European Journal of Soil Science最新文献

Acid sulfate soils are found globally and have significant environmental impact as a source for metals and acidity to surrounding streams that can cause, for example, large-scale fish kills. In the face of changing climate and its effect on groundwater fluctuations, the environmental risk associated with these soils needs to be thoroughly investigated. This study examined the water-soluble concentrations of multiple elements from the oxidized, transition and reduced zones of acid sulfate soil profiles situated on the Swedish coastal plains. By comparing untreated (naturally oxidized in field) and incubated samples from these zones, we gain insight into the current and near-future mobilization and leaching of acidity and metals that occur in these soils. The results showed that concentrations of Al, Cd, Co, Mn, Ni, S and Zn mobilized from incubated samples were about an order of magnitude higher than from the untreated samples. Notably, the concentrations of mobilized Co, Mn and Ni were higher than released by 1 M HCl at the same sites, highlighting the particularly high mobility of these metals from in situ oxidation of acid sulfate soils. Conversely, Fe and Cu showed lower than expected water-soluble concentrations and were also low compared to the 1 M HCl-extractable element concentrations, likely due to rapid re-mobilization of secondary Fe minerals. Arsenic, Cr and Pb showed overall low water-soluble concentrations in both the incubated and untreated samples, consistent with these elements not being abundantly leached from acid sulfate soils. This observation was further supported by the retention of these metals in secondary Fe-mineral phases such as jarosite and schwertmannite as reported in previous studies. A strong correlation between acidity and near-total S indicated that S can serve as an indicator for the acidification risks associated with acid sulfate soil oxidation. Overall, the findings demonstrated that even a small lowering of the groundwater table can lead to significant mobilization of metals and acidity. This highlights the increased risks of environmental degradation in the face of climate change and intensified drainage operations and, thus, the need for proper management to reduce the risks.

Over the last decade, the fact that novel perspectives on various aspects of soils have remained strongly controversial long after they emerged, without any kind of consensus being reached about them, raises question about the underlying reasons for this phenomenon. The on-going debate on the usefulness of aggregates to describe the functions of soils illustrates some of the key aspects of that question. Similar debates on other soil-related issues also appear stalled, or have been for a long time and are only now moving forward. This might suggest a fundamental aversion to change, which when it gets overcome, only does so slowly. However, at the same time, somewhat surprisingly, researchers appear willing to quickly seize opportunities provided by new idea or novel perspectives on other topics. In that context, the objective of the present article is to analyse in detail what may cause such contrasting reactions to novelty. We consider, then ultimately dismiss, explanations based on how strongly or not novel perspectives have been actively promoted, on how access to suitable technology may impede or only slow down perspective shifts and on whether a recent theory of the ‘slowed canonical progress in large fields of science’ applies to the relatively small soil science community. Then, taking soil aggregates as a case in point, we come to realize that it is the extent to which a novel perspective mandates an interdisciplinary approach that determines whether or not it is adopted quickly. From that standpoint, we envisage a number of practical actions that could be taken to facilitate in the future the emergence in soil science of interdisciplinary research efforts, which we argue are absolutely essential to successfully tackle the enormous complexity of soils and to come up with satisfactory answers to the daunting environmental and food security problems we currently face in their management.

Cover crops are grown between two main crops to reduce periods of bare fallow. In highly diverse crop rotations, the lengths of break periods between two main crops vary highly over time and consequently the cover cropping management differs from year to year. Long-term field trials are thus of limited use because the same cover cropping approach only appears once in several years. This increases the need to better determine the immediate effects of different cover cropping strategies on soil properties. This study evaluated two cover cropping strategies and monitored the temporal development of several soil properties on six fields in Eastern Switzerland in the 9 months period between harvest of winter wheat and sowing of spring crops. The two tested strategies were (a) double cover cropping (DCC) where two cover crops mixtures were grown subsequently and shallowly (3 cm) incorporated into the topsoil and (b) permanent soil cover (PSC) with one grass-clover mixture, which was harvested and thus not incorporated into the soil. Soil samples at three different soil depths (0–5, 5–10 and 10–20 cm) were sampled four times in high spatial resolution and analysed using a combined approach of visible near infrared spectroscopy and conventional lab methods. Differences between the sampling times and field sites were stronger than effects of different treatments. For soil organic carbon (SOC), no significant difference was measured between treatments in 0–20 cm soil depth. Only when analysed per depth segment, the PSC treatment showed significantly higher SOC increase in 5–10 cm soil depth than the DCC treatment. This could be due to the longer soil cover and thereby associated longer root growth period in the PSC treatment, leading to higher below ground C inputs than in the DCC treatment. On the other hand, the DCC treatment showed generally higher increases in permanganate oxidizable carbon stocks (0–5 cm), microbial C (0–10 cm), microbial N (0–10 cm) and mineral N (0–10 cm) than the PSC treatment. We conclude that maximizing cover crop above ground biomass input by planting two cover crops (DCC) benefitted soil microorganisms on most fields but was less beneficial on SOC than permanent soil cover (PSC) in 5–10 cm soil depth.

