European Journal of Soil Science最新文献

Saline-sodic paddy soils in the Songnen Plain suffer from nitrogen loss due to nitrification. The purpose of the study is to explore soil saline improvement and nitrification mitigation effects of polyaspartic calcium (PASP-Ca) by evaluating changes of soil quality, nitrification, and microbial communities. Four PASP-Ca application treatments (additions of 0, 500, 1000, and 1500 kg hm⁻²) were studied in an experiment in saline-sodic paddy soils of the Songnen Plain, China. Results showed that PASP-Ca application significantly decreased soil pH, electrical conductivity (EC), and water-soluble salt ions, and significantly increased soil total carbon (TC), total nitrogen (TN), urease activity (UA), and sucrase activity (SA). PASP-Ca application significantly slowed down soil nitrification, which was manifested in a significant increase in ammonium nitrogen ($��{\mathrm{NH}}_4^{+}�-�N�$) and a significant decrease in nitrate nitrogen ($��{\mathrm{NO}}_3^{-}�-�N�$) and ammonia monooxygenase activity (AMO). The composition and distribution of soil nitrifying microbial communities were affected by soil salinity, nutrient, and enzyme activities. Ammonia-oxidizing bacteria (AOB) plays an important role in the nitrification process of saline-sodic paddy soils, while PASP-Ca application significantly inhibited nitrification by suppressing AOB amoA gene abundance. This study shows that PASP-Ca, as an effective amendment, can improve soil salinization and slow down nitrification, which has an important role and significance in improving nitrogen utilization and reducing nitrogen loss of saline-sodic soils.

The bacterial communities that harbour the pyrroloquinoline quinone gene (pqqC-harbouring bacteria communities) play a pivotal role in the mobilization of inorganic phosphorus (Pi). However, there is limited knowledge regarding the connection between soil pqqC-harbouring bacterial communities and Pi fractions, as well as the factors that can regulate them, particularly under different fertilization strategies in the agricultural soil. High-throughput sequencing was used to investigate the pqqC-harbouring communities from the wheat (Triticum aestivum L.)–sweet potato (Ipomoea batatas L.) season in a 9-year field experiment, including without fertilization (control), nitrogen (N) and potassium (K) fertilization (NK), NPK fertilization (NPK) and the combined application of chemical NPK and organic fertilizer (NPKM), and to explore their relationships with Pi fractions and their regulatory factors. Long-term N fertilization and crop type substantially changed the community composition of pqqC-harbouring bacteria but had no effect on their diversity. In two crop seasons, long-term N fertilization significantly increased the content and proportion of moderately labile Pi (aluminium- and iron-bound P) and available P (AP) and significantly decreased the proportion of recalcitrant Pi (calcium-bound P) compared with the control. Specifically, AP increased by 79%–778%, Fe-P by 64%–88%, and Al-P by 71%–308%, while Ca-P decreased by 10%–59%. N fertilization increased the relative abundance of Micromonospora, which was significantly positively correlated with moderately labile Pi and AP. Moreover, the relative abundance of some Streptomyces increased by 391% in the sweet potato season, and they were positively correlated with AP. Structural equation modelling revealed that the interplay between the pqqC-harbouring community composition and Pi mobilization was mainly governed by pH, underscoring the role of pH in shaping the communities of Pi-mobilizing microbes and their effect on Pi mobilization processes. This study emphasized how N fertilization and crops reshape Pi-mobilizing microbial communities, which in turn affects Pi mobilization and P availability. Overall, these findings offer valuable insights into optimizing P cycles and availability through N fertilization strategies.

Biological invasion is one of the major challenges to changing ecosystems worldwide. Red fire ants are a prime example of invasive soil animals. However, the impacts of their invasion on the native soil animal communities are still poorly understood. Here, we investigated how the biomass and diversity of soil microarthropods (incl., Collembola and Acari) vary between areas affected by red fire ants at different degrees (i.e., OA, occurrence area, 0–20 m from the nest; PCA, prevention and control area, 20–50 m; POA, potential occurrence area, 50–100 m). We also tested whether the potential effects of ant invasion on other animals are associated with changes in soil properties in the invaded areas. Our results showed a decline of 64% in species richness, 74% in density, and 72% in biomass of microarthropods in OA in comparison with POA. This reduction was mainly driven by the decrease of Acari, while no reduction in Collembola biomass was observed. Despite soil properties being significantly different between ant-impacted areas, structural equation models indicated that the direct association of invasion with microarthropod communities is stronger than the indirect association mediated by soil properties. Therefore, we consider that direct biological interaction is more likely the major mechanism behind the observed changes in microarthropod communities. The effects of red fire ants were different among taxonomic and functional groups, with litter-dwelling Collembola, Oribatida, and Mesostigmata (Acari) affected more negatively than soil-dwelling and surface-dwelling Collembola. Further, red fire ants affected the turnover component of beta-diversity (i.e., replacement of species) for both Collembola and Acari. However, the impact on the nestedness component, which is related to species local extinction and population decline, was only detected for Acari. Our study shows that red fire ant invasion is associated with the depletion of soil microarthropod community, and especially highlights that Acari are more vulnerable to this invasion compared to Collembola. The divergent response between different taxonomic and functional groups of microarthropods and the consequent shift in microarthropod communities may have important significance to soil ecological functioning in the impacted areas.

