Proceedings - Soil Science Society of America最新文献

Bentonite, commonly used for geological disposal of high-level radioactive waste and landfill liners, can experience increased permeability under high groundwater salinity, compromising its effectiveness. This article presents a novel approach to enhance the anti-seepage performance of hydraulic barriers, particularly in hypersaline environments. The proposed design incorporates a gradient distribution of fixed net negative charges, based on the principles of the Donnan equilibrium and generalized Darcy's law. The Donnan equilibrium, caused by fixed net charges on clay particles, alters the salt concentration of pore water that seeps through the soil. This creates a semipermeable membrane effect on the clay, leading to a concentration difference of salts between the flowing water in the soil and the external water supply. The concentration difference is dependent on the density of fixed net negative charges on the clay surfaces. By artificially controlling the distribution of fixed net negative charges, a salinity gradient is induced in the pore water. Based on the generalized Darcy's law, the salinity gradient can counteract seepage driven by pressure gradients and effectively reduce the seepage velocity. The study discusses key factors affecting the gradient distribution of fixed net charges in the designed hydraulic barrier, including void ratio, external solution concentration, and cation exchange capacity. The new hydraulic barrier is compared with existing methods (traditional bentonite and polymer–bentonite mixtures), demonstrating the effectiveness of the proposed method in enhancing anti-seepage performance, especially in hypersaline environments.

Accurate estimation of sediment transport capacity is crucial for effective soil erosion modeling and management. While empirical methods offer a practical approach for calculating sediment transport capacity using limited data, existing equations often lack reliability and applicability across a broad range of scenarios. This study addresses this gap by developing an empirical equation based on extensive datasets encompassing a wide spectrum of hydraulic and physical conditions ranging from slopes (1%–45%), unit flow discharges (0–15 × 10⁻² m² s⁻¹), and median particle sizes from (0.021–10.5 mm). The proposed equation integrates slope, discharge, and particle size to predict sediment transport capacity, leveraging advanced machine learning techniques. It was rigorously tested against other empirical equations, demonstrating superior performance with a coefficient of determination (R²) of 0.99 and a Nash-Sutcliffe efficiency of 0.99. The equation's strong alignment with physical sediment transport principles, particularly its similarity to stream power equations, underscores its theoretical robustness and practical relevance. Findings indicate that sediment transport capacity increases with discharge and slope while decreasing with particle size. Notably, rainfall intensity and flow depth did not significantly impact sediment transport capacity, emphasizing the equation's focus on the most influential variables. This research presents a significant advancement in sediment transport modeling, providing a reliable and accurate tool for a wide range of conditions and contributing valuable insights for soil erosion and sediment management. Future work should involve further validation with additional datasets to enhance the equation's applicability and robustness.

Astropedology is the study of soils on other planetary bodies and stretches the definition of soil to materials on the surface of a planetary body altered in place by physical, chemical, or biological processes. This new disciplinary name was coined by Roy E. Cameron in 1966 from studies of desert soils and their microbes in Arizona and Antarctica as analogs for Martian soils to be investigated by NASA Viking missions. Astropedology now has documented numerous actual soil profiles exposed in cliff faces, natural cracks, or cores studied by robotic missions to the Moon, Venus, and Mars, with increasingly advanced and precise chemical and other analyses. Specimens are also available for study from Lunar and Martian meteorites, and from sample return from the Moon, also planned from Mars. Life has yet to be found beyond Earth, but Mars has surprisingly Earth-like soils, which can be identified as Gypsids in US taxonomy. Soil formation by micrometeoroid bombardment on the Moon and by melting and glazing on Venus are truly out of this world.

Phosphorus (P) fixation in soil following fertilizer application is a major issue that may be mitigated through a number of methods. Our main objective was to utilize an innovative unsaturated flow system to directly image the mobility of P in soil material as affected by AVAIL, a commercial copolymer phosphate fertilizer enhancer. Air-dried clayey soil material, passed through a 0.25-mm sieve and adjusted to pH 6, was packed in three side-by-side 1.4-cm wide, 20-cm long, and 0.6-cm deep tracks. Water was applied to the tracks under approximately 1 cm tension and moved downstream by sorptivity. Five microliters of aqueous solutions containing 400 mmol P/L and varying levels of AVAIL were applied at a point near the upstream end of each track. Once water passed approximately 6 cm from the point of P application, each track was sectioned into small blocks and air-dried. Synchrotron micro X-ray fluorescence (μ-XRF) images of P, silicon (Si), and aluminum (Al) were collected on block samples to measure relative movement of phosphorus along the soil tracks. Our results show that, despite the high affinity of soil minerals for P, it was relatively mobile with no enhancer under unsaturated flow conditions. Images showed diminished rate of P movement and enhanced clay dispersion with increasing proportion of AVAIL. We postulate that clay dispersion, corroborated by X-ray computed tomography imaging, affected P transport due to interactions with Si and Al minerals. Our results demonstrate the potential utility of our unsaturated flow system combined with μ-XRF imaging to measure convective mobility of plant nutrients or contaminants through soils.

