Document Type : Research Article

Authors

1 Department of Soil Science, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran

2 Department of Soil Science, Sari University of Agricultural Sciences and Natural Resources, Sari, Iran

3 Department of Horticulture Science. Faculty of Agriculture Sciences, University of Guilan, Rasht, Iran

10.22067/jsw.2025.89053.1420

Abstract

Introduction
The olive tree (Olea europaea L.) is one of the most significant and ancient cultivated plants in the Mediterranean region, prized for its edible fruit and high-quality oil. However, the increasing scale of olive oil production has led to the accumulation of large quantities of solid waste, particularly Olive Solid Pomace (OSP), which poses considerable environmental challenges due to its high organic load and phytotoxic components. Sustainable management and valorization of this waste are crucial for reducing environmental risks and improving the circular economy in agricultural systems. This study aimed to evaluate the effects of compost and vermicompost derived from OSP, both in enriched and non-enriched forms, on the yield of olive fruit and the quality characteristics of the resulting olive oil. To this end, a field experiment was conducted during the 2018 growing season in a traditional olive orchard located in Rudbar, Gilan Province, Iran. The experiment was carried out using a randomized complete block design (RCBD) with 12 treatments and three replications using the ‘Arbequina’ cultivar, a well-known olive variety cultivated for its high oil content and quality.
 
Materials and Methods
Compost and vermicompost were first produced from olive solid pomace. After analyzing their basic physicochemical properties, several treatments were biologically enriched using plant growth-promoting rhizobacteria (PGPR), including Bacillus megaterium (phosphorus-solubilizing), Azotobacter chroococcum (nitrogen-fixing), and Thiobacillus thioparus (sulfur-oxidizing). Additional treatments were chemically enriched by incorporating 1 kg each of urea (as a nitrogen source), triple superphosphate (as a phosphorus source), and elemental sulfur at a rate of 1% by weight. The experimental treatments included: raw olive pomace, unenriched compost, chemically enriched compost, biologically enriched compost, unenriched vermicompost, chemically enriched vermicompost, biologically enriched vermicompost, a full NPK fertilizer treatment, a manure-only treatment (10 kg of animal manure), and a no-fertilizer control. All olive waste-based amendments were applied at 3% w/w. NPK fertilizers included urea (750 g in three split applications), triple superphosphate (250 g), and potassium sulfate (750 g). Micronutrients such as magnesium sulfate, manganese, iron, zinc, copper, boric acid, and elemental sulfur were applied based on soil test recommendations. Uniform horticultural practices, including surface drip irrigation, weed control, pest management, and other cultural operations, were applied across all plots. Post-treatment, soil samples were collected at depths of 0–30, 30–60, and 60–90 cm to measure pH, EC, organic carbon, and available phosphorus. Foliar sprays were prepared with 1,000 ml solutions of urea and potassium sulfate (10 g/L), zinc sulfate (3 g/L), and boric acid (5 g/L) and applied twice at sunset using a handheld sprayer. Fruit yield, oil content, and selected oil quality parameters were then assessed.
 
Results and Discussion
Application of biologically enriched vermicompost significantly improved olive yield and oil quality. Trees receiving this treatment produced 50.33 kg of fruit per tree—an increase of 93.58% compared to the control. Similarly, the highest oil yield (11.14 kg per tree) was recorded in the biologically enriched vermicompost treatment. The lowest peroxide value (1.06 meq O₂ kg-1 oil) was also observed in this treatment, representing an 88.27% reduction compared to the control. Organic fertilizers positively influenced the oil percentage of the fruit, with biologically enriched compost yielding the highest oil content (57.7%), which was 132.2% higher than the control. The extinction coefficients K270 and K232, indicators of oil oxidation, were reduced by 96.2% and 78.5%, respectively, in the biologically enriched vermicompost treatment. Furthermore, this treatment resulted in the lowest free fatty acid content, 94.7% lower than the control. Leaf phosphorus content was also significantly enhanced, reaching 0.33% in the biological vermicompost treatment, a 230% increase over the control. These findings underscore the beneficial role of organic fertilizers, particularly biologically enriched vermicompost, in improving soil fertility, nutrient availability, and plant performance. The high phosphorus content in the compost and vermicompost, combined with microbial activity, played a pivotal role in enhancing both yield and oil quality. The application of PGPRs proved particularly effective, as they not only facilitated nutrient cycling but also contributed to improved physiological responses in olive trees.
 
