February 2019 - 10

Biodegradable mulch lessens labor pressure
By Dean Peterson
FGN Correspondent
Plastic mulch helps control weeds,
conserve moisture and speed soil
warmup - to name a few advantages -
but biodegradable plastic mulch offers
that and potentially even more.
" Plastic mulch is a very common tool
around the U.S. and around the world, but
what are some alternatives to plastic mulch
and what can mulch do for your soils? "
asked Carol Miles, professor in vegetable
horticulture at Washington State University
(WSU). Miles was a speaker at the recent
Great Lakes Fruit, Vegetable and Farm
Market EXPO in Grand Rapids, Michigan.
Many growers are hesitant to adopt
biodegradable plastic mulches because
of concerns over uncertainty, risk and
aesthetics.
WSU is completing the fourth year of
a study evaluating biodegradable plastic
mulch. If it performs as envisioned, the
mulch completely biodegrades without
harm to the soil or the environment
and offers benefits equal to polyethylene
mulch. Biodegradable plastic mulch
has lower labor costs because it doesn't
have to be removed and disposed of at
the end of the season - an important
consideration because of its higher cost.
" You till it in at the end of the season, "
Miles said. " The big advantage of
biodegradable plastic mulch is it saves
on labor. "
WSU is evaluating biodegradable
plastic mulches at Mount Vernon,
Washington, and with the University
of Tennessee at Knoxville, Tennessee.
Working at two locations has already
determined the rate of mulch
deterioration - measured as the percent
of soil exposure (PSE) through the
season - is much different at different
sites and varies with the year. In general,
expect faster deterioration in years with
more moisture and higher temperatures.
Researchers lay mulch at Boxx Berry Farm in Ferndale, Washington, where Washington State University researchers are studying
biodegradable mulches. Photo: Washington State University
At Knoxville in 2016, all products
held up well with about a 20 percent PSE
on Sept. 1. However, heavy rains and
high temperatures in 2015 made some
products fall apart with near 100 percent
PSE by mid-summer.
At Mount Vernon, with Washington's
cooler temperatures, the biodegradable
products held up even better in 2016 with
PSEs around 5 percent on Sept. 1. In 2015,
only one biodegradable product fell apart
and had PSE up to around 60 percent by
Sept. 1, but this was because the product
was folded in half by the manufacturer,
and the fold was a weakness that caused
the rapid deterioration.
Location matters
" The location, not the crops,
determines the amount of degradation, "
Miles said. " You really need to test these
products on your farm to see which of
these products works for you. Having
enough mulch intact through the length
of the growing season is very important
for weed control. "
Solid results on comparisons of weed
control were difficult to come by. " There
was a mixed response on weed control
because weed pressures are different at
different sites, " Miles said. " There are
more issues affecting weed control than
just mulch. "
Yield is a more consistent message.
" The site is what's really going to
determine yield, " Miles said. " All of the
black, biodegradable plastic mulches
had comparable yields to black,
polyethylene mulch. "
WSU has been testing the
products BioAgri, Exp.PLA/PHA (an
experimental film), Naturecycle, Organix
(black), Organix Clr (clear), standard
polyethylene and WeedGuardPlus.
The products vary in their bio-based
percentage. BioAgri is 20 to 25 percent
bio-based, Exp.PLA/PHA is 86 percent
bio-based and Naturecycle is equal
to or greater than 20 percent biobased.
Organix and Organix Clr are 10
percent bio-based while polyethylene
is less than one percent bio-based and
WeedGuardPlus is 100 percent biobased.
WeedGuardPlus is paper, 100
percent biodegradable, and allowable for
use in certified organic production.
The percentage of bio-based
composition is not the determining
factor in product quality or time of
degradation because the mulches can be
made in many ways.
Biodegradable plastics can be derived
from corn starch or other plant starches
or from the bacterial fermentation of
plant sugars or lipids. The biodegradable
polymers can also be made from
synthetic products containing ester
10 | FruitGrowersNews.com
bonds which are readily broken down by
microorganisms, sunlight and water.
A sticky situation
Biodegradable plastic mulch has a
reputation of sticking to heavy fruit and
causing problems with visible appearance.
The WSU study used pumpkins in the
trials to assess that problem.
The problem did emerge and the
mulch did stick to the pumpkins. In
a new study, Miles found the mulch
fragments could be wiped off the fruit
if the fruit was slightly damp when
it was picked due to humidity, dew
or irrigation and the fruit was wiped
immediately. " If you have a food grade
product going out of your field, you're
not going to want to take the time to
try to wash it off, " Miles said. " Consider
biodegradable plastic mulch carefully if
you're in this situation. "
" All of the black,
biodegradable
plastic mulches had
comparable yields to
black, polyethylene
mulch. "
− Carol Miles,
Washington State University
WeedGuardPlus in the study was
found to have a cooling effect on the
soil, which had a negative effect in
Washington's cool climate. In warmer
parts of the country, the cooling effect
could be a positive.
WeedGuardPlus also had the ability
to control yellow nutsedge. " It controlled
yellow nutsedge every year in the trial, "
See MULCH, page 12

http://www.FruitGrowersNews.com

February 2019

Table of Contents for the Digital Edition of February 2019