Rainwater Harvesting with Solar and Gravity Powered Irrigation for High Tunnels

Abstract

HIGHLIGHTS Captured rainwater supplied nearly all the irrigation required for high tunnels in Tennessee. Solar pumping and/or gravity flow adequately supplied the pressure required for irrigation in high tunnels. Rainwater harvesting costs need to be reduced in order to be more competitive with alternate water sources. Abstract . High tunnels use clear plastic film over a large metal frame to trap solar radiation as heat in order to extend the crop growing season and reduce environmental stress. High tunnels differ from high tech greenhouses in that they use the natural soil as the growing media and use natural ventilation without fans or heaters to control the growing environment. High tunnels can provide some of the benefits of greenhouses at a much lower cost. However, the protective cover cuts-off rain water to the crop and significantly modifies the crop-water use environment. In order to reduce reliance on external sources of water, The University of Tennessee–Biosystems Engineering and Plant Science Departments implemented three types of rainwater harvesting (RWH) for high tunnels that did not require an external source of power for irrigation: gravity flow, solar battery-powered pumping, and solar transfer pumping. RWH by gravity-flow stored water captured off the high tunnels at a high enough elevation to deliver water for irrigation at very low pressure while solar battery-powered pumping delivered pressurized water directly to the irrigation system. Solar transfer pumping moved harvested rainwater to a higher elevation tank that used gravity flow to irrigate at intermediate pressures. These RWH systems were designed to store 64 mm of rainfall from the high tunnel cover (6400 L per 100 m2 of footprint area) and were able to provide 75% to 100% of the spring crop and 90% to 100% of the fall crop irrigation based on 16 experiments over six years. The RWH systems were ranked in order of increasing cost, maintenance, and complexity as follows: 1) gravity flow, 2) solar transfer pumping, and 3) solar battery-powered pumping. However, all RWH systems had high initial cost when compared to well and municipal water supplies, $12,750 to $15,950 for two 9.2- × 29-m high tunnels. Significantly lower cost rain gutters and water storage were identified but not yet tested for RWH in high tunnels. Keywords: Drip irrigation, Evapotranspiration, Gravity irrigation, Greenhouses, High tunnels, Microirrigation, Rainwater harvesting, Solar pumping.

Beyond 2020, Vision of the Future: Selected Papers from the Sixth Decennial National Irrigation Symposium

“…Nearly 30% of the total irrigated land area in the U.S. is located in the eastern humid states, and the area continues to increase (USDA-NASS, 2018). Overall, eight journal articles for this ASABE Special Collection were related to agricultural irrigation in the humid region, with three articles specifically discussed in this section (Leib et al, 2020;Lena et al, 2020;Reinhart et al, 2020). The other five articles were discussed in the Technology and Innovation section (Chiu and Reba, 2020;Henry, et al, 2020;Lo et al, 2020), the Irrigation Systems section (Reba and Massey, 2020), and the Irrigation Management section (Zamora-Re et al, 2020).…”

“…Rainwater harvesting (RWH) was sufficient to meet irrigation needs for high tunnels (i.e., simple greenhouse structures using plastic film) in Tennessee (Leib et al, 2020) in a comparison of three different RWH systems (gravity flow, solar transfer pumping, and solar battery-powered pumping). The authors concluded that the costs of the three tested RWH systems were not competitive with the cost of using alternative water sources.…”