Conclusion
Overall, the results suggest that olive trees fertilized with biologically enriched organic amendments derived from olive pomace benefit from improved oil quality and fruit yield. The presence of adequate phosphorus and beneficial bacteria played a pivotal role in enhancing plant nutrition and oil characteristics. Therefore, the use of PGPR in the enrichment of composted organic materials can be an effective and sustainable strategy to improve the productivity and quality of olive oil. Among the treatments, biologically enriched vermicompost emerged as the most effective and is recommended for further field application. Future research should explore other organic amendments and their long-term effects on olive orchards.

Keywords

Main Subjects

©2025 The author(s). This is an open access article distributed under Creative Commons Attribution 4.0 International License (CC BY 4.0).

  1. Ahmad, R., Jilani, Gh., Arshad, M., Zahir, Z.A., & Khalid, A. (2007). Bio-conversion of organic wastes for their recycling in agriculture: an overview of perspectives and prospects. Annals of Microbiology, 57(4), 471-479. https://doi.org/10.1007/BF03175343
  2. Alikhani, H.A., & Hemmati, A. (2014). The effect of vermicompost enrichment with fertilizer and bacterial treatments on humicization and humic acid characteristics. Journal of Agricultural Science and Sustainable Production, 24(1), 113-125. (In Persian with English abstract)
  3. Busato, J.G., Lima, L.S., Aguiar, N.O., Canellas, L.P., & Olivares, F.L. (2012). Changes in labile phosphorus forms during maturation of vermicompost enriched with phosphorus-solubilizing and diazotrophic bacteria. Bioresoure Technology, 110, 390–395. https://doi.org/10.1016/j.biortech.2012.01.126
  4. Farahbakhsh, A., Ziaian, A.H., Besharti, H., & Jokar, L. (2014). Phosphate solubilizing bacteria roles on the mineral nutrition uptake and yield of sorghum. Journal of Soil Management and Sustainable Production, 4(2), 239-253. (In Persian with English abstract)
  5. Fatahinejhad, I., Siadat, A., Esfandiari, M., Moghdisi, R., & Moazi, A.A. (2012). Effect of phosphorus fertilizer on yield, oil and canola protein in dry farming in different groups of soil phosphorus fertility. Crop Physiology Journal, 5(18), 83-100. (In Persian with English abstract). http://cpj.ahvaz.iau.ir/article-1-63-fa.html
  6. Fayazi, H., Abdali Mashhadi, A., Kochzadeh, A., Popzen, A.H., & Arzanesh, M.H. (2018). The effect of organic and biological fertilizers on the content of nitrogen, phosphorus and potassium, photosynthetic pigments and the amount of the effective substance of the medicinal plant (Echinacea Purpurea). Agricultural Research of Iran, 16(2), 283-298. (In Persian with English abstract). https://doi.org/10.22067/gsc.v16i2.49182
  7. Hachicha, R., Rigane, H., Ben Khodher, M., Nasri, M., & Medhioub, K. (2003). Effects of partial stone removal on the co‐composting of olive‐oil processing solid residues with poultry manure and the quality of compost, Environmental Technology, 24(1), 59-67. https://doi.org/10.1080/09593330309385536
  8. Hashempour, A., Fatuhi Qazvini, R., Bakhshi, D., & Asadi Sanam, S. (2010). Evaluation of Virgin olive (Olea europaea) oil quality from cultivars, “Zard, Roghani and Mari”, Kazeroon region. Iranian Journal of Horticultural Sciences, 41(1), 47-53. (In Persian with English abstract). https://doi.org/10.2478/v10133-010-0053-z
