Effect of Actinomycete Isolates on Potassium Availability, Soil Characteristics, and Barley Growth

Document Type : Research Paper

Authors

1 Department of Soil Science, Faculty of Agriculture, University of Guilan, Rasht, 41635-1314, Iran.

2 Agriculture Organization of Guilan Province, Management of Plant Protection, Rasht, Iran

Abstract

This study comprises two complementary experiments to evaluate whether actinomycete isolates can (i) enhance potassium solubility and improve soil properties, and (ii) promote barley growth. Part I employed a completely randomized design with 29 actinomycete isolates cultured in Alexandrov medium (three replications per isolate) to evaluate their ability to dissolve potassium and to alter culture medium pH. Part II examined the effects of the two superior isolates on barley growth traits and soil properties using a completely randomized block design with four treatments: control (C), chemical fertilizer (CF), and the two selected isolates, S3C and S5A, each with three replications. A suite of soil properties, plant growth metrics, and plant nutritional status was measured. In Alexandrov medium, isolates S3C and S5A produced the lowest pH values (3.23 and 4.25, respectively) and the highest soluble potassium concentrations (4.83 and 4.73 mg L-1, respectively). In soil, both actinomycete containing treatments yielded the lowest pH and the highest available potassium. Additionally, the highest available soil phosphorus was observed in the S3C treatment, and the highest available nitrogen and iron in the S5A treatment. Plant analyses showed that the potassium content in barley increased approximately 3 times in the S3C and S5A treatments relative to the control. The highest plant phosphorus and iron contents were observed in the S3C and S5A treatments, respectively. Overall, these microorganisms not only release potassium into the soil but also enhance the broader soil nutrient status. These results support the potential of actinomycete isolates as biofertilizers to boost crop productivity and promote sustainable agricultural practices. Further field validation is warranted to translate these findings into agronomic recommendations.

Keywords

Main Subjects

Background and Objectives

Potassium (K) is an essential nutrient for plants, playing a critical role in their metabolism, growth, and resistance to both abiotic and biotic stresses. In soil, K exists in mineral forms that provide only small amounts to plants. Several factors can reduce K availability in soil, including fixation of K fertilizers into insoluble forms, leaching, and uptake by plants. Soil microorganisms, especially those that solubilize K, are vital to the natural potassium cycle. Among these microorganisms, actinomycetes represent one of the largest and most diverse groups of bacteria known for promoting plant growth in an environmentally friendly manner.

Methodology

This study aimed to investigate the ability of actinomycetes isolated from citrus orchards to enhance K solubility, improve soil properties, and promote the growth of barley plants. The research was conducted in two stages. In the first stage, a completely randomized design was used to screen 29 actinomycete isolates (each with three replicates) on Alexandrov medium for their ability to solubilize K and to alter the pH of the culture medium. This assessment led to the selection of the two most effective isolates: S3C and S5A. In the second stage, a completely randomized block design with four treatments was employed: a control (C), a chemical fertilizer treatment (CF), and treatments involving the two selected isolates S3C and S5A. Each treatment was replicated three times on barley plants. After 40 days of cultivation, a suite of soil physicochemical and biological properties was measured, including pH, electrical conductivity, available phosphorus, inorganic nitrogen, available potassium, available iron, organic carbon, microbial basal respiration, and microbial biomass carbon. Additionally, growth and morphological parameters of barley were evaluated, including stem length, root length, fresh and dry weights of shoots and roots. Plant nutritional status was also assessed by determining nitrogen, phosphorus, potassium, and iron contents in the aerial parts.

Results

The results indicated that the actinomycetes isolates had a significant impact on soluble K levels and pH (p<0.01). The pH values ranged from 3.23 to 6.68, while soluble K levels varied between 1.7 and 4.83 mg L-1. Among the isolates tested, S3C and S5A exhibited the highest K dissolution rates, measuring 4.8 and 4.7 mg L-1, respectively. The effects of the treatments on all measured characteristics, except for electrical conductivity, were significant (p<0.01). The lowest soil pH (7.1) and the highest K levels were recorded in treatments that included actinomycete isolates. The S3C treatment produced the highest levels of available soil phosphorus, whereas the S5A treatment resulted in the highest levels of available nitrogen and iron. In plant growth metrics, shoot length, root length, and shoot fresh weight did not differ significantly between the CF treatment and those involving actinomycete isolates (P>0.05). K contents in the plants treated with S3C and S5A increased three times compared to the C treatment. Additionally, the highest phosphorus and iron contents were found in the S3C and S5A treatments, respectively. Beyond providing K in the soil, these microorganisms enhanced the overall nutrient status by increasing the availability of nitrogen, phosphorus, and iron.

Conclusion

Overall, these microorganisms not only release potassium into the soil but also enhance the broader soil nutrient status. These results support the potential of actinomycete isolates as biofertilizers to boost crop productivity and promote sustainable agricultural practices. Further field validation is warranted to translate these findings into agronomic recommendations.

Funding

The study was funded by the University of Guilan, Iran.

Authorship contribution

For research articles with several authors, a short paragraph specifying their individual contributions must be provided. The following statements should be used “Conceptualization, Nasrin Ghorbanzadeh. and Mohammad Bagher Farhangi; methodology, Nasrin Ghorbanzadeh.; software, Mohammad Bagher Farhangi; validation, Nasrin Ghorbanzadeh. and Mohammad Bagher Farhangi and sina noorizadeh; formal analysis, Reza Talebi; resources, Nasrin Ghorbanzadeh; data curation, Reza Talebi; writing—original draft preparation, Reza Talebi; writing—review and editing, Nasrin Ghorbanzadeh; Mohammad Bagher Farhangi, supervision, Nasrin Ghorbanzadeh; project administration, Nasrin Ghorbanzadeh; funding acquisition, Nasrin Ghorbanzadeh. All authors have read and agreed to the published version of the manuscript.” Please turn to the CRediT taxonomy for the term explanation. Authorship must be limited to those who have contributed substantially to the work re-ported.

All authors contributed equally to the conceptualization of the article and writing of the original and subsequent drafts.

The authorships didn’t use generative AI and AI-assisted technologies in the writing process.

Data availability statement

Data available on request from the authors.

Acknowledgements

The authors would like to thank all participants in the present study. The authors also would like to thank anonymous reviewers for their valuable suggestions in manuscript revision.

Ethical considerations

The authors avoided data fabrication, falsification, plagiarism, and misconduct.

Conflict of interest

The author declares no conflict of interest.

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Iranian Journal of Soil and Water Research
Volume 57, Issue 1
March 2026
Pages 189-208

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