Biochar soil amendment has proven to be beneficial for soil fertility regulation, while the long-term mechanisms under different soil conditions remain largely unexplored. This study was based on two long-term field experiments in calcareous soils to explore the effect of biochar on fertility and phosphorus availability, as well as potential mechanisms. Experiments were conducted on Fluvo-aquic soil (6 years) and Cinnamon soil (5 years), respectively. Biochar was applied once at 20 t/ha level and mixed with the topsoil. We evaluated soil fertility and phosphorus fractions with and without biochar amendment and analyzed the related extracellular enzyme activity and functional gene abundance. The results indicate a persistent increase in crop yield by 10.8–24.3% in calcareous soils after 5–6 years of treatment. Biochar enhanced soil fertility, including increased SOC, available phosphorus, and potassium content. Moreover, it boosted the activity of extracellular enzymes related to soil carbon, nitrogen, and phosphorus cycling. This effect may be associated with the stability of morphological features and mineral element regulation on biochar surfaces. Biochar soil amendment led to a long-term increase in phosphorus availability, of which available phosphorus increased by 13.1–49.1%. Potential mechanisms included an increase in labile phosphorus forms and biological mechanisms of raising alkaline phosphatase activities and increasing the copy numbers of the phosphatase genes (phoD, phoX, and nifH). In conclusion, biochar soil amendment resulted in sustained improvement in soil fertility in calcareous soils and consistently increased phosphorus availability via biochemical mechanisms.

Greenhouse gas and NH₃ emissions are exacerbated by the inappropriate timing and excessive application of nitrogen (N) fertilizers in wheat cultivation in China. In this study, the impacts on N₂O, CO₂, and NH₃ emissions of a delayed and reduced N application regime on the Huang-Huai-Hai Plain were investigated. The treatments comprised the control (N₀), conventional N at 270 kg N ha⁻¹ (N₂₇₀) and optimized N application of 180 kg N ha⁻¹ (N₁₈₀), N₁₈₀ + biochar at 7.5 t ha⁻¹ (N₁₈₀B_7.5), N₁₈₀ + biochar at 15 t ha⁻¹ (N₁₈₀B₁₅), N₁₈₀ + DMPP (a nitrification inhibitor; N₁₈₀D), N₁₈₀D + biochar at 7.5 t ha⁻¹ (N₁₈₀DB_7.5), and N₁₈₀D + biochar at 15 t ha⁻¹ (N₁₈₀DB₁₅). Reduced N application (N₁₈₀) lowered N₂O and NH₃ emissions. Biochar application resulted in a 4–25% and 12–16% increase in N₂O and NH₃ emissions, respectively. Application of DMPP significantly decreased N₂O emissions by 32% while concurrently inducing a 9% increase in NH₃ emissions. Co-application of DMPP and biochar significantly reduced the activity of nitrification enzymes (HAD, NOO), resulting in a reduction of 37–38% in N₂O emissions and 13–14% in NH₃ emissions. No significant differences in CO₂ emissions were observed among the various N treatments except the N₀ treatment. Application of DMPP alone did not significantly affect grain yield. However, biochar, in combination with DMPP, effectively increases grain yield. The findings suggest that the N₁₈₀DB₁₅ treatment has the potential to reduce emissions of N₂O and NH₃ while concurrently enhancing soil fertility (pH, SOC) and wheat yield.

This study investigates the removal efficiency of Cu²⁺ from wastewater using a composite hydrogel made of carbon nanotubes (CNTs), sodium alginate (SA), and polyacrylic acid (PAA) prepared by free radical polymerization. The CNTs@SA/PAA hydrogel’s structure and properties were characterized using SEM, TEM, FTIR, XRD, rheology, DSC, EDS, elemental mapping analysis, and swelling. The adsorption performance for Cu²⁺ was tested in batch adsorption experiments, considering the pH, dosage, initial concentration, and contact time. The optimal conditions for Cu²⁺ removal were pH 5.0, an adsorbent dosage of 500 mg/L, and a contact time of 360 min. The adsorption followed pseudo-second order kinetics. Isotherm analyses (Langmuir, Freundlich, Temkin, Dubinin–Radushkevich, Sips, Toth, and Khan) revealed that the Freundlich isotherm best described the adsorption, with a maximum capacity of 358.52 mg/g. A thermodynamic analysis indicated that physical adsorption was the main interaction, with the spontaneity of the process also demonstrated. This study highlights the high efficiency and environmental friendliness of CNT@SA/PAA composites for Cu²⁺ removal from wastewater, offering a promising approach for water treatment.

Nitrogen is a vital element for soil fertility and crop productivity. The transformation of nitrogen is directly affected by tillage practices for the disturbing soil. The characteristics of different nitrogen forms under different tillage modes are still unclear. A 3-year cycle tillage experiment was carried out to assess the combination of rotary tillage (RT), deep tillage (DT), and shallow rotary tillage (SRT) on nitrogen transformation and distribution, wheat yield and nitrogen balance in fluvo-aquic soil from Huang-Huai-Hai Plain in China. The results showed the rotation tillage cycle with deep tillage in the first year increased the total nitrogen (TN), and the main nitrogen form content in 0–30 cm compared with continued rotary tillage (RT-RT-RT). Moreover, the nitrate (NO₃⁻-N) and ammonium nitrogen (NH₄⁺-N) content were improved in 20–40 cm by deep tillage practice with the highest value as 39.88 mg kg⁻¹ under DT-SRT-RT. The time, tillage, and depth significantly affected the different nitrogen forms, but there was no effect on dissolved organic carbon (DON) and soil microbial biomass nitrogen (SMBN) by the interaction of time and tillage. Moreover, compared with RT-RT-RT, the rotation tillage promoted the spike number and kernels per spike of wheat, further increasing the wheat yield and nitrogen partial productivity, and with a better effect under DT-SRT-RT. The NO₃⁻-N and NH₄⁺-N trended closer and positively correlated with wheat yield in 0–40 cm in 2019. The rotation tillage with deep tillage improved the different forms of nitrogen in 0–30 cm, wheat yield, and nitrogen partial productivity, and decreased the apparent nitrogen loss. It was suggested as the efficiency tillage practice to improve nitrogen use efficiency and crop yield in this area.