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Unformatted text preview: 17 Lectures 12 and 13 The development of plastic covers in the 1950s in the United States was the technological breakthrough that made protected horticulture suitable for China. The plastic greenhouse industry grew rapidly in the 1980s, and China is now the leading country for protected horticulture (Table 12-2) including multi-span greenhouses, plastic tunnels, and a specially devised energy ef f cient lean-to greenhouse (Jiang et al., 2004). This latter structure (Fig. 12-17) was developed in Liaoning province of northeast China and adapted for vegetable production without heating. This greenhouse is now found in all of north China from 33 to 47 on over 200,000 ha. The greenhouse (300 to 800 m 2 ) is essentially a half Quonset in which the north back wall and sidewalls are heat absorbers composed of brick and thermal materials. Curvature of the ribs is designed for maximum light penetration in the winter. In winter afternoons, when the air temperature inside the greenhouse falls below 17 to 18C, an insulating mat is rolled down the plastic cover to prevent heat...
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- Summer '10