The literature regarding how rill longitudinal profile (concave and convex) affects soil loss and flow resistance is still lacking. The only analysis available in the literature for rills is limited by the fact that measurements were performed for a unique mean slope value s_p (18%). In this article, further rill measurements were conducted on a plot with s_p = 15% and complex profile shapes and were used to widen the knowledge about the influence of longitudinal profile shape on rill scour, eroded volume, and flow resistance. The findings highlighted that the concave profile has a homogeneous spatial distribution of moderate scours, whereas the scours in the convex one are deeper and more confined, but they are not placed after the slope change as found for s_p = 18%. The mean scour depth, which accounts for the discharge and profile shape effects, is not (concave) or is weakly (convex) related to the flow discharge. The concave profile determined a reduction of approximately 57% of the total eroded volume when compared with the convex profile shape, confirming that a concave hillslope limits erosive phenomena. Finally, the flow resistance equation guaranteed a precise estimation of the Darcy–Weisbach friction factor.

Recent advances in the use of plant growth-promoting bacteria (PGPB) have highlighted their potential to significantly enhance crop yield and plant health. In desert areas with sandy soil, employing drip irrigation systems to inoculate PGPB serves as an efficient method that saves both time and labour. This study examined the absorption, transport and spatial distribution of two strains of Azospirillum brasilense (Sp7 and Cd) under two-dimension (2D) unsaturated transient water flow. We used sand as a substitute for sandy soil and evaluated bacterial surface characteristics, adsorption isotherms and transport under different irrigation and inoculation regimes. The research determined that, owing to its smaller size and lower adsorption, A. brasilense Cd exhibited enhanced mobility and occupied an inoculated area 33% larger than that of A. brasilense Sp7. Moreover, subsurface drip irrigation (SSDI) exhibited a 29% higher inoculation area than surface drip irrigation (SDI). The sequence of introducing PGPB suspension and irrigation water impacted the distribution, particularly for A. brasilense Sp7. The attachment/detachment numerical model adequately described the 2D bacterial distribution (R² ranged from 0.75 to 0.99), providing a useful tool for predicting bacterial distribution in soils and optimizing agricultural practices to enhance crop productivity. Overall, smaller bacteria, SSDI inoculation and inoculation before irrigation could enhance the extent of inoculation. This study provides novel insights into optimizing PGPB inoculation strategies in agricultural settings, highlighting the importance of considering bacterial physical properties, irrigation techniques and inoculation sequences to improve PGPB distribution within the rhizosphere.

Nitrification inhibitors, such as nitrapyrin (NI), are increasingly co-applied with nitrogen (N) fertilizers as part of sustainable agricultural practice. Several studies in temperate regions have documented the effectiveness of NI in retaining soil ammonium (NH₄⁺), minimizing N loss and increasing crop yields. However, less is known about the effects of NI in Mediterranean regions, where agricultural production is challenging and requires intensive irrigation and fertilization. We investigated the short-term impact of the nitrification inhibitor nitrapyrin (2-chloro-6-(trichloromethyl)pyridine) in a two-factor mesocosm experiment, using a typical Mediterranean soil, where NI was co-applied with a selection of urea-based fertilizers: urea (U), U with urease inhibitors (U + UI), methylene urea (MU) and zeolite-coated urea (ZU). NI co-applied with urea fertilizers resulted in higher availability of soil NH₄⁺ and a concurrent increase in NH₃ volatilization. Net cumulative soil NH₄⁺ availability was 1.5–3.3 fold greater when NI was applied. Concurrently, net cumulative nitrate (NO₃⁻) and nitrite (NO₂⁻) availability was reduced by 10%–60%; this was found for all the tested fertilizer types except MU fertilizer, where the net cumulative soil NO₃⁻ and NO₂⁻ doubled. Nitrous oxide (N₂O) emissions from urea fertilization were reduced by 40% with UI, 50% with NI and 66% with NI + UI. Interestingly, after 28 d, the composition of soil microbial communities was distinctly different, due to NI application. Specifically, NI application dramatically reduced the abundance of ammonia-oxidizing and denitrifying bacterial functional groups. NI was effective in reducing N₂O emissions in this calcareous soil; however, NH₃ emissions were remarkably enhanced. These findings have important implications for the large-scale adoption of inhibitor technologies in Mediterranean agroecosystems and for the reduction of greenhouse gas emissions.

