بخش تحقیقات خاک و آب، مرکز تحقیقات و آموزش کشاورزی و منابع طبیعی جنوب استان کرمان، سازمان تحقیقات، آموزش و ترویج کشاورزی، جیرفت، کرمان، ایران.
چکیده
زوال مرکبات در اثر تعامل تنشهای محیطی بهویژه گرما، خشکی و عوامل بیماریزا یک تهدید جدی برای پایداری باغات در مناطق خشک و نیمهخشک محسوب میشود. این مطالعه با هدف ارزیابی تأثیر مدیریت تلفیقی تغذیه و آبیاری بهینه، بهکارگیری مالچ گیاهی و ایجاد سایبان بر کاهش عوارض زوال و بهبود شاخصهای رشدی درختان مرکبات در جنوب استان کرمان، به صورت طرح بلوکهای کامل تصادفی با سه تکرار و چهار تیمار روی درختان والنسیا در یک باغ با خاک شنی آهکی اجرا شد. تیمارها شامل; (1) شاهد (مدیریت سنتی و عرف منطقه)، (2) تغذیه و آبیاری بهینه (بر اساس نتایج آزمون خاک، برگ و برآورد علمی نیاز آبی گیاه)، (3) تیمار دوم + مالچ گیاهی (برگ خرما) و (4) تیمار سوم + سایبان (توری 50 درصد) از اردیبهشت تا شهریور بودند. تعداد شاخه جدید، عملکرد، ابعاد میوه، سطح برگ و غلظت عناصر غذایی در برگ اندازهگیری و تجزیه آماری شدند. طبق نتایج، کلیه تیمارها تأثیر معنیداری (0.01 > p) بر تمامی صفات مورد بررسی داشتند. تیمار چهارم (ترکیب کامل) با 298/57 عدد شاخه جدید و عملکرد 78/29 کیلوگرم در هر درخت، به ترتیب افزایشی معادل 198/6 و 196/1 درصد نسبت به شاهد داشت. قطر و طول میوه نیز در این تیمار به طور معنیداری افزایش یافت. بالاترین غلظت نیتروژن، فسفر، پتاسیم و عناصر کممصرف (روی، آهن، منگنز) در برگهای درختان تحت تیمار چهار مشاهده شد. به نظر میرسد ترکیب تغذیه و آبیاری مناسب (رفع کمبودهای غذایی و آبی)، همراه با مالچ (حفظ رطوبت خاک و تعدیل دمای ریشه) و سایبان (کاهش تنش تابشی و گرمایی)، مقاومت درخت پرتقال در برابر عوامل زوال را تقویت میکند. این پژوهش مدیریت یکپارچه فوق را به عنوان راهکاری مؤثر برای کنترل زوال و افزایش بهرهوری در باغات مرکبات مناطق مشابه توصیه مینماید.
The Role of Integrated Management of Suitable Nutrition, Plant Mulch, and Shading in Reducing Decline in Orange Trees (Case Study: South of Kerman Province)
نویسندگان [English]
JAVAD SARHADI؛ MEHRI SHARIF
Soil and Water Department, South Kerman Agricultural and Natural Resources Research and Education Center, Agricultural Research, Education and Extension Organization (AREEO), Jiroft, Kerman, Iran.
چکیده [English]
Background and Objectives: Citrus decline, a multifactorial syndrome characterized by gradual growth reduction, yield loss, and eventual tree death, poses a severe threat to the sustainability of citrus orchards in arid and semi-arid regions. This phenomenon results from the complex interaction of biotic pathogens and abiotic stresses, including water deficit, nutritional imbalances, and particularly heat stress in warm climates. Southern Kerman province in Iran is a major citrus-producing area increasingly affected by this decline, linked to calcareous sandy soils with inherent limitations in organic matter and nutrient availability. Conventional singular management practices have proven inadequate in addressing this complex issue. Therefore, this study aimed to design and evaluate a holistic, integrated management strategy. The primary objective was to assess the combined effects of optimized nutrition and irrigation, organic mulch application, and artificial shading on mitigating decline symptoms, improving tree physiological status, and enhancing yield and fruit quality of Valencia orange trees (Citrus sinensis cv. Washington Navel) grown in calcareous sandy soils.
Materials and Methods: The research was conducted over two years (2021-2022) in a commercial Valencia orange orchard with calcareous sandy soil in Anbarabad, southern Kerman province. Initial soil analysis confirmed a sandy loam to loamy texture, high pH (7.5-7.7), low organic carbon (0.31-0.53%), and deficient levels of available phosphorus, potassium, and micronutrients (Zn, Fe, Mn). The experiment followed a randomized complete block design (RCBD) with three replications and four distinct treatments: (1) Controll: standard local orchard practices (conventional nutrition and irrigation). (2) Optimal Nutrition and Irrigation (ONI): Fertilization based on soil and leaf analysis, using chemical and organic amendments (including decomposed cow manure) applied via localized placement (pit method). Irrigation was optimized through a pressurized drip system with proper emitter placement and spacing to ensure adequate water supply. (3) ONI + Mulch (ONI+M): Treatment 2 supplemented with a surface layer of plant-based mulch (shredded palm leaves). (4) ONI + Mulch + Shade (ONI+M+S): Treatment 3 supplemented with a 50% shading net installed from late May to mid-September to mitigate summer heat stress. Key growth and physiological parameters were measured at the end of each growing season. These included vegetative growth (number of new shoots per tree), yield (kg per tree), fruit quality attributes (diameter and length), leaf area, and the concentration of macro- and micronutrients (N, P, K, Zn, Fe, Mn) in leaf tissue. Collected data were subjected to analysis of variance (ANOVA) using SAS software, and mean comparisons were performed using Duncan's multiple range test at the 1% significance level. Results: The integrated management strategy demonstrated highly significant and progressive improvements across all measured parameters. Treatment 4 (ONI+M+S) produced the most dramatic results, recording 298.57 new shoots per tree and a yield of 78.29 kg per tree. This represents increases of 198.6% and 196.1%, respectively, compared to the control (100 shoots, 26.44 kg/tree). Treatments 2 (ONI) and 3 (ONI+M) also showed significant improvements, with yield increases of 64% and 116.3% over the control, indicating the additive benefits of each component. Fruit diameter and length were significantly enhanced under the full integrated treatment (83.67 mm and 86.23 mm, respectively), corresponding to increases of 27.5% and 33.8% compared to control fruit (65.63 mm, 64.44 mm). This indicates a substantial improvement in fruit marketability and grade. Leaf analysis revealed a profound positive impact on tree nutritional health. Treatment 4 resulted in the highest concentrations of all measured nutrients. Most notably, micronutrient levels increased dramatically: by 126.7%, Iron (Fe) by 160.6%, and Manganese (Mn) by 98.8% compared to the control. Macronutrient levels (N, P, K) were also significantly higher in the integrated treatment compared to the control. Leaf area, an indicator of photosynthetic capacity, was also largest (39.63 cm²) in Treatment 4. ANOVA confirmed that the effect of treatments was significant (p < 0.01) for all studied traits.
Conclusion: This study conclusively demonstrates that citrus decline in calcareous sandy soils is a multifactorial challenge that cannot be effectively mitigated by conventional, piecemeal approaches. The integrated management package—combining scientifically guided nutrition and irrigation, organic mulching, and seasonal shading—proved to be a highly effective and synergistic strategy. The results provide clear evidence that this approach simultaneously alleviates multiple key stress factors: it corrects nutritional and water deficits, conserves soil moisture and moderates root-zone temperature, and reduces radiative and heat stress on the canopy.
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