Proceedings - Soil Science Society of America最新文献

Sulfate in soil is readily leached in humid tropical environments and sandy soils with low organic matter content. Elemental sulfur (ES), an alternative source of sulfur (S), requires microbial oxidation to sulfate (S-SO₄²⁻) to become available to plants. Due to its low solubility, ES oxidizes slowly, enabling a gradual S release. Two experiments evaluated the S oxidation dynamics in tropical soils using ES-based fertilizers. Five fertilizers were tested: ammonium sulfate (AS), UREA-ES14 (micronized elemental sulfur urea-based fertilizer 14) (micronized, 14.3% S), UREA-ES75 (micronized elemental sulfur urea-based fertilizer 75)-granulated (75% S), UREA-ES75-ground (75% S), and elemental sulfur pastille (ES pastille, 90% S), along with a control. The first assessed S oxidation rates over 180 days of incubation (13 samplings); the second analyzed S-SO₄²⁻ distribution in soil after simulated rainfall using polyvinyl chloride columns. In Experiment I, oxidation rates ranged from 22% to 32% for UREA-ES14, UREA-ES75-granulated, and UREA-ES75-ground. The ES pastille showed the lowest oxidation rate, ranging from 3% to 9%. In Experiment II, ES-based fertilizers retained higher S-SO₄²⁻ concentration in the upper soil layers, indicating lower leaching than AS. After simulated rainfall of 110 mm, 50%–55% of S-SO₄²⁻ from AS remained in the layer 0.00–0.05 m, compared to 58%–83% for ES-based fertilizers. The results suggest that the rate of ES oxidation is positively influenced by longer incubation periods and offers residual soil effects. However, the oxidation rate to S-SO₄²⁻ is limited and concentrated in soil surface layers, affecting long-term bioavailability to plants. ES-based fertilizers exhibited lower leaching potential, supporting ES uses as a slow release of S in tropical soils.

Climate-smart agriculture (CSA) practices can support carbon (C) sequestration and microbial communities, yet field-scale studies about their integrated benefits are limited. This study evaluated the integrated effects on soil health of a softwood pine-derived biochar (10 Mg ha⁻¹) and cover crop (cereal rye, Secale cereale L.) under a no-till soybean (Glycine max L.) system from 2022 to 2023. Treatments include no-till only, biochar only, cover crop only, biochar + cover crop, and conventional tillage without amendment. CSA had a significant effect on soil organic C (SOC; p < 0.0001) and bacteria phospholipid fatty acid (bacteria PLFA; p < 0.0001) in 2022 and 2023, and β-glucosidase (BG; p < 0.0001), N-acetyl-β-d-glucosaminidase (NAG; p = 0.0003), leucine aminopeptidase (p < 0.0001), and phosphatase (p = 0.0079) (pooled across years). In 2022, no-till, biochar, and biochar + cover crop increased SOC (12%–50%) compared to conventional tillage. SOC strongly correlated with total PLFA (R² = 0.81; p < 0.01), bacteria PLFA (R² = 0.88; p < 0.01), and Gram-positive bacteria PLFA (R² = 0.90; p < 0.01). Cereal rye had significantly higher SOCs (+30% to +42%) than biochar, no-till, and biochar + cover crop. Applying biochar alone or with cereal rye significantly increased activities of C-acquisition (+108% and +131% BG, respectively) and N-acquisition enzymes (+184% and +58.8% NAG) compared to conventional tillage. On average, SOC declined by 13% across treatments in 2023, but integrating biochar with cereal rye appeared to stabilize SOC loss, potentially mitigating positive priming effects. Overall, these results suggest that integrating biochar with cereal rye under no-till can support soil health through synergies that promote enzyme activities, whereas integrating cereal rye with no-till can promote SOC storage.

