بررسی اثر اسید هومیک بر کارایی مصرف آب، عملکرد و برخی ویژگی‌های فیزیولوژیکی گیاه فلفل دلمه‌ای تحت سطوح مختلف آبی

با توجه به بحران کم‌آبی و نقش به‌سزای اسیدهای آلی در کاهش اثرات منفی تنش خشکی، مطالعه‌ی حاضر با هدف بررسی اثر همزمان اسید هومیک و کم‌آبیاری بر کارایی مصرف آب، عملکرد و برخی ویژگی‌های فیزیولوژیکی گیاه فلفل دلمه‌‌ای به صورت آزمایش فاکتوریل در قالب طرح بلوک‌های کامل تصادفی با سه سطح اسید هومیک (صفر، 20 و 40 گرم بر گلدان) و چهار سطح آبیاری (60، 80، 100 و 120 درصد از تخلیه رطوبتی خاک)، در گلخانه‌ی تحقیقاتی دانشگاه بجنورد با چهار تکرار انجام شد. بهترین عملکرد میوه فلفل دلمه‌ای به ترتیب در تیمارهای l80h40، l100h40 و l120h40 مشاهده گردید که با یکدیگر اختلاف معنی‌داری نداشتند و کم‌ترین عملکرد (14.21 گرم در بوته) در تیمار l60ha0 مشاهده شد. هم‌چنین بیش‌ترین و کم‌ترین مقدار کارایی مصرف آّب به‌ترتیب در تیمار l80ha40 (7.45 کیلوگرم در مترمکعب) و تیمارl60ha0  (0.8 کیلوگرم در متر مکعب) مشاهده شد. مقادیر کلروفیل a، b، کل و کاروتنوئید گیاه با افزایش مقدار اسید هومیک مصرفی و سطوح آبیاری به‌صورت معنی‌داری افزایش و با اعمال تنش آبی، کاهش یافت. کاربرد 40 گرم بر گلدان اسید هومیک، سبب افزایش معنی‌دار وزن تر و خشک اندام هوایی، رنگیزه‌های فتوسنتزی و غلظت عناصر نیتروژن، فسفر و پتاسیم اندام هوایی در مقایسه با عدم کاربرد اسید هومیک گردید، به‌طوری‌که غلظت عناصر نیتروژن، فسفر و پتاسیم فلفل دلمه‌ای در تیمار ha40 نسبت به تیمار ha0 به ترتیب، 50/3، 34/8 و 14/5 درصد افزایش نشان داد. با توجه به نتایج می‌توان استفاده از اسید هومیک را برای کاهش اثرات منفی تنش کم‌آبی فلفل دلمه‌ای توصیه نمود.

investigating the effect of humic acid on the water use efficiency, yield, and some physiological characteristics of bell pepper plants under different water levels

1. introduction: an experiment in a randomized complete block design with three levels of humic-acid (0 (ha0), 2 (ha2), and 4 (ha4) gr/pot) and four irrigation levels (60 (l60), 80 (l80), 100 (l100), 120 (l120), percent of soil moisture depletion) with four replications was performed in the research greenhouse at faculty of agriculture of bojnourd university. to prepare the pots, the soil sample was passed through a 2 mm sieve, and humic acid was added to the soil sample according to the experimental treatments. two bell pepper seedlings were transferred to each pot, and all pots were irrigated according to the experimental treatments. eighty days after cultivation, plants were harvested, and soil samples were air dried. soil texture, soil ph, electrical conductivity (ece), soil organic carbon, total nitrogen, available phosphorus, total chlorophyll a, b, and carotenoid content, water use efficiency, stomatal conductance, and yield were determined by conventional methods.2. materials and methods: an experiment in a randomized complete block design with three levels of humic-acid (0 (ha0), 2 (ha2), and 4 (ha4) gr/pot) and four irrigation levels (60 (l60), 80 (l80), 100 (l100), 120 (l120), percent of soil moisture depletion) with four replications was performed in the research greenhouse at faculty of agriculture of bojnourd university. to prepare the pots, the soil sample was passed through a 2 mm sieve, and humic acid was added to the soil sample according to the experimental treatments. two bell pepper seedlings were transferred to each pot, and all pots were irrigated according to the experimental treatments. eighty days after cultivation, plants were harvested, and soil samples were air dried. soil texture, soil ph, electrical conductivity (ece), soil organic carbon, total nitrogen, available phosphorus, total chlorophyll a, b, and carotenoid content, water use efficiency, stomatal conductance, and yield were determined by conventional methods.3. results and discussion: the results showed that the best bell pepper fruit yield was observed in l80h40, l100h40, and l120h40 treatments, respectively, which had no significant difference, while the highest water use (7136.80 m3 ha-1) was seen in l120ha0. also, the lowest values of yield (14.21 g plant-1) and water use (3584.61 m3 ha-1) were observed in l60ha0 and l60ha40, respectively. moreover, the results showed that the maximum value of wue was obtained in l80ha40 (7.45 kg m-3), while the lowest wue value was obtained in l60ha0 (0.80 kg m-3) these results can be attributed to the ratio of yield to water use so that the yield has increased with the increase in water use, but the rate of increase in yield is lower than the rate of increase in water use. the amount of chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids of the plant increased significantly with the increase in the application of humic acid and irrigation levels. also, according to the results, it can be recommended to use humic acid to reduce the negative effects of drought stress in bell pepper. the results showed that with the use of the higher amount of humic acid (ha4) and less irrigation water consumption (80% soil moisture depletion), the fruit yield of bell peppers incresedand the water consumption was saved, on the other hand, by improving the physical and chemical characteristics of soil and improved the plant growth, crop production increased. therefore, the application of humic acid can be a sustainable solution to increase the growth of bell pepper in the conditions of drought stress. according to this study’s results, increasing the severity of drought stress will result in the reduction of the studied traits,however, humic acid fertilizer treatment can protect the plant against drought stress by increasing growth indicators such as root length, stem length, and relative water content of leaves, that leads to reduction of damage caused by stress.4. conclusion: in general, nutrient absorption, pepper growth, and pepper yield were observed in the ha40 treatment with an 80% soil moisture level. it seems that the use of humic acid can counteract the detrimental effects of water deficit in soil. applying humic acid increased the water efficiency in the experimental condition. more soil water content (100 and 120 percent of soil moisture discharge) did not show any significant effect in increasing bell pepper yield. so, based on the research results, ha application and less soil water content (l80) are valuable strategies for increasing the yield and wue in pepper plant production in greenhouse conditions.