European Journal of Soil Science最新文献

The water potential in drying soils, comprising both matric potential and osmotic potential components, can be measured using the dew point method (DPM). By combining DPM data with retention curve data acquired from techniques such as the suction plate method or the simplified evaporation method (SEM), it becomes possible to determine the soil water retention curve across the entire moisture spectrum. However, as the latter methods only determine the matric potential, the osmotic potential component in DPM data must either be negligible or known so that osmotic and matric potential components can be separated. This study aims to critically analyse common approaches for calculating the osmotic potential. To achieve this, we measured the water retention properties of a silt loam, a sandy loam and a sand across the entire moisture range by combining SEM and DPM. By using almost salt-free soil material, we characterized reference water retention curves with negligible osmotic potential components. The impact of salt on water potential was analysed by conditioning soils with MgCl₂ solutions of different concentrations, drying them, and measuring the water potential at different water contents using the DPM. The resulting water potentials were compared to the reference potentials and differences were interpreted as the osmotic potential component. The DPM-measured water potentials in drying soils can be significantly affected by osmotic potential, especially at higher matric potentials (low suctions). Two models accounting for ideal and one model accounting for non-ideal electrolyte behaviour were used to compare osmotic potential predictions with measurements. At low to medium salt concentrations, all models performed fairly well. At high concentrations, only the model accounting for non-ideal behaviour predicted the osmotic potential satisfactorily, whereas at very high concentrations, all models underestimated the impact of osmotic potential on water potential. This suggests that the surface properties of the soil matrix, such as the specific surface area and surface charges, may lead to a decrease in osmotic potential beyond what is expected in pure solutions.

Mined rock phosphate is expected to become a scarce resource within the next few decades as global phosphorus (P) deposits are declining. As a result, mineral P fertilizer will be less available and more expensive. Therefore, improved knowledge is needed on other P resources, for example, apatite fertilizers derived from the by-products of iron mining. Forestry is a potential future consumer of apatite-rich products with the aim of obtaining more wood per hectare. The actual P availability in apatite to plants has so far been barely quantified. We therefore examined tree P uptake using ³³P apatite under chamber-grown and outdoor conditions. We examined the P uptake for the two main conifer species spruce (Picea abies) and pine (Pinus sylvestris) used in Fenno-Scandinavian forestry. We synthesized ³³P-enriched apatite and applied it to mesocosms with growing seedlings of spruce and pine. The P uptake from ³³P-labelled hydroxylapatite was subsequently traced by (bio)imaging of radioactivity in the plants and by liquid scintillation counting (LSC) upon destructive harvest in all plant fractions (leaves, stem and roots) and rhizosphere soil. Two climatic conditions were compared, one at natural outdoor conditions and one set as 5°C warmer than the climate record from the previous years. Plant P uptake from ³³P-labelled hydroxylapatite was enhanced in chamber-grown compared with outdoor seedlings for both tree species. This uptake was manifested in the clear radioactive images obtained over ca. 1 month after soil apatite application. Furthermore, all aboveground plant fractions of both spruce and pine seedlings showed a higher P uptake in warmer than colder daytime environments. The observed quantities and rates of P uptake from ³³P-labelled hydroxylapatite by spruce (18 Bq g⁻¹ hour⁻¹) and pine (83 Bq g⁻¹ hour⁻¹; averages in chamber condition) are as to our knowledge unique observations. Natural forest soils in Sweden are often P-poor. Our research suggests that apatite-based P fertilization of spruce and pine forests can increase wood production by overcoming any existing P limitation.

