A Single Amendment With Flue Gas Desulfurization Gypsum Improves Saline‐Sodic Soil Quality: Evidence From a Decade‐Long Paddy Experiment

ABSTRACT Saline–sodic soils threaten global agriculture, and flue gas desulfurization (FGD) gypsum is a widely adopted reclamation practice. However, the associated long‐term (> 10 years) legacy effects and temporal dynamics remain poorly understood. We quantified the decadal dynamics of soil quality following a one‐time application of FGD gypsum (40 t ha −1 ) in a saline–sodic paddy field on the Songnen Plain. An in situ field experiment monitored key salinity‐sodicity and nutrient parameters in the 0–20 cm layer at 0, 3, 7, and 10 years post‐amendment. With the L 2 norm to establishing a minimum data set (MDS), the soil quality index (SQI) increased by 3.3‐, 4.2‐, and 4.8‐fold over the 3‐, 7‐, and 10‐year periods, respectively, representing full data set variability ( R 2 = 0.98). This improvement was driven by reductions in soil pH (26.2%–28.4%), exchangeable sodium percentage (ESP, 58.5%–90.1%), water‐soluble sodium (Na + , 52.0%–87.7%), and dispersive charge (DC, 47.5%–86.5%), alongside a 2.6‐ to 4.5‐fold increase in available phosphorus (AP). Actual land productivity supported the theoretical SQI improvements, with rice yield exhibiting a highly significant positive response. A partial least squares path model (PLS‐PM) confirmed that the sustained exchange between water‐soluble calcium (Ca 2+ ) and exchangeable sodium (EX‐Na + ) mediated structural stabilization and drove SQI enhancement and crop yield. Soil quality and productivity benefits plateaued around the 7‐year mark. We demonstrate that a single FGD gypsum application can establish a decade‐long ameliorative legacy and present a robust, cost‐effective strategy for the sustainable management of saline–sodic paddy systems, particularly in rice‐growing regions facing similar soil constraints.