Although the effects of plastic residues on soil organic carbon (SOC) have been studied, variations in SOC and soil carbon-enzyme activities at different plant growth stages have been largely overlooked. There remains a knowledge gap on how various varieties of plastics affect SOC and carbon-enzyme activity dynamics during the different growing stages of plants. In this study, we conducted a mesocosm experiment under field conditions using low-density polyethylene and poly (butylene adipate-co-terephthalate) debris (LDPE-D and PBAT-D, 500–2000 μm (pieces), 0%, 0.05%, 0.1%, 0.2%, 0.5%, 1%, 2%), and low-density polyethylene microplastics (LDPE-M, 500–1000 μm (powder), 0%, 0.05%, 0.1%, 0.5%) to investigate SOC and C-enzyme activities (β-xylosidase, cellobiohydrolase, β-glucosidase) at the sowing, seedling, flowering and harvesting stages of soybean (Glycine Max). The results showed that SOC in the LDPE-D treatments significantly increased from the flowering to harvesting stage, by 12.69%–13.26% (p 0.05), but significantly decreased in the 0.05% and 0.1% LDPE-M treatments from the sowing to seedling stage (p 0.05). However, PBAT-D had no significant effect on SOC during the whole growing period. For C-enzyme activities, only LDPE-D treatments inhibited GH (17.22–38.56%), BG (46.7–66.53%) and CBH (13.19–23.16%), compared to treatment without plastic addition, from the flowering stage to harvesting stage. Meanwhile, C-enzyme activities and SOC responded nonmonotonically to plastic abundance and the impacts significantly varied among the growing stages, especially in treatments with PBAT-D (p 0.05). These risks to soil organic carbon cycling are likely mediated by the effects of plastic contamination and degradation soil microbe. These effects are sensitive to plastic characteristics such as type, size, and shape, which, in turn, affect the biogeochemical and mechanical interactions involving plastic particles. Therefore, further research on the interactions between plastic degradation processes and the soil microbial community may provide better mechanistic understanding the effect of plastic contamination on soil organic carbon cycling.

Growing applications of nanoagrichemicals have resulted in their increasing accumulation in agricultural soils, which could modify soil properties and affect soil health. A greenhouse pot trial was conducted to determine the effects of three metallic nanoagrichemicals on several fundamental chemical properties of a rice paddy soil, including zinc oxide nanoparticles (ZnO NPs) and copper oxide nanoparticles (CuO NPs) at 100 mg/kg, and silicon oxide nanoparticles (SiO₂ NPs) at 500 mg/kg, as well as their bulk and ionic counterparts. The investigated soil amendments displayed significant and distinctive impact on the examined soil chemical properties relevant to agricultural production, including soil pH, redox potential, soil organic carbon (SOC), cation exchange capacity (CEC), and plant available As. For example, all amendments increased the bulk soil pH at day 47 to some extent, but the increase was substantially higher for SiO₃²⁻ (37.7%) than other amendments (5.8%–13.7%). Soil Eh was elevated markedly at day 47 after the addition of soil amendments in both the bulk soil (45.9%–74.4%) and rice rhizosphere soil (20.3%–68.9%). CuO NPs and Cu²⁺ generally exhibited greater impact on soil chemical properties than other agrichemicals. Significantly different responses to soil amendments were observed between bulk and rhizosphere soils, suggesting the essential role of plants in affecting soil properties and their responses to environmental disturbance. Overall, our results confirmed that the tested amendments could have remarkable impacts on the fundamental chemical properties of rice paddy soils.