Municipally sourced biosolids are commonly used as cost-effective fertilizers, diverting material from landfills and contributing to the circular economy. However, biosolids contain high concentrations of microplastics (MPs), which are emerging contaminants of concern due to their ubiquity in the environment. Despite this, there is a lack of environmentally relevant field studies. In 2022, composite topsoil samples (0–15 cm depth) were collected from seven agricultural fields in Southern Ontario, Canada, representing a chronosequence of biosolid applications ranging from 1 to 9 years since amendment and a control (untreated) field. MP particles down to 20 μm in size were extracted by density separation, enumerated, characterized by stereomicroscope and polymers identified using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Here, we report on the characteristics, abundance and polymer type of MP particles in the study area to assess their fate in biosolid-amended soils. The average MP concentration among fields was 6.87 ± 1.47 MP g⁻¹ (3.43 ± 0.74 mg MP kg⁻¹). Additionally, the MP soil pool increased with repeated applications of biosolids. The dewatered biosolid plastic content of 8816 ± 1809 MP g⁻¹ dry weight (11.6 ± 17.5 g MP kg⁻¹ dry weight) was used to estimate a mean MP loading of 94.5 ± 10.9 kg ha⁻¹ to each field per application, suggesting that 7% of the MP soil pool persisted over time. Quantifying the MP pool in biosolid-amended agricultural soil will inform evidence-based plastic policy changes in our global effort to understand and reduce plastic pollution.

The words we choose to describe our research ultimately directs its course. A dominant term in soil science now, is ‘sequestration’, referring to the removal of carbon (C) from air and its irreversible seclusion in soil, ideally as stable soil organic carbon (SOC). An emerging view, however, now sees SOC as an inherently dynamic assemblage of forms, all potentially vulnerable to decay, with no discrete, measurable fraction holding C in ‘sequestered’ form. Rather than speaking of C ‘sequestration’, then, we might refer instead to SOC ‘stewardship’. This word, now, enfolds the entire spectrum of SOC, not merely some elusive ‘persistent’ or ‘stable’ fraction, perhaps redirecting inquiry; for example, does C need to be ‘sequestered’ in stable form for SOC to serve as effective repository of excess atmospheric CO₂? ‘Stewardship’ explicitly accepts the relentless turnover of SOC, emphasizing the need to manage not only fixed stocks of C, but also the cyclical flows of C through ecosystems that drive their functions. Among other benefits, ‘stewardship’ might motivate us to consider all functions of SOC (not only climate mitigation), consider the entire C cycle (not only enhancing soil C), and preserve existing troves of SOC (not only augmenting them in selected places.) Perhaps most fundamentally, by its etymology, ‘stewardship’ poses a compelling, timeless question: for whom do we steward SOC? Asking why look after SOC, not only reflects our own underlying quest for resilience, but also expands our potential audience and entices the more creative minds that must succeed us. Although ‘stewardship’ may elicit new and fruitful inquiry, we may need to look for words even more evocative, more alluring, more true to our mandate of living well within the circling C that must always sustain us.

We have pleasure in introducing the latest EJSS Russell Review ‘Soil Carbon Stewardship: Thinking in Circles’ by Professor H. Henry Janzen (2024). The article forms the first of a series of our most prestigious invited reviews commissioned to celebrate the EJSS' 75th Anniversary (for further information see Dungait et al., 2024).

The author of this Russell Review, Prof H. Henry Janzen, is one of the world's foremost and respected experts on both the science and the philosophy of soil carbon and its integral place in sustaining our future on Earth. In this review, Prof Janzen eloquently makes the case for a new term, ‘carbon stewardship’, that emphasizes the essential relationship between society and soil carbon, and the urgent need to nurture it in all its forms. He presents a compelling argument for a radical change in the way we think and talk about the value that soils have for us.

The term ‘carbon sequestration’ was coined ~40 years ago. Both within and beyond academia, excitement about ‘carbon sequestration’ in soils as a nature-based solution to climate change continues to grow as the impacts of global warming manifest. Measuring, modelling and mapping soil carbon remain active areas of research, and considerable efforts have been expended to define ‘stable carbon’ and the underlying mechanisms leading to its stabilization, in order that this can be targeted to accrue soil carbon¹.

In this Russell Review, Prof Janzen argues that the benefits of soil carbon to human society go far beyond just locking it away. Rather than referring to ‘carbon sequestration’, he suggests that we replace the term with ‘carbon stewardship’ that ‘denotes recognizing and valuing the benefits that SOC [soil organic carbon] offers to land and all its inhabitants, and then caring for this treasured entity on behalf of other current and future beneficiaries of its goodness’.