Enhancing crop tolerance to water stress in acidic soils presents a significant problem for sustainable wheat production. This research investigates the combined application of lignin-based supplements and deficit irrigation techniques to improve soil quality, physiological performance, and water use efficiency (WUE) in wheat cultivation. This study systematically assessed the effects of five soil amendment treatments—no amendment (CO), calcium lignosulfonate (CL), CL combined with biochar (CL + B), CL combined with bioorganic fertilizer (CL + BOF), and a triple combination (CL + B + BOF)—applied under two regulated deficit irrigation regimes: DI90 (deficit irrigation at 90% field capacity, moderate stress) and DI60 (deficit irrigation at 60% field capacity, severe stress) on soil properties, root morphology, shoot physiology, and WUE in winter wheat. The results indicated that various soil amendment treatments (CL, CL + B, CL + BOF, and CL + B + BOF) can improve the soil properties and crop growth under both DI90 and DI60 regimes. Specifically, the integrated CL + B + BOF treatment produced the most significant improvements across a range of indicators. Under DI90, this treatment increased soil pH from 5.10 to 6.54, improved water-stable aggregates by 41%, and raised available nitrogen and phosphorus to 38.78 and 49.23 mg/kg, respectively. The root surface area and photosynthetic rate increased by 56% and more than threefold, while shoot biomass and WUE doubled compared to the control. Although the effects were less pronounced under DI60, CL + B + BOF still enhanced soil pH, aggregate stability, and root development, and increased grain yield, shoot biomass, and WUE by 163%, 113%, and 43%, respectively, over the control. These findings highlight that combining lignin-based amendments with regulated deficit irrigation offers a robust, sustainable strategy to improve soil health, optimize water use, and enhance wheat productivity in water-limited, acidic soils.

Tree thinning is a common practice in silvopastoral systems, but there is no standard percentage of thinning used by farmers. Moreover, it is unclear how the percentage of thinning affects soil chemical attributes throughout the soil profile and throughout the transect between eucalyptus lines. To address this gap, this study evaluated the effects of three percentages of eucalyptus thinning—0%, 50%, and 100%—on soil chemical attributes in a silvopastoral system in Brazil. The experimental design was a randomized block with a 3 × 4 factorial design comprising three treatments (thinning of 0%, 50%, or 100% of the eucalyptus trees) and four sampling positions relative to the eucalyptus line (0, 2.0, 4.0, and 6.0 m). Six years after eucalyptus thinning, soil samples were taken for chemical analysis and determination of fertility. Soil pH; total acidity pH 7.0 (H⁺ + Al³⁺); S-SO₄, P, K⁺, Ca²⁺, and Mg²⁺ contents; base saturation (BS); and cation exchange capacity were determined. Soil acidification was observed at depths of up to 0.2 m in the 0% thinning treatment, accompanied by a decrease in Al³⁺ content in the 0.6–1.0 m layer at 0 and 2.0 m from the line and an increase in S content in the 0.2–1.0 m layer at 4.0 and 6.0 m from the line. Under 50% thinning, BS and K⁺ and P contents increased, while 100% thinning increased pH and Mg²⁺ and K⁺ contents and decreased total acidity and P, S, and Ca²⁺ contents. The decomposition of accumulated plant material and of eucalyptus roots acidified the soil at 0 and 2.0 m from the line compared with 4.0 and 6.0 m from the line, decreasing pH and K⁺, Ca²⁺, and Mg²⁺ contents and increasing total acidity and Al³⁺ content. The decreases in K⁺, Ca²⁺, and Mg²⁺ contents also reflect the uptake of these nutrients by eucalyptus. These results can be used to guide improved practices for managing soil chemical fertility and the most appropriate thinning percentage in silvopastoral systems.