Calcium peroxide (CaO₂) has been proven to oxidize various organic pollutants when they exist as a single class of compounds. However, there is a lack of research on the potential of unactivated CaO₂ to treat mixed chlorinated organic pollutants in soils. This study examined the potential of CaO₂ in treating soils co-contaminated with p-dichlorobenzene (p-DCB) and p-chloromethane cresol (PCMC). The effects of CaO₂ dosage and treatment duration on the rate of degradation were investigated. Furthermore, the collateral effects of the treatment on treated soil characteristics were studied. The result showed that unactivated CaO₂ could oxidize mixed chlorinated organic compounds in wet soils. More than 69% of the pollutants in the wet soil were mineralized following 21 days of treatment with 3% (w/w) CaO₂. The hydroxyl radicals played a significant role in the degradation process among the other decomposition products of hydrogen peroxide. Following the oxidation process, the treated soil pH was increased due to the formation of calcium hydroxide. Soil organic matter, cation exchange capacity, soil organic carbon, total nitrogen, and certain soil enzyme activities of the treated soil were decreased. However, the collateral effects of the system on electrical conductivity, available phosphorus, and particle size distribution of the treated soil were not significant. Likewise, since no significant release of heavy metals was seen in the treated soil matrix, the likelihood of metal ions as co-pollutants after treatment was low. Therefore, CaO₂ can be a better alternative for treating industrial sites co-contaminated with chlorinated organic compounds.

Plastic mulching and straw incorporation are common agricultural practices in China. Plastic mulching is suspected to be a significant source of microplastics in terrestrial environments. Straw incorporation has many effects on the storage of soil organic carbon (SOC) and greenhouse gas emissions, but these effects have not been studied in the presence of microplastic pollution. In this study, 365-day soil incubation experiments were conducted to assess the effects of maize straw and polyethylene microplastics on SOC fractions and carbon dioxide (CO₂) and nitrous oxide (N₂O) emissions in two different soils (fluvo-aquic and latosol). Against the background of straw incorporation, microplastics reduced the mineralization and decomposition of SOC, resulting in a microbially available SOC content decrease by 18.9%. In addition, microplastics were carbon-rich, but relatively stable and difficult to be used by microorganisms, thus increasing the mineral-associated SOC content by 52.5%. This indicated that microplastics had adverse effects on microbially available SOC and positive effects on mineral-associated SOC. Microplastics also decreased coarse particulate SOC (>250 μm), and increased non-aggregated silt and clay aggregated SOC (<53 μm). Furthermore, microplastics changed microbial community compositions, thereby reducing the CO₂ and N₂O emissions of straw incorporation by 26.5%–33.9% and 35.4%–39.7%, respectively. These results showed that microplastics partially offset the increase of CO₂ and N₂O emissions induced by straw incorporation. Additionally, the inhibitory effect of microplastics on CO₂ emissions in fluvo-aquic soil was lower than that in latosol soil, whereas the inhibitory effect on N₂O emissions had the opposite trend.

A comprehensive understanding of the patterns and controlling factors of nitrate accumulation in intensive vegetable production is essential to solve this problem. For the first time, the national patterns and controlling factors of nitrate accumulation in soil of vegetable systems in China were analysed by compiling 1262 observations from 117 published articles. The results revealed that the nitrate accumulation at 0–100 cm, 100–200 cm, 200–300 cm, and >300 cm were 504, 390, 349, and 244 kg N ha⁻¹, with accumulation rates of 62, 54, 19, and 16 kg N ha⁻¹ yr⁻¹ for plastic greenhouse vegetables (PG); for open field vegetables (OF), they were 264, 217, 228, and 242 kg N ha⁻¹ with accumulation rates of 26, 24, 18, and 10 kg N ha⁻¹ yr⁻¹, respectively. Nitrate accumulation at 0–100 cm, 0–200 cm, and 0–400 cm accounted for 5%, 11%, and 17% of accumulated nitrogen (N) inputs for PG, and represented 4%, 9%, and 13% of accumulated N inputs for OF. Nitrogen input rates and soil pH had positive effects and soil organic carbon, water input rate, and carbon to nitrogen ratio (C/N) had negative effects on nitrate accumulation in root zone (0–100 cm soil). Nitrate accumulation in deep vadose zone (>100 cm soil) was positively correlated with N and water input rates, and was negatively correlated with soil organic carbon, C/N, and the clay content. Thus, for a given vegetable soil with relatively stable soil pH and soil clay content, reducing N and water inputs, and increasing soil organic carbon and C/N are effective measures to control nitrate accumulation.

