Proceedings - Soil Science Society of America最新文献

Agriculture is being called upon to increase carbon (C) storage in soils to reduce greenhouse gas (GHG) accumulation in the atmosphere. Cropping systems research can be used to support GHG mitigation efforts, but we must quantify land management impacts using appropriate assumptions and unambiguous methods. Soil C sequestration is considered temporary because it can be re-emitted as carbon dioxide (CO₂) if the effecting practice is not maintained and/or the soil–plant system is disturbed, for example, as the result of changing climate. Because of this, the climate benefit of soil C sequestration depends on the time that C is held out of the atmosphere. When assessing the net GHG impact of management practices, soil C storage is often aggregated with non-CO₂ (N₂O and CH₄) emissions after converting all components to CO₂ equivalents (CO₂e) and assuming a given time horizon (TH), in what is known as stock change accounting. However, such analyses do not consider potential re-emission of soil C or apply consistent assumptions about time horizons. Here, we demonstrate that tonne-year accounting provides a more conservative estimate of the emissions offsetting potential of soil C storage compared to stock change accounting. Tonne-year accounting can be used to reconcile differences in the context and timeframes of soil C sequestration and non-CO₂ GHG emissions. The approach can be applied post hoc to commonly observed cropping systems data to estimate GHG emissions offsets associated with agricultural land management over given THs and with more clearly defined assumptions.

Soil hydraulic and physical properties can be influenced by various land management practices, and they determine water movement and storage within the vadose zone, with both agronomic and environmental effects. The objective of this study was to evaluate the effects of two such practices (no-till [NT] and cover crops [CCs]) on soil hydraulic (e.g., saturated hydraulic conductivity [K_sat], and water retention) and physical (e.g., bulk density [BD], pore size distribution, air-filled pore spaces [AFPSs], and water-filled pore spaces [WFPSs]) properties. The CCs used included crimson clover (Trifolium incarnatum L.), hairy vetch (Vicia villosa Roth.), winter peas (Lathyrus hirsutus L.), oats (Avena sativa), winter wheat (Triticum aestivum L.), triticale (Triticale hexaploide Lart.), flax (Linum usitassimum L.), and barley (Hordeum vulgare L.). Soil samples were collected and analyzed during 2021 and 2022 right before CC termination at 0- to 10-cm, 10- to 20-cm, and 20- to 30-cm depths. Results showed that, during 2021 and 2022, BD was 18% and 14% higher, respectively, under NC compared with CC management, while K_sat was 2.2 and 1.9 times higher, respectively, under CC compared with NC management. Further, the non-capillary pores were significantly (p ≥ 0.05) higher under CC compared with NC management during both years of study. As a result, the majority of the total pores under CCs were filled with air, while the majority of total pores under NC management were filled with water. Therefore, this CC mix may be useful in lengthening the growing period during wet seasons by increasing air-filled pore spaces.

Soil and water conservation and protection are of great importance to China, as the source of the Pearl and Xiang Rivers, and the main rare earth mining area, the ecology of Dongjiang River Basin, is very fragile. In this paper, the Chinese soil loss equation and the Geodetector method are used to analyze the spatial and temporal patterns and the impact factors of soil erosion in this area from 2016 to 2020. The results show that (1) Soil erosion intensity in the Dongjiang River Basin from 2016 to 2020 is mainly mild, with the soil erosion intensity in the Dongjiang River Basin in 2016 being the largest in five years. (2) The erosion modulus shows an increasing trend with the increase of slope. In terms of vegetation, when the vegetation cover is <30%, the soil erosion modulus is the largest, which is easy to induce soil erosion. When the vegetation cover is >60%, the soil erosion modulus is the smallest, which effectively slows down the occurrence of soil erosion. Rainfall is proportional to the soil erosion modulus and soil erosion. (3) The results of Geodetector indicate that the single factor sizes are land use > vegetation > slope > precipitation, and interaction factors all show a nonlinear enhancement. (4) The proper allocation of land use types, the prohibition of steep slopes for cultivation, and the restoration of forestry can effectively prevent and control soil erosion in the area.

Manganese (Mn) oxide-coated sand has been suggested as an amendment for scrubbing metals in water filtration beds and also as a less concentrated medium for uniformly amending soils with Mn oxides in mesocosm scale studies. Earlier work at the lab bench scale, using potassium permanganate (KMnO₄) solutions that were reduced with sodium (Na) lactate, resulted in sands coated with about 0.13% Mn. The goal of this project was to increase the amount of Mn oxide that could be coated on sand to make it a more useful amendment and also to attempt to scale up the procedure to produce larger (kg) quantities of coated sand. Titration experiments examined the effects of (1) varying the molar ratio of Na lactate to KMnO₄, (2) varying the rate at which the titration was accomplished, and (3) varying the concentration (molarity) of the original KMnO₄ solution. The results of this work led to an optimal approach utilizing 0.32 M KMnO₄ solution that was titrated to a final lactate:permanganate ratio of ∼1.1 with 10% of the lactate being added every 10 min while the suspension was being stirred. The proportion of sand to an initial solution was also increased 5–20 fold to between 50 and 200 g per 100 mL of solution. Applying this method and using a large 20- to 30-L reaction vessel yields sands coated with up to 0.7% Mn in batches 5–10 kg is size, which could be useful as an amendment in mesocosm scale studies, or as a component of treatment filter beds. The examination of various size fractions of the coated sands demonstrated that more Mn was coated on finer sand fractions, which appears to be a function of the particle surface area available for the coating of Mn oxides, and at a rate of 0.3–0.5 µg Mn mm⁻² of the particle surface.

