Effect of Foliar Application of Different Sources of Nano-Chelate Fertilizer (Nitrogen and Potassium) and Chemical Fertilizers (Urea and Potassium Nitrate) on Yield and Oil’s Quantity Attributes of Olive Tree cv. Zard

علوم باغبانی

Article 10, Volume 38, Issue 1 - Serial Number 61, May 2024, Pages 147-164   

Document Type: Research Article

DOI: 10.22067/jhs.2023.81601.1246

Authors

Zohre Rohi Vishekaii^{* 1}; Ali Soleimani²; Mahmood Ghasemnejad³; Akbar Hasani⁴

¹Guilan Agricultural and Natural Resources Research and Education Center, Rasht, Iran

²Department of Horticultural Science, University of Zanjan, Zanjan, Iran

³Department of Horticultural Science, University of Guilan, Rasht, Iran

⁴Department of Soil Science, University of Zanjan, Zanjan, Iran

Abstract

Introduction
 Olive tree, with a thousand years of cultivation history, is one of the most important horticultural crops in Iran and has always played an important economical role for orchardists. In olive orchards traits such as an increased formation of incomplete flowers, low yield of fruits and oil are often found as major problems. It should be noted that these traits are affected by numerous environmental and management factors from which the nutrition status is one of the most important ones. Proper nutrition plays an important role in both olive fruit and oil yield. There is a wide range of fertilizer compounds with different formulas and efficiencies available in the world market, among which nano-products are becoming increasingly popular. However, there is limited information on their efficacy in different plant species.
 
Materials and Methods
In order to evaluate the impact of fertilizers on olive cultivation, a research was conducted during two successive years from 2019 to 2020 in a commercial orchard on 15 year old olive tree cv. ‘Zard’, in Manjil city of Guilan province. Foliar application included five treatments using two types of fertilizers; nano (nano-chelated nitrogen and potassium: nano-NK) and chemical fertilizers (urea and potassium nitrate; NK). Treatments involved application of two concentrations from each fertilizers sources; 1.02g and 0.81g (nano-N₁K₁ and N₁K₁), 1.36 g and 1.08 g (nano-N₂K₂ and N₂K₂) of pure nitrogen and potassium, respectively. Foliar application was conducted in four stages bud-swelling, before blooming, pit hardening and shortly after harvest of table olive. Spraying with water was considered as the control. The nano-chelated fertilizers were obtained from Khazra Company, Teheran, Iran (http://en.khazra.ir). Spraying with water was considered as control. The experiment was performed in a randomized block design with three replications. The measurement of leaf nutrient status and its chlorophyll and carbohydrate contents were carried out at two times each growing season; in August (during pit hardening stage) and October (shortly after the harvest of table olive). At the green ripening stage, fruits were collected and weighted to determine fruit yield. At the end of the experiment quantity and quality traits of oil were measured.
 
Results and Discussion
 The results showed that the trees under N₂K₂ treatment had the highest yield. In terms of mineral content, both forms of fertilizers increased the concentration of nitrogen and potassium leaf elements compared to the control trees. Chlorophyll content was affected by nano-N₁K₁ foliar application and carbohydrate content was affected by nano-N₁K₁ in the pit hardening stage and nano-N₂K₂ in shortly after the harvest of table olive. Nano-N₁K₁ treatment with the lower crop load not only increased oil content but also improved quality characteristics of olive oil (free fatty acids, peroxide value, specific ultraviolet absorbance K₂₃₂, K₂₇₀ and contents of pigments), total phenol content, antioxidant capacity and fatty acid composition. Generally, the results showed that olive trees responded well to fertilizer feeding. These trees produced better crop and higher quality oil in comparison with control trees. According to the results, fruit yield is better under urea and potassium nitrate treatment, and the quality of olive oil is more stable after nano-chelated nitrogen and potassium foliar application. It seems that the reason for the high amount of fruit yield with N₂K₂ in comparison to the slow-release property of nano-fertilizers is that using nitrogen and potassium in the form of ordinary chemical fertilizer regulates the biosynthesis, conversion and rapid translocation of assimilates and mineral elements into reproductive structures, which resulted in soaring yield. We assumed that nano-N₁K₁ foliar spray in the pit hardening stage and shortly after the fruit harvest for table olive might export the assimilation into the fruit to fulfill cell metabolism requirements for oil synthesis.
 
Conclusion
 The current findings indicated that two of four treatments, i.e. nano-N₁K₁ and N₂K₂, could be more effective on olive trees in terms of general fruit and oil attributes. It was remarkable that nano treatment with a lower concentration could provide adequate beneficial effects on quality characteristics of olive oil and is in line with good management strategies regarding the preservation of the environment. To the best of our knowledge, the current work is the first report considering the application of nano-chelated nitrogen and potassium and their is use as a foliar application on olive trees. Additional studies would be necessary to further optimize the concentration and timing of the applications with these new formulations.

Keywords

Antioxidant capacity; Fatty acid profile; Foliar fertilizer; Olive

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