Salinity drives bacterial community shift in paddy soils applied with perishable waste compost

Composting is an effective way to recycle perishable waste (e.g. food, vegetable and fruit waste), while the effects of varying compost application rates on soil properties and bacterial communities are not well understood. Soil samples were taken from pot experiments that included an unfertilized control, a mineral NPK-only treatment and four compost-amended mineral fertilizer treatments at 0.7%, 2.1%, 3.5% and 4.9% w/w. Soil analysis included pH, electrical conductivity (EC), soil organic carbon, total nitrogen, total soluble salt, and assessment of diversity and community of soil bacteria. Results showed that perishable waste compost application enhanced soil salinity by significantly increasing soil total soluble salt content (67–174%) and EC (24–152%) compared with mineral fertilizer. Perishable waste compost addition affected soil bacterial community composition by increasing Cyanobacteria and decreasing Firmicutes relative abundance, which reflected changes in soil salinity. Soil bacterial community stability and potential biological activity, together with soil phosphorus availability and rice yield (increased by 41% and 36% compared to mineral fertilizer) were promoted under the 2.1% perishable waste compost addition, which suggested this rate was recommended for optimal productivity in paddy soil. These findings advanced our understanding of the soil salinity risk for perishable waste compost use as organic fertilizer.