effect of polyethylene sheet application in the depth of soil on water retention and dryland wheat production in a light soil

iran as an arid and semi-arid country always faces with the problem of soil water shortage due to insufficient precipitation and, especially in light soils, low water holding capacity and high deep percolation. therefore, researchers have tried to use new methods for increasing this capacity to keep the water in the root zone and increase the amount of plant available water and water use efficiency of plants and reduce the stress of water scarcity. one of these methods is use of an impermeable barrier under the root zone such as asphalt layer, polyethylene membrane, and so on. the aim of this research was to use polyethylene membrane in sandy loam soil in two fields in ardebil, with high amount of deep percolation. to study the effect of this membrane with two different methods of application on soil moisture and plant growth response. this project was conducted with two treatments, one with using membrane in one and two depths and the other one without membrane (control), with three replications and using a completely randomized design. wheat was planted in two fields. during plant growth period, the soil moisture was measured by time domain reflectometry (tdr). after harvesting, wheat growth indices were measured. the results in field no.1showed that using polyethylene membrane had significant effect on soil moisture and increased it up to five volumetric percent. also, it increased grain yield by 0.6 ton per hectare: from 1.13 to 1.67 t/ha; while straw yield and total dry matter increased from 1.58 and 2.57 t/ha to 3.6 and 5.05 t/ha, compared to the control. but, in field no.2 with two depths of membranes, these indices did not show significant effects, the probable reason being that the 10 cm distance between the membranes allowed the water drainage from the root zone.