Proceedings - Soil Science Society of America最新文献

The specific role of each fraction of soil C (i.e., particulate [POC] or mineral-associated organic carbon [MAOC]) in each soil strength mechanism remains unexplored. We investigated the relationships of total organic C and its physical fractions with soil strength of two tropical soils (sandy clay loam [SCL_soil] and sandy clay [SC_soil]). We measured soil strength indicators from oven-dry aggregates [tensile strength (σ_t)] and some related to soil compaction [precompression stress (σ_p), compression index (λ), and penetration resistance (SPR) at constant matric potential (−100 hPa)]. These soil strength indicators were used as response variables in path analyses to determine direct effects of C, MAOC, and POC mediated by key physical strength inducers (bulk density or water content). Results suggest a C role conferring soil strength verified by positive correlation with tensile strength and SPR increase, positively influenced by MAOC in SCL_soil and C/POC/MAOC in SC_soil. For SPR, the C effect was mediated by water content or bulk density (i.e., indirect contribution for correlation). Organic C, in turn, showed limited effect on soil compressibility. These findings indicate that increases in soil carbon that enhance aggregate mechanical strength and penetration resistance do not result in reduced soil compressibility (i.e., resistance to compaction). In sandy clay loam soils, MAOC plays a key role in increasing soil strength, whereas all carbon fractions contribute to strength gains with increasing clay content. Thus, while organic carbon can promote beneficial structural stability in the long term, it may also increase SPR, which affects root growth.

This 3-year field study evaluated the effects of winter cover crop treatments, including no cover crop (control), elbon rye (Secale cereale L.), daikon radish (Raphanus sativus ssp. acanthiformis), Austrian winter field peas (Lathyrus hirsutus), and their mixture, on topsoil (0–10 cm) aggregate size distribution and stability, as well as soil organic carbon (SOC) and total nitrogen (TN) stocks in bulk soil and aggregate fractions under a no-till dryland cotton–corn rotation. Results revealed the <0.25 mm aggregates were the most dominant (63.6%–74.8%), exhibited the highest C and N preservation capacity due to their high aggregate content, and contributed the most to SOC and TN stocks, accounting for 40.8%–65.9% and 36.1%–65.1%, respectively. No significant differences in aggregate size distribution or stability were found among treatments. The treatment with radish, peas, and rye planted sequentially over 3 years exhibited the highest SOC stock (28.2 Mg ha⁻¹), while the peas treatment had the highest TN stock (3.1 Mg ha⁻¹) in bulk soil. The radish-radish-mixed (peas + radish + rye) sequence increased the proportion of SOC (38.8%) and TN (42.8%) within the 2–1 mm and 1–0.5 mm aggregate fractions. In the <0.25 mm aggregates, the peas treatment had the highest SOC (11.2 Mg ha⁻¹), and the treatment with 2 years of radish followed by a mixed species of peas, radish, and rye had the highest TN (0.8 Mg ha⁻¹). The main factors influencing bulk SOC stock were the C preservation capacity and SOC stock of the 0.5–0.25 mm aggregates, while bulk TN stock was primarily driven by the N preservation capacity and TN stock of the >2 mm aggregates. The findings suggest that cover crop strategies involving peas and species diversification, such as sequential planting of radish, peas, and rye, can enhance SOC and TN accumulation, particularly in the <0.25 mm aggregates, thereby improving soil health in no-till dryland systems.

The intricate interaction between plants and soil is multifaceted. Soil furnishes essential nutrients for plant growth, and plants can control the soil environment. However, in the context of urbanization, human disturbance seriously affects the road green space environment, and the relationship between green space vegetation and soil is still unclear. This study focused on five roads in Guiyang City, comparing the species diversity and soil properties of road green spaces with different configurations. Redundancy analysis was employed to elucidate the relationship between spontaneous plants and soil. The results showed the following: (1) The study area encompasses 90 plant species distributed across 81 genera and 47 families, including 41 spontaneous plant species from 38 genera and 20 families; (2) single and multiple tree layers green spaces exhibited higher overall species diversity, while the diversity of spontaneous plants did not differ significantly; (3) green spaces with single and multiple tree layers contained higher levels of chemical nutrients compared to zero-tree layer spaces; (4) as soil organic matter and water content increased, the dominance within groups decreased, diversity increased, and group distribution became more uniform; and (5) spontaneous plant diversity was positively correlated with increases in soil total potassium and water content, and leaf functional traits were primarily influenced by soil total potassium. In conclusion, road green spaces rich in vegetation types are more beneficial for soil and plant development. Soil water content and the availability of potassium nutrients are instrumental in promoting the growth and development of spontaneous plants.

