Heavy metal pollution, including that caused by cadmium (Cd), is a matter of increasing concern. Although in situ passivation remediation has been widely used to treat heavy metal-polluted soils, most studies have focused on acidic soils, while studies on alkaline soil conditions are scarce. In this study, the effects of biochar (BC), phosphate rock powder (PRP), and humic acid (HA) on Cd²⁺ adsorption were examined alone and in combination to choose an appropriate Cd passivation approach for weakly alkaline soils. Additionally, the combined impact of passivation on Cd availability, plant Cd absorption, plant physiology indexes, and soil microbial community was elucidated. BC had a higher Cd adsorption capacity and removal rate than those of PRP and HA. Moreover, HA and PRP enhanced the adsorption capacity of BC. A combination of biochar and humic acid (BHA), and biochar and phosphate rock powder (BPRP) significantly affected soil Cd passivation. BHA and BPRP decreased the plant Cd content and soil Cd-DTPA (diethylenetriaminepentaacetic acid) by 31.36 %, 20.80 %, 38.19 %, and 41.26 %, respectively; however, they increased the fresh weight by 65.64-71.48 % respectively, and dry weight by 62.41-71.35 %, respectively. Notably, only BPRP increased the node and root tip number in wheat. Total protein (TP) content increased in BHA and BPRP, with BHA showing lower TP than BPRP. BHA and BPRP showed a reduction in glutathione (GSH), malondialdehyde (MDA), H₂O₂, and peroxidase (POD); BHA showed a significantly lower GSH than BPRP. Additionally, BHA and BPRP increased soil sucrase, alkaline phosphatase, and urease activities, with BPRP showing considerably higher enzyme activity than BHA. Both BHA and BPRP increased the number of soil bacteria, altered the community composition, and critical metabolic pathways. The results demonstrated that BPRP could be used as a highly effective, novel passivation technique for the remediation of Cd-contaminated soil.

Cadmium is a common heavy metal pollutant. In some plants, its absorption is inhibited by exogenous phosphorus. Here, the effect of P supplementation on the growth of tall fescue exposed to Cd was evaluated in a hydroponic culture experiment. Plants were exposed to five concentrations of P (0, 0.25, 0.5, 0.75, and 1.0 mmol L-1) and three concentrations of Cd (50, 100, and 150 mg L-1), and plant growth, Cd content, absorption, physiological characteristics, and nutrient accumulation were investigated. P supplementation significantly reduced the Cd content, Cd translocation factor (TF), Cd removal efficiency, plant P absorption, chlorophyll content, glutathione levels, glutathione reductase levels, and superoxide dismutase (SOD) activity in tall fescue under Cd stress (P < 0.05). Moreover, it increased the vertical growth rate and biomass of tall fescue. At a constant P concentration, the biomass and vertical growth rate significantly decreased with an increasing Cd concentration, and the shoot Cd content, SOD activity, and TF significantly increased (P < 0.05). High P supplementation (0.75 and 1.0 mmol L-1) ameliorated the damage caused by 150 mg L-1 Cd stress, and the biomass, vertical shoot and vertical root growth rates were increased by 72.06-82.06%, 250.00-316.67%, 300.00-312.00%, respectively. In the plants subjected to 50 mg L-1 Cd stress, 0.5 mmol L-1 P supplementation enhanced biomass, vertical shoot and vertical root growth rates by 29.99%, 20.41%, and 21.43%, respectively, and reduced the Cd content in shoots (45.85%) and roots (9.71%). Except for the total potassium content and catalase activity, different concentrations of Cd negatively affected all parameters tested. Such negative effects were limited by P supplementation. Optimizing the nutrient composition and concentrations could minimize the potential negative impacts of Cd on plant growth.

Cadmium (Cd) water pollution threatens environmental systems and human health. Adsorption is the preferred method for purifying water bodies polluted by Cd, and the development of effective adsorption materials is critical. The performance of original phosphate rock powder (PRP) as an adsorption medium for purifying water bodies polluted by Cd was compared with that of phosphate rock powder modified with fulvic acid, chitosan, MnO₂, and sulfhydryl, respectively, and their appearance and adsorption properties were investigated. The surface structures of all modified powders were rougher than the original, and their functional groups were richer. The greatest Cd²⁺ adsorption capacity, 1.88 mg g⁻¹, was achieved with chitosan-modified PRP (CMPRP). This was 106.59% greater than that of PRP. The capacities of fulvic acid and MnO₂ were 15.38% and 4.40% greater than that of the original, respectively. When the fulvic acid-modified PRP, CMPRP, and manganese dioxide PRP reached adsorption equilibrium, the removal rates of Cd²⁺ were 51.86%, 93.26%, and 46.70%, respectively. Moreover, the removal rate of Cd²⁺ by CMPRP was 104.43% higher than that of PRP. The main Cd²⁺ adsorption mechanisms for the MPRPs were electrostatic interactions, ion exchange, co-precipitation, and complexation. Moreover, the processing of the phosphate rock powder was straightforward, harmless to the environment, and could be effectively used for the removal of Cd. These results show that CMPRP is promising as a new adsorption material to treat Cd-contaminated water.

