Alazba, A.A.; ElNesr, M.N.*; and Alradyan , N.A

1. 4th International Conference 'Hydrus Software Applications to Subsurface Flow and Contaminant Transport Problems', Prague, 2013 The Effect of Intermittent Water Flux Through Dripping Source on Water and Solutes Distribution in Soil Alazba, A.A.; ElNesr, M.N.*; and Alradyan, N.A King Saud University, Alamoudi Chair for Water Research. Results Background For flood irrigation, applying water in intermittent regime improves water distribution and reach, as well it enhances crop yield [1]; [2]; [3]. Similarly, several investigators used intermittent water application on drip irrigation; they named this application by numerous names; “intermittent drip irrigation” [4]; [5], “pulse/pulsating drip irrigation” [6]; [7], “Minute or ultra-low-flow microirrigation” [8]; [9], and “surge drip” [10]. This method improves water distribution under SDI through pulsating water to the soil allowing it to redistribute before the next water-pulse, which is assumed to speedup water movements laterally. Several application regimes were applied in literature, according to specific ON and OFF times [7], according to fixed number of ON times [11] ; [12] or according to the applied water depth [13] where they applied 0.1 inch per hour. The ON times were chosen from 1 minute to 15 minutes [14]; [13]. The OFF times were usually equals to the ON times in all the cited references. The benefits of intermittent drip irrigation could be summarized to the following: Limits emitters clogging [6], Increase yield [4];[7] ; [11] ; [12], Improve water use efficiency [7] ,Decrease chemicals and fertilizers and Reduce deep percolation [14] . The main differences in the wetting profile of the studied scenarios are noticed within the infiltration time and in the early stages of the redistribution stage. However, the water distribution patterns, Figure 2, show the state of the soil profile at an intermediate time of the eight scenarios, i.e. 240 minutes. Compared to the control scenario, it is noticed that the with high frequency values (=10) show smaller wetting bulb, that’s due to the small amount of water that has infiltrated in soil at the time of 240 minutes which is less than 50% of the time of infiltration completion (T) as shown in Table 1. The root water uptake patterns, Figure 3, were affected by the irrigation frequency as well. For the scenarios with longer OFF time (#4, #5, #6), the soil has more redistribution time, and the plant has more opportunity to take water. Figure 4 shows the root water uptake value with time for the studied scenarios. Objective Figure 2 The aim of this work was to simulate different intermittent SDI scenarios on Hydrus package, to study the effect of irrigation frequency and pulse rate on water, solutes, and roots’ extraction. Methods Eight intermittent application scenarios were studied in comparison with the normal application method, Table 1. In all scenarios, water is applied for a duration D=60 minutes then stopped until the next irrigation event after 48 hours. In the intermittent application scenarios, the flux application duration (ON-time) is divided into ω sections, and the OFF-time interval is  times the ON duration, for example if ω=5, and =10, then the ON-time=D/ω=60/5=12 minutes. And the OFF-time=12=1012= 120 minutes. The elapsed time (T ) till the total flux ended can be calculated by the formula T = D (1+  (ω-1)/ω). Simulations were carried out for 2,880 minutes (i.e., 2 days), the same irrigation conditions were repeated 15 times, resulting in the total time of 30 days. Table 1 Figure 3 The transport domain for all scenarios was considered to be axisymmetrical around a vertical axis. Figure 1 shows the studied domain geometry, the transport domain was 100 cm wide (radius) and 130 cm deep (depth). The emitter was located 15 cm below the soil surface. The boundary conditions (BCs) are shown on the same figure as well. In all simulated scenarios, the upper boundary of the transport domain was subjected to atmospheric conditions, while the lower boundary of the domain was free drainage. Figure 1 Figure 4 Summary Intermittent application of irrigation water is taking an increasing interest nowadays. Several works were made to investigate its