Simple humus balance calculators were developed for farmers and consultants to determine the best crop rotation and amount of organic fertilizer required to improve soil quality and prevent nutrient leaching in croplands. Although the potential of these tools to infer the impact of different agricultural practices on soil organic carbon (SOC) dynamics in croplands is not well studied, they have been integrated in several farm-level climate or environmental impact assessment calculators. Here we examine the correlation between humus balance values estimated with two different tools developed in Germany/Central Europe and observed changes in SOC content at 14 long-term sites in Switzerland. The first tool was developed by the Association of German Agricultural Investigation and Research Institutes and is referred to as the VDLUFA. The humus balance calculator STAND is a descendent of the VDLUFA that accounts for pedoclimatic factors in Central Europe. Crop rotations were distinguished based on cultivation practice, whereby those with mixed fertilization were supplied with mineral fertilizer alone and in combination with organic materials, while those with organic fertilization include unfertilized and organic fertilizer treatments. An analysis of 133 short-term observations (i.e. individual crop rotations of five and 6-year duration) and 26 long-term observations (i.e. several crop rotations with a total duration of ≥10 years) showed that humus balance values (kg C ha⁻¹ year⁻¹) of short-term crop rotations were not or only poorly correlated with the observed change in SOC content (%) (R² = 0.06 in STAND and R² = 0.05 in VDLUFA for crop rotations with organic fertilization, and R² < 0.01 for crop rotations with mixed fertilization). The correlation did not improve when the humus balance values of long-term observations with mixed fertilization were compared with decadal SOC development (R² = 0.04 for STAND and R² = 0.06 for the VDLUFA). Stronger correlations were found only for long-term observations with organic fertilization (R² = 0.68 for STAND and R² = 0.64 for the VDLUFA). These findings underline that while the studied humus balance calculators are able to distinguish the effect of different fertilizers (organic vs. mineral) on a farm's humus supply on the longer term, neither are suited for predicting SOC trends over single crop rotations. Although this study was carried out in Switzerland, the results should apply to any region with temperate climate and similar soil properties.

The quantification of soil strength parameters is a crucial prerequisite for constructing physical models related to hydro-geophysical processes. However, due to ignoring soil spatial variability at different scales, traditional parameter assignment strategies, such as assigning values depending on land use classification or other classification systems, as well as those extrapolation and interpolation methods, are insufficient for physical process modelling. This work addressed this deficiency by proposing a method to derive stochastic soil strength parameters under hybrid machine learning (ML) models, taking into account the grain-size distribution (GSD) of soil with scaling invariance. The nonlinear connection between GSD parameters (derived from GSD curves, such as μ and D_c), moisture content, and soil shear strength parameters was fitted by the suggested hybrid ML model. An analysis of a case study revealed that: (i) the Multi-layer Perceptron optimized by the African Vulture Optimization Algorithm (AVOA) algorithm performs the best and can estimate the shear strength parameters of soil mass on vegetated slopes; (ii) all the selected ML models showed significant improvements in predictive performance after optimization with the AVOA, with R² scores increasing by 24.72% for Support Vector Regressor, 34.04% for eXtreme Gradient Boosting, and 35.53% for Multi-layer Perceptron; and (iii) soil cohesion has an increasing relationship with the GSD parameter μ, while soil internal friction angle has a negative correlation with the grain-size parameter D_c. The proposed methodology can give predictions of soil shear strength distribution parameters, providing parameter support for the physical modelling of surface process dynamics.

Despite a decrease in industrial nitrogen and sulfur deposition over recent decades, soil acidification remains a persistent challenge to European forest health, especially in regions of intense agriculture and urbanisation. Using topsoil eDNA metabarcoding and functional annotations from a sample of 49 plots (each 30 × 30 m) located in The Netherlands and Germany, we investigated the effect of severe acidification on bacterial taxonomic diversity under different forest types and explored potential functional implications for nutrient cycling. Furthermore, we assessed which soil parameters known to influence soil bacterial communities affect these acidophilic communities. Here, we are the first to demonstrate under natural conditions that soil bacterial diversity in extremely acidic soils (pH <4.5) continues to decline similarly across forest types as pH further decreases under intensifying human activity. Our results confirmed pH as the key driver of soil bacterial communities, even in extremely acidic soils. Ongoing severe acidification continues to reduce bacterial communities, favouring taxa adapted to extreme acidity and primarily involved in recalcitrant carbon-degradation compounds (e.g. cellulolysis potential = 0.78%–9.99%) while simultaneously diminishing taxa associated with nitrogen cycling (e.g. fixation potential = 6.72%–0.00%). Altogether, our findings indicate a further decline in bacterial diversity in already extremely acidic soils, likely disrupting nutrient cycling through changes in immobilisation and mineralisation processes. Our study highlights the continuous acidification of European temperate forests to extremely low pH levels, further disrupting forest ecosystem functioning. The significant reduction in bacterial diversity under such a severe acidification gradient, as demonstrated here, underscores the necessity to include severely acidified forests in conservation programmes and monitoring to prevent further degradation of European soils beyond repair.

