Cropping in Arid-Area Greenhouse

Abstract

In hot, arid regions, yields are usually low and unstable. Greenhouse technology can stabilize and improve yields. But its adoption is impeded by the requirement of large amounts of water for cooling. Evaporative cooling is the most common method. Arid Area Greenhouse (AAG) is being developed for hot arid regions, particularly to reduce or eliminate the water needed for cooling. To achieve this, AAG employs earth-tube-heat-exchanger (ETHE) and static vents for environmental control. A prototype was installed in 2002 in an arid region, at village Kothara (ƒ� 23�X 14 N, ƒ� 68�X 45 E, at 21 m a.s.l.) for study. The single span saw-tooth greenhouse is 20 X 6 X 3.5 m. The ETHE is buried 3m deep directly below and coupled to it in closed-loop mode. ETHE is made of a bundle of eight mild steel pipes arranged in two tiers. Each pipe is 23 m long and 20 cm diameter. ETHE provides 20 air changes per hour. Initial cost of ETHE (material, fabrication, transport and installation) was $ 5000, nearly equal to that of greenhouse excluding instrumentation. There are three continuous closable vents - two along the base of long sides and one along the ridge. A retractable shading cover is provided over the roof. The aim was to determine (a) the extent to which ETHE and natural ventilation meet the need for environmental control and the associated costs (b) the extent to which productivity is increased, cropping season extended. By summer of 2007 five rounds of cropping have been done. ETHE was able to heat the greenhouse easily from 9�XC to 22-23�XC in half hour in the cold winter nights. Static ventilation along with shading was effective for day time control till February keeping the temperature about 34�XC inside. Subsequently, ETHE was operated. It limited the greenhouse temperature to 36-37�XC with top shaded and crop inside. If grid supply is steady it is operated for five-six hours in the day. House is closed in May-June. Yield of tomato has been close to 2 times that of the open-fields in the province. Water used was 44% of that used in open-field. The water used was mostly for plants, only a small part was for supplementary cooling using foggers. ETHE and static vents hold promise as environmental control device for greenhouses in hot arid regions. There is need to reduce installation cost by substituting plastic pipes for metal. It is also necessary to develop a more easily scalable design than the present one.