A new study published in Engineering demonstrates that applying halotolerant plant growth-promoting bacteria (PGPB) via drip irrigation during the crop growth period can effectively alleviate soil salinity stress, enhance jujube productivity and fruit quality, and restructure rhizosphere bacterial communities in saline agricultural soils. The research addresses the limitations of traditional one-time PGPB inoculation methods, such as soil basal application, seed dressing and plant infestation, which often fail to ensure stable bacterial colonization and consistent plant benefits under salt stress.

Field experiments were conducted in China, over two consecutive years on jujube trees, a major cash crop in the region. Seven halotolerant PGPB strains were applied in small, high-frequency doses through a drip irrigation system directly to the root zone during the growing season. The results show that drip irrigation with these bacteria significantly lowered soil pH and electrical conductivity (EC), key indicators of soil salinity, across the flowering, fruit enlargement, white ripening and full ripening stages of jujube growth.

Among the tested strains, Bacillus licheniformis (BL) and Bacillus mucilaginous (BM) performed most prominently, lifting jujube yield and vitamin C (VC) content by 23% and 22% respectively compared to the control group without PGPB irrigation. All PGPB treatments elevated plant antioxidant enzyme activities, including superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), which help plants scavenge excessive reactive oxygen species induced by salt stress. The treatments also increased soil available nutrients, including available nitrogen, available phosphorus, available potassium and organic matter, supporting better nutrient uptake for crop growth.

Further 16S rRNA gene amplicon sequencing reveals that PGPB application enriched the alpha diversity of the rhizosphere bacterial community, marked by higher Richness and Shannon indices relative to the control. The relative abundance of beneficial phyla including Cyanobacteria and Nitrospirota, and genera such as Psychrobacter, Flavobacterium and Steroidobacter, increased notably in PGPB-treated soils. Bacterial co-occurrence networks became more complex with elevated node and link numbers, and the keystone taxa involved in soil nutrient cycling were reshaped compared to the untreated control.

Functional prediction using FAPROTAX indicates that PGPB applications modified bacterial metabolic functions, reducing pathways related to nitrate respiration, plant pathogens and aromatic compound degradation while enhancing functions associated with nitrogen fixation, nitrate reduction, fermentation and nutrient mineralization. Structural equation modeling confirms that drip-applied halotolerant PGPB suppress soil salinity, improve soil nutrient availability and boost plant antioxidant capacity by regulating bacterial community composition, diversity and interactions, collectively contributing to improved crop performance.

The study validates drip irrigation as a feasible and efficient delivery method for halotolerant PGPB in saline soils. This approach uses existing fertigation equipment without extra investment, and long-term application does not worsen emitter clogging, supporting its practical value for sustainable saline soil agriculture.

The paper “Halotolerant PGPB Delivered by Drip Irrigation Improve Crop Yield and Quality Through Changes in the Soil Bacterial Community,” is authored by Yunpeng Zhou, Bernard R. Glick, Hassan Etesami, Hongbang Liang, Felipe Bastida, Xin Wu, Naikun Kuang, Yunkai Li. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.03.040. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.