Coastal wetland soils are frequently underlain by sulfidic materials. Sea level fluctuations can lead to oxidation of sulfidic materials in acid sulfate soils (ASS) and increased acidity which mobilises trace metals when water levels are low, and inundation of coastal wetland soils and reformation of sulfidic materials when water levels are high. We measured the effect of surface water level fluctuations in soils from coastal wetland sites under four different vegetation types: Apium gravedens (AG), Leptospermum lanigerum (LL), Phragmites australis (PA) and Paspalum distichum (PD) on an estuarine floodplain in southern Australia. We assessed effects of fluctuating water levels on reduced inorganic sulfur (RIS) in terms of acid volatile sulfide (AVS), chromium reducible sulfur (CRS) and trace metals (Fe, Al, Mn, Zn, Ni). Intact soil cores were incubated under dry, flooded and wet–dry cycle treatments of 14 days for a total of 56 days. The flooded treatment increased RIS concentrations in most depths in the AG, PA and PD sites. Lower CRS concentrations occurred in all sites in the dry treatment due to oxidation of sulfidic materials when the surface layer was exposed to lower water levels. CRS was positively correlated with SOC in all treatments. The highest net acidity occurred in the dry treatment and lowest occurred in the flooded treatment in most sites. Inundation with seawater caused SO₄²⁻ reduction and decreased soluble Fe in the PA and PD sites. General decreases in Al, Zn and Ni concentrations in flooded treatments may have been due to adsorption onto colloids or co-precipitation with slight increases in pH. SO₄²⁻ concentrations decreased in the LL, PA and PD sites in the flooded treatment due to reformation of pyrite. In general, accumulation of RIS in soils under different vegetation types following brackish water inundation varied according to vegetation type, which may be linked to differences in organic material input and particle size distribution. Geochemical characteristics reflected whether oxidation or reduction processes dominated at each site in the wet–dry cycle treatments, with oxidation dominating in the LL and PA sites and reduction dominating in the AG and PD sites. This is likely due to more readily decomposable organic matter forming sulfidic materials during short periods of inundation.

The non-Lambertian surface features varying particle size and discrete distribution, resulting in reflectance to be unevenly distributed in different directions. Mine soil with a high content of coarse particles and non-uniform particle distribution exhibits significant non-Lambertian properties on its surface. Consequently, not only vertical observation of the reflectance spectra but also multi-angle reflectance spectra are related to the physical and chemical properties (e.g. soil organic carbon, moisture content and particle size) of mine soil. Understanding the bidirectional reflectance distribution of mine soil with various particle sizes is essential for accurately estimating soil properties using spectroscopy. Current estimations of soil properties using spectroscopy mainly focus on vertical observations, overlooking the bidirectional reflectance characteristics. This study reports the bidirectional reflectance distribution of mine soil with various particle sizes. Furthermore, the performance of different bidirectional reflectance distribution function (BRDF) models in simulating the bidirectional reflectance of mine soil with various particle sizes was evaluated. Soil samples from three typical mine areas were collected and sieved into seven particle sizes ranging from 25 to 3500 μm. The bidirectional reflectance in the Vis–NIR wavelength region was measured in a laboratory using the Northeastern University bidirectional reflectance measurement system. The performance of five BRDF models (isotropic multiple scattering approximation, anisotropic multiple scattering approximation, H2008, H2012 and SOILSPECT) in modelling the bidirectional reflectance distribution of mine soil with different particle sizes was compared. Sobol's sensitivity indices were used to quantify the contributions of the parameters in the BRDF models. The results showed that (1) small mine soil particles (25 μm) exhibited greater reflectance than large particles (3500 μm). Large particles (3500 μm) exhibited backward scattering, whereas small particles (25 μm) exhibited extremely forward scattering characteristics because of the high silicon dioxide content; (2) the SOILSPECT model outperformed the other BRDF models in simulating the bidirectional reflectance of mine soil and had the smallest root mean square error (0.004–0.04); (3) the single-scattering albedo (ɷ) parameter had the greatest contribution in the SOILSPECT model. Four parameters in the phase function (b, b′, c and c′) effectively indicated the scattering behaviour of mine soil with different particle sizes. These findings improve our understanding of the scattering characteristics of mine soil with various particle sizes and can be used to improve the accuracy of extracting particle size and other soil properties from mine soil.