In light of climate change and increasing global temperatures, it is important to equally prioritize the study of inorganic carbon dynamics in calcareous soils within temperate ecosystems, as has been done for arid or semiarid environments. A significant area of vineyards in Germany is established on calcareous soils. However, the potential influence of inorganic carbon on CO₂ emissions in these vineyards has not been sufficiently explored when evaluating the carbon footprint of management practices in relation to carbon storage. Therefore, we aimed to differentiate between organic and inorganic sources of CO₂ emissions from six vineyard soils located in the southwest of Germany that had previously received organic soil amendments (OA). Inorganic carbon content varied between 8 and 55 g kg⁻¹ across different sites, with variations observed in the inorganic-to-organic carbon ratio. Soil samples were incubated under standard laboratory conditions for 48 h, and the source of emitted CO₂ was determined using a two-end-member mixing model. The contribution of inorganic carbon to CO₂ emissions was influenced by the quantity of inorganic carbon, with an increase in contribution with increasing inorganic-to-organic carbon ratio. On average, abiotic sources accounted for 5% to 40% of the emitted CO₂ at the different sites, with one site showing no significant contribution of inorganic carbon. CO₂ production from inorganic carbon was higher in the subsoil compared with the topsoil, likely related to the higher content of inorganic carbon in the subsoil. Notably, there was no discernible influence of OA on carbonate dissolution. This study emphasizes the significance of considering abiotic sources of CO₂ emissions in addition to soil respiration in calcareous soils and highlights the need for further investigation to apply these findings at the field scale.

Microorganisms help govern soil organic carbon (SOC) turnover and accumulation. Whilst it is increasingly clear that microbial necromass is a precursor of SOC formation, the relationship between living microorganisms, necromass turnover and SOC persistence remains elusive. In this study, we used phospholipid fatty acids and amino sugars to quantify living versus dead microbial carbon concentrations and evaluated the utility of each pool as an indicator of SOC persistence across a range of climates (low-, mid- and high-latitude sites) and ecotypes (old-growth forests vs. managed croplands). We found that microbial necromass was higher in forest than in cropland soils and was positively correlated with soil moisture, SOC and total nitrogen (TN). However, the flow of microbial biomass into necromass and SOC was decoupled in forest sites, likely because the high soil SOC/TN ratio accelerated necromass turnover and recycling by living microorganisms. In contrast, microbial biomass and necromass pools were tightly coupled in croplands and influenced by multiple environmental and biological factors (e.g., necromass concentrations exhibited greater variability in soils with more bacteria than fungi, and those with more gram-positive than gram-negative taxa). Contrasting our expectations, the proportion of microbially-derived necromass in SOC was decoupled from soil properties and microbial biomass in both ecotypes. Whilst SOC and pH appear to be universal drivers of necromass cycling, feedbacks between living biomass, necromass and SOC are shaped by local factors. Our results contribute to ecological theory by highlighting the environmental and biological factors underpinning SOC formation and turnover that can be used to inform land-management practices that optimize below-ground carbon sequestration.

In this study, we derive an analytical solution to address the problem of vertical infiltration within 1D homogeneous bounded profiles. Initially, we consider the Richards equation together with Dirichlet boundary conditions. We assume constant diffusivity and linear dependence between the conductivity and the water content, resulting to a linear partial differential equation of diffusion type. To solve the simplified initial boundary value problem over a finite interval, we apply the unified transform, commonly known as the Fokas method. Through this methodology, we obtain an integral representation of the solution that can be efficiently and directly computed numerically, yielding a convergent scheme. We examine various cases, and we compare our solution with well-known approximate solutions. This work can be seen as a first step to derive analytical solutions for the far more difficult and complex problem of modelling water flow in heterogeneous layered soils.

Aggregate stability is an important structural feature of soils, since it controls surface erosion, water infiltration, plant growth and carbon stabilisation. As such, it might be considered as a potential descriptor of soil health in repeated national to continental-scale soil monitoring programmes, which is, as of now, rarely the case. This might be related to (i) the conception that it can be predicted reasonably well by standard soil parameters, and (ii) the lack of a high-throughput method. Here, we used a paired plot approach with 50 cropland and adjacent grassland field margin plots to specifically test (i) if measuring aggregate stability is added value over its mere estimation based on soil properties, and (ii) if a high throughput image recognition method can bear comparison with more classical methods. We evaluated the mean weight diameter (MWD), water stable aggregates (WSA) using classical setups, as well as the slaking index (SI) via imagine recognition. Methods were compared regarding their sensitivity to considered parameters as well as their reproducibility. Soil organic carbon (SOC) as well as aggregate stability were significantly higher under grassland than under cropland soils. Remarkably, the specific design of the study could reveal that the difference in aggregate stability between land use types was not solely affected by SOC content and quality, derived from mid-infrared spectroscopy. Quality and spatial distribution of organic matter inputs, absence of disturbance, as well as biotic parameters might all be relevant factors. Nevertheless, an important finding was that SOC quality had a higher explanatory power than SOC content alone for two out of three methods. Overall, the MWD was the most sensitive to the assessed drivers and together with the WSA the most reproducible method, with coefficients of variation below 6%. By contrast, those of the SI were as high as 192%, which hampered the detection of clear patterns along the soil property gradient and between land use types. For high-quality scientific applications, 2D image recognition cannot be recommended. Instead, we recommend the use of the MWD or WSA method for scientific purposes with a low number of technical replicates in larger-scale assessments to further unravel the importance of aggregate stability for healthy soils, and to better determine the underlying factors.