Improper land-use changes may lead to a loss of soil resources and cause environmental pollution. Chinese Torreya plantation (hereafter CTP) is an important cash tree plantation for nuts production in the mountainous areas of subtropical China. The increasing development of CTPs, to increase seed production, can result in the complete erasure of local natural vegetation.In this study, the vulnerability to soil erosion, loss of soil organic carbon (SOC) and nutrients in CTPs due to land-use change were evaluated. The results indicated that the rates of diffusive soil erosion in the young CTPs with extreme precipitation were about six-fold higher than with the natural vegetation. At sites with a similar slope, there was no significant difference in soil erosion levels between the young and old CTPs. The old CTPs did not hold significantly higher levels of SOC and soil total nitrogen (STN) in their topsoil when compared with the young CTPs. The natural mixed broadleaved subtropical forests lost about 35% of their SOC and 25% of their STN after they were converted into CTPs, but the CTPs had higher soil total phosphorus. The C: N ratios at the different sites were close to 11:1, but the N: P ratios were diverse. There were high levels of organic carbon, nitrogen and phosphorus in stream water. Adequate coverage of natural vegetation within or around the CTPs should be maintained to decrease soil erosion and nutrient loss. Suggestions to develop CTPs while protecting the environment are discussed. Overall, it was determined that aspects of the current management practices and strategies for developing CTPs should be changed to decrease soil erosion and nutrient loss.

A composite material comprising of nanoscale zero-valent iron (nZVI) supported on vinegar residue (nZVI@VR) was prepared and applied for remediation of soils contaminated by hexavalent chromium (Cr(VI)). Sedimentation test results revealed that the nZVI@VR displayed enhanced stability in comparison to the bare-nZVI. Remediation experiments exhibited the immobilization efficiency of Cr(VI) and Crtotal was 98.68% and 92.09%, respectively, when using 10 g nZVI@VR (nZVI 5%) per 200 g Cr-contaminated soil (198.20 mg kg−1 Cr(VI), 387.24 mg kg−1 Crtotal) after two weeks of incubation. Further analyses demonstrated that almost all the exchangeable Cr was transformed into Fe–Mn oxide bound and organic matter bound. Moreover, the application of nZVI@VR enhanced soil organic carbon content and reduced redox potential. After granulation, the immobilization efficiency of Cr(VI) and Crtotal achieved 100% and 91.83% at a dosage of 10% granular nZVI@VR. Granular nZVI@VR also accelerated the transform of more available Cr (exchangeable and bound to carbonates) into less available fractions (Fe–Mn oxide bound and organic matter bound), thus resulting in a remarkable reduction in the Cr bioavailability. These results prove that nZVI@VR can be an effective remediation reagent for soils contaminated by Cr(VI).

