Construction Variation Coefficient and Seepage Behavior of Clay Emitters with the Aim of Their Application in Subsurface Irrigation

Development Research Institute during the last three decades has produced clay emitters and has implemented the system on a small scale in several areas of Kerman province in pistachio orchards. Because the hydraulic characteristics of the emitters used in the gardens are unknown and their operating time is also unknown, therefore, it is impossible to evaluate the performance of emitters used in these gardens. In order to evaluate the hydraulic performance of the emitters in terms of the coefficient of construction variation and also changes in the seepage behavior in laboratory conditions. 400 clay emitters were studied at Agricultural Engineering Research Institute of Karaj. To investigate the coefficient of construction variation, the emitters were grouped into groups of 20, and each group was tested at a constant hydrostatic pressure of 1.75 m using water with a quality of 0.83 dS/m. The results showed that the values of the coefficient of variation of the 20 packages under test were in the range of 23 to 73%, which was higher than the declared 20% of the ASAE standard and was found to be unacceptable, and if these emitters are used, the plants in different parts of the farm/garden will not receive equal water. Therefore, in these conditions, the use of these emitters in the subsurface irrigation of plants is not recommended. To investigate the seepage behavior of clay emitters over time, the discharge changes of 7 emitter groups at three hydrostatic pressures of 0.5, 1, and 2 m were tested. Seepage measurements from clay emitters for 1000 hours showed that as water passes through the pores of the emitter’s body, the water-soluble salts precipitate over time in the porous environment of the clay emitters and cause clogging. The average maximum initial seepage of clay emitters in groups of 7 at hydrostatic pressures of 0.5, 1, and 2 meters was 1.537, 2.578, and 4.783 L/hr.m, respectively. After 1000 hours of continuous testing, the values of final seepage reached 0.939, 1.483, and 1.296 L/hr.m, respectively. Descending values of seepage showed that water-soluble salts precipitate over time in the pores of the emitter body and reduce the emitter permeability. Due to the reduction of emission permeability, it is not possible to sustainable use of them to supply the water needed by crops/gardens in the long term.