نوع مقاله : مقاله پژوهشی

نویسندگان

• زهرا مهدیان ¹
• عبدالمجید لیاقت ²
• فرهاد میرزایی ²
• آرمین حسن‌زاده ³

¹ دانشجوی دکتری مهندسی آبیاری و زهکشی، گروه مهندسی و مدیریت آب، دانشکده کشاورزی، دانشگاه تربیت مدرس، تهران، ایران.

² استاد، گروه مهندسی آبیاری و آبادانی، دانشکدگان کشاورزی و منابع طبیعی، دانشگاه تهران، کرج، ایران.

³ دانش‌آموخته کارشناسی ارشد مهندسی فضای سبز، گروه باغبانی و فضای سبز، دانشکدگان کشاورزی و منابع طبیعی، دانشگاه تهران، کرج، ایران.

چکیده

محدودیت منابع آب در مناطق خشک و نیمه‌خشک، توسعۀ سامانه‌های آبیاری کم‌مصرف مانند آبیاری زیرسطحی را ضروری ساخته است. این پژوهش با هدف بررسی اثر بسترهای مختلف پیرامونی استوانۀ PVC بر توسعۀ هندسی و تغییرات زمانی پیاز رطوبتی در خاک لوم رسی سیلتی، در ایستگاه تحقیقاتی دانشکدگان کشاورزی و منابع طبیعی دانشگاه تهران (کرج) به­اجرا در آمد. استوانه‌های PVC مدفون منافذی با قطر 1/5 تا 2/5 میلی‌متر دارند و آبیاری با حجم ثابت ۱۰۰ لیتر توسط بابلر صورت گرفت. هشت بستر پیرامونی شامل ماسه‌بادی، پوکه کشاورزی، خاک منطقه (شاهد)، پرلیت، شن بادامی، ژئوتکستایل، ورمی‌کمپوست و کوکوپیت بررسی شدند. پیاز رطوبتی در روزهای ۱، ۳ و ۷ پس از آبیاری به روش ترانشه‌برداری برداشت و در نرم‌افزار AutoCAD بازسازی دو‌بعدی و سه‎بعدی صورت گرفت. نتایج تحقیق نشان داد ورمی‌کمپوست و ژئوتکستایل، به دلیل انسداد منافذ خروجی، توسعه رطوبت را محدود کرده­اند. پرلیت متعادل‌ترین الگو را با بیشترین مساحت و حجم (۵۲۲۷ سانتی‌متر مربع و ۳۴۸۸۷۷ سانتی‌متر مکعب در روز هفتم) نشان داد. پوکۀ کشاورزی بیشترین توسعه عمقی را به دلیل مسیرهای جریان ترجیحی و کوکوپیت با وجود توسعه اولیۀ محدود، بیشترین افزایش نسبی زمانی (۱۵۳ و ۲۰۵ درصد در مساحت و حجم) را داشتند. ماسه‌بادی و شن بادامی نیز از نظر توسعۀ پیاز رطوبتی عملکردی مشابه و در حد متوسط داشتند. نتایج بیانگر آن است که انتخاب بستر مناسب، با تأثیر بر ویژگی‌های هیدرولیکی، تخلخل و ظرفیت نگهداشت آب می‌تواند عملکرد سامانه‌های آبیاری زیرسطحی مبتنی بر استوانه را بهبود بخشد.

کلیدواژه‌ها

• آبیاری زیرسطحی
• استوانه PVC
• پیاز رطوبتی
• توسعه رطوبت
• محیط‌های متخلخل

موضوعات

• سامانه های نوین آبیاری

عنوان مقاله [English]

Effect of Different Surrounding Media on the Geometric and Temporal Development of the Wetting Bulb in PVC Cylinder–Based Subsurface Irrigation

نویسندگان [English]

• Zahra Mahdian ¹
• Abdolmajid Liaghat ²
• Farhad Mirzaei ²
• Armin Hasanzadeh ³

¹ Ph.D. Student in Irrigation and Drainage Engineering, Department of Water Engineering and Management, Faculty of Agriculture, Tarbiat Modares University, Tehran, Iran.

² Professor, Department of Irrigation and Reclamation Engineering, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran.

³ M.Sc. Graduate in Landscape Engineering, Department of Horticultural Sciences and Landscape Engineering, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran.

چکیده [English]

