Water-Yield Relations and Water Use Efficiency of Maize Under Nitrogen Fertigation for Semiarid Environments: Experiment and Synthesis

Abstract

We examined the main and interactive effects of nitrogen (N) and deficit irrigation (DI) on the yield response factor (K_y), water use efficiency (WUE), and irrigation water use efficiency (IWUE) of silage maize from a semiarid region of Iran. Experiments were conducted in 2003 and 2004 that included three N fertigation rates (0, 150, and 200 kg N ha⁻¹ N0, N150, and N200, respectively) and four irrigation levels (0.7, 0.85, 1.0, and 1.13 of soil water depletion, W1, W2, W3, and W4, respectively). The soil water content measurements showed that most of the water was extracted from the top 60 cm of the soil profile. DI increased WUE for all N fertilizer treatments with the maximum value being observed at the W2 level. The average of the IWUE for the two years of the study showed that the lowest IWUE was 1.38 kg m⁻³ for the N0W1 treatment, while the highest IWUE was 1.8 kg m⁻³ for the N200W3 treatment. A linear relationship was observed between evapotranspiration and the total biomass for all N fertilizer levels in 2003 and 2004. The minimum K_y to water was obtained from the N0 level as 0.64 in 2003 whereas the maximum K_y was recorded from the N200 level as 0.95 in 2004. This reveals that higher N rates application would enhance corn yield sensitivity to water stress. Overall, the sensitivity of the silage maize to water stress was affected by different planting date and nitrogen fertilizer levels. We also discuss emergent trends in water and nutrient management in light of the increased need for food security in the face of changing climate and growing populations.

Introduction

Water availability is the major factor limiting crop yield in arid and semiarid zones of the world (Er-Raki et al., 2007). To optimize cost, yield, quality, and effort, a robust and effective irrigation strategy for these regions must be evaluated (Dahmardeh, 2011b, Ghrab et al., 2013). Deficit irrigation (DI) is a well-accepted practice to optimize increase water use, thereby saving cost, by allowing crops to withstand mild water stress with no or only marginal decreases in yield and quality (Costa et al., 2007, Geerts and Raes, 2009). The implementation of DI, however, requires knowledge about the crop's response to and management of limited water availability (Farré and Faci, 2009).

The water–yield relationship is typically evaluated by the yield response factor (K_y), which is determined by the slope of a linear function between water stress and yield for the entire duration or a specific development stage of the growing season (Vaux and Pruitt, 1983). Water use efficiency (WUE) and irrigation water use efficiency (IWUE), on the other hand, are used to assess the amount of productivity (i.e., some measure of yield, biomass, carbon) as a function of effectiveness of evapotranspiration and irrigation, respectively (Sinclair et al., 1984). Here, WUE is defined as yield per unit area divided by the total water evapotranspirated during the growing season (Kg Yield M^-3 soil volume) (Howell, 2006). IWUE is defined as the total amount water input into the system (Kg Yield M^-3 soil volume) (i.e., applied via the irrigation system), and includes other stand-scale stocks and fluxes of water, e.g., water stored in the soil column, losses from lateral flow, runoff, etc. Using these terms in conjunction, along with their component variables, provides additional interpretive power when evaluating the efficacy of DI, and to understand thresholds of water delivery and water stress to optimize management decisions (Kirda and Kanber, 1999, Johnson and Henderson, 2002, Yazar et al., 2002).

Many studies have investigated the effect of management decisions on WUE, IWUE, and K_y of maize (Zea mays L.), an important economic crop grown for silage and kernel in many regions of the world. These include; DI strategies (Kang et al., 2000, Kipkorir et al., 2002, Cakir, 2004, Daĝdelen et al., 2006, Oktem, 2008, Ko and Piccinni, 2009, El-Hendawy and Schmidhalter, 2010, Ayana, 2011, Karimi and Gomrokchi, 2011, Pejić et al., 2012, Domínguez et al., 2012, Qassim et al., 2013), the type of irrigation system (Howell et al., 1995, Pablo et al., 2007, Kang et al., 2010, Arbat et al., 2013, Rudnick and Irmak, 2013), and N source and the timing of application (Vegh et al., 1998, Binder et al., 2000, Asadi et al., 2002, Berenguer et al., 2009, Gheysari et al., 2009, Abbasi et al., 2013, Hu et al., 2013). However, only a few studies examined the interaction effect of water balance, stress, and nitrogen fertigation.

For example, Eck (1984) reported when using DI, water limited the yield of (grain) maize more than N, in other words, N controlled the yields when water was not limiting, e.g., at optimal levels of irrigation. In SW Spain and under furrow irrigation, Fernandez et al. (1996) reported that the water usage of (grain) maize was not affected when N fertilization was reduced from 510 to 170 kg N ha⁻¹ yr⁻¹. Pandey et al. (2000) found that the larger the N application, the more the (silage) yield was reduced, whereas Liua and Zhang (2007) and Stone et al. (2010) found that the production of (grain) maize responded positively to an increased amount of water and N applied until an optimum (threshold) level has been reached. Ogola et al. (2002) pointed out that the effect of N on crop water use is expected to vary with the availability of soil moisture, and that moist soils require more N than dry soils in order to achieve the maximum (grain) yield (Moser et al., 2006). To prove this point, Di Paolo and Rinaldi (2008) found that nitrogen rates increased WUE and IWUE in (grain) maize from a 2-year factorial experiment that included 3 fertilizer treatments. They also showed that the water–yield relationship of maize was more linear with higher N applications. Interestingly, Mansouri-Far et al. (2010) found increased IWUE with N application only after one DI event during the vegetative stage (grain maize), and reduced IWUE after one DI event during the reproductive stage or with more than one DI (at either stage). These results point to the need for further study to elucidate and optimize the relationship among fertilization, irrigation, environment and climate, soils and crop phenological stages (Payero et al., 2006, Garcia et al., 2009, Gebremedhin et al., 2012, Gilmanov et al., 2014).

Most of the arable lands in Iran have an arid to semiarid climate (Badripour, 2006). In addition, many of the important agricultural areas in Iran are suffering from an inadequate supply of water to support current and future agronomic practices (Agrawala et al., 2001). During the last decade, the area under the cultivation of silage maize as a summer crop has increased significantly due to the increasing demand of dairy farms (Kamalzadeh et al., 2008) and prolonged drought (Agrawala et al., 2001, Eslami and Chavoshi Borojeni, 2000). Silage maize is typically planted after harvesting winter wheat and barley at the beginning of the summer and irrigated by sprinkler irrigation systems (Gheysari et al., 2006). However, there is no information about the combined effects of water stress and N fertilizer on K_y and water efficiency terms of maize under sprinkler irrigation in Iran. Moreover, concerns over food production and security have been the focus of many national and international planning efforts (Holdren, 2013; ICSU, 2012; PCAST, 2011; MEA, 2005; GEO, 2012). Hence, the objectives of this study were to (1) determine the interactions among different levels of water and N fertilizer on WUE, IWUE, on the yield response factor to water (K_y) for silage maize grown under sprinkler irrigation in a semiarid region, (2) outline how best community practices are manifest into an experimental design, (3) provide management guidelines to regional growers and irrigation agencies to water management programs for maize in the region, and (4) provide a synthesis of the controls on cultivated maize production from arid and semiarid regions.