| چکیده انگلیسی مقاله |
Extended Abstract
Introduction
Citrus decline is a significant deteriorating factor in citrus cultivation, imposing costly damages to many orchards worldwide, including in Iran. Key factors contributing to citrus decline include environmental stresses such as the physical and chemical conditions of the soil, soil nutritional status, soil moisture condition, and biotic stresses. Environmental stresses, particularly mineral deficiencies and water stress, appear to play a crucial role in citrus deterioration. The Jiroft region is one of the major agricultural centers in south of Iran. Despite its pivotal role in citrus production of the country, the region's orchards experience widespread deterioration, causing considerable annual losses. However, no research has yet explored the potential benefits of simultaneous use of management and nutritional treatments in these orchards. Therefore, this study aims to investigate the effect of management and nutritional treatments on alleviating both biotic and abiotic stresses and reducing citrus fruit deterioration.
Materials and Methods
The current study employed a randomized complete block design over two years in Jiroft, south of Iran, incorporating the following treatments: 1. Control: No intervention. 2. Optimal Management: This included timely irrigation, fertilization (chemical and organic amendments based on soil and leaf tests), and gardening practices (pruning, fruit thinning, and weed removal). 3. Optimal Management + Potassium Silicate: This treatment received optimal management plus potassium silicate fertilizer applied through irrigation water three times at a rate of 30 L ha-1 (as determined by soil test). 4. Optimal Management + Shading: This treatment consisted of optimal management with shading (integrated or individual) at approximately 25% during the hot season, along with plant mulch. 5. Optimal Management + Biocontrol & Fungicides/Nematicides: This treatment combined optimal management with Mycorrhizal and Trichoderma fungi, along with fungicides and nematicides. 6. Optimal Management + Calcium Nitrate Injection: Trees received calcium nitrate injection (30%) directly into the trunk twice a year. 7. Optimal Management + Calcium Nitrate Fertilizer & Foliar Spray: This treatment involved optimal management with calcium nitrate fertilizer applied three times (500 grams per tree, one-month intervals) through irrigation water supplemented by foliar sprays containing calcium chelate and micronutrients (zinc, manganese, iron, and copper) applied three times. Then, leaf samples (both 5–6-month-old leaves and new leaves) and fruits were collected and transported to the laboratory for analysis. This analysis included measurements of number of new leaves, leaf area (average surface area per tree leaf), yield, fruit length and diameter, and the concentration of specific macro- and microelements in the leaves.Results and Discussion
The results revealed an inverse relationship between the average number of new leaves per tree and the severity of decay. Treatment-4 displayed a 1.5-fold increase in new leaves compared to the control (treatment-1). Additionally, the number of final shoots (spring and summer regrowth) was 191 in the treatment-4 and 76 in the control treatment. In the treatment-4, the mean leaf area was 41.8 cm2, compared to 29.4 cm2 in the control treatment, demonstrating an increase of 42.20%. Statistical comparisons of other responses also indicated a significant increase in treatment-4 compared to the others. Treatment-4 also exhibited the greatest improvements in fruit size. Fruit diameter and length increased by 35.5% and 33.9%, respectively, compared to the control. Treatment-4 resulted in the largest average leaf area (41.8 cm²) compared to the control (29.4 cm²). Fruit yield followed a similar trend, the lowest fruit yield (22.9 kg/tree) being observed in the control treatment. Conversely, treatment-4 (optimal irrigation management with shading and mulch) achieved the highest fruit yield (50.2 kg/tree), representing a significant increase of 119.2%, 45.9%, 52.5%, 2,100.0%, 95.3%, and 77.4% compared to control, treatment-2, treatment-3, treatment-5, treatment-6, and treatment-7, respectively. Treatment-4 also demonstrated the highest concentrations of zinc, manganese, and iron in the fruits. These elements increased by 1.50, 1.52, and 1.65 times, respectively, compared to the control. The results overwhelmingly favored treatment-4 compared to the control and other treatments. This superiority likely stems from the combined effects of shade mesh and mulch, which are unique to treatment-4. Shade mesh not only provides shade but also reduces radiation intensity, ultimately minimizing heat stress, sunburn, and water loss through evaporation and transpiration from the tree's foliage. Beneficial effects of Treatment-4 go beyond shade and mulch by ensuring optimal plant nutrition based on soil tests, addressing a crucial factor in citrus health. Inadequate nutrition can contribute to tree decline. By providing the necessary macro and micronutrients and adjusting environmental conditions like temperature and humidity, particularly around the roots, we can minimize disruptions in nutrient uptake and promote overall tree health.
Conclusions
Given the warm climatic conditions of Jiroft at Kerman's southern region, citrus decline arises from a combination of biotic and abiotic stresses. Consequently, solutions targeting either biotic or abiotic constraints are unlikely to provide a sustainable solution to the citrus decline question. An integrated approach, incorporating optimal irrigation and combined nutrient management, was found to be more effective. Therefore, implementing optimal irrigation and combined nutrition management, using plant mulch in the shaded area of the trees, and employing netting as a shade was proven to be a suitable solution to the citrus decline in the Jiroft at southern region of Kerman province, Iran.
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