Humic Acid Intercalated Vermiculite for Sandy Loam Salt-Affected Soil Improvement

Expanded vermiculite (EV) is rich in exchangeable Ca²⁺/Mg²⁺ and humic acid (HA) abounds in organic matter and available phosphorus, thus exhibiting complementary properties for soil improvement. To mitigate the issues of excessive Na⁺ input and severe nutrient loss caused by the direct application of HA to salt-affected soil, we fabricated HA intercalated EV (EVHA) via a simple water-mediated assembly method, whereby HA was intercalated into EV interlayers through cationic bridging and hydrogen bonding. Notably, EVHA extended the sustained release period of HA by 4-18 times compared with pure HA, and its release behavior was jointly governed by intercalated HA content, temperature and time, fitting distinct kinetic models under different experimental conditions. Soil improvement experiments verified that EVHA reduced soil salt content by 40% while increasing soil organic matter content by approximately 15%. Furthermore, corn pot experiments demonstrated that EVHA increased plant dry weight and leaf area by up to 2.95-fold and 1.43-fold relative to the blank control, respectively, and also significantly enhanced root activity. This work provides a slow-release material for efficient salt-affected soil improvement and sustainable agriculture.