Contents lists available at ScienceDirect Agricultural Water Management journal homepage: www.elsevier.com/locate/agwat Developing an optimization model in drip fertigation management to consider environmental issues and supply plant requirements Nasrin Azad a , Javad Behmanesh a, ⁎ , Vahid Rezaverdinejad a , Fariborz Abbasi b , Maryam Navabian c a Water engineering department, Urmia University, Urmia, Iran b Agricultural Engineering Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran c Water engineering department, Guilan University, Guilan, Iran ARTICLE INFO Keywords: HYDRUS (2D/3D) Nitrate leaching Nitrogen uptake Particle swarm optimization (PSO) Simulation ABSTRACT Recently, groundwater contamination has increased due to incorrect use of nitrogen fertilizers so that it has caused public concern. To solve the problem, the most appropriate approach is to manage on-time and correct application of water and fertilizer. The objective of this study was to provide an optimization program of drip irrigation and fertigation to maximize the nutrients uptake by plants and minimize water and solute losses in field by optimizing the design and management parameters of drip fertigation. In this research, the HYDRUS (2D/3D) model was used to simulate water and nitrogen transport in soil. For this purpose, the requirement data for calibration and validation of the model were collected by carrying out corn field experiments and performing drip irrigation and fertigation. Then, the calibrated model was used to simulate water and nitrogen behavior in soil and optimization process. To optimize the design and management parameters of fertigation, a two-stage optimization program was considered. In the first stage, the amount of irrigation flow rate, duration of fertilizer injection, and the start time of the injection were simultaneously optimized with the aim of minimizing nitrate leaching in a fertigation cycle. The results showed that by selecting the irrigation rate of 0.8 L h -1 and minimum duration of fertigation at the end of irrigation, nitrate leaching was minimum in the period of fertigation. In the second stage, the amount of fertilizer injection at each stage of fertigation was optimized throughout the growth season using the optimum values of the previous step. In fact, in addition to supplying nitrogen requirement of the plant, the amount of nitrate leaching and its accumulation at the end of each fertigation, especially at the end of the growing season, were also minimized to prevent leaching by post-harvest rainfall. 1. Introduction In recent years, population growth and the need for producing more food have led to an increase in the use of chemical fertilizers in agri- culture. However, due to the lack of proper management in water and fertilizer consumption, soil nutrient balance has been disturbed and many environmental problems have arisen. Nitrogen is a necessary nutrient for plants, and nitrate- a very mobile and leachable element- is one of the most important forms of nitrogen found in soil (Alva et al., 2008). Studies have indicated that nitrate is the most common and widespread contaminant of groundwater in the world and can lead to health problems (Marinov and Marinov, 2014). Best management practices that reduce the amount of water and nitrogen influx without decreasing the yield can decline the potential of nitrate pollution of groundwater (Shrestha et al., 2010). This manage- ment should consider different soil moisture management strategies for nitrate transport and managing the application of nitrogen (amount and time) by considering the plant requirement for nitrogen (Shrestha et al., 2010). Inappropriate irrigation management causes water and nutrient losses from the root zone and, as a result, contaminates groundwater. Therefore, optimal irrigation planning is important in improving the water and nutrient uptake efficiency (Alva et al., 2006). Overuse of fertilizers is another reason for nitrogen leaching. With an increase in nitrogen application, nitrate leaching rapidly increases (Zvomuya et al., 2003). Recent studies have emphasized that there is a positive corre- lation between the groundwater nitrate and the intensity of nitrate application in agriculture (Costa et al., 2002). For example, West Bengal's villages have recorded high concentration of nitrate in their underground water because of using high levels of nitrogen fertilizer (Kundu and Mandal, 2009). On the other hand, split application of fertilizer can play an important role in improving fertilizer uptake by plants and reduce fertilizer leaching and environmental https://doi.org/10.1016/j.agwat.2018.06.030 Received 25 November 2017; Received in revised form 18 June 2018; Accepted 25 June 2018 ⁎ Corresponding author at: Urmia University, 11 Km Sero Road, Post box: 165, Urmia, Postal code: 5756151818, Iran. E-mail addresses: n.azad@urmia.ac.ir (N. Azad), j.behmanesh@urmia.ac.ir (J. Behmanesh), v.verdinejad@urmia.ac.ir (V. Rezaverdinejad), f.abbasi@areo.ir (F. Abbasi), Navabian@guilan.ac.ir (M. Navabian). Agricultural Water Management 208 (2018) 344–356 0378-3774/ © 2018 Elsevier B.V. All rights reserved. T