The retractable liquid foam technology improved greenhouse climate

study in HortTechnology featured a new technology that improved greenhouse climates by reducing solar heat radiation and temperatures during the hot summer season. The study, published by a team of Canadian researchers, was the first investigation into the effects of application of the liquid foam technology as a shading method. Results showed that the technology improved greenhouse and plant microclimates and decreased air temperature more than conventional shading curtains traditionally used by greenhouse growers.

Excess temperature, solar radiation, and high vapor pressure deficit are major greenhouse concerns during the summer season. These extreme conditions increase plant stress and decrease crop productivity and fruit quality. Methods such as cooling pads and fogging systems have been used to prevent plant heat stress during the day, and various shading techniques are often used by growers to decrease solar radiation and reduce air and leaf temperatures. Shade cloths reduce the amount of solar energy entering the greenhouse and consequently decreased air temperature by partially cutting the heat portion of the solar radiation, but this incoming energy commonly contains more than 50% heat (infrared radiation), which is not useful for plant growth in the summer.

Sunarc of Canada, Inc. developed an innovative new shading technology that generates retractable liquid foam and distributes it between two layers of polyethylene film used as a greenhouse covering material. The Canadian research team set out to determine the effects of different shading strategies using the liquid foam technology on greenhouse and plant microclimates. The research was conducted over 2 years in two different areas of Canada, where experimental greenhouses were retrofitted with the new technology. Tomato and sweet pepper plants were used with two shading strategies: a conventional nonmovable shading curtain in comparison to the liquid foam shading system based only on outside global solar radiation, and foam shading applications based on both outside global solar radiation and greenhouse air temperature. The team recorded data on the greenhouse microclimate (global solar radiation, air temperature, and relative humidity), the canopy microclimate (leaf and bottom fruit temperatures), and ventilation (opening/closing).

"This study showed that the retractable liquid foam technology improved greenhouse climate", noted Kamal Aberkani, main author of the report. "Under very sunny, very hot conditions, a difference of up to 6 �C in air temperature was noted between the unshaded and shaded greenhouses as a result of liquid foam application at 40-65% shading".

As per the report, additional benefits of the technology included an increase of up to 12% in greenhouse relative humidity, a decrease in the frequency of roof ventilation operation, and an increase in the length of time bottom fruit temperature remained cool after shading ended.

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Climate change complicates plant diseases of the future

Researchers evaluate soybean plants within a ring of ozone in the SoyFACE facility in Urbana, Ill. Credit: Carrie Ramig, USDA-ARS & University of Illinois

University of Illinois researchers are studying the impact of elevated carbon dioxide, elevated ozone and higher atmospheric temperatures on plant diseases that could challenge crops in these changing conditions.

Darin Eastburn, U of I associate professor of crop sciences, evaluated the effects of elevated carbon dioxide and ozone on three economically important soybean diseases under natural field conditions at the soybean-free air-concentrating enrichment (SoyFACE) facility in Urbana.

The diseases downy mildew, Septoria brown spot, and sudden death syndrome were observed from 2005 to 2007 using visual surveys and digital image analysis. While changes in atmospheric composition altered disease expression, the responses of the three pathosystems varied considerably, Eastburn said.

Elevated carbon dioxide levels are more likely to have a direct effect on plant diseases through changes to the plant hosts rather than the plant pathogens.

"Plants growing in a high carbon dioxide environment tend to grow faster and larger, and they have denser canopies," Eastburn said. "These dense plant canopies favor the development of some diseases because the low light levels and reduced air circulation allow higher relative humidity levels to develop, and this promotes the growth and sporulation of many plant pathogens."

At the same time, plants grown in high carbon dioxide environments also close their stomata, pores in the leaves that allow the plant to take in carbon dioxide and release oxygen, more often. Because plant pathogens often enter the plant through the stomata, the more frequent closing of the stomata may help prevent some pathogens from getting into the plant.

In elevated ozone, plant growth is inhibited and results in shorter plants with less dense canopies. This can slow the growth and reproduction of certain pathogens. However, ozone also damages plant tissues that can help pathogens infect the plant more easily.

"Elevated levels of carbon dioxide and ozone can make a plant more susceptible to some diseases, but less susceptible to others," Eastburn said. "This is exactly what we've observed in our climate change experiments."

U of I's SoyFACE was the first facility to expose plants to elevated ozone under completely open-air conditions within an agricultural field.

"The SoyFACE facility allowed us to evaluate the influence of natural variability of meteorological factors such as drought and temperature in conjunction with imposed atmospheric composition (elevated carbon dioxide and ozone) on naturally occurring soybean diseases across several growing seasons," Eastburn said.

He believes rising temperatures and changes in rainfall patterns will also affect development of plant disease epidemics.

"In some cases, changes of only a few degrees have allowed plant diseases to become established earlier in the season, resulting in more severe disease epidemics," Eastburn said. "The ranges of some diseases are expanding as rising temperatures are allowing pathogens to overwinter in regions that were previously too cold for them."

For example, warmer winters may allow kudzu to expand its range northward. Because kudzu is an alternate host for the soybean rust pathogen, one result of rising temperatures may be that soybean rust arrives in Illinois earlier in the soybean growing season, Eastburn said.

"Information derived from climate change studies will help us prepare for the changes ahead by knowing which diseases are most likely to become more problematic," he said. "Now is the time for plant pathologists, plant breeders, agronomists and horticulturalists to adapt disease management strategies to the changing environment."

Eastburn's soybean research, "Elevated atmospheric carbon dioxide and ozone alter soybean diseases at SoyFACE," was recently published in Global Change Biology. Researchers also included Melissa DeGennaro and Evan DeLucia of the U of I, Orla Dermody of Pioneer Hi-Bred Switzerland, and Andrew McElrone of the University of California - Davis.

Provided by University of Illinois at Urbana-Champaign