The ability to communicate one's scientific research in a way that captures hearts as well as minds is an enviable skill. It takes expertise, integrity and passion, and Prof Janzen has all of these ‘in spades’ (no soil science pun intended!). Anyone who has had the privilege of witnessing in person his presentations on the importance of the soil, and soil carbon in particular, cannot help but be inspired by his depth of knowledge of soil science and the power of his mesmeric storytelling. This ability extends to the written word, and the Invited Review published in the EJSS a decade ago, ‘Beyond carbon sequestration: soil as conduit of solar energy’ (Janzen, 2015), stimulated new ways of thinking about the carbon cycle, within and beyond academia. We are sure that this Russell Review will continue Prof Janzen's legacy of inspiration and commend it to EJSS' readers.

Rapid urbanization has increased the areas of urban forests that store considerable soil carbon (C). Different soil C fractions may show distinctive contents and spatial patterns in view of their contrasting sensitivities to various drivers. However, current studies on soil C fractions are mostly limited to natural ecosystems and little is known about the large-scale patterns and drivers of soil C fractions in urban forests. Based on a field survey of urban forests across a north–south transect in eastern China, we analysed the spatial variations and main drivers of topsoil (surface layer, 0–10 cm; subsurface layer, 10–20 cm) C fractions (i.e., soil organic C, SOC; soil inorganic C, SIC; particulate organic C, POC; mineral-associated organic C, MAOC). Our results showed that topsoil contents of POC, MAOC and SOC changed non-linearly with latitude, with lowest values occurring in the cities in the warm temperate region. In contrast, SIC content showed the highest values in the warm temperate region. POC instead of MAOC was found to be a major fraction of SOC in urban forests. The spatial variation in topsoil POC content was mainly explained by mean annual temperature, soil clay and silt content, and park age. The spatial variation in MAOC content was mainly explained by soil clay and silt content, mean annual precipitation, mean annual temperature and park age. In contrast, the spatial variation in SIC content was mainly explained by mean annual precipitation and soil pH. These findings demonstrate distinct features of different soil C fractions in urban forests and provide useful implications for urban soil carbon management.

Replacing the burnt sugarcane harvesting system with unburnt sugarcane is important for the sustainability of the sugarcane sector in Brazil. Thus, quantifying the impact of the change in the sugarcane harvesting system on soil organic carbon (SOC) stock in Brazil is necessary, as it will allow the refinement of data on SOC, which is essential for the preparation of the national inventory of emissions and removal of greenhouse gases (GHGs), in addition to contributing to national public policies. We used data from both soil sampling and literature review in this study, resulting in 210 pairs of comparisons: 84 for the conversion from burnt sugarcane to unburnt sugarcane; 95 for the conversion from native vegetation to unburnt sugarcane; and 31 for the conversion from native vegetation to burnt sugarcane (NV–burnt), which we analysed using a mixed linear model. In Brazil and the South-Centre region, burnt–unburnt conversion results in a progressive increase in SOC stocks over time, in surface and subsurface layers. Over 20 years, the NV–burnt conversion showed SOC losses between 15% and 32%, and the NV–unburnt conversion showed losses between 27% and 35%. SOC change rates showed gains of 0.32 and 0.59 Mg C ha⁻¹ year⁻¹ for burnt–unburnt, and losses ranging from 0.82 to 1.06 Mg C ha⁻¹ year⁻¹ for conversions from native vegetation. The time required to offset the negative carbon balance of the NV–unburnt conversion is 6.4 and 8.2 years, being shorter than the payback time of the NV–burnt conversion, which is 9.9 and 9.2 years, in the 0–30 and 0–50 cm layers, respectively.

