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Use of plastic films as mulches and in enclosures has become a standard practice in horticulture
to aid in weed control, conserve soil water, and raise soil and air temperature. However, their
potential as a means to adapt to climate change with increased occurrence of extreme weather
conditions has not been explored. This has become more relevant with the availability of modern
speciality films, such as low-albedo black films, high albedo white films, photosyntheticallyactive radiation blocking infrared transmitting films, black-on-white, and lower longwave
transmitting films (e.g., Thermax). We studied the effects of nine state-of-the-art commercially
available plastic films as mulches and in low tunnels for their ability to modify microclimates
and affect plant growth at three certified organic farms: UBC Farm (Vancouver, BC), Mackin
Creek Farm (Near Soda Creek, BC) and Cropthorne Farm (Westham Island, BC). First of all,
these nine plastic films were characterized for their radiative properties in the laboratory and
outside under the sun using a shortwave spectroradiometer. Their use as mulches in an
experiment conducted at UBC Farm showed that black plastic films reflected very little sunlight
(i.e. low albedo) and increased soil temperature. In contrast, white plastic films reflected more
sunlight (i.e. high albedo), and typically decreased soil temperature. While transparent plastic
films reflected a similar amount of sunlight as the soil surface they covered, they caused the
largest increase in measured soil temperature. Highest achievable soil temperature occurred with
black and transparent plastic films for high and low degrees of contact, respectively. Overall,
these plastic film mulches provided a wide range of soil cooling and warming potential (-20% to
55%).
The effect of using Thermax and two high shortwave transmissivity regular and perforated
polyethylene films in low tunnels on soil temperature and energy balance was studied at UBC
Farm. On a sunny day, all three plastic films transmitted 90% of the incoming shortwave
radiation to the black plastic mulch floor for heating inside air. However, due to lower net loss of
longwave energy for Thermax compared to polyethylene films, it was about 30% more efficient
in heating the inside of the low tunnels. In another experiment, also at UBC Farm, growth of
Padrón pepper was studied in low tunnels covered with regular polyethylene and Thermax in
comparison to no cover. Low tunnel grown peppers produced more peppers per harvest period,
but by mid to late August, the harvest rate declined for the low tunnel grown peppers, most likely
due to a depletion of CO2 during the daytime. These results suggest the need to examine the
value of periodic tunnel ventilation or CO2 fertilization. Nevertheless, regular polyethylene and
Thermax tunnels yielded ~12% more peppers than no-cover during the entire harvest period. At
Cropthorne Farm and Mackin Creek Farm, regular polyethylene low tunnels increased zucchini
and broccoli yields by 20% and 200%, respectively.
This research is beneficial to make decisions for choosing appropriate films depending upon
seasons and eco-climate regions in BC. The outcome of this research was disseminated to
scientists, students, extension workers and farmers through (1) eleven presentations at different
5
fora, (2) two fact sheets, (3) one handout, and (4) a video project on “Crop-protection research
and innovation for adaptation to climate change in BC”.
to aid in weed control, conserve soil water, and raise soil and air temperature. However, their
potential as a means to adapt to climate change with increased occurrence of extreme weather
conditions has not been explored. This has become more relevant with the availability of modern
speciality films, such as low-albedo black films, high albedo white films, photosyntheticallyactive radiation blocking infrared transmitting films, black-on-white, and lower longwave
transmitting films (e.g., Thermax). We studied the effects of nine state-of-the-art commercially
available plastic films as mulches and in low tunnels for their ability to modify microclimates
and affect plant growth at three certified organic farms: UBC Farm (Vancouver, BC), Mackin
Creek Farm (Near Soda Creek, BC) and Cropthorne Farm (Westham Island, BC). First of all,
these nine plastic films were characterized for their radiative properties in the laboratory and
outside under the sun using a shortwave spectroradiometer. Their use as mulches in an
experiment conducted at UBC Farm showed that black plastic films reflected very little sunlight
(i.e. low albedo) and increased soil temperature. In contrast, white plastic films reflected more
sunlight (i.e. high albedo), and typically decreased soil temperature. While transparent plastic
films reflected a similar amount of sunlight as the soil surface they covered, they caused the
largest increase in measured soil temperature. Highest achievable soil temperature occurred with
black and transparent plastic films for high and low degrees of contact, respectively. Overall,
these plastic film mulches provided a wide range of soil cooling and warming potential (-20% to
55%).
The effect of using Thermax and two high shortwave transmissivity regular and perforated
polyethylene films in low tunnels on soil temperature and energy balance was studied at UBC
Farm. On a sunny day, all three plastic films transmitted 90% of the incoming shortwave
radiation to the black plastic mulch floor for heating inside air. However, due to lower net loss of
longwave energy for Thermax compared to polyethylene films, it was about 30% more efficient
in heating the inside of the low tunnels. In another experiment, also at UBC Farm, growth of
Padrón pepper was studied in low tunnels covered with regular polyethylene and Thermax in
comparison to no cover. Low tunnel grown peppers produced more peppers per harvest period,
but by mid to late August, the harvest rate declined for the low tunnel grown peppers, most likely
due to a depletion of CO2 during the daytime. These results suggest the need to examine the
value of periodic tunnel ventilation or CO2 fertilization. Nevertheless, regular polyethylene and
Thermax tunnels yielded ~12% more peppers than no-cover during the entire harvest period. At
Cropthorne Farm and Mackin Creek Farm, regular polyethylene low tunnels increased zucchini
and broccoli yields by 20% and 200%, respectively.
This research is beneficial to make decisions for choosing appropriate films depending upon
seasons and eco-climate regions in BC. The outcome of this research was disseminated to
scientists, students, extension workers and farmers through (1) eleven presentations at different
5
fora, (2) two fact sheets, (3) one handout, and (4) a video project on “Crop-protection research
and innovation for adaptation to climate change in BC”.
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