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Understanding the responses of the microbial community and greenhouse gas (GHG) emissions to the incorporation of different organic amendments is essential for their proper utilization. In this study, laboratory‐incubated microcosm experiments were conducted to investigate the short‐term effects of pine‐wood biochar and lignite‐based amendment on the microbial communities and GHG emissions from agricultural soil. Soils amended at five different application rates were incubated for 19 d under the conditions of 60% water‐filled pore space and 25 °C. Microbial biomass in the amended soil after incubation was measured by the solid colony counting method, and the soil microbial diversity was assayed using a Biolog EcoPlate. The biochar and lignite‐based amendment had distinct effects on the soil microbial communities and GHG emissions. The microbial community growth and utilization of C sources were improved by the biochar but restrained by the lignite‐based amendment in most cases. The biochar and lignite‐based amendment had a minor impact on methane emissions. Carbon dioxide emissions were promoted by the biochar and inhibited by the lignite‐based amendment during the short‐term incubation period. Nitrous oxide emissions decreased with the application rate of biochar but increased with the rate of lignite‐based amendment. The addition of biochar at a rate of 3–4% and lignite‐based amendment at a rate of <1% has the potential to improve soil quality. Salt leaching is required to avoid accumulation when the biochar and lignite‐based amendments are applied. The findings can provide a reference for the application of biochar and lignite‐based amendment in silt loam soil. [ABSTRACT FROM AUTHOR]

Soil evaporation and its associated processes are vital for agricultural production and ecosystems in seasonal frozen regions. However, soil evaporation and its impact on salt accumulation in different landscapes during freeze–thaw periods have not been well elucidated. In this study, field experiments were carried out to investigate soil evaporation and salt accumulation patterns in three typical landscapes—namely, cropland, woodland, and natural land—in an arid seasonal frozen region located in the upper reaches of the Yellow River basin from November 2018 to April 2019. The results indicated the highest soil evaporation occurred on natural land with a total amount of 148.5 mm during the freeze–thaw period from 2018 to 2019, whereas woodland had the smallest soil evaporation of 56.9 mm. Over 75% of soil evaporation occurred during the thawing stage for all three landscapes. The average daily evaporation was below 1 mm d–1 for the whole freeze–thaw period and was 0.1 mm d–1 for the stable freezing stage. Compared with humidity and wind speed, temperature and soil water content had a greater impact on soil evaporation. At the end of the thawing stage, the salt content in the topsoil (0–10 cm) layer increased significantly with an increasing rate of 70–225%. Salt concentrations in the topsoil were significantly and linearly related to the cumulative soil evaporation during the freeze–thaw period. The current research is expected to provide implications for water management and salinity control in the upper reaches of the Yellow River basin and in other arid regions with similar conditions. [ABSTRACT FROM AUTHOR]

Core Ideas: Heat loss is the main reason for water flux underestimation.Two methods were proposed to quantify the heat loss.More accurate hydraulic properties can be estimated with the addition of heat loss. Heat has been widely used to investigate water flow in soils and aquifers during the past few decades. However, heat loss as an important characteristic has not been well considered in laboratory heat‐tracing experiments. To evaluate the impact of heat loss on the estimation of hydraulic and thermal properties, a laboratory experiment was conducted using a sandbox packed with heterogeneous silica sand under steady‐state flow condition. Thermocouple probes were used to simultaneously measure the temperature inside and outside of the silica sand during the experiment. The measured temperature of the sand layer was used to estimate the hydraulic conductivities and longitudinal and transverse thermal dispersivities via curve fitting using HYDRUS software. We found that >50% of the sensible heat was dissipated into the shell of sandbox and the surrounding air rather than being absorbed by the sand. Two methods were then proposed to quantify the heat loss and to improve the accuracy of parameter estimation: (i) a conceptual heat balance method that accounted for the change in heat storage in different parts of the system and (ii) a physical process‐based method that described the thermodynamic processes of heat transfer among different parts of the system. On combining these two methods, the relative error between the estimated and measured water flux significantly decreased from 19% to nearly 2%. The results imply that the heat‐tracing method is capable of obtaining accurate hydraulic and thermal properties in a heterogeneous porous medium with the addition of heat loss. [ABSTRACT FROM AUTHOR]

Core Ideas: We quantified heterogeneity and reproducibility of repacked sand column microstructure.The averaged pore geometric properties were quantified using Minkowski functionals.Spatial heterogeneity was analyzed using a mathematical morphological operation. Column experiments are widely used for mechanism and application studies in different fields. A major challenge and an advantage of the repacked porous column are its uniformity and reproducibility. Bulk density is a commonly used parameter to evaluate the uniformity and consistency of random packing. The internal structure of pore space is usually ignored and lumped into the bulk density. However, flow and transport characteristics of the repacked porous media are not fully defined from the bulk density but also depend on the internal structure. In this paper, we quantitatively assessed the heterogeneity and reproducibility of repacked sand columns using integral geometry methodology. X‐ray computed tomography is applied to visualize the pore space of the column repacked with different silica sands. The acquired tomography images are processed and quantitatively analyzed using Minkowski measures. The Minkowski functionals combined with the granulometric density function were applied to describe the spatial heterogeneity of microstructures. The results have demonstrated that the Minkowski functionals proportional to the well‐known geometric quantities are able to characterize the average geometrical properties of complex pore space. The pore size distributions of sand column are obtained through morphological opening operation. The two‐parameter Weibull distribution has been found reasonably describe the granulometric density acquired from the morphology analysis. The Minkowski densities joint with the critical pore diameter as well as parameters of Weibull function at different locations of each column have demonstrated the heterogeneity of the sand column. The small variation in the finer sand column indicates the heterogeneity is relatively smaller than that of the coarser ones. The relatively small differences among the repetitions of finer sand columns suggest more reliable reproducibility in comparison to the coarser sand columns. [ABSTRACT FROM AUTHOR]