Evaluation of wetted area of moisture bulb in surface and subsurface drip irrigation with continuous and pulsed flow

Abstract
Background and Objectives: The lack of available water resources and its optimal use in arid and semi-arid areas have forced experts and authorities in the agricultural sector to apply high-efficiency irrigation systems such as surface drip irrigation (DI) and subsurface drip irrigation (SDI). SDI can reduce evaporation losses and increase irrigation efficiency due to water movement in the soil and drying of soil surface. For designing of DI and SDI, in addition to the dimensions of moisture bulb, that are the main parameters in determining the installation depth and the spacing of the laterals, wetted area of emitter around is very important. Most studies have been conducted on the distribution of moisture bulb in a continuous drip irrigation system and few studies have been done on wetted area in pulsed drip irrigation. Then, in this research, we focused on wetted area of emitter around in pulsed drip irrigation and its effective factors.
Materials and Methods: In this study, experiments were conducted in a transparent plexyglass tank (0.5m*1m*3m) using three different soil textures (fine, heavy and medium). The emitter discharges were considered 2.4, 4 and 6 lit/hr. The emitters were installed at 3 different soil depths (surface, 15cm and 30cm). Also, these experiments were carried out for two continuous and pulse irrigation systems. In pulse irrigation, the pulse cycles were considered 30-30, 20-40 and 40-20 min. The first number was the irrigation time (on) and the second number was the rest time (off) of the system in each cycle.
Results: The results of this research showed that the largest area of wetted bulb in the DI and SDI with pulsed application (for the same water volume of at the end of irrigation), is related to emitters with higher discharge rate in the light texture, and in Heavy texture is related to lesser outflow rate. The results of the effect of soil texture on the wetted area indicated that in continuous and pulsed drip irrigation systems (for all emitter outflows at the end of irrigation), the highest and lowest wetted area of moisture bulb was related to light texture and heavy texture, respectively. Also, the results showed that for all treatments, the down wetted area of emitter in the DI would be higher than the SDI. Also, the results showed that in DI and SDI (the different discharge and texture), the down wetted area of emitter in pulsed irrigation (30-30) is relatively more than two other pulses (40-20, 20-40) and continuous irrigation. This difference will be clearly seen in light texture and in SDI.
Conclusion: The results of the research show that the wetted area of around the emitter is different for different outflows and soil textures, as well as for continuous and pulsed method. Considering these parameters in the design of drip irrigation system increases the water application efficiency and decrease deep percolation losses.