Diversity and function of soil microorganisms in response to paddy–upland rotation system in sustainable restoration of saline-sodic soils

Context Rapid desalination by planting rice in saline soil consumes large amounts of water, which is not environmentally friendly. Aims Herein, we propose rapid desalination by planting rice, then shifting to cultivating upland plants to attain substantial resource-saving and higher yield simultaneously with restoration of saline-sodic soil. Methods Field experiments were run for two consecutive years with five treatments: unreclaimed wasteland (WL) as control, rice cultivation followed by fallow (RF), rice–rice continuous cropping (RR), rice–ryegrass rotation (RG), and rice–sorghum rotation (RS). Physicochemical properties, including pH, electrical conductivity, and exchangeable sodium percentage were determined, and 16S rRNA sequences were used to evaluate soil microbial composition and stability. Key results The soil total organic carbon, total nitrogen, available phosphorus, and biomass in RR, RG, and RS treatments were all higher than RF and control. Notably, RR, RG, and RS increased the soil microbial biomass carbon and nitrogen, and significantly reshaped the soil communities of bacteria, fungi, and archaea relative to RF and WL. Conclusions Despite the lower efficiency of RG and RS in ameliorating saline-sodic soil, there were dramatic savings in irrigation water, and the improvements in microbial diversity and functionalities indicated that the paddy–upland crop rotation system had substantial influence on sustainability of soil quality. Implications Providing a balance between salt desalination performance with irrigation water input and yield, the paddy–upland rotation system is a robust, replicable, and environmentally friendly practice in saline-sodic soil remediation.