Agricultural Water Management 98 (2010) 190–198 Contents lists available at ScienceDirect Agricultural Water Management journal homepage: www.elsevier.com/locate/agwat Effect of irrigation uniformity on the profitability of crops E. López-Mata, J.M. Tarjuelo, J.A. de Juan, R. Ballesteros, A. Domínguez ∗ Centro Regional de Estudios del Agua (CREA), Universidad de Castilla-La Mancha, Ctra. de las Pe˜ nas, km 3.2 02071 Albacete, Spain article info Article history: Received 4 November 2009 Accepted 10 August 2010 Available online 22 September 2010 Keywords: Coefficient of uniformity Deficit irrigation Model Gross margin abstract There are numerous models capable of simulating crop behavior under different water stress conditions. However, none of them takes into account the effect of irrigation water uniformity on yield. The model developed simulates the uniformity effect on yield and the repercussion on gross margin (GM). The application of the model to a maize crop in Albacete (Spain) indicates that for the same irrigation depth, an increase in uniformity of water in the soil (CU) corresponds to a 4% increase in yield for the common irrigation strategy in the area, and a 6.8% increase in yield for the optimal irrigation schedule established by the model. Values of percentage of adequately irrigated area (a) between 50 and 80% appear to be adequate for values of CU > 80%. This effect has special relevance on the GM mainly when designing the irrigation strategy of areas with limited water resources. This leads to improvement of CU from 75 to 95% for the common irrigation depth applied to maize and may increase GM up to 27%. For small irrigation depths, the effect of CU on GM is reduced. The maximum GM is reached at ET a /ET m < 1 and a <100%. The paper also describes a methodology for determining the most suitable irrigation schedule under regulated deficit irrigation conditions. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Due to the general decreasing tendency of water availability for agriculture and the increases in energy costs, it is becoming even more important to efficiently use water and energy in agriculture. These aspects condition the viability of irrigation activities in many areas in the world. In general, when an irrigation event takes place on a plot, not all water is stored within the area of the soil reached by the crop roots. Part of that water is lost by drift, evaporation, run-off and deep percolation, but the latter two losses may be used by other areas of the same hydrological system. Each kind of these losses varies according to the type of soil and management of the irrigation system. Consequently, the lack of uniformity can affect both yield and water use efficiency (WUE) (Warrick and Gardner, 1983; Letey et al., 1984; Mantovani et al., 1995). A continuous reduction in water availability for agriculture cre- ates a need to improve WUE by the plant (Hatfield et al., 2001). From an agronomic point of view, WUE is defined as the relation- ship between yield (Y) and crop evapotranspiration (ET) (López Bellido, 1998). Given the difficulty in measuring the water actually consumed by the crop, most publications refer to the relationship between yield and water received by the crop, both from irriga- tion and rain, by calculating the efficiency of water received by ∗ Corresponding author. Tel.: +34967599200; fax: +34967599269. E-mail address: alfonso.dominguez@uclm.es (A. Domínguez). the crop (EWRc). Howell (2001) indicates that the main way to increase EWRc in irrigated agriculture is by increasing produc- tion per unit of water (engineering and agronomic aspects), reduce water losses and water degradation (environmental aspects) and reallocate water to higher priority uses (social aspects). Water productivity (WP) can be defined as the ratio between the actual yield achieved and the total water use (Lorite et al., 2005; Rodrigues and Pereira, 2009). WUE is commonly used as a syn- onym of WP (Steduto, 1996), but recently the term biomass WP was introduced to more clearly refer to the physiological and ecophys- iological processes of biomass production (Steduto et al., 2007). When referring to irrigation, it is preferable to assess WP relative to total water use (TWU) or irrigation water use (IWU) when eval- uating the performance of a given irrigation system (Rodrigues and Pereira, 2009). Crop yield uniformity, when water is the only limiting factor, depends on the uniformity of the available water in the root area. This is conditioned by the effect of accumulated irrigation received, the interception of the water by the canopy and its redistribution, soil water dynamics and the development of the crop root system (Stern and Bresler, 1983; Li and Kawano, 1996; Chen et al., 2004). To obtain the gross depth of application for satisfying crop water requirements, soil water uniformity should be considered rather than water application uniformity of individual irrigation events. A good approximation of soil water uniformity is the value corre- sponding to the set of irrigation events, at least when the irrigation interval is less than 3 or 4 days (Ortega et al., 2004a,b; de Juan et al., 2008; Jiménez, 2008). 0378-3774/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2010.08.006