Research on zoning，classification and gradient-based protective development system for saline-alkali land in Songnen Plain

To address intensifying salinization of Songnen Plain（severe saline-alkali land increased from 17% to 24% over a decade）and extensive development models, a systematic zoning classification and gradient development system was proposed．Technologically, a closed-loop system was integrated with remote sensing/GIS-based diagnosis, engineering measures（irrigation/drainage and micro-topography modification）, organic amelioration（biochar/humic acid）, bioremediation（microbial-plant synergism）, and intelligent management（ET water conservation/drones）．At model level development modes were stratified by salinization degree．Mildly zone（salinity <0.3%）focused on grain production, moderately zone（salinity 0.3%～0.6%）adopted integrated crop-livestock systems, and severely zone（salinity >0.6%）implemented ecological restoration．Institutionally, an inter-provincial ecological compensation fund and carbon sink trading mechanism were established．Results showed that mildly and moderately saline-alkali areas could be transformed into high-yield farmland（rice yield of 6750～8250 kg/hm²）, supporting all-encompassing approach to food．Severely saline-alkali areas exhibited prominent ecological value Suaeda glauca net carbon sequestration of 2.8～5.0 t CO₂eq/（hm²·a）．Cross-regional compensation mechanisms resolved funding shortages．It has realized a transformation of saline-alkali land from an "ecological burden" to a "resource reservoir", strengthening national food security and ecological barriers．