Proceedings - Soil Science Society of America最新文献

Slope aspect is a significant terrain attribute influencing soil physical and chemical processes. Yet its impact on soil quality and erosion has rarely been studied on gently sloping farmlands. The objective was to evaluate the effects of slope aspect on soil quality and its response to soil erosion in the black soil region of northeast China, a temperate environment featuring gently sloping farmlands. Over a nearly north-south symmetric sloping farmland spanning ∼3500 m, fifteen soil physical and chemical properties were investigated at every 40 m, and an integrated soil quality index (SQI) was calculated combining principal component analysis and scoring functions. The mean annual erosion rate (ER) was estimated using the cesium-137 tracing technique. Compared to the south-facing slope, the north-facing slope possessed significantly lower pH and higher saturated hydraulic conductivity, sand content, and almost all the essential nutrient contents, therefore overall better soil quality (p < 0.05). No statistical difference was spotted in ER between the two slopes (p > 0.05); however, erosion was found to deteriorate soil quality via distinct pathways. On the north-facing slope, erosion affected SQI predominantly through its negative impact on soil organic carbon content and wet-aggregate stability, and conservation tillage practices were suggested. However, on the south-facing slope, the detrimental influence was primarily driven through the depletion of soil nutrient contents, particularly available phosphorus and total nitrogen, and contour tillage and hedgerows were strongly recommended. These findings hold important practical implications for agricultural management in temperate environments.

Clay nanoparticles (NPs) are recognized as natural soil amendments. However, the effects of different types of clay NPs and their application rates on the physical, chemical, and biological characteristics of soils, solute transport, and plant photosynthesis parameters have not been thoroughly investigated. This study focused on amending two soil textures—sandy loam and loam—by adding 3% nano clay. The original and amended soils were packed into soil columns to conduct cultivation experiments with quinoa (Chenopodium quinoa Willd) plants and displacement solute transport experiments. The goal of column experiments was to explore the impact of the nano clay amendment on the photosynthetic properties of quinoa plants and solute transport in soils. The results indicated that adding NPs to loam soil improved photosynthesis and stomatal conductance. Additionally, the introduction of nano clays reduced sub-stomatal CO₂ levels in the amended soils compared to the control soils. In sandy loam soil, both with and without cultivation, the addition of nano clay enhanced saturated hydraulic conductivity, dispersivity, and maximum chloride concentration when compared to the control. However, it also resulted in a decrease in immobile water content and a reduction in peak travel time. In loam soil, the application of nano clay—regardless of cultivation method—increased dispersivity and immobile water contents while reducing maximum chloride concentration. It simultaneously decreased hydraulic conductivity compared to control conditions and also increased it in some instances. This research demonstrates that the nano clay amendment significantly alters soil's physical and chemical properties, affecting solute transport and the photosynthetic parameters of the quinoa cultivar.

Extracellular enzymes play a key role in microbe-mediated organic matter decomposition in soils, and the efficiency of these enzymes in substrate decomposition depends on their mobility and specific activity in soils. In this work, we explored the influence of biochar adsorption on extracellular enzyme activity across a spectrum of environmental conditions, from simple to complex. Batch adsorption results showed that biochar adsorption of two hydrolytic enzymes—α-amylase and amyloglucosidase (AMG)—similarly decreases with pH and follows the Langmuir isotherm, suggesting electrostatic interaction between them. Activity of AMG and alkaline phosphatase (ALP), which belong to carbon and phosphorus cycling enzymes, was measured using a novel calorimetric method. The technique demonstrated advantages over conventional enzyme assays, such as in situ real-time measurement of reaction rate and the ability to identify potential interferences. The technique enabled the measurement of specific activity of biochar-adsorbed AMG, which ranged from 10% to 90% of that of free AMG. The effect of substrate adsorption on activity measurement was demonstrated through the examination of two substrates for ALP, which suggested the use of effective substrate concentration (instead of nominal concentration) in calculating enzyme activity kinetics. Soil column experiments showed that biochar amendment can affect the activity of AMG in starch hydrolysis through changing the mobility of AMG (and accessibility to substrate) and its specific activity. Results from this work improve our understanding of the effects of biochar adsorption on enzyme activity and suggest the need to appropriately interpret enzyme activity data and account for confounding processes.