Incorporating large amounts of woody biomass into soil, such as in whole orchard recycling (WOR), can promote carbon sequestration, nutrient recycling, and ecosystem health in agricultural fields. Yet uncertainty regarding the effects of WOR on soil carbon (C) and nitrogen (N) dynamics influences management decisions. The objective of this research was to evaluate the effects of woodchip (WC) size and interaction with N fertilization on carbon dioxide (CO₂) and nitrous oxide (N₂O) emissions. An 8-month incubation experiment incorporating WC (4% w/w, equivalent to ∼40 tons per acre) in four sieved sizes (0.2–1.6, 1.6–3.2, 3.2–6.4, and 6.4–12.7 mm) with and without N applications was conducted. All treatments with WC showed that CO₂ emission peaked within the first week, then decreased drastically afterward. The CO₂ peak delayed as the peak value decreased (WC size increased). The finest WC (<1.6 mm) yielded the lowest total CO₂ emissions and resulted in the greatest increase in soil C at the end of incubation. Nitrogen application reduced total CO₂ emissions by 1% in the smallest WC size and by 8%–9% for those larger than 1.6 mm. The N₂O emissions spiked following each fertilizer application with lowest total emissions from the smallest WC size, suggesting substantial N immobilization. The results imply that larger WC sizes can delay C mineralization and reduce initial N immobilization risks, but the smallest WC size may have stabilized and increased soil organic carbon. This research increased our understanding on WC mineralization that can be used in WOR management.

Using manure appropriately may enhance organic carbon and hydro-physical properties while avoiding the negative impact on the environment. However, how manure impacts soils, especially at lower depths, is still not well studied. Therefore, the objective of this study was to assess the impact of different manure and inorganic fertilizer application rates on soil profile organic carbon and hydro-physical properties under corn (Zea mays L.)–soybean (Glycine max L.)–spring wheat (Triticum aestivum L.) rotation at Beresford (established in 2003) and Brookings (established in 2008) sites in South Dakota. The treatments included low manure (LM), medium manure (MM), high manure (HM), medium fertilizer (MF), high fertilizer (HF), and control (CK). Four replicated intact soil cores were collected from all the treatments at 0- to 10-cm, 10- to 20-cm, 20- to 30-cm, and 30- to 40-cm depths. Considering treatments by depth interactions, the LM and MM decreased bulk density (ρ_b) by 6.9%–22.1%, as compared to the CK at 0–30 cm for either site. The HM decreased ρ_b by 16.4%–24.7%, as compared to the HF at 30–40 cm for either site. On observing treatment as the main effect, the MM and HM increased the soil water retention (SWR) at 0 and −5 kPa compared to MF, HF, and CK in Brookings, and the MM increased the SWR at −30 kPa as compared to the MF in Beresford at 0- to 40-cm depths. The data suggest that continuous manure application may enhance organic carbon and hydro-physical properties at lower depths. Therefore, this study concluded that long-term manure application showed greater improvements when compared to long-term application of inorganic fertilizer alone. It can improve hydro-physical properties, thereby stabilizing the soil structure and improving water retention at lower depths.

This study aimed to evaluate the effects of water salinity and sodicity on the least limiting water range (LLWR) of two clay loam and sandy loam soils. The undisturbed soil samples were subjected to different water qualities, including three levels of sodium adsorption ratio (SAR, 1, 5, and 12) and electrical conductivity (EC, 1, 6, and 10 dS m⁻¹). Our findings indicate that increasing EC at each SAR led to greater soil water retention. This was attributed to salinity affecting pore size distribution toward smaller pores by altering the diffuse double layer and causing soil particle flocculation. With increasing SAR levels at each EC level, soil water content at the wilting point also rose due to structural changes, clay swelling, and dispersion, resulting in more micropores and increased adsorptive surfaces in the soil. Additionally, soil volumetric water content at a 10% air-filled porosity decreased, while values at a critical penetration resistance of 2 MPa increased with higher bulk density across all treatments. The LLWR showed a negative correlation with bulk density in clay loam soil across all SAR and EC treatments. The LLWR increased with higher water EC but decreased with increasing water SAR. The highest LLWR was observed at SAR = 1 and EC = 10 dS m⁻¹, while the lowest occurred at SAR = 12 and EC = 1 dS m⁻¹. The results revealed that elevated values of SAR in irrigation water reduced soil water accessibility for plants. However, as irrigation water salinity increased, the detrimental effects of SAR diminished.

The visual evaluation of soil structure (VESS) is an affordable and easy-to-use method for assessing soil quality that could help in the early detection of soil quality changes in pasturelands of less developed countries where ranchers cannot afford quantitative soil studies. Here, we assessed the soil quality of three pasture areas in the Colombian Amazon region using the VESS method and tested its suitability through a correlation analysis with key physical and biochemical soil indicators of quality measured at the same study locations. Moreover, by integrating all assessed soil indicators, we determined a soil quality index (SQI) to correlate with VESS scores. A forest area was used as a reference to evaluate changes in soil indicators and soil quality due to pasture use for >25 years. Our results revealed high VESS scores, indicating poor soil quality in pasture areas and suggesting a compaction process that starts at 6.5 cm soil depth, corroborated by increases in soil bulk density, soil resistance to penetration, and reduction in soil porosity. Soil C and N contents were 35% and 33% lower in pasture than forest. This same pattern was observed in the geometric mean of the enzymatic activity. The VESS scores were significantly correlated with most of physical and biochemical soil indicators and with the overall SQI, demonstrating the ability of VESS to integrate and reflect attributes related to the essential physical, chemical, and biological functioning of soils from the Colombian Amazon region, becoming a useful tool for detecting signs of soil quality degradation in pasturelands.