Soils, especially permafrost in the Arctic and the Tibetan Plateau, are one of the largest reservoirs of mercury (Hg) in the global environment. The Hg concentration in the grassland soils over the Tibetan Plateau and its driving factors have been less studied. This study analyzes soil total mercury (STHg) concentrations and its vertical distribution in grassland soil samples collected from the Tibetan Plateau. We adopt a nested-grid high-resolution GEOS-Chem model to simulate atmospheric Hg deposition. The relationship between STHg and soil organic carbon (SOC), as well as atmospheric deposition, are explored. Our results show that the STHg concentrations in the Tibetan Plateau are 19.8 ± 12.2 ng/g. The concentrations are higher in the south and lower in the north in the Tibetan Plateau, consistent with the previous results. Our model shows that the average deposition flux of Hg is 3.3 μg m⁻² yr⁻¹, with 57% contributed by dry deposition of elemental mercury (Hg⁰), followed by dry (19%) and wet (24%) deposition of divalent mercury. We calculate the Hg to carbon ratio (RHg:C) as 5.6 ± 6.5 μg Hg/g C, and the estimated STHg is 86.6 ± 101.2 Gg in alpine grasslands in the Tibetan Plateau. We find a positive relationship between STHg and SOC in the Tibetan Plateau (r² = 0.36) and a similar positive relationship between STHg and atmospheric total Hg deposition (r² = 0.24). A multiple linear regression involving both variables better model the observed STHg (r² = 0.42). We conclude that SOC and atmospheric deposition influence STHg simultaneously in this region. The data provides information to quantify the size of the soil Hg pool in the Tibetan Plateau further, which has important implications for the Hg cycles in the permafrost regions as well as on the global scale.

Riparian areas are widely recognized as the main areas for carbon sequestration and nitrogen pollution removal, while little is known about the effects of the respective sand mining activities on riparian zones. In this study, the effects of sand mining activities on the soil organic carbon (SOC) storage, different N-removal processes (Feammox, anammox, and denitrification), and composition of the relative bacterial community at a depth of 0–40 cm were determined based on investigations in riparian sand mining areas and adjacent forestlands. The SOC density of the sand mining areas (2.59 t ha⁻¹, depth of 0–40 cm) was lower than that of the riparian forestlands (80.42 t ha⁻¹). Compared with those of the riparian forestland, the sand mining area exhibited a dramatic reduction in the CO₂-fixed gene abundances (cbbL) and a significant change in the composition of cbbL-containing bacteria. The rates of the Feammox (0.038 ± 0.014 mg N kg⁻¹ d⁻¹), anammox (0.017 ± 0.017 mg N kg⁻¹ d⁻¹), and denitrification (0.090 ± 0.1 mg N kg⁻¹ d⁻¹) processes at a depth of 0–20 cm in the soil layer of the sand mining area were reduced by 70.17%, 91.5%, and 93.62% compared with those of the riparian forestland, respectively. The riparian areas in the study area (approximately 12 ha, depth of 0–40 cm) destroyed by sand mining activities released approximately 933.96 t stored soil carbon, which reduce the annual carbon sequestration potential by 28.8–40.8 t. Moreover, the potential N-removal rates in the riparian forestlands (depth of 0–20 cm) by the Feammox, anammox, and denitrification processes were 1514.21–1530.95 kg N ha⁻¹ year⁻¹, whereas the potential N-removal rates in the sand mining area were only 121.2–126.19 kg N ha⁻¹ year⁻¹. Therefore, more investigations are necessary for comparing the benefits and damage of sand mining activities in riparian areas before more sand mining activities are approved.

Application of controlled release urea (CRU) is recommended to reduce the undesirable environmental effects resulting from urea application. However, the overall effects of CRU on maize productivity and reactive nitrogen (N) losses remain unclear. Our global meta-analysis based on 866 observations of 120 studies indicated that application of CRU instead of urea (same N rate) increased maize yield by 5.3% and nitrogen use efficiency (NUE) by 24.1%, and significantly decreased nitrous oxide (N₂O) emission, N leaching and ammonia (NH₃) volatilization by 23.8%, 27.1% and 39.4%, respectively. The increase of NUE and reduction of N₂O emission by CRU application were greater with medium and high N rates (150 ≤ N < 200 and N ≥ 200 kg N ha⁻¹) than with low N rates. The reduction in N₂O emission and N leaching with CRU application were enhanced when soil organic carbon (SOC) content was <15.0 g kg⁻¹, and soil texture was medium or coarse. The reduction in N₂O emission and NH₃ volatilization with CRU were greater in soils with pH ≥ 6.0. We concluded that use of CRU should be encouraged for maize production, especially on light-textured soils with low organic matter content.