The change in land-use from woodland to crop production leads to increased nitrous oxide (N2O) emissions. An understanding of the main N2O sources in soils under a particular land can be a useful tool in developing mitigation strategies. To better understand the effect of land-use on N2O emissions, soils were collected from 5 different land-uses in southeast China: shrub land (SB), eucalyptus plantation (ET), sweet potato farmland (SP), citrus orchard (CO) and vegetable growing farmland (VE). A stable isotope experiment was conducted incubating soils from the different land use types at 60% water holding capacity (WHC), using 15NH4NO3 and NH415NO3 to determine the dominant N2O production pathway for the different land-uses. The average N2O emission rates for VE, CO and SP were 5.30, 4.23 and 3.36 μg N kg−1 dry soil d−1, greater than for SB and ET at 0.98 and 1.10 μg N kg−1 dry soil d−1, respectively. N2O production was dominated by heterotrophic nitrification for SB and ET, accounting for 51 and 50% of N2O emissions, respectively. However, heterotrophic nitrification was negligible (<8%) in SP, CO and VE, where autotrophic nitrification was a primary driver of N2O production, accounting for 44, 45 and 66% for SP, CO and VE, respectively. Denitrification was also an important pathway of N2O production across all land-uses, accounting for 35, 35, 49, 52 and 32% for SB, ET, SP, CO and VE respectively. Average N2O emission rates via autotrophic nitrification, denitrification and heterotrophic nitrification increased significantly with gross nitrification rates, NO3− contents and C:N ratios respectively, indicating that these were important factors in the N2O production pathways for these soils. These results contribute to our understanding and ability to predict N2O emissions from different land-uses in subtropical acidic soils and in developing potential mitigation strategies.

Biochar addition to soil may change the hydrophobicity of amended soil and influence soil hydraulic properties. Soil hydrophobicity, i.e. soil water repellency (SWR) can interrupt water infiltration and form preferential flow leading to a potential risk of soil erosion or groundwater pollution. Up to date, the effect of different biochars on soil hydrophobicity remains unclear and the association of SWR with soil hydraulic properties is still unknown. To link the biochar hydrophobicity to SWR and soil water holding capacity (WHC), the surface structure and chemical composition of 27 biochars with different feedstocks and pyrolysis temperatures were characterized, and the SWR and soil WHC of biochar-added soil were investigated. Carboxylic groups on the biochar surface, surface area and pore volume were mostly influenced by pyrolysis temperature, which suggested the dominant factor determining the severity of biochar hydrophobicity was pyrolysis temperature. Hydrophilic soil became hydrophobic after biochar amendment. A higher addition rate led to a stronger SWR of hydrophilic soil. Biochar addition increased soil WHC of hydrophilic soil with low total organic carbon (TOC) content. Biochar did not have significant influence on SWR and soil WHC of hydrophobic soil with high TOC content. It implied that the influence of biochar on SWR and soil hydraulic properties mainly depended on soil original hydrophobicity and TOC content. Therefore, the properties of biochar and influence on soil hydrophobicity and hydraulic properties should be considered before processing biochar application.

This study aimed at assessing the effects of increased air temperature and reduced soil moisture content on the multi-generation toxicity of a soil polluted by metal/metalloid mining wastes. Enchytraeus crypticus was exposed to dilution series of the polluted soil in Lufa 2.2 soil under different combinations of air temperature (20 °C and 25 °C) and soil moisture content (50% and 30% of the soil water holding capacity, WHC) over three generations standardized on physiological time. Generation time was shorter with increasing air temperature and/or soil moisture content. Adult survival was only affected at 30% WHC (∼30% reduction at the highest percentages of polluted soil). Reproduction decreased with increasing percentage of polluted soil in a dose-related manner and over generations. Toxicity increased at 30% WHC (>50% reduction in EC50 in F0 and F1 generations) and over generations in the treatments at 20 °C (40–60% reduction in EC50 in F2 generation). At 25 °C, toxicity did not change when combined with 30% WHC and only slightly increased with 50% WHC. So, higher air temperature and/or reduced soil moisture content does affect the toxicity of soils polluted by metal/metalloid mining wastes to E. crypticus and this effect may exacerbate over generations.