Biocrusts are a critical surface cover in global drylands, but knowledge about their influences on surface soil thermal properties are still lacking because it is quite challenging to make accurate thermal property measurements for biocrust layers, which are only millimetres thick. In this study, we repacked biocrust layers (moss- and cyanobacteria-dominated, respectively) that had the same material as the original intact biocrusts but was more homogeneous and thicker. The thermal conductivity (λ), heat capacity (C) and thermal diffusivity (k) of the repacked and intact biocrusts were measured by the heat pulse (HP) technique at different mass water contents (θ_m) and mass ratios (W_t), and the differences between repacked and intact biocrusts were analysed. Our results show that biocrusts substantially alter the thermal properties of the soil surface. The average λ of moss (0.37 W m⁻¹ K⁻¹) and cyanobacteria biocrusts (0.90 W m⁻¹ K⁻¹) were reduced by 63.0% and 10.3% compared with bare soil (1.00 W m⁻¹ K⁻¹), respectively. Edge effects including heat loss and water evaporation caused the λ and k of the biocrusts to be underestimated, but the C to be overestimated. The differences in thermal properties were significant (p <0.001), except for the differences in thermal conductivity between repacked and intact cyanobacteria biocrusts, which were not significant (p = 0.379). Specifically, in the volumetric water content (θ_v) range of 0 to 20%, the λ and k of the repacked moss biocrusts were underestimated by 59.1% and 61.8%, respectively, and the C was overestimated by 23.9% compared with the intact moss biocrusts. The λ and k of the repacked cyanobacteria biocrusts were underestimated by 15.8% and 79.2%, respectively, and the C was overestimated by 34.8% compared with the intact cyanobacteria biocrusts at the θ_v range of 0 to 30%. Typically, this difference increased as the θ_v rises between repacked and intact biocrusts. Our new measurements provide evidence that the thermal properties of biocrusts were previously misjudged due to the measurement limitations imposed by their limited thickness when measured in situ. Biocrusts are likely more significant in regulating soil heat and temperature in drylands than was previously assumed.

Agricultural management practices can profoundly influence soil phosphorus (P), with effects accumulating over time. To test the overarching hypothesis that soil P pools estimated by sequential fractionation would be altered by long-term agricultural practices, we used an experiment established in 1876 in the north-central US to quantify 145-year impacts of crop rotation (continuous maize [Zea mays L.], maize-soybean [Glycine max L. Merr.] and maize-oat [Avena sativa L.]-alfalfa [Medicago sativa L.]) and 117-year impacts of fertilization (unfertilized and fertilized) with rock phosphate, manure or synthetic fertilizer on soil P fractions at 15 cm intervals across 0–90 cm depth. Fertilization impacts on soil P were mostly limited to the surface (0–30 cm) depth, but extended to 90 cm depth under diverse rotations. Under fertilization, soil total P concentration increased by 51% at 0-30 cm while concomitantly decreasing by 30% at 60–90 cm compared to no fertilization, indicating that vertically stratified surface soil P accumulation and subsoil P depletion can co-occur even under positive P balances. Positive P balances (1222–1494 kg/ha) induced by fertilization enriched inorganic P (P_i) (+39% to 358%) and labile organic P (P_o) fractions (+11%) while depleting non-labile P_o fractions (−31%), with depletion increasing with the degree of crop diversification. Fertilization had minor impacts on P fractions beyond 30 cm depth, except for acid extractable P_i (HCl-P_i) depletion under continuous maize and maize-soybean rotations (−16% to −78%) and accumulation under maize-oat-alfalfa rotation (+41% to +84%) at 60–90 cm. In contrast, without fertilization, diversifying maize rotations with oat and alfalfa decreased HCl-P_i and residual P (−21% to −57%) but increased non-labile P_o fractions (+54%), suggesting potential mining of non-labile P_i pools by deep-rooted legumes under nutrient limitation. The 1–2 orders of magnitude greater changes in stocks of P fractions than stocks of total P emphasize the importance of distinguishing P pools even with operational fractionation to fully capture changes in P cycling beyond total P stocks. Our study revealed that a positive P balance under 117 years of fertilization (i) enriched P_i and labile P_o pools but (ii) depleted non-labile P_o pools, (iii) largely at 0–30 cm, and (iv) non-labile P_o depletion increased with crop diversification under 145-year rotation treatments.