Effect of Using Plastic Mulch in Drip Irrigation on Growth, Yield, and Water Use Productivity of Pistachio

To study the effects of using plastic mulch on soil moisture and salinity changes under drip irrigation system in mature pistachio trees (Ohadi cultivar), a research was conducted in a randomized complete block design in two orchards with different treatments in terms of water consumption (4100 and 6170 m³/ha), irrigation frequency (8 and 12 days), and trees growth. The study was carried out in the western suburbs of Rafsanjan, Iran. In each of the orchards, three mulch treatments including: without mulch (treatment C), black-and-white plastic mulch (treatments M_B, M_W), with three replications were used. At the end of the season, data on growth characteristics, quality and quantity of the product, and water use productivity (WUP), were averaged and compared using Duncan multiple range test to determine the effects of using plastic mulch on these traits. The results showed  significant effect of plastic mulch on all growth factors, quantity and quality of yield, and water use productivity. Moreover, in most cases, the color of mulch did not affect these traits. Overall, using plastic mulch in orchard 1 increased the dry product up to 271 g per tree, reduced blanking to 10.6 percent, increased splitting by 11.2 percent, reduced the number of grains per ounce of pistachios by 2.3 units, and increased the water use productivity by 100 percent compared to the control. Also, in orchard 2, plastic mulch increased the dry product upto 1090 g per tree and increased the water use productivity by 36 percent compared to the control. Measurement of soil moisture changes in between two consecutive irrigations indicated significant effect of mulching on conserving soil moisture in comparison with the control. Considering the Permanent Wilting Point (PWP) and Readily Available Water (RAW) of the experimental soils,  proper irrigation frequency for pistachio trees in uncovered loamy sand to sandy loam soils under drip irrigation is 5 to 9 days, and in the use of plastic mulch, it is 11 to 15 days.