Lhamo Pasang

Soil amendments play a crucial role in modern agriculture, as they effectively enhance the planting environment. This study innovatively proposes the use of gel as a crosslinking agent to embed biochar and hydroxyapatite (HAP), thereby preparing a novel soil amendment. Furthermore, this study investigates the soil improvement effects of this amendment as well as its influence on plant growth. This study employed a hydrothermal method to combine corn stalk (CB) or sludge (SB) biochar with HAP at different ratios (0–20%). Subsequently, sodium alginate gel (SA) was utilized to encapsulate the biochar and minerals, successfully forming a ternary composite gel material (corn stalk biochar/sludge biochar–sodium alginate gel-hydroxyapatite: CB/SB-SA-HAP). Finally, the practical effectiveness of this amendment was verified through potted soil experiments. The results indicate that the CB/SB-SA-HAP composite materials exhibited a micrometre-scale spherical structure with well-developed micropores and possess the functional groups of CB/SB, SA, and HAP, along with unique mineral properties. Through pot experiments, it was verified that the composite material effectively enhances multiple soil properties. After 21 days of cultivation, the soil pH values stabilized within the neutral range (pH = 7 ± 0.3) across all treatment groups. Except for the CB0 (CB:HAP = 1:0) and CB2.0 (CB:HAP = 1:2) treatments, the remaining treatments significantly reduced the soil EC values by 3.27% to 47.92%. All treatments significantly increased the contents of alkali-hydrolysable nitrogen (AHN) (34.89~57.91%), available phosphorus (AP) (35.93~56.55%), and available potassium (AK) (36.41~56.80%) in the soil. In comparison, although the SB treatment was more effective in regulating the pH and electrical conductivity (EC) of saline–alkali soil than the CB treatment, it was less effective in promoting plant growth in the short term. Through correlation analysis and redundancy analysis, a significant positive correlation was found between soil pH and ryegrass germination rate and plant height, particularly with the most pronounced impact on soil pH observed in the CB1.0 and SB0 (SB:HAP = 1:0) treatments. This study underscores the potential of CB/SB-SA-HAP composite materials in soil improvement and plant growth promotion, providing valuable insights for soil remediation, enhancement, and plant cultivation advancements in the agricultural sector.

Biochar adsorption and microbial remediation have great potential in the field of soil remediation, but since both are stressed by high concentrations of toxic heavy metals when applied alone, combining the two may become an effective remediation method. In this study, the application effect of phosphorus-solubilizing bacteria (PSB) combined with rice husk biochar on the remediation of Pb/Cd-mixed pollution and the form differences of toxic metal were studied qualitatively and quantitatively. Compared with the contaminated soil, the combined remediation of biochar and PSB significantly increased the pH, carbon and phosphorus by 9.0%, 299.4% and 157.0%. Meanwhile, combined remediation increased the total microbial, bacterial and fungal biomass by 92.11%, 103.13% and 138.10%. This confirmed that the addition of biochar increased the soil nutrients and provided good conditions for PSB or native microorganisms to flourish. The extraction results showed that the stable form of Pb/Cd with biochar + PSB was better than that with biochar/PSB alone. Combined remediation significantly increased the acid-soluble and non-bioavailable fraction of Pb/Cd by 5/15 times and 14/5.8 times in contaminated soil. The acid-soluble and non-bioavailable fractions are the main fraction of toxic metals after combined remediation (>80%). The acid-soluble and non-bioavailable fractions were mainly carbonates and phosphate-based Pb/Cd minerals (XRD analysis). PCA and a GWB model further confirmed that the release of pH and phosphorus was the key to the passivation of Pb/Cd in a short time. Meanwhile, the combination of the biochar (phosphorus supply guarantee) and PSB (acid-soluble phosphorus function) can reduce soil acidification and improve soil nutrients, thus increasing microbial abundance in contaminated soil, even more than that in non-contaminated soil.