A sulfate-palygorskite composite amendment for saline-alkali soil: Simultaneous alkalinity reduction, nutrient enrichment, and crop growth promotion

This study introduces a composite amendment, containing CaSO₄, MgSO₄, Fe₂(SO₄)₃, and Palygorskite (PGS), for concurrently improving saline-alkali soil physicochemical properties and promoting crop growth via in situ soil regulation and nutrient release. Experimental results demonstrated Layered Double Hydroxide (LDH) structure formation within the amended soil after 20 days, a key in situ mineralization mechanism absent in the control. This process significantly reduced soil pH from 9.85 to 7.86 (a 20.2 % decrease) and drastically lowered CO₃²⁻ content from 33.43 g/kg to 5.12 g/kg (an 84.68 % reduction), effectively mitigating soil alkalinity. Concurrently, exchangeable Na⁺ content decreased markedly from 700.7 mg/kg to 183.67 mg/kg (a 73.8 % reduction), alleviating sodicity. Furthermore, the amendment substantially increased water-soluble nutrient ions: Ca²⁺ (1.17–30.35 mg/kg), Mg²⁺ (0.125–9.58 mg/kg), total available Fe (49.78–89.35 mg/kg), and available SO₄²⁻ (2.06–21.62 g/kg). Notably, the amendment enhanced Soil Organic Matter (SOM) retention after simulated leaching; SOM in amended soil (6.81 g/kg) remained significantly higher than the control (5.14 g/kg), indicating improved carbon stabilization. Pot experiments using ryegrass confirmed the amendment's efficacy, showing significantly enhanced germination, root length, and shoot length, even enabling immediate planting post-application. In summary, the composite amendment leverages in situ LDH formation for stable CO₃²⁻ immobilization and alkalinity reduction, while enriching the soil with essential nutrients (Ca, Mg, Fe, S). This dual action facilitates immediate crop establishment, integrating soil regulation with controlled fertilizer distribution.