Investigating the maize (Zea mays L.) water use efficiency in hot areas under climate change conditions

Iran is located in an arid and semiarid region that is vulnerable to environmental changes. So, it would appear that the occurrence of climate change in this region would have a significant impact on agricultural production systems (Eyshi Rezaie and Bannayan, 2012). Climate change might affect the water available for agriculture and, consequently, lead to drought occurring in semiarid areas (Koocheki et al., 2006). Evaluating adaptation strategies, such as changing the planting of dates, can help to increase maize water use efficiency under climate change conditions (Ramprasad et al., 2016). One of the cheapest ways to measure the effects of climate change on agricultural production is through a modelling approach and application of simulation models (Manschadi et al., 2010). This study aims at investigating the sowing date as a strategy for maize adaptation and improving its water use efficiency under climate change conditions in Khuzestan Province. For this purpose, six locations in Khuzestan Province were selected (Ahwaz, Behbahan, Dezful, Izeh, Ramhormoz and Shushtar). Daily long-term climatic data including minimum and maximum temperatures, rainfall and global radiation in a baseline period (1980-2010) were collected for these locations from their meteorological stations. Then, daily long-term climatic data were generated for the future period of 2040-2069 in these locations by using a method proposed by AgMIP under two climate scenarios (RCP4.5 and RCP8.5). In this study, the SC704 cultivar was used. Taking into account three sowing dates (4 February, 19 February [a common sowing date] and 5h March), six locations, and two climate scenarios over 30 years, a total of 1620 simulation experiments were carried out in this study. In order to simulate the growth and yield of maize under different sowing dates, the APSIM model was applied. Results indicated that early sowing date (4 February) with 10117.1 kg ha-1 had a higher economical grain yield compared to 19 February (10061.3 kg ha-1) and 5 March (7194.6 kg ha-1). Also, in the future period, the reduction percentage in economical grain yield at the different sowing dates compared to the baseline common planting date (19 February) showed that the early sowing date of 4 February recorded less reduction (-3.3 and -4.5 percent under RCP4.5 and RCP8.5, respectively) than 19 February (-6.5 and -6.7 percent under RCP4.5 and RCP8.5, respectively) and 5st March (-31.1 and -23.2 percent under RCP4.5 and RCP8.5, respectively). On average in Khuzestan Province, an early sowing date indicated higher water use efficiency (WUE) )11.8 kg ha-1 mm-1) compared to 19 February (10.7 kg ha-1 mm-1) and 5 March (7.6 kg ha-1 mm-1) in the baseline period. However, under climate change conditions, reduction of WUE in different planting dates compared to the baseline common sowing date (19 February) revealed that 4 February (2.8 and 3.3 percent under RCP4.5 and RCP8.5, respectively) was superior compared with 19 February (-12 and -11 percent under RCP4.5 and RCP8.5, respectively) and 5 March (-40.1 and -32.5 percent under RCP4.5 and RCP8.5, respectively) in term of WUE in Khuzestan Province. In general, according to the results found the common sowing date of maize in Khuzestan is not optimal for maize in terms of water use efficiency and economical grain yield. Accordingly, to increase economical grain yield and water use efficiency in both the future and baseline periods at Khuzestan Province, farmers should
choose the early sowing date (4 February) compared to the common and late ones.