Anion exchange membranes (AEMs) are widely used to assess soil phosphorus (P) cycling. However, the routine reuse of AEM for soil extractions may impact the surface properties of AEM and thus phosphate-P exchange. We evaluated changes in AEM surface morphology, chemical composition, and phosphate-P exchange capacity after varying degrees of use: never, lightly (20–30 extractions), and intensively (>100 extractions). Scanning electron microscopy and elemental analysis revealed increased surface roughness and accumulation of metal-containing particles (e.g., Al and Fe) on reused AEMs compared to never used AEMs. Fourier-transform infrared (FTIR) spectroscopy corroborated the presence of Fe/Al-based minerals on the surface of reused AEM. Phosphate-P exchange capacity increased with AEM reuse: +24% for lightly used and +95% for intensively used AEM relative to never used AEM. Kinetic experiments revealed phosphate-P exchange rate increased with AEM reuse, suggesting that soil-derived coatings provided additional binding sites. Regardless of usage degree, however, AEM showed reduced phosphate-P exchange in the presence of competing anions (i.e., chloride, nitrate, and sulfate), indicating that the polymeric head groups remained critical for exchange reactions on reused AEM. Further research should investigate the degree to which specific soil minerals may modify AEM and the extraction of phosphate-P.

Martian surface minerals have abundant perchlorate salts existing in both solid and liquid phases that will impair agricultural operations, biological life-support systems, and in situ resource utilization due to their toxicity. Thus, simple and effective perchlorate remediation strategies will be necessary for the successful use of Martian surface minerals as a plant growth substrate among other uses. The low thermal decomposition, high solubility, reluctant nature to sorb to minerals, and biological metabolism of perchlorate offer attractive solutions for remediation. Using JSC Mars-1 simulant spiked with varying concentrations (1–10 g kg⁻¹) of magnesium perchlorate, it was found that a 470°C thermal decomposition in a furnace led to near elimination of perchlorate. Additionally, three leaching events at a 1:5 (solid:liquid) ratio followed by distillation of leachate also eliminated magnesium perchlorate from simulated Martian surface minerals and leachate water. For biological perchlorate reduction, a native soil microbiome was bio-prospected from agricultural fields. A directed evolution of the native soil microbiome proved successful in increasing perchlorate reduction rates from 35% to 52%. The directed evolution microbiome was compared to pure cultures of six bacteria and one fungus known to be capable of perchlorate reduction, with the directed evolution microbiome having similar perchlorate reduction rates to the pure cultures. Overall, the thermal decomposition and leaching with distillation approaches were considered low technology, highly effective options to remediate perchlorate from Martian surface minerals, although their energy inputs and alteration of soils may be undesirable in certain circumstances.

Tidal marsh soils have some of the largest carbon stocks of any ecosystem, yet uncertainty remains about the best approach to quantify these C stocks. We tested whether separating tidal marshes into pedogeomorphic units (PGUs) could improve regional-scale blue C accounting in two separate regions on the Atlantic coast: southern New England (NE) and northern Southeast (SE). We identified four dominant PGUs in each region and measured soil C stocks in 105 pedons to 2 m. Average carbon stocks among PGUs ranged from 84 to 430 and 140 to 790 Mg C ha⁻¹ for the 1- and 2-m sampling depths, respectively. We found significant differences in C stocks among PGUs (p < 0.0001) in each region with NE marshes having significantly higher per area C stocks compared to SE at both sampling depths. A common benchmark in blue C inventories is to sample to 1 m, but we found that on average 40% of the C within 2 m occurred in the lower meter, underscoring the need to sample to 2 m. Recent studies suggest that until a better approach is identified, a single value of 27 kg C m⁻³ be used for C accounting in tidal marshes. On average, this overestimated C stocks in the SE by 37% and underestimated in the NE by 35%. Our findings emphasize that C stocks in tidal marshes can vary greatly by geomorphic setting and suggest a pedogeomorphic framework with sampling to at least 2 m offers an effective approach for future tidal marsh C accounting.