  9. Hashempour, E., Farhani Rasti, M.B., Gurbanzadeh, N., & Fazli Sangani, M. (2018). Studying the release of phosphorus from olive solid residue by Bacillus bacteria in soil. Master's thesis, Department of Soil Science, Faculty of Agriculture, Gilan University, Rasht, 77 Pp. (In Persian with English abstract)
  10. Kapoor, K.K., Yadav, K.S., Singh, D.P., Mishra, M.M., & Tauro, P. (1983). Enrichment of compost by Azotobacter and phosphate solubilising microorganisms. Agricultural Wastes, 5, 125-133.
  11. Khaja Haghvardi, M., Ardakani, M.R., Abbaszadeh, B., & Nejatkhah Manavi, P. (2018). The effect of vermicompost, biochar and mycorrhizal symbiosis on some quantitative and qualitative characteristics of pumpkin (Cucurbita pepo). Iranian Journal of Iranian Medicinal and Aromatic Plants Research, 34(1), 87-100. (In Persian with English abstract). https://doi.org/10.22092/ijmapr.2018.114886.2095
  12. Khosravi, A., Zarei, M., & Ronaghi, A.M. (2017). Effect of Claroidoglomus atonicatum fungus, vermicompost and phosphate sources on root colonization and growth of lettuce. Journal of Soil Management and Sustainable Production, 7(2), 167-181. (In Persian with English abstract). https://doi.org/10.22069/ejsms.2017.11499.1663
  13. López-Piñeiro, A., Albarrán, A., Rato Nunes, J.M., & Barreto, C. (2008). Short and medium-term effects of two-phase olive mill waste application on olive grove production and soil properties under semiarid mediterranean conditions. Bioresource Technology, 99, 7982–7987. https://doi.org/10.1016/j.biortech.2008.03.051
  14. Majeed, A., Munawar Mehdi, Sh., Niaz, A., Mahmood, A., Ul-Haq, E., Ahmad, N., Javid, Sh., & Mehmood, A. (2018). Influence of P-enriched compost application on economics and P use efficiency of a maize–wheat rotation system. The crop Journal, https://doi.org/10.1016/j.cj.2018.05.007
  15. Michailides, M., Christou, G., Akratos, C.S., Tekerlekopoulou, A.G., & Vayenas, D.V. (2011). Composting of olive leaves and pomace from a three-phase olive mill plant. International Biodeterioration & Biodegradation, 65, 560-564. https://doi.org/10.1016/j.ibiod.2011.02.007
  16. Montemurro, F., Fiore, A., D’Andrea, L., & Diacono, M. (2016). Olive mill by-products application: Organic olive orchard yield performance and soil fertility. Journal of Agricultural Sciences Technology, 18, 1883-1896. http://jast.modares.ac.ir/article-23-1360-en.html
  17. Pandit, N.R., Mulder, J., Hale, S.E., Schmidt, H.P., & Cornelissen, G. (2017). Biochar from "Kon Tiki" flame curtain and other kilns: Effects of nutrient enrichment and kiln type on crop yield and soil chemistry. Plos One. https://doi.org/10.1371/journal.pone.0176378
  18. Pan, I., Dam, B., & Sen, S.K. (2012). Composting of common organic wastes using microbial inoculants. Biotechnology, 2, 127–134. https://doi.org/10.1007/s13205-011-0033-5
  19. Rahmani Iranshahi, D., Sepehri, M., Zarei, M., & Jahandideh Mahjanabadi, V. (2016). The effect of endophytic fungi on phosphorus efficiency indices and wheat tolerance to P deficiency stress. Journal of Plant Process and Function, 5(18), 193-205. (In Persian with English abstract). https://doi.org/20.1001.1.23222727.1396.6.19.10.8
  20. Sadegh Zadeh, F., Fallah Tolekolai, S., Bahmanyar, M.A., & Emadi, M. (2018). Application of biochar and compost for enhancement of Rice (Oryza sativa) grain yield in calcareous sandy soil. Communications in Soil Science and Plant Analysis, 49(5), 552–566. https://doi.org/10.1080/00103624.2018.1431272
