Calcium-lactate water-retaining agent enhances soil health and nutrient cycling via microbial regulation in saline-alkaline farmland

Saline-alkaline soil degradation poses a severe threat to agricultural sustainability globally, and developing eco-friendly amendments is urgently needed. This study aimed to explore the regulatory effects of calcium lactate water-retaining agent (CLW) on soil chemical properties, enzyme activities, and microbial communities in low-salinity high-alkalinity soil, and elucidate the microbial ecological mechanisms underlying soil health improvement.

A two-year field experiment was conducted in Changyi, Shandong, on moderately saline-alkaline farmland (pH 8.3, EC 890 μS cm⁻¹). Treatments included CK (no agent), CLW gradients (T1:20, T2:40, T3:60 kg·ha⁻²), and a commercial water-retaining agent (T4:40 kg·ha⁻²). Soil exchangeable Ca, SAR, pH, nutrients, enzyme activities, and microbial community (16S rRNA sequencing) were determined.

CLW significantly increased topsoil exchangeable calcium content (by 147.7%–228.6% across CLW treatments vs. CK), reduced SAR (by 30.9%–44.5%) and pH, with T2 (40 kg·ha⁻²) performing best overall. T2 showed consistent superiority across key indicators, with amelioration effects stronger than T4, T1, and T3. It also significantly enhanced urease, phosphatase, protease, and catalase activities, increased the Chao1 index, and elevated the relative abundance of beneficial phyla including ProteobacteriaandActinobacteria. A dose–response trend was observed, yet T2 balanced effectiveness and practicality, representing the optimal application rate.

CLW alleviates saline-alkaline stress via a mechanism of Ca²⁺-driven amelioration, moisture-regulated microhabitat and microbe-activated nutrient cycling. T2 is the optimal rate, enhancing soil health and adaptability. CLW (40 kg·ha⁻¹) is a promising eco-friendly material for saline-alkaline land green improvement.