This study evaluated the effects of mixed cover crop (CC) species on biomass production, nitrogen (N) uptake, soil N dynamics, and crop performance in a rainfed corn (Zea mays L.)–soybean (Glycine max L.) and continuous corn system in eastern Nebraska from 2021 to 2023. Four treatments—cereal rye, mixture-1 (cereal rye, winter pea, and triticale), mixture-2 (barley, Kura clover, and canola), and a no-cover control—were fall-seeded each year. Due to below-average precipitation, CC establishment was poor, resulting in low biomass (<0.2 Mg ha⁻¹) and modest N uptake (4.1 kg N ha⁻¹). Consequently, CC species did not significantly affect spring soil nitrate (NO₃–N) or ammonium (NH₄–N) concentrations across crop phases. Cropping year showed a strong influence on soil NH₄–N, with concentrations markedly higher in 2023 than in 2022. Cereal rye exhibited a higher residue C:N ratio and contributed to increased residual fall soil NO₃–N and NH₄–N in upper soil layers (0–15 cm), suggesting slow biomass decomposition and potential late-season N release. Neither crop rotation nor CC treatment significantly influenced corn or soybean yields, consistent with limited CC biomass production. Favorable weather in 2023 improved corn N uptake and yield. Corn–soybean rotation enhanced corn vigor (normalized difference vegetation index [NDVI]), and CC mixtures improved soybean NDVI over cereal rye. Grain yields correlated with NDVI but not with CC biomass or N uptake, highlighting the limitations of CCs under dryland conditions. Overall, drought-limited CC growth constrained N scavenging and yield benefits, underscoring the importance of environment-specific CC management in rainfed agroecosystems.

Raw oil palm (Elaeis guineensis Jacq.) empty fruit bunch (EFB) and its biochar derivative (EFB_BC) share some properties but differ in ways that influence soil characteristics. Yet, relatively limited research exists on their effects in low-fertility, structurally poor tropical soils. This study evaluated the impact of EFB applied as organic amendment (EFB_OA) and EFB_BC on soil chemical properties such as pH, organic carbon (SOC), electrical conductivity, cation exchange capacity (CEC), specific surface area (SSA), and physical properties comprising soil water retention (SWR), gas transport, and pore characteristics in a tropical sandy clay loam Acrisol. Treatments included EFB_OA and EFB_BC applied at rates of 20 and 40 t ha⁻¹, along with a unamended control (0 t ha⁻¹). Twenty-one months post-application, intact and disturbed soil samples were analyzed. Both amendments, especially at 40 t ha⁻¹, significantly (p < 0.05) reduced bulk density and increased pH, SOC, CEC, and SSA compared to the control. SOC was highest under the 40 t ha⁻¹ EFB_BC treatment. SWR between matric potentials of −10 and −50 hPa was significantly increased by the EFB_BC at 40 t ha⁻¹. Neither of the amendments significantly affected available water content. At 40 t ha⁻¹, EFB_BC increased air-filled porosity and relative gas diffusivity by 40%–60% and 67%–200%, respectively; EFB_OA increases ranged from 20%–71% and 54%–67% compared to the control. Neither treatment significantly altered soil pore structure complexity. The enhancements in SOC and related soil properties suggest these amendments have the potential to improve water and gas dynamics in weathered tropical soils. Long-term effects, however, require further investigation beyond 21 months.

Soil organic carbon (SOC) in grasslands plays a central role in global carbon cycling, yet how long-term grazing intensity (GI) and soil texture interact to affect SOC fractions remains unclear. We evaluated SOC partitioning into particulate organic matter carbon (POM-C) and mineral-associated organic matter carbon (MAOM-C) after more than 80 years of cattle grazing in a semiarid mixed-grass prairie in South Dakota. Soils (0–30 cm) were sampled across six pastures managed at high, medium, and low grazing intensities and stratified by texture (clay loam vs. silty clay). Bayesian mixed-effects models accounting for pasture-level variation revealed that while GI did not significantly affect MAOM-C stocks, surface POM-C (0–7.5 cm) was significantly higher under high and medium grazing in clay loam soils, with no significant grazing effects observed in silty clay soils. Across depths, POM:MAOM ratios were elevated in coarser soils and under heavier grazing, suggesting greater POM-C accrual but also increased vulnerability to loss. Correlations showed only modest coupling (r ≈ 0.3, p < 0.001) between POM-C and MAOM-C, underscoring that these pools respond to distinct processes. Overall, our findings indicate that soil texture strongly modulates grazing effects on carbon fractions, with coarse-textured soils favoring POM accumulation and finer soils maintaining more stable MAOM stocks. These results highlight the importance of accounting for soil physical context when evaluating grazing as a tool for enhancing grassland carbon sequestration.