Diffuse reflectance spectroscopy offers a rapid and cost-effective alternative to traditional soil property measurement. Advances in spectrometer technologies have enhanced portability and affordability, expanding their use for soil property estimation. However, developing training datasets for new spectrometers is expensive and time-consuming. Leveraging existing spectral datasets is crucial, yet variations between different spectrometers reduce prediction accuracy. To address this issue, we conducted model training and testing using Mississippi and Texas datasets from the USDA National Soil Survey Center–Kellogg Soil Survey Laboratory mid-infrared (MIR) spectral library (n = 2564) and regional dataset (n = 1521) across four Fourier-transform MIR spectrometers/modules. We assessed calibration transfer techniques using preprocessing (individual/combinations) and spectral/model transfer for predicting soil properties. Among preprocessing techniques, combination of first derivative with Savitzky–Golay, baseline correction (BC), standard normal variate (SNV), and combination of BC, SNV outperformed others, though no single approach was optimal for all properties. Spectral/model transfer techniques such as external parameter orthogonalization and spiking effectively harmonized predictions, while slope-bias correction, direct standardization, and piecewise direct standardization showed limited success. A combined approach of BC and SNV spiking significantly improved model performance across spectrometers/modules and soil properties. On average across all the soil properties, the mean R² improvement compared to models trained without calibration transfer was 0.354 when using the spectral library for training and regional dataset for testing, and 0.401 when using regional dataset for both training and testing. This study demonstrated that existing spectral datasets can be effectively used for new spectrometers with calibration transfer, allowing real-time and field-scale soil property measurement.

Soil salinization is a significant global environmental issue. Despite increased focus on the reclamation of salt-affected soil in recent years, the mechanisms that underlie reclamation-induced improvements in soil hydraulic properties have not been clarified. To explore how soil aggregation and pore structure contribute to these improvements, we conducted a 7-year reclamation experiment in a sodic soil and evaluated how changes in hydraulic properties corresponded to variations in soil structure across different stages of reclamation. Following the application of an inorganic calcium amendment, hydraulic conductivity decreased by 8.15%, and available water content increased by 9.46%. Hydraulic conductivity increased by 1527% and available water content increased by 6.92% with the application of organic calcium fertilizer. X-ray-computed tomography showed that, compared to the sodic wasteland, the number of soil node pores decreased by 37.73% under inorganic calcium amendment but increased by 52.73% under organic calcium fertilizer, indicating differential evolution of pore connectivity. However, changes in soil aggregation were similar under the two reclamation approaches. Partial least squares path modeling demonstrated that reclamation-induced reductions in soil sodicity and accumulation of soil nutrients and organic matter improved the soil pore structure (particularly the connected pore network), thereby enhancing soil hydraulic properties. This work advances understanding of how sodicity influences soil physical and hydraulic properties.

Soil health conditions can vary by inherent (climate, soil texture) and management (land use, practices) factors. A robust database to reference soil health conditions is a priority, particularly for soil metrics that vary by method. A survey of soil properties under 309 grassland fields and 29 farm woodlots on private farms was conducted across North Carolina. Classifying soil texture simply by sand concentration (kg kg⁻¹) into fine (<0.2), medium (0.2–0.5), and coarse (>0.5) categories effectively separated the magnitude of most soil health metrics, particularly between medium and coarse textures. Most populations of soil properties under grasslands did not differ from those of a previous land use survey on research stations in North Carolina and private farmland in Virginia. Some exceptions were greater Mehlich-3-extractable phosphorus (P), zinc (Zn), and copper (Cu) under private grasslands in North Carolina, suggesting greater prevalence of animal manure applications. Similarity in populations of soil properties between studies indicates that consistent interpretations could be made across the region. Most soil chemical, physical, biological, and biogeochemical properties were greater under grassland than under woodland, while basal soil respiration and total, particulate, and non-particulate organic carbon (C) were lower under grassland than under woodland. Soil health scores (0–1) using median values for each soil texture group were greater (p < 0.001) under grassland (0.54 ± 0.02) than under woodland (0.37 ± 0.02). This study confirms that populations of dynamic soil properties sorted by soil textural group were effective to assess soil health across a diversity of soil types within a similar environmental setting, such as the southeastern US.

