pail, some solid braid nylon rope (7/16 inch works well) and a
razor knife. Wash the rope with detergent or soap, rinse and let dry.
Hang in the sun for a week or two if possible. Trim the fuzz from one
end of the nylon rope and using a flame melt the nylon end, then with a
gloved hand or stick shape the tip into a point (care is needed, as the
hot melted nylon can easily cause burns). For a regular bottle, cut or
punch a hole smaller than the rope near the bottom, and for a sports
type drinking bottle, cut out the web (the small crossed plastic piece)
in the bottle valve and cut a flap in the bottom of the bottle for
refilling. Pull the rope through until 30-40 cm (14-16 inches) are left
exposed and then tie a knot and cut the pointed end free to go on the
next bottle. For a hybrid wick system that adds advantages of capillary
and gravity wicking insert the wick about halfway up the bottle in a
plastic tube. It will act as a gravity wick at first, then as the water
level drops it will transition into a capillary wick.

Plant the seedling and wick together. If it is a taproot type plant and
the soil is soft, one can push the wick deep into the soil with a metal
needle. The wick should be exposed to the roots of the shrub or tree as
it comes out of the container. Multiple wicks can also be used from one
reservoir to guide root development to improve wind firmness. Wick
placement may also be used to reduce tree root/annual crop interference.
After planting add a tree shelter, cage, sticks, branches, rock mulch or
other protection from wind, sun and browsing animals.

For a more adjustable wick system use a threaded to barbed plastic
fitting (preferably nylon or polypropylene) and a piece of 12 mm (1/2”)
inside diameter clear vinyl tubing. Drill a hole in the bottom edge of
the reservoir with a drill bit the size of the diameter of the fitting
at the valley at the bottom of the threads so the fitting will screw
into the container. For flexible plastic the hole size can be even a
little smaller. Then lay a bead of polyurethane glue (e.g., Gorilla
glue) around the hole and screw in the fitting. Let dry. Cut a short
length of tubing to carry the wick from the reservoir and down at least
5-10 cm (2-4”) into the soil. Slip a hose clamp over the tubing and then
push the wick up into the tube several inches. Push the vinyl tube onto
the barbed fitting and then tighten the hose clamp until the wick is
securely fastened. For a project with many wicks test flow rates at
different tightness to obtain an appropriate flow. Refill as needed.
Adjust screw clamp to modulate flow rates.

------------------------------------------------------------------------

Bainbridge, D. A. 2012. Restoration of arid and semi-arid lands. Chapter
10, Pp. 115-129 in J. van Andel and J. Aronson, Restoration Ecology: The
New Frontier. Blackwell.

Bainbridge, D. A. 2007. A Guide for Desert and Dryland Restoration: New
Hope for Arid Lands. Island Press, Washington, DC.

Bainbridge, D. A. 2006. Beyond drip irrigation – hyper efficient
irrigation systems. Proceedings American Society of Agricultural and
Biological Engineering Annual International Meeting, Portland, Oregon.
ASABE #062073. St. Joseph, Michigan 10 p.

Bainbridge, D. A. 2002. Alternative irrigation systems. Ecological
Restoration. 20(1):23-30.

Bainbridge, D. A. 2001. Buried clay pot irrigation. Agricultural Water
Management 48(2):79-88.

Bainbridge, D. A. 1994. Treeshelters improve establishment on dry sites.
Treeplanter's Notes. Winter 45(1):13-16.

Cannon, W. A. 1917. Relation of the rate of root growth in seedlings of
Prosopis velutina to the temperature of the soil. Plant World 20:320-333.

Chambers, R., N. C. Saxena and T. Shah. 1991. To the Hands of the Poor.
Intermediate Technology Publications, London, UK 273 p.

Cohen, M. E. 2002. Utilizing microcatchment systems to increase tree
establishment rates in the Bolivian high plains. MS Thesis, Forestry.
Michigan Technological University. Houghton, MI.
http://forest.mtu.edu/pcforestry/people/1998/cohen.pdf Accessed June 18,
2012

Dai, A. 2010. Climate change: Drought may threaten much of the globe
within decades. University Corporation for Atmospheric Research,
National Center for Atmospheric Research, Boulder, CO. October 19, 2010.
www2.ucar.edu/atmosnews/news/2904/climate-change-drought-may-threaten-much-globe-within-decades
Accessed March 25, 2012.

Editor. 1955. New aids to living – Waterwick. Popular Science 167(4):170.

Editor. 2010. A 100 best innovations of 2010. Popular Science.
www.popsci.com/technology/gallery/2010-12/gallery-looking-back-100-best-innovations-2010?image=46

Evenari, M., L. Shanan and N. H. Tadmor. 1982. The Negev: the challenge
of a desert. Harvard University Press, Cambridge, MA.

Hazell, P., C. Poulton, S. Wiggins and A. Dorward. 2007. The Future of
Small Farms for Poverty Reduction and Growth. 2020 Discussion Paper No.
42. International Food Policy Research Institute. Washington, D.C.

Mari Gowda, M. H. 1974. Dry orcharding. The Lal Baugh 19(1/2):1-85.

NOAA. 2012. North American Drought Monitor.
www1.ncdc.noaa.gov/pub/data/cmb/drought/nadm/nadm-201201.pdf Accessed
Feb 23, 2012

Neal, C. A. and R. W. Henley. 1992. Use and runoff comparisons of
greenhouse irrigation systems. Proceedings Florida State Horticultural
Society. 105:191-194.

------------------------------------------------------------------------

*ORIGINAL SOURCE*

Bainbridge, David A. 2012. Wick Irrigation for Tree Establishment.
Permanent Agriculture Resources, Holualoa, Hawaii. http://www.overstory.org

------------------------------------------------------------------------

*AUTHOR BIO*

David Bainbridge is a restoration ecologist based in San Diego,
California. He is currently working on a book, “Beyond Drip,” describing
the many traditional irrigation systems that can be more efficient than
drip and can be used by resource limited farmers. His work appeared in
Overstory #175--Deep Pipe Irrigation in 2006. He can be contacted at:
sustainabilityleader@gmail.com

------------------------------------------------------------------------

*RELATED EDITIONS OF THE OVERSTORY*

The Overstory #209--Soil Compaction & Trees
The Overstory #175--Deep pipe irrigation
The Overstory #111 - Land Husbandry
The Overstory #104--Soil and Water Conservation
The Overstory #96--Sheet Mulch
<http://www.agroforestry.net/overstory/overstory96.html><http://www.agroforestry.net/overstory/overstory96.html>
The Overstory #88--Revegetation Planning for Farm Forestry
<http://www.agroforestry.net/overstory/overstory88.html><http://www.agroforestry.net/overstory/overstory88.html>
The Overstory #80--Forests and Water
<http://www.agroforestry.net/overstory/overstory80.html><http://www.agroforestry.net/overstory/overstory80.html>
The Overstory #73--Buffers, Common-Sense Conservation
<http://www.agroforestry.net/overstory/overstory73.html><http://www.agroforestry.net/overstory/overstory73.html>
The Overstory #45--Vegetative Erosion Barriers in Agroforestry
<http://www.agroforestry.net/overstory/overstory45.html><http://www.agroforestry.net/overstory/overstory45.html>

------------------------------------------------------------------------

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  • [permaculture] Fwd: The Overstory #249: Wick Irrigation for Tree Establishment, Lawrence F. London, Jr., 09/21/2012

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