The degradation of metformin (MET) and guanylurea (GUA) fortified separately in freshly collected two top soils (0–10 cm) from New Zealand's pastoral region was studied under controlled laboratory conditions. Incubation studies were carried at 30 °C under aerobic conditions at 60% of maximum water holding capacity and at two (0.5 mg/kg and 5 mg/kg) nominal soil concentrations. Degradation profiles revealed a bi-phasic pattern of both the compounds with an initial rapid degradation followed by slow dissipation rate, resulting in poor fits by simple first order kinetics. However, the use of three non-linear mathematical models sufficiently described the measured data and well supported by an array of statistical indices to judge model's ability to fit the measured datasets. Further evaluation using box-whisker plots showed that double first-order in parallel (DFOP) and first-order two-compartment (FOTC) models best fitted the data points followed by the Bi-exponential (BEXP) model. Mechanistic assumptions from DFOP and FOTC suggest that degradation of MET and GUA proceeds at two different rates, possibly in two compartments. The calculated DT50 using both models were in the range of 2.7–15.5 days and 0.9–4 days, while 90% dissipation time (DT90) varied between 91 and 123 days and 44 and 137 days for MET and GUA, respectively. Degradation of both compounds were dependent on soil types and properties, incubation conditions and initial substrate concentration. Formation of GUA with decrease in MET concentration over time confirmed that GUA is a transformation product concomitantly formed from aerobic degradation of MET in soil.

Cover systems can efficiently limit acid mine drainage generation from sulfidic mine wastes by controlling oxygen diffusion. Their performance relies on their high degree of saturation, as oxygen diffusion is substantially reduced in water or saturated medium. However, natural soils available in the mine vicinities do not necessarily have the hydrogeological properties required for the construction of sealing layers. A common strategy is to improve the characteristics of local soils using bentonite amendment, but this usually induces high costs and environmental footprint. An alternative is to reuse (or valorise) waste materials, such as mine wastes or industrial wastes like green liquor dregs (GLD). Blends of till and GLD can have advantageous properties regarding water retention capacity and hydraulic conductivity. In this study, the effective oxygen diffusion coefficient Dₑ of till-GLD blends was evaluated using 81 diffusion tests. Various quantities and different types of GLD were tested. The diffusion coefficient was found to vary greatly depending on the degree of saturation. Even though the GLD contained naturally a substantial amount of water, a high water content of the till was still required to reach a low Dₑ. Measurements were also compared with modified Millington-Shearer predictive model which could generally predict the diffusion coefficient within an acceptable range. Results also indicated that the till-GLD mixes should not be exposed to evaporation as significant performance loss may rapidly occur upon drying. Main experimental results are presented in this paper together with recommendations in terms of cover design using till-GLD mixes.

In this study, the performance of Datura stramonium, an invasive weed of soybean and solanaceous crops, was examined under different elements of climate change. Experiments conducted in CO₂ chambers at ambient CO₂ (400 ppm) and elevated CO₂ (700 ppm) levels under both well-watered and drought conditions exhibited the fertilization effect of elevated CO₂. This was, however, limited by drought. Clearly, growth of D. stramonium will be significantly enhanced by enriched atmospheric CO₂ concentration under well-watered conditions, producing taller plants with greater biomass and higher seed output. Glasshouse experiments were conducted to evaluate the effect of different soil moisture regimes (100%, 75%, 50% and 25% water-holding capacity (WHC)) on the growth and fecundity of D. stramonium. Plants grown in 75% WHC had the highest plant height (15.24 cm) and shoot diameter (4.25 mm). The lowest leaf area (305.91 mm²), fresh weight (14.48 g) and dry weight (4.45 g) were observed in 25% WHC conditions. The ability of D. stramonium plants to grow and complete their life cycle with high seed output, even under limited water availability, shows the weedy nature of this species which is well adapted to survive future inhospitable climatic conditions. Radiant heat treatment on the plants indicated that temperatures of 120 °C and above for more than 180 s were enough to kill the plants, suggesting that thermal weeding or wildfires will be adequate to act as a circuit breaker on the D. stramonium invasion cycle, thus allowing other control measures to be engaged for greater control.

