Comparing sprinkler and drip irrigation systems for full and deficit irrigated maize using multicriteria analysis and simulation modelling: Ranking for water saving vs. farm economic returns

Highlights

• Economics of maize deficit irrigation depend on commodity price, production costs and field size.

• Water productivity strongly relates to beneficial water use.

• Multicriteria analysis was applied to rank all alternatives.

• Ranking when prioritizing water saving diverges from that relative to economic results.

• Sprinkling ranks high when economic results are prioritized and drip ranks higher for water saving.

Abstract

This study aims to assess the economic feasibility of full and deficit irrigated maize using center pivot, set sprinkler systems and drip tape systems through multicriteria analysis. Different irrigation treatments were evaluated and compared in terms of beneficial water use and physical and economical water productivity for two commodity prices and three irrigation systems scenarios applied to a medium and a large field of 5 and 32 ha respectively. Results show that deficit treatments may lead to better water productivity indicators but deficit irrigation (DI) feasibility is highly dependent on the commodity prices. Various well-designed and managed pressurized irrigation systems’ scenarios – center-pivot, set sprinkler systems and drip tape systems – were compared and ranked using multicriteria analysis. For this, three different prioritization schemes were considered, one referring to water savings, another relative to economic results, and a third one representing a balanced situation between the first two. The rankings of alternative solutions were very sensitive to the decision-maker priorities, mainly when comparing water saving and economic results because the selected alternatives were generally not common to both priority schemes. However, some of the best alternatives for the balanced priorities scheme are common to the other two, thus suggesting a possible trade-off when selecting the best alternatives. Deficit irrigation strategies also rank differently for the various scenarios considered. The study shows that deficit irrigation with exception of mild DI is generally not economically feasible. The adoption of well designed and managed irrigation systems requires consideration of priorities of farm management in terms of water saving and economic results since that some water saving solutions do not allow appropriate recover of the investment costs, particularly with DI. Basing decisions upon multicriteria analysis allows farmers and decision-makers to better select irrigation systems and related management decisions. Results also indicate that appropriate support must be given to farmers when adopting high performance but expensive irrigation systems aimed at sustainable crop profitability.

Introduction

Maize is one of the main crops in Portugal. It is the fourth most produced commodity in the country, averaging more than 760 thousand tonnes from 1992 to 2010 (FAO, 2012a). The percentage of the cultivated area equipped for irrigation increased from 28.87 to 30.75% from 1990 to 2007 (FAO, 2012b) and the agricultural sector is responsible for more than 73% of the country total water withdrawal. With the increasing water scarcity, there is the need to optimize water use, mainly for irrigation purposes (Pereira et al., 2009). Thus, farmers are forced to adopt improved irrigation managements in order to optimize water use, including the adoption of deficit irrigation and enhancing irrigation performance, thus leading to higher water productivities (WP). The pathway to achieve an efficient irrigation water use imposes the need to systematically optimize the soil and water management practices and the irrigation equipment (Knox et al., 2012).

The optimization of water use and productivity, whose indicators are defined by Pereira et al. (2012), may be achieved through the adoption of deficit irrigation (DI). DI consists of deliberately applying irrigation depths smaller than those required to fully satisfy the crop water requirements but keeping a positive economic return. Many authors assessed the impacts of DI on maize yields (Cabelguenne et al., 1999, Farré and Faci, 2009, Popova and Pereira, 2011, Ma et al., 2012), water productivity (Payero et al., 2009, Katerji et al., 2010) and economic returns (Rodrigues and Pereira, 2009, Abd El-Wahed and Ali, 2012, Domínguez et al., 2012). Consequently, authors searched irrigation schedules that could achieve the feasibility of DI because this technique highly depends upon the adopted management, i.e., when those deficits are applied (Bergez et al., 2004), as well as on irrigation and water costs (Kampas et al., 2012, Montero et al., 2012). Modelling can play a main role in determining rational deficit irrigation schedules (Mailhol et al., 2011, DeJonge et al., 2012, Ma et al., 2012).

Higher WP may be achieved by adopting high performance irrigation systems, having high distribution uniformity (Pereira et al., 2002, Pereira et al., 2009). Numerous studies show that there is great potential to achieve a more efficient water use, mainly through an enhanced distribution uniformity when improving surface irrigation (Raghuwanshi and Wallender, 1998, Horst et al., 2007, Gonçalves et al., 2011) or pressurized sprinkler and drip irrigation (Namara et al., 2007, Pedras et al., 2009, López-Mata et al., 2010, Ørum et al., 2010, Mailhol et al., 2011, Abd El-Wahed and Ali, 2012, van Donk et al., 2012). Choosing the most suitable irrigation system involves numerous factors, such as irrigation scheduling, soils, system performance, irrigation costs, and the performance of the off farm systems. The latter are particularly important because adopting an optimized irrigation scheduling in collective irrigation systems requires that off farm systems are dependable and reliable in terms of discharges and time of deliveries in surface irrigation systems (Gonçalves et al., 2007, Zaccaria et al., 2010), and in terms of timing, discharge and pressure in case of pressurized systems (Lamaddalena and Pereira, 2007, Lamaddalena et al., 2007, Calejo et al., 2008). The adoption of more uniform systems involves a trade off between increased capital expenditure on equipment and the benefits associated with reduced water application when it is uniformly distributed (Brennan, 2008).

When modelling to rank the best irrigation management alternatives, simulation outputs may be difficult to handle and the selection of the most feasible alternatives may be hard to achieve. However, a variety of design and management alternatives can be created and then ranked by adopting multicriteria analysis (MCA) (Roy and Bouyssou, 1993, Pomerol and Romero, 2000), multi-attribute modelling (Bartolini et al., 2007), or multi-objective optimization (Groot et al., 2012). When aiming at combining different actors in decision-making, e.g., farmers and stakeholders, instead of ranking solutions, fuzzy cognitive mapping may be used; however, few studies have been applied to irrigation (Giordano et al., 2007, Mouratiadoua and Moranb, 2007, Kafetzis et al., 2010). MCA proves to be a useful approach that can incorporate a mixture of quantitative and qualitative information and take into account the preferences of users. Various applications of MCA to irrigation are reported in the literature (Tecle and Yitayew, 1990, Bazzani, 2005, Manos et al., 2006, Riesgo and Gómez-Limón, 2006, Bartolini et al., 2010) and are applied to irrigation systems design (Gonçalves et al., 2007, Gonçalves et al., 2011, Pedras et al., 2009, Darouich et al., 2012).

Considering the aspects analyzed above and previous developments by Rodrigues and Pereira (2009), the main goal of this study is to assess the economic impacts of water deficits, commodity prices and enhanced irrigation systems performance on the physical and economic water productivity of irrigated maize in the Vigia Irrigation District, Southern Portugal. Multicriteria analysis is adopted to rank alternative solutions and help understanding contradictory results due to assigning priorities to water saving vs. farm economic results.