Effects of organic compost application with green tuff addition on paddy rice growth associated with soil pH elevation and microbial community shifts

Green tuff, a porous volcanic ash-derived material with zeolite-like properties, is often produced as a byproduct of building stone processing in Japan. Organic compost is widely used in organic farming to improve soil fertility and stimulate microbial activity. Herein, we evaluated the effects of green tuff on paddy rice growth and soil prokaryotic communities in a 3-month pot experiment using paddy soil amended with three types of organic compost (OC1, OC2, and OC3). Green tuff application significantly increased plant height with OC1 (1.30-fold) and OC3 (1.18-fold), but not with OC2, compared to controls. It also elevated soil pH by 0.4–0.5 units across all composts tested, accompanied by shifts in microbial composition, including increased abundances of Chloroflexota and Anaeromyxobacter , taxa associated with carbon decomposition and nitrogen fixation. These findings suggest that green tuff may promote rice growth through soil pH elevation and prokaryotic community modulation. • Combined application of green tuff and organic compost significantly enhanced rice growth in paddy soil. • Green tuff increased soil pH and altered the composition of prokaryotic community. • Relative abundance of Chloroflexota and Anaeromyxobacter increased following green tuff application.