Proceedings - Soil Science Society of America最新文献

Direct measurements of free-living nitrogen fixation (FLNF) using ¹⁵N-labeled dinitrogen (¹⁵N₂) have been complicated by a lack of standardization regarding soil sampling and storage, and because key incubation parameters have yet to be systematically optimized. With the aim of developing a standardized protocol for laboratory assay of carbon (C)-stimulated FLNF, studies with four Illinois soils were conducted with respect to sampling depth, storage condition and period, surface exposure, moisture content, C source and pH, phosphorus (P) amendment, and incubation period. Among the major findings, diazotrophic activity was greatest with surface (0−7.5 cm) sampling, and storage effects were minimized when field-moist samples were kept at room temperature (25°C) or in a refrigerator (5°C) for ≤1 day with or without sieving (<2 mm). In the presence of exogenous C (4 mg C g⁻¹ dry soil), the rate of ¹⁵N₂ fixation was maximized at ≥200% water-holding capacity, with a 3-day incubation period, and by increasing atmospheric exposure with the use of a shallow soil container. A simulated corn (Zea mays L.) root exudate was identified as the optimal C source, regardless of a divergent preference observed for soil samples collected before and after a 6-month interval. By standardizing several key parameters pertinent to the measurement of C-stimulated FLNF, the work reported can help facilitate research to define the ecological importance and agricultural potential of a process that has largely been unexplored in the soil N cycle.

Integrating cover crops into conventional cropping systems can improve soil health, but field management, soil type, and climate can limit the rate of improvements. This study evaluated the effects of cereal rye (Secale cereale) cover crops on soil organic carbon (SOC) content and physical properties in a no-till, corn–soybean rotation on a poorly structured silt loam in southeastern Indiana. An earlier assessment of this trial found cover crops had increased aggregate stability after just 4 years but had no significant effect on bulk density (BD), water dynamics, or SOC. Revisiting this trial after an additional 6 years, we observed significant improvements across multiple soil health indicators. Cover crops increased SOC by 7.5% and total nitrogen by 12.9%, alongside improvements in BD (−2.9%) and water holding capacity (+8.6%). Aeration porosity was significantly enhanced (+7.7% at 0–10 cm, +9.0% at 10–20 cm, and +30.1% at 20–40 cm), indicating potential improvements in water infiltration. Aggregate stability remained a strong indicator of cover crop benefits, higher by 33% in the top 10 cm and by 35% at 10–20 cm as compared to no cover plots. These results align with findings from similar long-term trials and underscore how aggregate stability may be a valuable early predictor of broader improvements. Our findings support cereal rye as an effective strategy to enhance soil health and resilience in Midwestern no-till corn-soybean systems.

The Northeast Region Phosphorus Index (NR P-index) is a risk assessment tool that evaluates phosphorus (P) loss potential using soil test P (STP) concentrations, transport factors, and management practices. It informs whole-farm P strategies by guiding site-specific manure application decisions. This study aimed to (1) evaluate the implications of grid-based versus whole-field STP concentrations on P management implications according to the NR P-index, and (2) examine if different grid sizes impact NR P-index-based management implications. Soil samples were collected from 20 corn (Zea mays L.) fields across six farms in New York, each with varying STP concentrations, and analyzed at three grid resolutions (0.2, 0.5, and 1.0 ha). Grid sampling allowed for more precise P management in fields with moderate STP concentrations (20–80 mg kg⁻¹), through identification of areas with higher or lower P-index score compared to whole-field assessment. For fields with STP concentrations in the agronomic range (<20 mg kg⁻¹ Morgan P) or excessive levels (>80 mg kg⁻¹ Morgan P), whole-field assessments can be used to inform P recommendations. Grid sizes finer than 1.0 ha did not impact the management implications, indicating limited benefit from higher spatial resolution when STP concentrations are largely uniform or fall within a single P-index category. These findings suggest that grid sampling for P-index assessment was most effective for these fields with moderate STP concentrations and P-index scores, allowing for more targeted P management.