Storage temperature (ST) and grain moisture content (GMC) critically influence cereal quality during storage. However, their interactive effects, the associations among oxidative indicators, quality components and major volatile organic compounds (VOCs) variations in millet during storage are not fully understood. In this study, foxtail millet was stored for 360 days at three STs (−18 °C, 4 °C and 25 °C) and three GMC levels (11.50%, 12.80% and 14.30%). Changes in oxidative indicators (malondialdehyde [MDA], electrical conductivity [EC] and catalase activity [CAT]) and quality components (crude protein [CP], yellow pigment [YP] and soluble sugar [SS]) were monitored. Viscosity characteristics and VOCs were analysed after storage. Under this study, ST was the primary factor driving the changes in oxidative indicators and quality components during the storage stage. The viscosity characteristics of stored millet are primarily influenced by ST, while the changes in major VOCs are mainly affected by ST, GMC, and their interaction effects. Significant negative correlations were observed between EC or MDA and dodecanenitrile and (E/Z)-4-heptenal, whereas the YP, CP, and SS were significantly positively correlated with both compounds. After day 360, the samples stored at −18 °C with 11.5% GMC exhibited 34.05% lower MDA content and 29.55% lower EC than those stored at 25 °C with 14.3% GMC. The treatment better preserved CAT, SS, YP, viscosity characteristics and major VOCs, including (E/Z)-4-heptenal. These findings provide a scientific basis for optimising storage conditions to maintain the nutritional and sensory quality of foxtail millet.

Cadmium (Cd) not only significantly threatens crop growth and food safety but also degrades soil quality and reduces microbial activity. Hydrochar is a carbon-rich material derived from biomass via hydrothermal carbonisation, due to its large specific surface area and abundant surface functional groups, shows great potential for immobilisation remediation of Cd-contaminated soils. We determined hydrochar’s (1) optimal application conditions for soil Cd immobilisation and (2) regulatory effects on foxtail millet growth and development, photosynthesis, antioxidant enzyme activity, resistance gene expression and Cd accumulation. Hydrochar was prepared at two temperatures (240 and 160 °C) and applied at two concentrations (1% and 2%). Hydrochar application reduced soil available Cd by 4.59–10.09% and shifted Cd fractions from acetic acid-extractable to residual forms. Soil organic matter (SOM) and microbial biomass carbon (MBC) increased. Hydrochar application increased plant antioxidant enzyme activity, downregulated SiNRAMP5 and SiHMA2 and upregulated SiHMA3, SiPCS1 and SiMT2. Hydrochar prepared at 240 °C and applied at a 2% concentration exhibited the highest efficiency in immobilising Cd, enhancing plant photosynthesis and antioxidant defence, activating soil microorganisms and increasing SOM and MBC, offering a promising remediation strategy for weakly alkaline Cd-contaminated farmland in northern China.

Yellow River alluvial sandy soil suffers from poor structural stability and low fertility, constraining soybean productivity. We hypothesised that co-applying straw return with an organic–inorganic composite would modify Fe–Al oxide fractions, promote water-stable macroaggregate formation, and thereby improve soybean physiological performance and yield components, with the ternary combination outperforming single or binary regimes. A soil-column experiment was conducted at Shandong Agricultural University Experimental Station, Tai’an, China, using a completely randomised design (n = 3) with six treatments: straw-only control (CK), organic fertiliser (JO), biochar (JB), organic fertiliser+attapulgite (JOA), biochar+attapulgite (JBA), and organic fertiliser+biochar+attapulgite (JOBA). Compared with CK, JOBA increased water-stable macroaggregates (>0.25 mm) by 268.82%, mean weight diameter by 89.88%, and decreased soil bulk density by 19.97%; it also increased catalase activity by 35.74%, pods per plant by 110.34%, seeds per plant by 128.57%, and 100-seed weight by 60.82%. The JOBA showed the greatest overall improvement, reflecting complementary functions among amendments. However, these findings were obtained in a controlled short-term column experiment; field validation and even long-term evaluation are required.