تأثیر بارشهای متغیر انتهای فصل، آبیاری تکمیلی و همزیستی میکوریزایی بر عملکرد و کیفیت (علوفه و دانه) عدس دیم

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Inroduction Water scarcity and low atmospheric precipitation are the major challenges faced by crop production in arid and semi-arid regions. Lentil (Lens culinaris Medik, Fabaceae family), under rainfed production conditions, is subjected to end-season drought stress. The occurrence of end-season water deficit stress in rainfed system can result in crop failure and yield loss. The quantitative and qualitative yield reductions are more pronounced and unpredictable under varying rainfall situation. Supplemental irrigation is the most effective and efficient way to prevent fluctuations in yield and the achievement of desired lentil production in arid and semi-dry lands. In order to compensate for water deficit-induced damage, the biological methods such as mycorrhizal symbiosis are used as one of the most useful interactions in agricultural ecosystems. The mycorrhizal fungi can improve profitability and nutritional status of host plant due to enhanced water and nutrient (especially P) uptake under irrigated and rainfed conditions (Habibzadeh et al., 2013). Materials and Methods The 2-year (2014-2015) factorial experiment was conducted based on randomized complete block design with three replications at West Azarbaijan Agricultural and Natural Resources Research Center. Treatments were rainfall interruption (30 May, 13 June and 27 June), mycorrhizal symbiosis (non-mycorrhizal plants and inoculation with Glomus intraradices) and irrigation (rainfed and one supplemental irrigation). Lentil (Lens culinaris Medik. cv Ziba) seeds were cultivated on March 16-2014 and April 5-2015 with a density of 125 plants per square meter. Supplemental irrigation was carried out on the basis of the rainfall interruption, on 8, 14 and 17 June of the first year, and on 6, 12 and 15 June of the second year (from the beginning up to 50% of podding). The amounts of irrigation water for each of two years were respectively, 400, 465 and 470 m3/ha in 30 May, 13 June and 27 June when rainfalls interrupted. Forage (ash, protein, calcium, potassium and phosphorus) and grain (protein, potassium and phosphorus) quality were respectively determined at podding and seed maturity stage. Results and Discussion The results of the two-year combined analysis showed significant interactions of year, rainfall interruption, mycorrhiza and supplemental irrigation on the lentil forage and grain yield (quantity and quality). Significant interaction effects were found among “year×rainfall interruption ×mycorrhiza×supplemental irrigation” on forage protein, “rainfall interruption ×mycorrhiza×supplemental irrigation” on forage calcium and year×mychorrhiza×supplemental irrigation on forage ash. Forage yield was significantly influenced by the year effect (Table 2). Forage quality (phosphorus, calcium and protein) and grain nutrients (phosphorus) of mycorrhizal irrigated lentil plants were improved in comparison with rainfed condition. With the late interruption of rainfall (27 June), lentil grain yield under treatment of G. intraradices significantly increased in both rainfed and supplemental irrigation conditions. However, the grain yield was consistently higher when lentil plants received supplemental irrigation as compared to no irrigation (rainfed) where the greatest grain yield (472.96 ha/kg) was obtained from the mycorrhizal lentil involving supplemental irrigation under the conditions that rainfall continued till 27 June, which was 28.72 % higher than the lowest yield, which was associated with the early interruption of rainfall (May 30) and the non-mycorrhizal treatment under rainfed condition. Supplemental irrigation is a managerial factor for yield improvement and stability, which ultimately minimizes the possibility of crop failure under water deficit conditions (Oweis et al., 2004). In both two rainfed and supplemental irrigation conditions, mycorrhizal lentil produced higher forage yield. It is reported that mycorrhiza has positive impact on phosphorus and nitrogen uptake by plant leaf, leading to increased yield in both water stress and non-stress conditions (AL-Karaki et al., 2004). Lentil gave more forage yield (1048.81 kg/ha) in the second year of the experiment than the first year (939.59 kg/ha). It seems that relatively higher qualitative and quantitative yields in both mycohrrizal and non-mychorrizal lentil in the second year was due to the trial being conducted in the first year which made it possible to effectively control all the cultivation operations and provide better care for the plant in the second year. The maximum yield and quality in both lentil forage and grain were obtained from irrigated mycorrhizal treatment, indicating a synergistic effect of mycorrhiza and irrigation on the productivity of the legume crop.