بررسی اثر مقادیر مختلف آهن، روی و منگنز بر عملکرد خیار گلخانه‌ای (مطالعه موردی: در شرایط جیرفت)

Objectives
This study was designed to address a critical agronomic challenge in one of Iran's foremost greenhouse production hubs. The primary objectives were: 1) to determine the precise optimal application rates of iron (Fe), zinc (Zn), and manganese (Mn) micronutrient fertilizers for greenhouse cucumber (Cucumis sativus L.) cultivation in the distinctive alkaline, sandy, and organic-poor soils in Jiroft region; 2) to evaluate the individual and combined effects of these micronutrients on key quantitative and qualitative yield parameters, including total yield, fruit diameter, and fruit nitrate concentration; 3) to investigate the presence and strength of synergistic interactions among Fe, Zn, and Mn in influencing cucumber performance; and 4) to develop a scientifically-grounded, efficient, and localized fertilization strategy that maximizes productivity and fruit quality while preventing the economic losses and environmental risks associated with both deficiency and toxicity from imbalanced micronutrient application.
Material and Methods
The research was conducted during the 2021-2022 growing season in a fully equipped polyethylene greenhouse at the Agricultural and Natural Resources Research Center of southern Kerman Province, Jiroft. The experiment employed a factorial arrangement based on a Randomized Complete Block Design (RCBD) with three replications. The three fertilizer factors were: Fe-EDDHA chelate at three levels (namely, 0, 11, and 13 kg/ha), zinc sulfate (ZnSO₄) at three levels (namely, 0, 50, and 80 kg/ha), and manganese sulfate (MnSO₄) at three levels (namely, 0, 50, and 120 kg/ha). This yielded 27 combined treatment combinations plus a control (i.e., no micronutrient application). Prior to planting, an exhaustive soil analysis was performed to find that the soil was sandy loam in texture, alkaline (pH 7.7), low in electrical conductivity (EC 2.50 dS/m), very low in organic carbon content (0.18%), and deficient in available Fe (3.60 mg/kg), Mn (2.30 mg/kg), and Zn (0.80 mg/kg) as extracted by the DTPA method.
Uniform cucumber seedlings at the 3-4 leaf stage were transplanted. All the micronutrient treatments were applied in solution through a drip irrigation system in three splits: at planting, at the beginning of flowering, and at early fruit set. Macronutrient (N, P, K) application was uniform across the plots based on soil test recommendations. Standard pest, disease, and crop management practices were applied uniformly. At final harvest, the following traits were measured: total marketable yield (t/ha), fruit diameter (cm) as measured by a digital caliper, and spectrophotometrically determined fruit nitrate concentration (mg/kg). The data thus collected were subjected to Analysis of Variance (ANOVA) using SAS software (v. 9.4), and mean comparisons were performed using Duncan's Multiple Range Test at the 5% probability level.
Results
Soil analysis confirmed the initial micronutrient deficiencies. ANOVA revealed that the main effects of Fe, Zn, and Mn fertilization were highly significant (p≤0.01) on all the measured traits of total yield, fruit diameter, and nitrate concentration. Furthermore, all the two-way interactions (Fe×Zn, Fe×Mn, Zn×Mn) and the three-way interaction (Fe×Zn×Mn) were found to have significant effects on yield and fruit diameter, underscoring the complex interplay among these nutrients.
The separate application of optimal levels of each single micronutrient was observed to outperform the control treatment in a significant manner. The optimal levels were identified as: 11 kg/ha for Fe-EDDHA (yield: 311.18 t/ha; fruit diameter: 14.56 cm), 50 kg/ha for ZnSO₄ (yield: 310.10 t/ha; fruit diameter: 14.60 cm; nitrate: 48.57 mg/kg), and 50 kg/ha for MnSO₄ (yield: 309.73 t/ha). Application of Zn at 50 kg/ha also resulted in a significant reduction (16.5%) in fruit nitrate concentration compared to the control (58.20 mg/kg).
The most compelling results emerged from the interaction studies. More specifically, the two-way interactions consistently showed that the combination of the optimal level of one element with that of another (e.g., Fe11 with Zn50) produced significantly higher yields and larger fruits than any sub-optimal combination did. The pinnacle of this synergistic effect was observed in the three-way interaction such that the combined application of all the three optimal levels (Fe11Zn50Mn50) produced the absolute maximum values: a yield of 364.30 t/ha and a fruit diameter of 14.83 cm. This result was significantly superior to those obtained from all the other treatment combinations and the individual optimal applications, demonstrating a powerful synergistic interaction. Importantly, applying levels higher than these identified optima (e.g., 13 kg/ha Fe, 80 kg/ha Zn, or 120 kg/ha Mn) provided no additional benefit and, in some cases, even led to a relative decrease in performance, indicating the risk of imbalance or incipient toxicity.
Conclusion
This study conclusively establishes that balanced micronutrient fertilization is a decisive factor contributing to successful greenhouse cucumber production in the alkaline, impoverished soils in Jiroft region. The research identifies a highly efficient and specific fertilization formula of 11 kg/ha of Fe-EDDHA chelate, 50 kg/ha of zinc sulfate, and 50 kg/ha of manganese sulfate. While the individual application of each of these optimal levels significantly enhances yield and fruit size, the key finding is the pronounced synergistic interaction among Fe, Zn, and Mn so that their simultaneous application at optimal rates yields a supra-additive effect, leading to the highest possible productivity and fruit quality. Hence, the critical superiority of an integrated and balanced nutritional program over the single-element fertilization cannot be overemphasized.
A significant quality-related outcome was the role optimal zinc nutrition played in significantly reducing nitrate accumulation in fruits to enhance the product's safety for consumption. The results also delivers a crucial cautionary note: application rates exceeding the identified optima are economically unjustified and potentially counterproductive, as they do not improve yield but may induce nutrient imbalances or environmental loading. In summary, this research provides a robust, evidence-based protocol for micronutrient management in greenhouse cucumber cultivation under conditions similar to those in Jiroft. This strategy promises maximized yield and quality, improved economic returns for growers, and enhaced environmental sustainability by preventing both deficient and excessive fertilizer application.