The present European Union (EU) Sewage Sludge Directive (86/278/EEC) is undergoing modifications aimed at enhancing its applicability in the agricultural sector. The Directive's existing limit values for heavy metal concentrations in soils are in the process of being revised. However, to comprehensively understand their effects on EU agricultural lands, additional evaluations are necessary. This is particularly important given that ecological risk assessments are often performed on a site-specific basis, potentially overlooking broader regional implications. The main objective of the current work is to introduce a methodological approach to quantify the impact of sewage sludge (SS) application on agricultural soils in the EU and the United Kingdom. Concentrations of heavy metals (HMs) (Cd, Cu, Hg, Ni, Pb and Zn) in agricultural land from Land Use/Land Cover Area Frame Survey (LUCAS) 2009 topsoil database were used as a baseline. Maximum quantities of SS that can be safely applied to agricultural lands were obtained by a modeling procedure was used to determine the maximum safe quantities of SS that can be applied to agricultural lands for each country within the European Member States and the United Kingdom. Accumulation of HMs in soils was modelled by using a representative SS composition, distributed over 10 successive years at 5 Mg ha⁻¹ year⁻¹ rate. Ecological risk impact was assessed by using both the single ecological risk index (E_r) and the integrated potential ecological risk index (RI). Maximum quantities of SS applied on agricultural soils in EU + UK were estimated to be 45 Mg ha⁻¹ at the country level. We found that 19% of agricultural land (around 28,471,900 ha) in the EU + UK shows a higher RI than moderate risk after long time application of the representative SS. We show that the combination of the HM concentrations from the LUCAS topsoil survey and assumptions on the SS composition and soil HM partitioning can be used to define the actual and potential soil pollution rate in EU + UK. We demonstrate that the proposed methodology can be used by policymakers, farmers, regional authorities and other stakeholders, with possible adaptions based on local in-depth soil and SS knowledge.

This study demonstrates that phosphate oxygen isotope (δ¹⁸O_PO4) analysis effectively detects and monitors fire-induced transformation in soil phosphorus (P). Fires increase bioavailable P, potentially limiting primary production in terrestrial ecosystems. However, understanding the effects of fire on soil P dynamics in the field remains challenging due to the interaction between fire spread and soil properties with high spatial heterogeneity. Soil burning experiments were conducted using a surface soil sample collected in central Japan. The soil was burned in an electric furnace from 50 to 550°C for 3 h, and P concentrations and δ¹⁸O_PO4 values were determined. The results revealed that high temperatures (>350°C) depleted the soil of organic P (P_o) and increased labile and stable inorganic P (P_i) concentrations while significantly decreasing δ¹⁸O_PO4 values. By contrast, low temperatures (150°C) increased labile P_i and P_o concentrations without isotopic shift, indicating that low-intensity fires could increase bioavailable P while conserving soil organic matter. These findings indicate that δ¹⁸O_PO4 analysis can provide insight into the relationship between P transformations and fire intensity and track subsequent changes in P dynamics over time. Our research highlights the potential of δ¹⁸O_PO4 in predicting and managing postfire ecological and agricultural impacts.

In digital soil mapping, modelling soil thickness poses a challenge due to the prevalent issue of right-censored data. This means that the true soil thickness exceeds the depth of sampling, and neglecting to account for the censored nature of the data can lead to poor model performance and underestimation of the true soil thickness. Survival analysis is a well-established domain of statistical modelling that can deal with censored data. The random survival forest is a notable example of a survival-related machine learning approach used to address right-censored soil property data in digital soil mapping. Previous studies that employed this model either focused on mapping the probability of soil thickness exceeding certain depths, and thereby not mapping soil thickness itself, or dismissed it due to perceived poor performance. In this study, we propose an alternative survival model to map soil thickness that is based on the inverse probability of censoring weighting. In this approach, calibration data are weighted by the inverse of the probability that soil thickness exceeds a certain depth, that is, a survival probability. These weights can then be used with most machine learning models. We used the weights with a regular random forest, and compared it with a random survival forest, and other strategies for handling right-censored data, through a comprehensive synthetic simulation study and two real-world case studies. The results suggest that the weighted random forest model produces competitive predictions, establishing it as a viable option for mapping right-censored soil property data.