Drip-Irriwater: Computer software to simulate soil wetting patterns under surface drip irrigation G. Arbat a,⇑ , J. Puig-Bargués a , M. Duran-Ros a , J. Barragán b , F. Ramírez de Cartagena a a Department of Chemical and Agricultural Engineering and Technology, University of Girona, C. de Maria Aurèlia Capmany, 61, 17071 Girona, Spain b Department of Agricultural and Forestry Engineering, University of Lleida, Av. de l’Alcalde Rovira Roure, 191, 25198 Lleida, Spain article info Article history: Received 3 January 2013 Received in revised form 5 August 2013 Accepted 11 August 2013 Keywords: Soil water modeling Drip irrigation design Graphical user interface abstract Drip irrigation provides greater efficiency in terms of water usage and energy. These factors are very important in light of the current competition for water resources between the various users, especially in the Mediterranean region due to water scarcity. The shape and dimensions of the volume of wet soil below the emitter are some of the most influential variables in the optimal design and management of drip irrigation systems. This paper presents Drip-Irriwater, a code for determining soil wetting patterns under a single emitter in order to suggest planning factors for a drip irrigation system. The code solves Richards’ equation using the finite difference method subject to appropriate boundary conditions for drip irrigation. The boundary conditions on the surface of the soil allow us to consider forming a pond under the emitter. The user interface enables users to simply enter the input parameters (discharge rate, soil type and horizons, irrigation time, initial water content and total simulation time). The code then displays the soil water content and pressure heads, enabling a visual distinction between the wetted radius and depth, the parameters required for subsequent drip irrigation design. The results obtained with Drip-Irri- water were compared with those obtained with HYDRUS and with results from field tests carried out on three different soil types. The soil water distribution, as well as the wetted radius and depth, calculated from the Drip-Irriwater and HYDRUS code, were very similar. Field tests conducted to verify the results of the code confirmed that Drip-Irriwater gave a good approximation of the wetted radius and depth, and could therefore be used to design a drip irrigation system. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Water scarcity in many regions of the world, combined with the large amount of water used in agriculture, is promoting the adop- tion of more efficient irrigation practices. Micro-irrigation, which allows irrigation at a low rate, achieves high efficiency in terms of water usage and is easily automated, is being used more and more. For instance, in Spain in 1999, micro-irrigation was adopted on 17% of the total irrigated land, while in 2011, this increased to 48% (MAGRAMA, 2011). Nevertheless, the use of micro-irrigation alone does not guaran- tee high efficiency. It requires adequate design and conscientious management (Phene, 1995). The agronomic design must be per- formed prior to designing the hydraulic network. This initial stage of the design process consists of establishing the discharge of the emitters, the distance between them and the emitter volume in or- der to wet a specific soil volume according to the extension of the rooting system and the needs for irrigation water. This set of vari- ables is critical in order to achieve optimal application efficiency. Soil type plays a major role in adequate irrigation planning. Car- rying out field tests which consist of excavating a soil pit to mea- sure the extension and depth of the wetted soil volume under an emitter, is probably the most reliable method for selecting the ade- quate emitter rate and separation between emitters (Keller and Bliesner, 1990; Battam et al., 2003). Nevertheless, field tests are costly, and it is sometimes difficult to visually distinguish the wet- ted soil from the dry soil. For this reason, they are rarely conducted. The application of empirical or physical models could be an alter- native. Schwartzmass and Zur (1986) equations, obtained empiri- cally, are easy to use and allow us to obtain the width and depth of the wetted soil volume. However, due to the great variation in the hydraulic properties of the soils, their predictions are not reli- able (Keller and Bliesner, 1990). Amin and Ekhmaj (2006) and Mal- ek and Peters (2011) developed similar equations using several different experimental datasets. Kandelous et al. (2008) developed several equations to characterise the wetting front from the sub- surface emitter, applying dimensional analysis using experimental data from a single soil type and emitter flow. 0168-1699/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.compag.2013.08.009 ⇑ Corresponding author. Tel.: +34 972 418 459; fax: +34 972 418 399. E-mail address: gerard.arbat@udg.edu (G. Arbat). Computers and Electronics in Agriculture 98 (2013) 183–192 Contents lists available at ScienceDirect Computers and Electronics in Agriculture journal homepage: www.elsevier.com/locate/compag