Majallah-i ̒Ulum-i Bāghbānī (Feb 2017)
Effect of Black and Clear Polyethylene Mulch on Yield and Yield Components of Melon in Salinity Stress Condition
Introduction: The term of Mulch, is the German word (Molsh) means the soft, however, not soft, and made of plant debris or synthetic substances. Many positive effects attributed to the use of plastic mulch such as adjusting the temperature in the root environment, conserve moisture, reduce weeds, increase root growth, reduce soil erosion, and soil condensation and improve germination and early plant establishment. The use of mulch can reduce the harmful effects of salt in plants. Materials and Methods: To evaluate the effects of black and clear polyethylene mulch on yield and yield components of melon in salinity stress condition, a study was conducted in 2011 using split plot randomized based on complete block design with three replications in Varamin region. Three salinity levels of irrigation water of 2, 5 and 8 dS-1 as main factor and three plastic mulch treatments (no mulch, clear mulch and black mulch) were considered as sub-plots. At harvest and after determining the yield and number of fruits harvested from each plot, the average number of fruits per plant was measured and fruit pulp thickness was recorded with calipers. Results Discussion The results showed interactive effects of salinity and mulch on fruit yield, number of fruits per plant, average fruit weight, fruit length, days to first harvest and fruit soluble solids percentage were statistically significant. In salinity levels of 2, 5 and 8 dS m-1, fruit yield increased, respectively, 19.6, 59, and 45.4 %in clear mulch compared to control. Similarly these increases for the black mulch were equal to 15.7, 41.9, and 21.4 percent, respectively. With 2, 5 and 8 dS m-1 salinity levels, fruit yield in the first harvest were 7.44, 7.72, and 6.98 t ha -1, respectively, which was significantly higher than without mulch and black mulch. Mulch can reduce evaporation and increase the level of moisture in the soil and thereby dilute the salt and reduce the harmful effects of salinity. Some researchers believe that increase in crop yield by using plastic mulch than plant debris mulch is due to the simultaneous increase in moisture and soil temperature. Effect of plastic mulch on soil temperature and crop yield depends on the color and usually transparent plastic are more effective in this regard than black polyethylene mulch. In terms of rising temperatures in the microclimate around the plant roots, transparent mulches are more effective than dark mulches. Unlike dark mulch, clear mulch have minimal absorption of light, approximately 85 to 95 percent .The inner surface of clear mulch is covered with water that the short wave passes and outgoing long wave radiation is absorbed from the soil and thus prevent heat loss. Water use efficiency with use of clear and dark mulches in compared to control treatment was increased by 17.3 and 13.4 %, respectively. Under salinity conditions, plastic mulches can reduce the harmful effects of salinity. Water use efficiency in salinity 2, 5 and 8 dS m-1, respectively, were 12.6, 7.6 and 3.1 kg m-3.Research results indicated that when water use efficiency based on the economic performance expression (e.g. present study) reduced water use efficiency but when water use efficiency expressed based on the total dry weight, water use efficiency is independent of salt concentration and the amount of water use efficiency is the function of plant and plant yield. Conclusion For using salty water, which may be unavoidable for many agricultural areas, use of mulch (especially transparent mulch) can have a significant role in increasing yield and more efficient utilization of water. From a practical perspective, in areas where irrigation water quality has declined due to reducing the level of the underground water table, the indiscriminate use of water resources and similar cases and use of these resources will lead to a gradual increase in soil salinity, application of mulch with the impact on the soil water content prevent of crop yield loss and cause earliness product.