Effects of low-temperature thermal desorption (LTTD) treatment on the ecological properties of soil contaminated by petroleum hydrocarbons were assessed. For this purpose, various ecological properties related to soil health and physicochemical properties of the oil-contaminated soil before and after LTTD treatment were investigated. Total petroleum hydrocarbon concentration, electrical conductivity, organic matter, and total nitrogen decreased while water-holding capacity and available P₂O₅ increased. The soil color was also changed but textural class was not changed after LTTD. The microbial number and dehydrogenase activity increased following LTTD, but there was no significant difference in the β-glucosidase and acid phosphatase activities. Seed germination succeeded after LTTD, but the germination rate was still lower than that in non-contaminated soil as the growth of plants and earthworms was. The results showed that overall soil health related to biological productivity and environmental functions was improved after LTTD and suggested that LTTD could be a better alternative to other harsh remediation methods. However, ecological indicators still show differences to the adjacent non-contaminated level. Therefore, to ensure safe soil reuse, the change in eco-physiochemical properties as well as contaminant removal efficiency during the remediation process should be considered.

Chemical cross-linking and the high molecular weight of superabsorbent copolymers (SAPs) are the two main causes of their resistance to biodegradation. However, SAP particles are colonized by microorganisms. For the purposes of this study, the dry technical copolymer of acrylamide and potassium acrylate containing 5.28 % of unpolymerized monomers was wrapped in a geotextile and incubated in unsterile Haplic Luvisol soil as a water absorbing geocomposite. The highest number of soil bacteria that colonized the hydrated SAP and utilized it as the sole carbon and energy source was found after the first month of incubation in soil. It was equal to 7.21–7.49 log₁₀ cfu g⁻¹ of water absorbed by the SAP and decreased by 1.35–1.61 log₁₀ units within the next 8 months. During this time, the initial SAP water holding capacity of 1665.8 g has decreased by 24.40 %. Moreover, the 5 g of SAP dry mass has declined by 31.70 %. Two bacteria, Rhizobium radiobacter 28SG and Bacillus aryabhattai 31SG isolated from the watered SAP were found to be able to biodegrade this SAP in pure cultures. They destroyed 25.07 and 41.85 mg of 300 mg of the technical SAP during the 60-day growth in mineral Burk’s salt medium, and biodegradation activity was equal to 2.95 and 6.72 μg of SAP μg⁻¹ of protein, respectively. B. aryabhattai 31SG and R. radiobacter 28SG were also able to degrade 9.99 and 29.70 mg of 82 mg of the ultra-pure SAP in synthetic root exudate medium during the 30-day growth, respectively.

Rhamnolipid is a biosurfactant produced by several Pseudomonas species, and can wet hydrophobic soils by lowering the cohesive and/or adhesive surface tension. Because of its biodegradability, rhamnolipid is believed to have minimal adverse impact on the soil and groundwater after usage. Applications of rhamnolipid to improve irrigation in agricultural soils thus have obvious advantages over other chemical wetting agents, especially under drought conditions. Due to global warming, soil amendment with biochar has been commonly practiced in agricultural soils to increase the soil water-holding capacity. As such, rhamnolipid transport in biochar-amended agricultural soils needs to be characterized. In this research, we found that rhamnolipid transport in biochar-amended agricultural soils was hindered by retardation (equilibrium adsorption) and deposition (kinetic adsorption), which was well represented by the advection-dispersion equation based on a local equilibrium assumption. A linear equilibrium adsorption was assumed in the advection-dispersion equation simulation, which was proved to be acceptable by studying the breakthrough curves. Both rhamnolipid equilibrium adsorption and kinetic adsorption increased with the increase of the biochar content in the agricultural soil.