New Methodologies to Generate, Conserve, and Predict, Renewable Energy Output for Season Extension of Warm and Cool Season Vegetable Crops

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Virginia Tech


Due to concerns for the environmental and sociological implications of hydrocarbon use, farmers have begun to examine renewable energies and conservation techniques for crop production. Historically, most of the energy needs for climate control in tunnel systems have been met via passive heating, with fossil fuels occasionally providing a supplementary heat source. Five heating techniques were examined for kale (Brassica oleracea) and summer squash (Cucurbita pepo) season extension. Treatments consisted of a low tunnel heated by a solar-powered electrical strip placed under a water tube, a low tunnel heated by a passively heated water tube, a low tunnel heated by an earth-to-air heat-exchange tube, a traditional low tunnel, and a control unprotected plot. Aerogel blankets and SolaWrap® floating covers were also examined as floating covers to protect crops from cold temperatures. To predict energy output, the USDA ARS Virtual Grower was compared against data from the tunneled treatments. Treatments were tested in fall 2020 and spring 2021 with data was collected for air, soil, and tube temperature (ºC), crop growing degree - days, squash seed germination and kale height (cm) and dry biomass (g). The electrically heated water tube produced the highest mean spring day air (28.2 ºC), fall soil temperatures (14.6ºC), thermal tube temperature for the 24 - hour, day and night timeframe for both seasons. However, for soil, the passively heated water tube showed the best results amongst the two seasons heating the soil surface at a 24 - hour mean of 13.8 ºC for fall and 18.2 ºC for spring. The earth tube warmed tunnel air in spring with a mean internal 24 - hour temperature of 19.5 ºC for spring against the 15.7 ºC recorded during fall, while providing the highest mean minimum temperatures. For growing degree-days, all treatments outperformed the uncovered control, with the earth tube treatment performing better for the kale degree day 24 - hour mean of 9.1 for fall 2020 against its spring output of 12.6. The electric heated thermal tube and earth tube improved germination of summer squash during the fall 2020 trial, while the passive tube positively influenced germination during the spring 2021. No differences were observed amongst the treatments in either season for final kale canopy height or dry biomass, though the earth tube displayed the highest range and means. However, kale plants were taller and had greater dry biomass when grown in spring compared to fall. Solar powered heated water tube, earth tube and passively heated water tube accelerated kale development in spring. For the floating cover trial, while the SolaWrap® had the highest mean 24-hour temperature 21.0 ºC, the aerogel blanket showed temperature parity in the daily minimum and night temperatures, and both mean and cumulative kale and summer squash growing degree-days. The Virtual Grower program produced a significantly higher mean and summative kJ output compared to collected by factoring climate, solar radiation, and wind speeds. In the fall study, light limitations arrested kale and squash production rather than a freezing event with treatments being more effective in spring due to increasing daylength. The most effective treatment for spring was the solar powered heated water tube because it provided a first harvestable kale and summer squash at 2-3 whole weeks before conventional spring harvesting, while the earth tube showed a better performance in degree-day accumulation for the cool season kale and warm season squash for the fall extension trial, each having a 24 - hour mean of 9.1 and 12.6.



solar panel, earth tube, low-e