Soil detachment capacity (D_c) is a key parameter for characterizing the soil erosion process. Polyacrylamide (PAM) mitigates soil erosion, but the mechanism by which it acts on soil–rock mixtures is unclear. This study investigated the impact of applying PAM on detachment of soil–rock mixtures and predicted D_c using machine learning models. Small-sample scouring tests were conducted in a flume with a 30° slope, under flow discharges of 4, 8, 12, 16, and 24 L·min⁻¹; gravel content of 0%, 10%, 30%, 50%, and 70%; and PAM (anionic type, molecular weight 12 million, degree of hydrolysis 20%) application rates of 0, 1, 2, 3, 4, and 5 g·m⁻². When flow discharge was lower than 16 L·min⁻¹, the best D_c inhibition effect was achieved by applying 4 g·m⁻² PAM rate. From 16–24 L·min⁻¹, the optimal application rate of PAM for D_c inhibition varied according to gravel content: 3 g·m⁻² for gravel content of <50% and 4 g·m⁻² for gravel content of 50%–70%. PAM primarily influenced D_c indirectly by enhancing shear strength, but as gravel content increased, PAM effect on shear strength reduced. At 30% gravel content, the soil–rock mixture was more stable, and D_c remained consistently low. The extreme gradient boosting model trained using four parameters (PAM application rate, gravel content, shear strength, and stream power) outperformed multiple regression equations when used to predict D_c.

For a degraded soil it is assumed that improvements in key physical-hydraulic properties occur at an optimum superabsorbent polymer (SAP) application rate, following repeated wetting and drying cycles. A column experiment was carried out in a shade house (Ceará State, Brazil), following a completely randomized design, in a 6 × 4 factorial scheme in which six SAP application rates (0—control, 0.15, 0.30, 0.60, 1.20, and 2.40 g kg⁻¹) were incorporated into a sandy loam soil and subjected to four numbers of wetting and drying cycles (one, three, six, and nine cycles), with three replications. Soil bulk density, total porosity, macroporosity and microporosity, degree of flocculation, plant available water, and pore distribution by size were evaluated. After six wetting and drying cycles, the highest SAP rate reduced soil bulk density by 4%–9% compared to the control. At an SAP application rate of 1.2 g kg⁻¹ the degree of flocculation increased by 25%, mainly after six wet and drying cycles. From the rate of 0.15 g kg⁻¹ SAP onward, there was a 20% reduction in macroporosity and a 28% increase in microporosity, increasing total porosity, particularly after six cycles. SAP rates ranging from 0.15 to 0.6 g kg⁻¹ increased available water by 12%–33%, while the highest polymer rate increased available water by 40%–50% compared to the control. This increase in soil available water is of strategic importance for water use efficiency, crop yields, and restoration activities in degraded dryland sandy soils.

Agricultural application of sludge has become an increasingly appealing and sustainable approach worldwide. Hence, assessing the risk of sludge application is essential for informed decision-making regarding its use in agriculture. This study primarily evaluated the ecological risks of farmland soil and the human health risks via dietary intake under sludge compost application in maize (Zea mays L.) cultivation. Field trials were conducted with different ratios of sludge compost and chemical fertilizer, including single application of fertilizer (S0) as the control, sludge compost based on fertilizer nitrogen 20% + 80% fertilizer nitrogen (S1), sludge compost based on fertilizer nitrogen 50% + 50% fertilizer nitrogen (S2), sludge compost based on fertilizer nitrogen 100% (S3), and sludge compost based on fertilizer nitrogen 200% (S4). The potential ecological risk assessment (R) of soil potentially toxic elements was characterized as a slight risk level except for treatment S4, which had an R value of 164.44 (greater than 150, indicating a moderate risk level). The heavy metal content in maize grains increased with the application rate of sludge, but it did not exceed the maximum limits for contaminants in cereals (GB2762-2017). Monte Carlo simulation was applied to estimate the total cancer risk (TCR) and health risk index for combined contamination with multiple potentially toxic elements (HI) values for both adults and children via the ingestion pathway, and HI value for adults ranged from 0.10 to 0.86, indicating low risk as values were below the reference value of 1, but the HI value slightly exceeded the safe levels for children (1.36–2.42). The TCR values for both adults (4 × 10⁻⁴ to 3 × 10⁻³) and children (3.9 × 10⁻³ to 6.1 × 10⁻³) exceed the safe range. This indicates that cultivating corn in farmland with excessive application of sludge compost poses health risks to humans, particularly to children. Therefore, it is necessary to conduct long-term risk assessment research on sludge application, especially the situation of excessive application of sludge compost targeting different crops and soil types.

Modern maize (Zea mays L.) production relies on intensive fertilization with synthetic N and generates massive amounts of residue C. The short-term effect of these inputs on N mineralization in two soils of contrasting N supply was studied by continuously monitoring CO₂ production during a 60-day laboratory incubation experiment that also involved periodic sampling for gross N mineralization and for determination of soil microbial biomass N (MBN) and protease and deaminase enzyme activities. Residue decomposition was promoted by the addition of either KNO₃ or (NH₄)₂SO₄ and was more rapid in the low- than high-N-supplying soil, whereas the opposite trend was observed for MBN and both enzyme activities. No consistent soil- or treatment-specific differences occurred in measuring gross N mineralization by ¹⁵N pool dilution. Because N is subject to microbial recycling, short-term incubations are unlikely to be effective for studying N mineralization stimulated by organic or mineral inputs.