Colloidal stability plays a critical role in regulating nutrients transport and contaminant mobility in paddy soils. This study systematically investigated the mineral composition, stability characteristics, and controlling factors of water-dispersible colloids across pedogenic horizons (Ap1, Ap2, Br, and Brs) in a representative Ultisol with over 200 years of cultivation history. Four colloidal size fractions (<0.1, 0.1–0.45, 0.45–1, and 1–5 µm) were characterized using scanning electron microscope and X-ray diffraction. Colloidal stability was quantified through critical coagulation concentration measurements in KH₂PO₄ and NaCl solutions (0–100 mg L⁻¹). Results show that: (1) smaller colloids (<0.1 µm) exhibited the highest stability due to its expandable minerals constituents and pronounced weathering features; (2) Colloidal stability showed significant positive correlations with surface-area-normalized carbon and nitrogen content, as well as total organic matter, while being negatively associated with amorphous aluminum oxide content; (3) Electrolyte effects followed concentrations-dependent thresholds, with Na⁺ (>80 mmol L⁻¹) inducing flocculation and H₂PO₄⁻ (20–80 mg L⁻¹) enhancing colloidal dispersion. These results provide fundamental insights into pedogenically-driven colloidal behavior and offer practical implications for optimizing nutrient management strategies in intensive paddy farming systems.

Microbial biomass (MB) plays a critical role in the soil nitrogen (N) cycle. However, its effect on nitrous oxide (N₂O) production, and how this is influenced by N availability and exogenous carbon (C) inputs, remains unknown. In this study, grassland soil (GS) and cropland soil (CS) originating from the same parent material but differing in soil matrix were selected. MB size was manipulated by preincubating soils with glucose. The soils with altered MB sizes were then amended with exogenous C sources, either ryegrass (Lolium perenne L.) residue or water-extracted ryegrass, which differed in C:N ratios (low and high, respectively), with or without N addition, to examine their effects on N₂O production. In the absence of exogenous C and N inputs, the increased MB led to a 105% and 18% increase in N₂O production in CS and GS, respectively. Among the GS treatments, combining low C:N ryegrass residues and N addition resulted in the greatest N₂O production, while in CS, high C:N water-extracted ryegrass and N addition induced the highest N₂O production. Furthermore, the CS with increased MB responded primarily to exogenous C inputs, while GS showed a greater sensitivity to N addition, particularly through shifts in microbial biomass N and inorganic N, which are key regulators of N₂O emissions. These findings highlight the importance of MB size in shaping N₂O emissions in response to external C or N inputs, and demonstrate how the stoichiometric traits of exogenous C sources interact with microbial and soil properties to drive N₂O production.

Stratified substrate systems (i.e., layering substrates of differing physiochemical properties within a container) can increase crop growth and quality by improving the profile hydraulic properties; however, no research has examined if these systems enhance gas supply to the rootzone. In this study, we used a one-chamber gas diffusion apparatus to understand how peat-based stratified systems (7:3 by vol. peat:perlite layered over unscreened bark; 1:1 depth layer ratio by vol.) influenced gas exchange when compared to a non-stratified control (100% of a container filled with 7:3 by vol. peat:perlite). We also examined if relative gas diffusivity (D_s/D₀) was modified for different rooting levels (0, 14, and 28 days of growth of a Helianthus annus Lemon Queen crop) and relative wetness of maximum water storage (<10%, ∼50%, and ∼75% of container capacity values). Crops grown in the stratified system generally exhibited more root growth compared to those grown in non-stratified systems, including longer roots and greater surface area and volume. The linear increase in rooting measured through time within treatments had negligible effects on D_s/D₀; however, D_s/D₀ varied with relative wetness for both substrate profiles. When moisture was present, stratified systems supplied the rhizosphere with oxygen faster than non-stratified systems. Stratified systems can (1) improve rootzone environments through reduced waterlogging, (2) better resupply oxygen, and (3) decrease peat inputs by nearly 50%.

Soil health is an expanding discipline with implications for research, policy, and agribusiness. A key soil health tenet is the integrated assessment of the three dimensions of physical, chemical, and biological properties. Yet, few studies have examined whether research meets this goal or differs from decades of soil quality work. This study evaluated how soil health and soil quality research assessed these dimensions under different management practices in California's agroecosystems. We mapped the ecosystem services linked to indicators within each dimension to understand the implications for multifunctional agroecosystems. We identified 43 articles using the term “soil quality” from 1976 until 2024 and 26 articles using “soil health,” the latter appearing for the first time in 2015, highlighting a recent growing interest. Cover crops dominated soil health studies (30%), whereas organic amendments and wastewater management were the most frequent practices for soil quality (31% and 24%, respectively). Almost 85% of soil health papers measured a biological component compared to 60% for soil quality, supporting the driver of the soil health discipline. Soil physical and chemical properties were less studied, meaning research on soil quality has been similar, if not more comprehensive than soil health (51% vs. 46%, respectively). Most indicators were associated with supporting soil fertility and nutrient cycling, highlighting the need for more attention on food production, soil carbon sequestration, and water regulation. Regardless of terminology, this review suggests that research has not comprehensively assessed soils. Integrated assessments are crucial for benefiting farmers and providing multiple ecosystem services for society.