Extended Abstract
Introduction
Water scarcity in arid and semi-arid regions has increased the need for irrigation technologies that improve water-use efficiency while minimizing water losses. Subsurface irrigation delivers water directly to the root zone through buried emitters, thereby reducing surface evaporation and runoff. PVC cylinder–based subsurface irrigation systems have attracted attention because of their simple design, low cost, and adaptability. However, the medium surrounding the cylinder can strongly influence water transfer into the soil and, consequently, the geometry and temporal development of the wetting bulb. Differences in porosity, hydraulic conductivity, pore structure, and water-retention capacity among surrounding media may alter water-flow pathways and wetting patterns. Therefore, this study investigated the effects of eight surrounding media on wetting-bulb depth, width, area, and volume at 1, 3, and 7 days after irrigation.
Methodology
The experiment was conducted at the research station of the College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran, using a silty clay loam soil (30% clay, 56% silt, and 14% sand), with a bulk density of 1.13 g cm⁻³ and total porosity of 47%. The antecedent soil water content was 0.07 cm³ cm⁻³ for all treatments. Perforated PVC cylinders (6 cm internal diameter and 55 cm length) were installed vertically to a depth of 50 cm, leaving 5 cm above the soil surface for connection to a bubbler emitter. Each cylinder had eight outlet perforations distributed at four depths (10, 20, 30, and 40 cm), with perforation diameters determined using an orifice-flow relationship to achieve uniform discharge. Eight surrounding media—aeolian sand, agricultural pumice, local soil (control), perlite, pea gravel, non-woven geotextile, vermicompost, and cocopeat—were evaluated, with one PVC cylinder used for each treatment. Each treatment received a single 100-L irrigation application at an inlet pressure of 0.1 bar. Wetting-bulb development was monitored using the trench method. The same trench was progressively extended at 1, 3, and 7 days after irrigation to expose the advancing wetting front while avoiding repeated backfilling and re-excavation that could disturb soil structure and preferential flow pathways. To minimize evaporative losses from the exposed soil surface, the trench was covered with a plastic sheet between successive observations. Wetted-zone boundaries were traced and digitized in AutoCAD, and two-dimensional and three-dimensional reconstructions were used to determine wetting-bulb depth, width, area, and volume.
Results and Discussion
Because one PVC cylinder was used for each treatment, the results represent observed differences rather than statistically tested treatment effects. Vermicompost and non-woven geotextile progressively restricted outlet flow, causing an inflow–outflow mismatch and water overflow; consequently, both were excluded from further analysis. Among the remaining six media, perlite produced the most balanced wetting pattern and the greatest wetted area and volume. By day 7, its wetted area and volume reached 5,227 cm² and 348,877 cm³, representing increases of approximately 50% and 80%, respectively, relative to day 1. This performance may be associated with its high porosity, low bulk density, and favorable hydraulic properties, which could facilitate lateral and vertical water redistribution. Agricultural pumice produced the greatest wetting depth, suggesting that its coarse and heterogeneous pore structure may have promoted greater vertical redistribution. Thus, pore-size distribution and pore continuity, in addition to hydraulic conductivity, may influence dominant flow pathways. Aeolian sand and pea gravel exhibited relatively rapid initial wetting but limited subsequent expansion. By day 7, wetted area and volume had increased by approximately 24% and 29% for sand and 32% and 50% for gravel, respectively. The local-soil control produced a more restricted wetting bulb than most amended media. Cocopeat showed the most limited initial wetting but the greatest relative expansion over time, with wetted area and volume increasing by approximately 153% and 205%, respectively, by day 7. This behavior may be related to its fibrous structure and high water-retention capacity, which can support gradual redistribution of stored water.
Conclusions
The surrounding medium strongly influences the hydraulic performance and geometric and temporal development of wetting bulbs in PVC cylinder–based subsurface irrigation. Vermicompost and non-woven geotextile may be unsuitable for direct placement around concentrated outlets because they restricted discharge and caused overflow. Among the functional media, perlite produced the greatest wetted area and volume and the most balanced wetting pattern, whereas agricultural pumice resulted in the greatest wetting depth. Cocopeat, despite limited initial wetting, exhibited the greatest relative expansion over time, indicating potential for gradual water redistribution. Therefore, surrounding-medium selection should consider the intended hydraulic function—maximizing wetted volume and spatial coverage or promoting gradual redistribution—rather than relying on a single hydraulic property such as saturated hydraulic conductivity. These findings are limited to the tested soil texture, irrigation volume, discharge conditions, seven-day observation period, and single-cylinder design. Further studies using multiple replicates, different soil textures, and non-destructive moisture monitoring are recommended.
 Acknowledgments
The authors would like to express their sincere appreciation to the Editor-in-Chief and the anonymous reviewers for their valuable time, thorough evaluation, and insightful comments and suggestions. Their constructive feedback substantially contributed to improving the scientific quality, methodological rigor, structural organization, and overall clarity of this manuscript.
Conflict of Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Funding
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
Data Availability Statements
The datasets generated and/or analyzed during the current study are available from the corresponding author upon reasonable request.
 
Authors’ Contributions

All authors contributed equally to the conceptualization of the research problem and to the preparation of both the original draft and the final version of the manuscript. Z.M. was responsible for the methodology, literature review, execution of the research, data collection, data analysis, and preparation of the preliminary draft of the results section. A.H. contributed to the implementation of the experimental work, including laboratory and field experiments, as well as data collection. A.L. and F.M.A.S. jointly supervised the research, validated the findings, provided the facilities and resources required for the study, and critically reviewed and edited the manuscript. All four authors contributed to the conceptualization of the research problem, participated in preparing the original and subsequent drafts of the manuscript, and have read and approved the final published version.

کلیدواژه‌ها [English]

• Sub-irrigation
• bulb shaped PVC cylinder
• zone expansion
• porous media