نوع مقاله : مقاله پژوهشی
نویسندگان
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
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [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.
کلیدواژهها [English]
Timmer, L. W., & Menge, J. A. 2007. Compendium of Citrus Diseases (2nd
)