effect on flood irrigation, and their results were encouraging. On the other hand, there is less research on the intermittent drip irrigation. However, the few published works show a promising future for this technology. The aim of this work was to simulate the intermittent application of drip irrigation on the Hydrus 2D/3D package in order to trace the movement of water and solutes in the soil profile on the application of such method of irrigation. The simulations were successfully accomplished, showing that the intermittent irrigation application affects wetting pattern and root water uptake in the flux times, but this effect was not significant after the end of redistribution stage. More studies are needed considering root solutes uptake. The boundaries at both vertical sides were assigned a “No Flux” boundary condition. The Emitter was represented as half circles with a radius of 1 cm, located on the left vertical boundary of the transport domain. The upper emitter was assigned a “Variable Flux 1” BC. Time-variable boundary conditions were used to simulate drip irrigation. The dripper discharge (Q) was considered to be 3.75 L/h, which is equivalent to a flux of about 5 cm/min ( q=Q/4r2), where q is the boundary flux [cm/min], Qis the emitter discharge [cm3/min], and r is the wetted radius of the emitter [cm]). The root-water uptake of selected crops was simulated using the Feddes[15] model with the default values of required parameters provided by the Hydrus model. Cited Literature [8] Mead, R. (2012). Minute Microirrigation, Pulsating Microirrigation for Optimal Water Use and Control in the Soil. http://bit.ly/13QORFc [9] Signe (2010). Ultra low flow microirrigation. Article in Americal Farm website. Last accessed 6/5/2012. http://bit.ly/16oqYEK [10] Alazba, A. A. (2007). Surge Flow in SDI with Single and Dual Lines. ASABE Annual International Meeting 2007 Minneapolis, USA. Paper # 072083 [11] Harmanto, A., Salokhe, V. M., Babel, M. S., and Tantau, H. J. (2005). “Water requirement of drip irrigated tomatoes grown in greenhouse in tropical environment.” Agr. Wat. Manag., 71(3), 225–242. [12] Bakeer, G., El-Ebabi, F., and El-Saidi, M. (2009). “Effect of Pulse Drip Irrig.onYield and Water Use Efficiency of Potato Crop Under Organic Agriculture in Sandy Soils.” Misr J. Ag. Eng., 26(2), 736– 765. [13] New, L., and Roberts, R. E. (2012). “Drip Irrigation For Greenhouse Vegetable Production.” Aggie Horticulture. [14] Kenig, E., Mor, E., and Oron,, G. (1995). “Pulsating Microirrigation for Optimal Water Use and Control in the Soil.” American Society of Agricultural Engineers,, Orlando, Florida, 615 to 620. [15] Feddes, R. A., P. J. Kowalik, and H. Zaradny, (1978). Simulation of Field Water Use and Crop Yield, John Wiley & Sons, New York, NY. [1] Blair, A. W., Smerdon, E. T. (1985). Improving Surge Flow Irrigation Efficiency Based on Analysis of Infiltration and Hydrodynamic Effects. Technical report # 138, Texas Water Resources Institute, Texas A&M University. {July-1985} 68pp. [2] Monserrat, J., Vilaró, J., Casalí, J. and Barragán, J. (1993). Comparison Between Continuous And Surge Flow Irrigation In Borders And Furrows (Segre Basin, Spain). Acta Hort. (ISHS) 335:455-460 [3] Horst, M.G., Shamutalov, S.S., Gonçalves, J.M. and Pereira, L.S., (2007). Assessing impacts of surge-flow irrigation on water saving and productivity of cotton. Agric. Wat. Management 87(2): 115–127. [4] Vyrlas, P., and Sakellariou, M. (2005). “Intermittent Water Application through Surface and Subsurface Drip Irrigation.” 2005 ASAE Annual International Meeting, Tampa, Florida. [5] Elmaloglou, S., and Diamantopoulos, E. (2008). “The effect of intermittent water application by surface point sources on the soil moisture dynamics and on deep percolation under the root zone.” Comp. and Elect. in Agric., 62(2), 266–275. [6] Al-Naeem, M. A. (2008). “Use of pulse trickles to reduce clogging problems in trickle irrigation system in Saudi Arabia.” Pakistan Journal of Biological Sciences: PJBS, 11(1), 68–73. [7] Zin El-Abedin, T. (2006). “Effect of Pulse Drip Irrigation on Soil Moisture Distribution and Maize Production in Clay Soil.” Misr J. Ag. Eng., 23(4). * Corresponding author,: Email: melnesr@ksu.edu.sa, drnesr@gmail.com, Mob. +966544909445