Open-hole effects of perforated plastic mulches on soil water evaporation

Plastic film mulch technology is a cropping system feature for water saving that is used extensively in and 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 experiments 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 distributions were also analyzed. Our measurements indicated that film hole mulch had a restraining effect on evaporation and that the restraining effect 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 evaporation 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 perforated plastic mulches. The resulting equations presented in this paper provide an approach for describing evaporation from plastic mulch-covered soil.