WABOL: A conceptual water balance model for analyzing rainfall water use in olive orchards under different soil and cover crop management strategies U. Abazi a,⇑ , I.J. Lorite b , B. Cárceles c , A. Martínez Raya c , V.H. Durán c , J.R. Francia c , J.A. Gómez d a Agricultural University of Tirana, Kodër-Kamez, Tirana, Albania b IFAPA Centro ‘‘Alameda del Obispo’’, Box 3092, 14080 Cordoba, Spain c IFAPA Centro ‘‘Camino de Purchil’’, Box 2027, 18080 Granada, Spain d Instituto de Agricultura Sostenible, CSIC, Box 4084, 14080 Cordoba, Spain article info Article history: Received 27 February 2012 Received in revised form 25 October 2012 Accepted 13 November 2012 Keywords: Water balance Soil management Simulation model Olive orchard abstract A water balance model developed to simulate the effect of different soil management alternatives, as for instance conventional tillage or cover crop, on soil water balance has been implemented in a user friendly interface in order to allow its use by technicians and other stakeholder in the olive sector. In spite of this simplified interface for the user, the model uses process-based methodologies to describe the key pro- cesses controlling water balance in rainfed olive orchards, such as runoff, deep percolation, cover crop growth, soil evaporation and olive and cover crop transpiration. Model predictions were evaluated using 3-year period of runoff and soil moisture data for different soil managements from an experimental field located in an olive orchard in Southern Spain. Comparison of simulated results with experimental data suggests that the model predicts satisfactorily runoff losses and soil moisture. Thus, annual runoff simulation provided a RMSE of 4.4 mm and the model efficiency was in general higher than 0.5. This suggests that the described model could be a useful tool for stake- holders to carry out a complete evaluation of different soil management alternatives in olive orchards. Finally, an example of an application of the model is presented. In this example, the model is used to eval- uate the impact of using a cover crop, including different mowing dates, on the different components of the soil water balance compared to conventional tillage for the conditions of Cordoba, Southern Spain, using a 50 year long record. This exercise indicates that the use of a cover crop in these conditions have a negative impact on olive transpiration (25% average reduction), although this impact can be mitigated using an early date killing of the cover crop, March 15th for the conditions simulated in this exercise. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction In arid and semiarid environments, water availability is the main limiting factor for crop yield productivity (Henderson, 1979). In these regions, different factors as the human population growth or the increasing need for water in the preservation of the environment are competing with agriculture for the available water resources (Falkenmark, 2000; Hsiao et al., 2007). In arid and semiarid regions, rainfed agriculture has progressed using crops and varieties better adapted to an optimum use of rainfall water, and developing techniques such as weed control or direct seeding, aimed to reduce runoff and water losses by direct evapo- ration from the soil to increase crop transpiration (Unger and Par- ker, 1976; Steiner, 1989). In the case of rainfed tree orchards in arid or semiarid environments, their design and management has also been focused on insuring the survival of the plantation during dry periods within each season, and also drought years that period- ically occur. One approach to evaluate the effect of different soil management alternatives on water balance and yield is using field experiments in which the several alternatives are tested for a num- ber of years, measuring several variables, at least water content and yield, to be able to perform a statistical analysis among treat- ments (e.g. Monteiro and Lopes, 2007; Wortmann et al., 2010; Van den Putte et al., 2010). Usually these studies are complemented with crop model analysis aimed to improve the interpretation of the field results, and also their scope, extrapolating the results to different conditions to those of the field studies (e.g. Wegehenkel and Mirschel, 2006; Jin et al., 2007). For this kind of analysis sev- eral crop models have been developed during the last decades. These simulation models describe mathematically the processes of the soil water balance, the plant growing and yield expression to calculate their evolution during the simulation period. There 0168-1699/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.compag.2012.11.010 ⇑ Corresponding author. E-mail address: uranabazi@yahoo.it (U. Abazi). Computers and Electronics in Agriculture 91 (2013) 35–48 Contents lists available at SciVerse ScienceDirect Computers and Electronics in Agriculture journal homepage: www.elsevier.com/locate/compag