Hydroxyapatite is an important phosphorus (P) sink in calcareous soils. The activity of carbonate in soil pore water, however, is often underestimated because soil respiration and solution-calcite equilibria could elevate CO₂(g) concentration much greater than 415 ppmv (i.e., pCO₂: ∼0.3 mm Hg). Thus far, the role of CO₂(g) or pCO₂ in the hydroxyapatite formation in calcareous soils has not been extensively investigated. Accordingly, the effects of CO₂ concentration (415, 8000, and 20,000 ppmv) on hydroxyapatite formation were investigated at pH 8 using experimental geochemistry and X-ray diffraction (XRD) analysis. XRD analyses showed the formation of hydroxyapatite under all CO₂ concentrations, but the extent of calcite formation increased with increasing CO₂ concentration. The formation of calcium (Ca) carbonate phosphate was also observed after 30 days under [CO₂(g)] up to 8000 ppmv. This is attributed to an increase in calcium carbonate formation. Scanning electron microscopy showed rounded hydroxyapatite particles. The variability of [CO₂(g)] in subsoils should be considered in the P cycle in calcareous soils.

Soybeans (Glycine max (L.) Merr.) are mainly grown in Brazil during the rainy season. However, there are typically periods of rainfall deficiency, which causes water-deficit stress to the crop. Plant growth-promoting rhizobacteria (PGPR) can help alleviate these stresses by inducing water deficit tolerance. The objective of this study was to evaluate the role of PGPR in enhancing soybean tolerance to water-deficit stress. Six PGPR isolates, two for induction of water-deficit tolerance (ESA 441, BRM 034008), two AIA-producing (Ab-V5, BRM 063574), and two phosphate solubilizing (BRM 063573, BRM 67205), and their combination were evaluated, for a total of 16 treatments. The experiment was conducted in a greenhouse using a randomized block design with three replicates. Effects were measured on gas exchange parameters (stomatal conductance, transpiration, internal CO₂ concentration, and photosynthetic rate), growth parameters (shoot dry weight, root dry weight, root length, root surface area, root diameter, and root volume), and yield components (pod weight, number of pods, number of grains, and grain weight). Co-inoculation significantly reduces the effects of water stress on gas exchange, plant growth, and productivity compared to single inoculation. Notable combinations, such as BRM 063574 + BRM 67205 + BRM 034008 and BRM 063574 + BRM 063573 + ESA 441, improved root and shoot growth under stress conditions. Yield components also improved with co-inoculations, with combinations such as BRM 063574 + BRM 67205 + ESA 441 showing the highest efficacy. These results suggest that specific PGPR co-inoculations can improve soybean resilience to water deficit stress and promote better growth and yield.

Mathematical models are used extensively to estimate soil pesticide leaching in regulatory risk assessments and are often solved numerically, which can obscure simple insights. We developed an analytical solution that highlights the role of the ratio of sorption to degradation in compound leaching, denoted as the sorption-extinction (S_e) coefficient. We extend the classic analytical work of Jury to derive a steady-state solution for pesticide concentrations as a function of soil depth considering nonlinear sorption. We consider degradation in the soil water and solid phases and transport driven by advection, diffusion, and dispersion. Nonlinear sorption was handled using the mathematical technique of asymptotic expansions. We compared the steady-state analytic solution with extended duration simulations of the European regulatory numerical model PEARL for all FOCUS scenarios (i.e., nine European regions). The analytic solution was consistent with the long-term PEARL results across most FOCUS scenarios, and the results show that for a fixed S_e coefficient, similar mean pesticide concentrations at the regulatory leaching depth (1 m) are obtained despite varying the sorption and degradation by an order of magnitude. This indicates that the S_e coefficient is a dominant component of mean leaching behavior rather than degradation or sorption alone. However, as the absolute value of degradation and sorption decreases, variability of the pesticide concentration increases. While we demonstrate the approach using the FOCUS scenarios weather and soil data, this method can be applied as a rapid and time-efficient predictive tool for any region with either highly or more scarcely parameterized soil/weather data.

Soil thermal conductivity (λ) is essential for understanding coupled matter and energy flux in porous systems. However, its prediction has remained unsettled due to its intricate relationship with soil properties such as soil moisture content (θ) and texture. This study investigates λ–θ relationship in 15 tropical soils from Ghana. The results show that soil λ–θ relationship is strongly nonlinear and depends on texture with fine-textured soil exhibiting a flat tail in λ the dry range. Four distinct domains, namely, hydration, pendular, funicular, and capillary, ranging from dry to wet condition, were identified. Two modeling approaches, percolation-based effective medium approximation (P-EMA) and an empirical sigmoidal model (SM), were evaluated on the λ(θ) dataset. An explicit λ(θ) P-EMA variant outperformed a θ(λ) variant, achieving performance on par with the SM. However, the explicit λ(θ) P-EMA performs well in the hydration regime, whereas the SM performs well in the capillary regime. The explicit λ(θ) P-EMA and SM had difficulty fitting the nonlinear behaviour at intermediate θ beyond the pendular domain, possibly due to the structural complexity, which is also linked to phase distribution. This study advances our knowledge on λ–θ relationships in Ghanaian soils.