  21. Sánchez, Ó.J., Ospina, D.A., & Montoya, S. (2017). Compost supplementation with nutrients and microorganisms in composting process. Waste Management, 69, 136–153. https://doi.org/10.1016/j.wasman.2017.08.012
  22. Sarikhani, M.R., Chelbianlu, N., & Alavi Kia, S.S. (2015). Investigating the distribution of phosphate dissolving bacteria and soil phosphatase activity in different uses. Water and Soil, Agricultural Sciences and Industries, 29(6), 1673-1662. (In Persian with English abstract).
  23. Seyedi, A., Hamid Oghli, Y., Ghasemnejad, M., & Ghorbanzadeh, N. (2018). Effect of olive oil mill wastewater application on soil biological properties, oil quality and fruit yield of two cultivars of olive. Journal of Iranian Horticultural Sciences, 49(2), 365-374. (In Persian with English abstract).
  24. Seyedi Morghaki, A., Hamid Oghli, Y., & Qasimnejad, M. (2017). Effect of olive mill pomace compost on yield, oil percentage and the leaf elements content in two olive cvs ’Zard’ and ’Roughany ’. Journal of Plant Production Research, 24(2), 125-138. (In Persian with English abstract).
  25. Seyedi, A., Ghasemnejad, M., & Hamid Oghli, Y. (2016). The effect of wastewater and olive pomace compost on vegetative growth, reproduction and oil quality of two local yellow and oily olive varieties. Department of Horticultural Sciences (Fruit Cultivation), Master's Thesis, Gilan University, Rasht, 152 Pp. (In Persian with English abstract)
  26. Seifi, I., Jalali, A., Ebrahimnia, S., & Feridouni, H. (2016). Comparison of the biochemical composition of three varieties of olive oil (Olea europaea) in different regions of Golestan province. Journal of Plant Environmental Physiology, 11(43), 52-65. (In Persian with English abstract)
  27. Shahabifar, J., Panahpour, I., Moshiri, F., Gholami, A., & Mansherari, M. (2013). Phosphorus release and uptake in wheat using organic and chemical fertilizers on calcareous soils. Quarterly Journal of Plant Cell and Molecular Biology, 8(3 and 4), 29-39. (In Persian with English abstract)
  28. Taheri, M., Basirt, M., Khosh zaman, T., Mehshari, M., & Shakri, M.A. (2017). Integrated management of soil fertility and plant nutrition in olive trees. Ministry of Agriculture. Agricultural research, education and extension organization. Soil and Water Research Institute, 105 Pp. (In Persian with English abstract)
  29. Toscano, P., Casacchia, T., Diacono, M., & Montemurro, F. (2013). Composted olive mill by-products: compost characterization and application on olive orchards. Journal of Agricultural Sciences and Technology, 15, 627-638. http://jast.modares.ac.ir/article-23-2628-en.html
  30. Vahedi, R., & Rasouli Sadekiani, M.H. (2019). The effect of biochar and rhizospheric growth-promoting bacteria on the activity of phosphomonoesterase enzymes and phosphorus bioavailability. The 16th Iran Soil Science Congress, Zanjan, Iran. (In Persian with English abstract)
  31. Wang, J., Xia, K., Waigia, M.G., Gaoa, Y., Odingaa, E.S., Linga, W., & Liua, J. (2018). Application of biochar to soils may result in plant contamination and human cancer risk due to exposure of polycyclic aromatic hydrocarbons. Environment International, 121, 169–177. https://doi.org/10.1016/j.envint.2018.09.010
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