1 0038-075X/03/16811-000–000 November 2003 Soil Science Vol. 168, No. 11 Copyright © 2003 by Lippincott Williams & Wilkins, Inc. Printed in U.S.A. T HE annual evaporative demand of arid and semiarid regions near Xinjiang in northwest China exceeds 2000 mm whereas annual precip- itation is less than 200 mm (Yearbook of water conservation for Xinjiang, China, 2001). Thus, a great need exists in the area to make efficient use of all agricultural water. Plastic mulch cultivation, a management TECHNICAL ARTICLES OPEN-HOLE EFFECTS OF PERFORATED PLASTIC MULCHES ON SOIL WATER EVAPORATION Yi Li 1 , Mingan Shao 1 , Quanjiu Wang 1,2 , and Robert Horton 3 1 Institute of Geographical Sciences and Natural Resources Research (Beijing 100101) and Institute of Soil and Water Conservation (Yangling 712100) of Chinese Academy of Sciences, China. Dr. Shao is corresponding author. E-mail: mashao@ms.iswc.ac.cn 2 Institute of Water Resources, Xian University of Technology, Xian 710048, China. 3 Agronomy Dept., Iowa State University, Ames, IA 50011. Received April 15, 2003; accepted Aug. 22, 2003. DOI: 10.1097/01.ss.0000100475.96182.16 Plastic film mulch technology is a cropping system feature for water saving that is used extensively in arid and semiarid areas of northwest China. When evaporative demand is fairly strong, film mulching can greatly reduce soil water evaporation. However, research on water flow beneath and through various open hole ratios of the perforated film mulches is limited, and questions concerning soil water flow and soil heat transfer for this type of water-saving system remain unanswered. It is, therefore, very important to perform research on soil water evaporation and soil temperature distribution with various open hole ratios of the perforated plastic mulches. A series of soil water evaporation experi- ments using different open hole ratios of perforated plastic mulches was conducted. The columns received mulches with various open hole ratios: 0% (covered with a solid plastic mulch), 1.39%, 2.84%, 7.24%, 30.5%, and 100% (nonmulched bare surface). In conjunction with the water movement of evaporation from film hole studies, soil temperature dis- tributions were also analyzed. Our measurements indicated that film hole mulch had a restraining effect on evaporation and that the restraining ef- fect decreased with the increase in open hole ratios. Compared with bare soil evaporation, the percentage of evaporation reduction rates for open hole ratios of 0%, 1.39%, 2.84%, 7.24%, and 30.5% were 69.26%, 33.09%, 22.80%, 20.05%, and 11.82%, respectively. The results showed a linear relationship between cumulative water evaporation and square root of time for the different open hole ratios of the perforated plastic mulches, and the coefficients of the linear function, i.e., the C parameters, were fitted well with the open hole ratios—u(C  0.0101u 0.1019  0.0075). On this basis, mathematical relations of relative evaporation rate and evapo- ration based on hole areas of perforated plastic mulches were analyzed and discussed. These results extend the Gardner evaporation equation to bare soils to include water evaporation from soils covered by various per- forated plastic mulches. The resulting equations presented in this paper provide an approach for describing evaporation from plastic mulch- covered soil. (Soil Science 2003;Volume 168:000–000) Key words: Evaporation, irrigation, mulching, water conservation.