تاثیر تنش خشکی و سطوح مختلف کود نیتروژن بر صفات مرفولوژیک، فیزیولوژیک و ماده خشک کل در ارقام هاشمی و گیلانه برنج

این پژوهش با هدف بررسی پاسخ صفات مرفولوژیک و فیزیولوژیک برگ به تنش خشکی و مصرف کود نتیروژن در دو رقم برنج در سال های1396 و 1397 در رشت اجرا گردید. طرح آزمایشی مورد استفاده کرت‌های دوبار خرد شده با سه تکرار بود. فاکتور اصلی آبیاری در سه سطح غرقاب، دور آبیاری 7 و 14 روز و کرتهای فرعی کود نیتروژن در سه سطح 50، 75 و 100 کیلوگرم در هکتار و نتایج نشان داد که اثر سال بر ارتفاع ساقه، طول، عرض و محتوای نسبی آب برگ پرچم، عدد کلروفیل‌متر و ضریب خاموشی نور غیر معنی‌دار و بر شاخص سطح برگ بیشینه و ماده خشک تولیدی معنی‌دار شد. برهمکنش سه عامل مورد مطالعه بر عدد کلروفیل‌متر، ضریب خاموشی نور، محتوای نسبی آب برگ پرچم، سطح برگ بیشینه و ماده خشک تولیدی در سطح یک درصد معنی‌دار بود. افزایش دور آبیاری، ماده خشک، شاخص سطح برگ بیشینه، محتوای نسبی آب برگ، عدد کلروفیل‌متر و طول برگ پرچم را در هر دو رقم کاهش داد. افزایش مصرف کود نیتروژن نیز این صفات را در هر سه سطح آبیاری بهبود داد. کم‌ترین ضریب خاموشی نور (0.14) در آبیاری غرقاب و مصرف 100 کیلوگرم در هکتار کود ازته حاصل گردید که در دو رقم یکسان بود. بیش‌ترین تجمع ماده خشک (803.3 گرم بر متر مربع در سال 1396 و 760.7 گرم بر متر مربع در سال 1397) با مصرف 100 کیلوگرم در هکتار کود نیتروژن در آبیاری غرقاب و در رقم گیلانه حاصل شد. تنش خشکی صفات مرفولوژیک و فیزیولوژیک مورد بررسی را کاهش داد، درحالی که مصرف 100 کیلوگرم در هکتار کود نیتروژن نسبت به دو سطح دیگر در هر دو رقم توانست این صفات را در شرایط تنش و عدم بروز تنش بهبود داده و ماده خشک بیش‌تری را در هر دو سال مطالعه تولید نماید.

Effect of drought stress and different levels of nitrogen fertilizer on morphological and physiological traits and total dry matter in two rice cultivars (cvs. Hashemi and Gilaneh)

IntroductionDrought stress is a limiting factor for growth in crops. Water and nitrogen relationships in the crop change in drought stress. The role of nitrogen in plant response during drought stress depends on the stress intensity and fertilizer level. Plants with relatively high nitrogen availability show better growth compared to plants with low nitrogen in drought stress. Therefore, the objectives of the present study were to investigate the effect of drought stress and different levels of nitrogen fertilizer on morphological and physiological traits in two rice cultivars.Materials and methodsThe present study was conducted in Rasht in 2017 and 2018. The experimental design was split plot plot arrangement in randomized complete block design with three replications. The experimental factors were drought stress (main factor) at three levels (continuous submergence, 7 and 14 days irrigation interval), N fertilizer (sub factor) in three levels (50, 75 and 100 kg ha1) and sub sub factor in two levels (cv. Hashemi, Gilaneh). The size of the experimental units was 9 m2 (plot dimensions 3 × 3). To control weeds, butachlor herbicide (3 L ha1) was used after planting and manual weeding. To calculate the maximum leaf area index, 10 days after transplanting, 7 sampling steps were performed every 10 days until the harvest stage and in each sampling, four mounds from each floor plot and total leaf area were determined. To determine the dry matter, sampling was done in the complete ripening stage after removing the margins from the middle rows of plots and all one square meter plants were harvested. The samples were placed separately in an oven at 75 ° C for 72 hours and then weighed and recorded.Results and discussionResults showed that the impact of year and on shoot height, flag leaf length and width, RWC, SPAD and k were not significant but on LAImax, total dry matter were significant. Impact of drought stress × N fertilizer × cultivar on RWC, SPAD and k were significant. Impact of year × drought stress × N fertilizer × cultivar on LAImax and total dry matter were significant (p<0.01). Shoot height, LAImax, total dry matter, flag leaf length and width, RWC, SPAD were decreased by drought stress and were improved by increase of N fertilizer consumption under the three condition of drought stress. The lowest k (0.14) was obtained in continuous submergence and consumption of 100 kg ha1 N fertilizer, which was same in two cultivars. The highest total dry matter accumulation (803.3 g m2 in 2017 and 760.7 g m2 in 2018) was obtained in Gilaneh with consumption of 100 kg ha1 nitrogen fertilizer in continuous submergence. The highest number of SPAD in flooding with 51.8 with 100 kg of pure nitrogen per hectare in Gilaneh cultivar and the lowest with 50 kg of nitrogen fertilizer per hectare in 14 days irrigation cycle and in Gilaneh cultivar (27.65) was obtained. Hashemi cultivar showed the highest plant height (131.1 cm) in flood irrigation and the lowest plant height in 14 day irrigation (131.6 cm). Gilaneh cultivar, similar to Hashemi cultivar, showed the highest height (110.5 cm) in flood irrigation and the lowest height (100.6 cm) in 14 day irrigation. ConclusionsDrought stress showed adverse effects on morphological and physiological traits, while the application of 100 kg ha1 of nitrogen fertilizer compared to the other levels improve these traits in both cultivars stress and notstress, and produce more dry matter in both years of study. Therefore, when there is not enough water for irrigation, it is possible to moderate the effects of water stress by using the optimal amount of nitrogen fertilizer. It can help to produce more dry matter and achieve higher yield.