Long-term wastewater irrigation leads to the loss of calcium carbonate (CaCO3) in the tillage layer of calcareous land, which irreversibly damages the soil's ability to retain cadmium (Cd). In this study, we selected calcareous agricultural soil irrigated with wastewater for over 50 years to examine the recalcification effects of sugar beet factory lime (SBFL) at doses of 0%, 2.5%, 5%, and 10%. We found that SBFL promoted Cd transformation in the soil from active exchangeable species to more stable carbonate-bonded and residual species, which the X-ray diffraction patterns also confirmed results that CdSO4 reduced while CdS and CaCdCO3 increased. Correspondingly, the soil bioavailable Cd concentration was significantly reduced by 65.6-84.7%. The Cd concentrations in maize roots and shoots were significantly reduced by 11.7-50.6% and 13.0-70.0%, respectively, thereby promoting maize growth. Nevertheless, SBFL also increased the proportion of plant-unavailable phosphorus (P) in Ca8-P and Ca10-P by 4.3-13.0% and 10.7-25.9%, respectively, reducing the plant-available P (Olsen P) content by 5.2-22.1%. Consequently, soil P-acquiring associated enzyme (alkaline phosphatase) activity and microbial (Proteobacteria, Bacteroidota, and Actinobacteria) community abundance significantly increased. Our findings showed that adding SBFL to wastewater-irrigated calcareous soil stabilized Cd, but exacerbated P limitation. Therefore, it is necessary to alleviate P limitations in the practice of recalcifying degraded calcareous land.

Calcareous sands often display wide ring grain configurations, high intragranular porosity, a complex structure, and low grain hardness. These attributes typically do not meet the strength criteria necessary to sustain overlying infrastructure in civil engineering applications. This study investigates gel stabilization techniques, blending gel material with calcareous sand at concentrations ranging from 5% to 22%, followed by curing periods of 3 to 28 days to evaluate the load-bearing capacity. Subsequently, an unconfined compressive test is performed to determine the gel material content in stabilized specimens and investigate the influence of gel material types. The gel material-to-sand ratios employed are set at 5%, 10%, and 16% for Portland cement and 13%, 16%, and 22% for gypsum. After that, a triaxial consolidated undrained test is conducted to assess mechanical behavior, pore water pressure, and mechanical properties. The findings reveal increased dilation, stress-strain hardening, and softening post-yield, regardless of gel material type. Principal stress ratios, secant modulus, and cohesion show a positive correlation with maintenance duration and binder content, with implications for improved load-bearing capacity. The study also elucidates the qualitative relationship between secant modulus E50 and confining pressure.

The ecotoxic effect of Zn species arising from the weathering of the marmatite-like sphalerite ((Fe, Zn)S) in Allium cepa systems was herein evaluated in calcareous soils and connected with its sulfide oxidation mechanism to determine the chemical speciation responsible of this outcome. Mineralogical analyses (X-ray diffraction patterns, Raman spectroscopy, scanning electron microscopy and atomic force microscopy), chemical study of leachates (total Fe, Zn, Cd, oxidation-reduction potential, pH, sulfates and total alkalinity) and electrochemical assessments (chronoamperometry, chronopotentiometry, cyclic voltammetry, and electrochemical impedance spectroscopy) were carried out using (Fe, Zn)S samples to elucidate interfacial mechanisms simulating calcareous soil conditions. Results indicate the formation of polysulfides (S-n(2-)), elemental sulfur (S-0), siderite (FeCO3)-like, hematite (Fe2O3)-like with sorbed CO32- species, gunningite (ZnSO4H2O)-like phase and smithsonite (ZnCO3)-like compounds in altered surface under calcareous conditions. However, the generation of gunningite (ZnSO4H2O)-like phase was predominant bulk-solution system. Quantification of damage rates ranges from 75 to 90% of bulb cells under non-carbonated conditions after 15-30 days, while 50-75% of damage level is determined under neutral-alkaline carbonated conditions. Damage ratios are 70.08 and 30.26 at the highest level, respectively. These findings revealed lower ecotoxic damage due to ZnCO3-like precipitation, indicating the effect of carbonates on Zn compounds during vegetable up-taking (exposure). Other environmental suggestions of the (Fe, Zn)S weathering and ecotoxic effects under calcareous soil conditions are discussed.