Role of Rhizobium inoculation and mycorrhizal fungi in enhancing growth of soybean seedlings in sterilized gypsum soil fertilized with phosphorus

Abstract

Importance of the work: Soybean production in sterile gypsum soils is constrained by
low fertility and poor nutrient availability, particularly of nitrogen and phosphorus, which
are essential for plant growth. Although biological inoculants, such as Bradyrhizobium
japonicum Kirchnerand Glomus mosseae T.H. Nicolson & Gerd, are known to improve
nitrogen fixation and phosphorus uptake, there is insufficient understanding of their
combined effects under gypsum soil conditions, especially in relation to phosphate
fertilization.
Objectives: To assess the impact of Rhizobium, mycorrhizal fungi and phosphorus
fertilization on soybean growth in sterilized gypsum soil.
Materials and Methods: A field experiment was conducted using a 4 × 2 × 2 factorial
arrangement in a randomized complete block design with three replications.
The experimental factors consisted of phosphorus applied at four levels (0 kg/ha (control),
80 kg/ha, 160 kg/ha, 240 kg/ha), two rhizobial treatments (with and without B. japonicum
inoculation) and two mycorrhizal treatments (with and without G. mosseae inoculation).
Results: The analysis of variance revealed significant 3-way interaction effects for
all measured traits. Single inoculation with Rhizobium or mycorrhiza and phosphorus
application significantly increased plant height (up to 71.13 cm/plant), vegetative dry weight
(up to 3.22 g/plant) and root dry weight (up to 0.58 g/plant). Co-inoculation enhanced
phosphorus concentration in the vegetative part (up to 0.63%). Mycorrhizal infection rates
reached 67.33%. Phosphorus application and biofertilizer co-inoculation significantly
improved all growth parameters and symbiotic efficiency in early soybean development.
Main finding: The triple interaction of Rhizobium, mycorrhizal fungi and phosphorus
fertilizer significantly boosted soybean early growth, offering a sustainable strategy for
improving productivity in nutrient-poor soils.