Non-exchangeable potassium (Nex-K) released slowly from minerals is a key component of long-term K fertility of agricultural soils. Two extraction methods are widely used to determine soil Nex-K: the boiling nitric acid (HNO₃) method and the tetraphenylborate (TPB) method. However, it is unclear from which minerals the methods extract the Nex-K. The Nex-K was determined for 322 agricultural soils sampled across Japan using both methods. The major soil minerals, including three K-bearing minerals—trioctahedral micas (Micas[Tri]), dioctahedral micas (Micas[Di]), and potassium feldspar (K-feldspar)—were determined by X-ray powder diffraction (XRPD). The multiple regression analysis revealed that the boiling HNO₃ method extracts Nex-K mainly from Micas(Tri) and partly from K-feldspar, whereas the TPB method extracts Nex-K mainly from Micas(Di) and partly from Micas(Tri) and K-feldspar. The cluster analysis, based on the XRPD-based mineral content, revealed that the soils had at least three geological parent materials. The soils with granitic mineralogical characteristics had high Micas(Tri) and Nex-K contents, as determined by the boiling HNO₃ method. In conclusion, the mineralogy of the parent material influences the types and quantities of K-bearing minerals present in soil, thereby controlling the amount of Nex-K and its extractability by different methods. This understanding allows for the estimation of long-term K fertility of agricultural soils.

Particle size is a key factor in shaping water and air retention properties and drainage capacity of growing media. Thus, manufactured growing media are made of screened, crushed, or sieved raw materials whose particle sizes are adapted to cropping objectives. The relationships between the particle size distribution of the growing media constituents and the resulting structure are, however, not well known, which requires better understanding of particle arrangement and its change with water upon shrinkage. A proper characterization of the structure would help to guide substrate manufacturing, which is inherently complex due to the use of various materials made up of heterogeneous particles in terms of size and shape. To this aim, we analyzed the shrinkage of white and black peats, coir, pine bark and wood fiber, raw material, and derived particle size fractions extracted by sieving. Hyprop systems coupled to linear vertical displacement transducers were used to determine the shrinkage curves. The dual porosity shrinkage XP model (XP model) was used to analyze the hydrostructural behavior of the different growing media constituents. The possible distinction of interparticle and intraparticle pores, based on the dual pore system assumption of the shrinkage model, was discussed. Interparticle porosity volume represented the major part of the total porosity, whatever the materials and particle size fractions. Greater volume shrinkage of interparticle porosity was observed for the smaller particle size fractions of materials. Conversely, intraparticle porosity volume shrinkage is of the same magnitude for all particle size fractions. The use of the XP model to study growing media is relevant, although no residual domain on the shrinkage curves was observed. This work revealed that particle arrangement and physical behaviors during drying of materials depend on the nature of constituents but also highly on particle size fraction. These results provide a complementary approach for characterizing the pore functional properties of growing media.

The intensification of global agriculture has led to excessive fertilizer use, posing significant challenges to sustainable agricultural development. Organic fertilizers, rich in organic matter, improve soil structure by enhancing aeration and water retention, making them widely adopted for cultivating economic crops such as tobacco. Despite the rich organic matter content of tobacco stalks, their natural decomposition can contribute to long-term soil acidification, resulting in their underutilization as organic fertilizers. Here, the present study conducted field experiments to assess the feasibility of using composted tobacco (Nicotiana tabacum L. ‘CB-1′) stalks to enhance tobacco production. The analysis focused on soil nutrient levels, plant agronomic traits, microbial community composition and function, and associated production costs, offering a comprehensive evaluation of this approach's potential to improve sustainability in tobacco cultivation. As a results, tobacco stalk compost (T2) significantly elevated soil pH and nitrogen levels compared to traditional organic fertilizers (T1). Agronomic assessments revealed superior growth performance in T2, with single-leaf area increasing by 11.0% compared to T1, respectively. Economic output value analysis indicated that T2 achieved 13.5% higher profitability than T1. Microbial community analysis showed enhanced diversity and stability under compost treatment, accompanied by proliferation of unique taxa and increased abundance of microbiome involved in nitrogen and sulfur cycling. Additionally, T2 exhibited greater cost-effectiveness, reducing production costs by 171.1 Chinese yuan (RMB)/t compared to T1. Overall, our findings demonstrate that T2 not only improves soil ecological health and crop productivity but also serves as an economically viable alternative to T1.