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Abiotic stresses represent a major impediment to crop productivity, especially in arid regions. Thus, over two years of 2014 and 2015, a field experiment was undertaken at El Nubaria region, Egypt to assess the productivity and water use efficiency (WUE) of sunflower as affected by planting dates (April 21, May 21, and June 21) and irrigation levels (ET100%, ET85% and ET70%,). Results clarified that leaf chlorophyll a content was higher by sowing in May than in either April or June sowings, while leaf carotenoides of plant sown in May or June surpassed those sown in April. The minimal value of proline was obtained with sowing in May. Sowing in May increased plant height by 52.2 and 22.3 as well as LAI by 19.3 and 73.1% than sowing in April and June, respectively. The reductions in seed yield, oil yield and WUE amounted to 10.5 and 12.8, 13.7 and 18.3 as well as 11.8 and 9.8 % with April and June sowings, respectively, compared to May sowing. ET100% showed superiority over than ET85% and ET70% in improving sunflower yields and its attributes, but WUE did not affect. Sunflower sown in May and irrigated with ET100% gave the maximum values of seed yield and its attributes and WUE surpassing other interaction treatments. In June, WUE value increased under severe water deficit i.e. ET70% comparing to moderately water–stressed (ET85%) or well–watered conditions (ET100%). INTRODUCTION Although the strategic importance of oilseed crops for Egyptian people could not negligible, Egypt is suffering from a huge gap of oil ranging between 87−90 %. There are many annual oil crops can be cultivated, however, the area devoted for this purpose is limited, not exceeding 1.58% of the total crop acreage (CAPMAS, 2014)*. This is due to the intense competition between oil crops and other strategic, notably grain and forage, ones. For shrinking this issue, the expansion vertically and horizontally is crucial. However, in dry land cropping systems, water is the most important limiting factor for crop production (Ashrafi and Razmjoo, 2009). Regarding oil production, sunflower is one of the four most important oilseed crops (Demir et al 2006). It represents a source of high quality edible oil containing about 55-65% of linoleic acid, 20-30 % oleic and different fatty acids (Joksimovic et al 2006). In addition, because of the seed has high oil and protein, being 36–52% and 28–32%, respectively (Rosa et al 2009) as well as the extracted oil has low cholesterol and high unsaturated fatty acids (Flagella et al 2002; Qahar et al 2010) which suit proper nutrition, sunflower has been receiving trustworthy attention. Sunflowers, moreover, can response well under different climatic and soil conditions (Kaleem et al 2011). Drought is one of the major constraints to crop production in the world (Farooq et al 2012). Increasing disquiet of water incompetence and more continual and harsh drought due to climate change has stimulated research toward water-aving irrigation programs aiming at producing more ‘crop per 1484 Shahin; El–Bially; Saudy and El-Metwally Arab Univ. J. Agric. Sci., Special Issue, 26(2B), 2018 drop’ (Dodd, 2009; Morison et al 2008). In this respect, usage water below full crop–water requirements is regarded one of the significant pattern to overcome shortage water resources through diminishing irrigation water amounts (Fereres and Soriano 2007; Kang et al 2000). Such practice planed to improve water savings in agriculture (Bashir and Mohamed, 2014) but it should be performed taking crop species into account. Productivity of sunflower is mightily regulated by the availability of water and greatest yield losses manifest when water shortage occurs (Yawson et al 2011). Different climatic conditions based on temperature predominant in varying seasons during the crop growth stages may lead to variations in yield components (Kll and Altunbay, 2005). Solar radiation, air temperature and rainfall as crop growth factors are related with sowing dates (Aguirrezábal et al 2003; Izquierdo et al 2009). Temperature is considered the main factor that affects plant growth, development and productivity (Aiken, 2005; Kaleem et al 2009). High temperature stress can also be avoided by crop management practices such as selecting proper sowing methods, choice of sowing date, cultivars, irrigation methods, etc (Hasanuzzaman et al 2013). Temperature variations in the field can be created by planting crops at different dates in the season, thus crop will grow at different temperature, sunshine, and relative humidity (Qadir et al 2007). Unfavorable temperatures and low water supply, as abiotic stresses, promote overproduction of reactive oxygen species (ROS) in plant cell which are highly reactive and toxic and eventually results in oxidative stress (Gill and Tuteja, 2010). Elevated levels of ROS lead to the inactivation of proteins and inhibit the activity of multiple enzymes involved in metabolic pathways, and result in the oxidation of other macromolecules including lipids and DNA (Hossain et al 2014). Therefore, plant cells are equipped with splendid antioxidant defense mechanisms to detoxify the harmful effects of ROS. For this, determining the optimum irrigation scheduling coupling with sowing date of sunflower under the newly reclaimed lands was the aim of this study. MATERIALS AND METHODS During 2014 and 2015 seasons, a field experiment was performed at the experimental farm of National Research Centre, El-Nubaria region, ElBehaira Governorate, Egypt (latitude 30 o 30 \ 1.4 \\ N, longitude 30 o 19 \ 10.9 \\ E, and mean altitude 21 m above sea level). The experimental soil was sandy with pH 8.3 and EC 0.38 dS m –1 . The study area belongs to arid regions with no rainfall and hot dry in summer (April–September). The preceding cultivated crop was wheat in both seasons. The study aimed to investigate the effect of irrigation water levels and sowing dates on productivity and water use efficiency (WUE) of sunflower (Helianthus annuus) under the environmental conditions of the study's area. The study comprised nine treatments, which were the combinations of: 1. Three sowing dates: April 21, May 21, and June 21, represent early, mid, and delayed dates, respectively. 2. Three irrigation water levels: 100, 85 and 70% of crop evapotranspiration (ETc), denoting as ET100%, ET85% and ET70%, and representing well–watered, moderately water–stressed, and severely water–stressed conditions, respectively. The experimental design was a strip–plot with four replicates. The treatments of the two experimental factors were allocated as follows: sowing dates in the vertical plots, while irrigation levels in the horizontal ones. The experimental unit area was 12.25 m 2 , involving five ridges each of 3.5 m long and 0.7 m wide. From weather factors, irrigation water requirement for sunflower was calculated by determining daily reference evapotranspiration (ETo) as illustrated in Table 1 using FAO Penman–Monteith equation (Allen et al 1998). From ET0, crop evapotranspiration (ETc) was computed using the following equation according to Doorenbos et al (1977): ETc = ETo Kc  (1) Where: ETc = Crop evapotranspiration (mm day –1 ); ETo = Reference evapotranspiration (mm day –1 ), and Kc = Crop coefficient (0.6–1.2). Amount of irrigation requirement was calculated according to Keller and Bliesner (1990) as follows: IR = ETc x LR x. 4.2 / Ea  (2)

SOWING DATE AND IRRIGATION EFFECTS ON PRODUCTIVITY AND WATER USE EFFICIENCY IN SUNFLOWER