The western slope of Haleakalā, Maui, demonstrates a wide range in soil development (eight mapped soil orders), thus providing a unique opportunity to investigate how climate and volcanic ash deposition influence soil development on basalt. The objective of this study was to examine soil chemical and physical properties across climatic gradients and elevation to address how climate and relatively recent volcanic ash deposition affect pedogenesis across western Haleakalā. Sixteen pedons were sampled: five in a coastal climosequence uninfluenced by volcanic ash (15–224 m elevation; 461–2768 mm mean annual precipitation [MAP]; 22°C–23°C mean annual temperature [MAT]; 3357–5577 mm potential evapotranspiration [PET]), and eleven in an elevational transect variably influenced by volcanic ash (73–1362 m elevation; 283–2267 mm MAP; 13°C–24°C MAT; 1555–2704 mm PET). Pedogenic thresholds for dynamic soil properties (base saturation [BS], pH, organic C, and Al/Si extracted by ammonium oxalate) occurred at about 0.4 MAP/PET (1500 mm MAP) along the coastal climosequence and at about 0.8 MAP/PET (1600 mm MAP) along the elevational transect due to an increase in soil moisture availability and leaching potential. Greater clay/Fe (extracted by citrate dithionite [CD]) and crystalline Fe (CD minus hydroxylamine hydrochloride-hydrochloric acid [HH]) in drier lowland soils more distant from the summit indicate they are likely older and occur on older landforms. The ratio MAP/PET is an effective climatic index for understanding trends in pedogenesis and indicating pedogenic thresholds in climosequences and elevational transects in Hawaiian ecosystems.

The entry of ¹³⁷Cs into the soil can lead to its presence in food and water. Understanding how ¹³⁷Cs behaves in soil is important for predicting its environmental fate. Thirteen agricultural and one pasture soil sample were collected from various locations. A comprehensive analysis of the soil's physicochemical properties and climate and geographical factors was conducted. ¹³⁷Cs activity and clay mineralogy were determined using γ-spectrometer and x-ray diffraction. Correlation analysis between measured factors with ¹³⁷Cs activity revealed that the presence of carbonate minerals played a significant role in the negative correlation between pH and ¹³⁷Cs activity (r = −0.43). While a weak negative correlation was observed between clay mineral content and ¹³⁷Cs activity (r = −0.12), the type of clay minerals presents proved to be more influential on ¹³⁷Cs adsorption. Smectite minerals exhibited a positive correlation with ¹³⁷Cs activity (r = 0.46), aligning with the correlation between ¹³⁷Cs activity and precipitation (r = 0.49). The strong positive correlation between longitude and ¹³⁷Cs activity (r = 0.66, p < 0.01) was not directly indicative of longitude's influence on nuclear fallout distribution. Instead, this correlation was attributed to the interplay of other factors, including precipitation, smectite, calcium carbonate, and chlorite minerals. The possible effect of soil erosion, land use, and human activity on ¹³⁷Cs activity was discussed in provinces with similar soil and climate characteristics. This research explored the potential influence of various factors on ¹³⁷Cs activity, highlighting the complexity of environmental factors in accurately estimating ¹³⁷Cs levels in soil.

Urban soils are key components of urban ecosystems and can contribute to the solution for many ecological and environmental problems such as stormwater runoff, pollution mitigation, and urban food production. Urbanization processes often result in highly disturbed and spatially variable urban soils. Besides heterogeneity, one of the unique and intriguing aspects of urban soil is the nature and properties of organic carbon, with a significant percentage being anthropogenic carbon such as black carbon, which is less biologically active than natural organic matter. We sampled 13 soil profiles covering a wide range of soil conditions, including both anthropogenic and native soils, across New York City. At each site from each horizon, soil samples were collected for laboratory determination of total carbon and nitrogen, black carbon, microbial biomass carbon and nitrogen, and pools of readily mineralizable carbon and nitrogen. We hypothesized that the carbon present in urban soil profiles derived from human-altered and human-transported (HAHT) parent materials has a lower capacity to support microbial biomass and a limited nitrogen supplying ability compared to the carbon found in urban soils derived from native parent materials. We found that total carbon and nitrogen were as high, or even higher in soils derived from HAHT parent materials than in native soil profiles, but that labile pools were lower in the HAHT soils. Assessment of the quality of organic carbon, which is strongly affected by HAHT materials, is important for understanding the ability of urban soils to support a wide range of ecological and environmental functions.