Bio-Based Plant Growth Regulator Reduces Inorganic Fertilizer Requirement and Improves Nodulation of Soybean (Glycine max L.) on Acid Ultisol of Bengkulu, Indonesia

Fiana Podesta; Dwi Fitriani; Novitri Kurniati; Rita Zurina; Ines Liem Lien Olivia Monica S

doi:10.59535/fvaj0r67

Authors

Fiana Podesta Department of Agrotechnology, Faculty of Agriculture, Universitas Muhammadiyah Bengkulu, Bengkulu, Indonesia Author
Dwi Fitriani Department of Agrotechnology, Faculty of Agriculture, Universitas Muhammadiyah Bengkulu, Bengkulu, Indonesia Author
Novitri Kurniati Department of Agrotechnology, Faculty of Agriculture, Universitas Muhammadiyah Bengkulu, Bengkulu, Indonesia Author
Rita Zurina Department of Agrotechnology, Faculty of Agriculture, Universitas Muhammadiyah Bengkulu, Bengkulu, Indonesia Author
Ines Liem Lien Olivia Monica S Department of Agrotechnology, Faculty of Agriculture, Universitas Muhammadiyah Bengkulu, Bengkulu, Indonesia Author

DOI:

https://doi.org/10.59535/fvaj0r67

Keywords:

Biostimulant, Bradyrhizobium, Nutrient Use Efficiency, Soil Acidity, Soybean Yield

Abstract

Soybean (Glycine max L.) production on Ultisol soils in Bengkulu, Indonesia, is constrained by low pH, aluminum toxicity, and phosphorus fixation, all of which suppress root nodulation and push farmers toward heavy inorganic fertilizer use. This study evaluated whether a bio-based plant growth regulator (bio-PGR), formulated from seaweed extract and humic acid, could reduce the inorganic NPK requirement of soybean while improving nodulation on acid Ultisol. A field trial used a factorial randomized complete block design with two factors: bio-PGR (absent or applied as a seed treatment plus two foliar sprays) and NPK dose (25, 50, 75, or 100% of the recommended rate), each combination replicated three times. Bio-PGR increased nodule number by 72% and nodule dry weight by 82% relative to the untreated control, averaged across NPK doses, and lowered soil exchangeable aluminum from 2.85 to 2.31 cmol(+) kg-1. The combination of bio-PGR with 50% of the recommended NPK dose produced grain yield (2.38 t ha-1) statistically equivalent to the full NPK dose without bio-PGR (2.41 t ha-1), while nodule number in that treatment was more than double that of the untreated full-dose control. Bio-PGR did not compensate for the lowest fertilizer dose tested (25%), where phosphorus limitation likely capped the response. These results indicate that bio-PGR can substitute for a substantial share of inorganic fertilizer input on acid Ultisol without a yield penalty, offering a practical route to lower fertilizer cost in smallholder soybean systems.

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