Industrial-scale coffee ground waste has the potential to serve as a nutrient-rich soil amendment, which would offer growers an opportunity to reduce applications of traditional fertilizers. Composted spent coffee grounds (CSCGs) and noncomposted spent coffee grounds (NCSCGs) were evaluated for their potential as organic N fertilizers. Nitrogen mineralization of NCSCGs and CSCGs was compared to commonly used synthetic and organic N fertilizers: urea and Milorganite. Net N mineralization and microbial activity were measured in a fine sandy loam field soil at 25°C and 60% water holding capacity weekly for 100 days. Despite a C:N of 13:1, the CSCGs appeared to have slow mineralization. Total inorganic N was lower in both CSCGs and NCSCGs than the control throughout the 100-day incubation with no additional N to the system. Greater CO₂─C respiration was recorded with SCGs, suggesting microbial activity is required for the breakdown of SCGs relative to other treatments. CSCGs may serve as a long-term fertilizer due to the time it takes to mineralize; however, over a shorter period, it may increase the nutrient- and water-holding capacity of soil, which can improve plant growth.

The use of ¹⁵N-labeled dinitrogen (¹⁵N₂) affords the only direct means of measuring free-living nitrogen fixation (FLNF); however, progress in utilizing this approach has been impeded by methodological limitations arising from the presence of nitrogenous contaminants, a lack of atmospheric uniformity, and incomplete description of procedural details. Such constraints are eliminated with an ex situ technique comprehensively described herein, which involves circulating ¹⁵N₂ generated by hypobromite oxidation through a closed system that includes chemical (sulfuric acid–potassium permanganate) and cryogenic (isopentane–liquid N₂) traps for atmospheric purification and an incubation chamber consisting of a desiccator equipped with a pressure gauge. Studies to evaluate the circulation system described showed that a uniform atmosphere was readily achieved with a 10-L desiccator by pumping for 30 min, and that both chemical and cryogenic traps were necessary to ensure complete (98.8%–99.6%) removal of gaseous contaminants subject to physicochemical retention by sterilized soil samples. The method proposed was successfully demonstrated in detecting the stimulatory effect of organic carbon (C) on FLNF in active soils, and can be further utilized to improve the reliability of ex situ assessment of FLNF in relation to soil processing and storage, climatic conditions, microbial dynamics, and land management practices.

The conversion of forest into coffee plantation through deforestation has become one of the main land use changes in tropical region, yet its impact on soil organic carbon (SOC) and methane (CH₄) uptake remains unclear, leading to uncertainties in estimating carbon fluxes in tropical area. The main coffee planting areas in China and the adjacent forests were selected to explore the effects of forest-to-coffee conversion and coffee stand ages on SOC and CH₄ uptake. We conducted our study by comparing coffee plantations of varying ages to the nearby forests within the same area. We treated the different-aged coffee plantations as our experimental groups and used the forests as our control groups. This paired comparison allowed us to exclude external factors such as climate, soil type, and vegetation differences, ensuring that our analysis focused on the effects of stand age alone. The 25-year, 43-year, and 55-year coffee plantations reduced SOC by 51%, 66%, and 65% compared to nearby forests, while soil microbial biomass carbon decreased by approximately 60%. Coffee stand age influenced ambient CH₄ uptake significantly: soils in 43- and 55-year-old coffee plantations and natural forests acted as CH₄ sinks, while the 25-year-old stand showed weak CH₄ emission. In 25-year, 43-year, and 55-year coffee plantations, the CH₄ uptake rates were 87%, 54%, and 65% lower, respectively, compared to the CH₄ uptake rates in the natural forests nearby. Soil moisture, inorganic nitrogen content, and CH₄ monooxygenase (MMO) activity were the main factors affecting CH₄ uptake rates across land uses in the ambient CH₄ background. Further CH₄ metabolism indicated a close relationship between ambient CH₄ uptake, CH₄ oxidation, and methanogenesis pathways. Our study highlights the reduction of SOC pools in coffee plantations in China is accompanied with the reduction of CH₄ uptake and changed metabolism of CH₄-oxidizing microorganisms.

Phosphorus (P) is one of the most limiting essential nutrients for agricultural production and its availability to crops is assessed by various methods. Mehlich-3, however, remains the most used method worldwide. For decades, the colorimetric method by blue ascorbic acid-molybdate reaction has been used to determine soil P concentration following Mehlich-3 extraction. Since early 1990s, the use of automated methods to quantify soil nutrients including P has expanded rapidly, and the inductively coupled plasma (ICP) emission spectroscopy is becoming one of the most popular instruments in routine soil testing. The main objective of this study was to compare ICP (where M3P is Mehlich-3 P, M3P-ICP) with colorimetric (M3P-Col) methods to estimate soil P using data from soil samples (3020) collected between 2005 and 2021 from 16 experiments conducted under different agroecosystems in Canada and Europe. Five case studies were assessed: (1) laboratory incubation, (2) native lowbush blueberry, (3) soil depth, (4) soil tillage, and (5) annual field crops versus perennial forage. In each study, a regression equation was established between soil M3P-ICP and M3P-Col. Results indicated that the two methods were strongly related in all studies (0.82 < r² < 0.99; p < 0.001), where soil P measured by ICP (2.1–352 mg kg⁻¹) was higher than that measured by colorimetry (0.6–339 mg kg⁻¹) except for the incubation study. Most important P differences were observed with forage and blueberry. Further analysis revealed that large differences between M3P-ICP and M3P-Col occurred primarily due to soil total C content. Soil pH, clay and Fe content, and previous crops also affected the relationship.

Water content of the soil has a significant role to play in the hydrological cycle and environmental processes. This study includes two phases: (1) approximation of soil moisture at the farm level based on optical-thermal images of Landsat-8 satellite and (2) retrieval of soil moisture by the dual-polarized basis decomposition model with the help of approximate soil moisture that is obtained by the optical-thermal model. In this research, two mechanisms, volume scattering and surface scattering, are considered. Furthermore, in order to model surface scattering, Bragg matrix has been used. The proposed radar model estimates soil moisture without using ground data, although few ground measurements have been used in the optical-thermal model. The Carlson triangular model has been used to approximate soil moisture using optical-thermal images. Three indices, normalized difference vegetation index (NDVI), normalized difference moisture index (NDMI), and moisture stress index (MSI), have been used in the optical-thermal model. Two ground soil moisture datasets are used in this study: (1) Cook Agronomy Farm (CAF) soil moisture data located in the United States and (2) real-time in situ soil monitoring for agriculture (RISMA) soil moisture data located in Canada. The radar model (base decomposition model) achieved a lowest root mean square error (RMSE) of 3.33% and a highest of 11.21%, showing strong accuracy in soil moisture retrieval. The optical-thermal model had a slightly higher minimum RMSE of 4.04% and a maximum of 9.68%. These results suggest that the radar model generally outperforms the optical-thermal model, making it more reliable for accurate soil moisture estimation in agricultural applications, which is crucial for optimizing irrigation and managing resources.

The application of compost increases soil organic matter (SOM) content; however, there is a lack of information on the short- and long-term effects of compost application on the dynamics of labile SOM pools in compost-amended soils in semiarid region. The goal of this study is to distinguish between parameters that can be used for investigating the accumulative effects of compost application and parameters that are sensitive for short-term changes but diminish with time. To address this goal, we focused on (1) the effects of compost application rates on short-term dynamics of soil contents of microbial biomass carbon (MBC), cold water-extractable organic carbon (WEOC), and hot water-extractable organic carbon (HWEOC), respectively, and (2) composition of WEOC and HWEOC characterized using (i) absorbance at 254 nm (Abs₂₅₄) representing the presence of aromatic components and (ii) fluorescence spectroscopy of excitation–emission matrices coupled with parallel factor analysis. Soil samples were taken from a long-term field experiment in semiarid region, which investigated the effects of the annual load of a cattle manure-based compost (at rates of 0, 20, 40, or 60 m³ ha⁻¹ year⁻¹) on soil properties and crop performance. C concentrations in soil water extracts were found to be sensitive indicators of compost-load effect on soil organic carbon content. Compost dose had a strong short-term (2 weeks) impact on MBC, but no long-term (over months and years) effect was observed. Of the variables examined in the short term, the MBC, WEOC, and Abs₂₅₄ values of the extracts were found to be the most responsive to compost load. The proportion of the fluorescent constituents out of the WEOC and HWEOC decreased with compost dose. UV- and fluorescence-spectroscopy were found to be useful means to characterize the influence of compost load on the composition of water-extractable organic matter and hot water-extractable organic matter in semiarid region.