| 1. |
- Fukumasu, Jumpei, et al.
(författare)
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Oxalate-extractable aluminum alongside carbon inputs may be a major determinant for organic carbon content in agricultural topsoils in humid continental climate
- 2021
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Ingår i: Geoderma. - : Elsevier BV. - 0016-7061 .- 1872-6259. ; 402
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Tidskriftsartikel (refereegranskat)abstract
- The relative importance of various soil mineral constituents (e.g. clay-sized particles, aluminum- and iron-bearing mineral reactive phases) in protecting soil organic carbon (SOC) from decomposition is not yet fully understood in arable soils formed from quaternary deposits in humid continental climates. In this study, we investigated the relationships between soil physico-chemical properties (i.e. contents of oxalate-extractable aluminum (Alox) and iron (Feox) and clay size particle < 2 mu m), grain yield (as a proxy for carbon input) and total SOC as well as SOC in different soil fractions for samples taken from the topsoil of an arable field at Bjertorp in south-west Sweden. We found a positive correlation between Alox and total SOC content, where Alox explained ca. 48% of the spatial variation in SOC. We also found that ca. 80% of SOC was stored in silt- and claysized (SC) fractions, where Al-bearing reactive mineral phases (estimated by Alox) may be important for organicmineral associations and clay aggregation. Our results were supported by data collated from the literature for arable topsoil in similar climates, which also showed positive correlations between SOC and Alox contents (R-2 = 23.1 - 74.5%). Multiple linear regression showed that including spatially-variable crop yields as a proxy for carbon inputs improved the prediction of SOC variation across the Bjertorp field. Other unquantified soil properties such as exchangeable calcium may account for the remaining unexplained variation in topsoil SOC. We conclude that Al-bearing reactive mineral phases are more important than clay content and Fe-bearing reactive mineral phases for SOC stabilization in arable topsoil in humid continental climates.
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| 2. |
- Jarvis, Nicholas, et al.
(författare)
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Interactions between soil structure dynamics, hydrological processes, and organic matter cycling: A new soil-crop model
- 2024
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Ingår i: European Journal of Soil Science. - 1351-0754 .- 1365-2389. ; 75
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Tidskriftsartikel (refereegranskat)abstract
- The structure of soil is critical for the ecosystem services it provides since it regulates many key soil processes, including water, air and solute movement, root growth and the activity of soil biota. Soil structure is dynamic, driven by external factors such as land management and climate and mediated by a wide range of biological agents and physical processes operating at strongly contrasting time-scales, from seconds (e.g., tillage) to many decades (e.g., faunal activity and soil aggregation). In this respect, positive feedbacks in the soil-plant system may lead in the longer term to soil physical degradation or to the recovery of structurally poor soils. As far as we are aware, no existing soil-crop model can account for such processes. In this paper, we describe a new soil-crop model (USSF, Uppsala model of Soil Structure and Function) that accounts for the effects of soil structure dynamics on water and organic matter cycling at the soil profile scale. Soil structure dynamics are expressed as time-varying physical (bulk density, porosity) and hydraulic properties (water retention, hydraulic conductivity) responding to the activity of biological agents (i.e., earthworms, plant roots) and physical processes (i.e., tillage, soil swell-shrink) at seasonal to decadal time-scales. In this first application of the model, we present the results of 30-year scenario simulations that illustrate the potential role and importance of soil structure dynamics for the soil water balance, carbon storage in soil, root growth, and winter wheat yields on two soils (loam and clay) in the climate of central Sweden. A sensitivity analysis was also performed for these two scenarios using the Morris method of elementary effects, which revealed that the most sensitive parameters controlling soil structure dynamics in the USSF model are those determining aggregation induced by organic matter turnover and swell/shrink. We suggest that the USSF model is a promising new tool to investigate a wide range of processes and phenomena triggered by land use and climate change. Results from this study show that feedback in the soil-crop system mediated by the dynamics of soil physical and hydraulic properties are potentially of central importance for long-term predictions of soil water balance, crop production, and carbon sequestration under global change.
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| 3. |
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| 4. |
- Klöffel, Tobias, et al.
(författare)
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Freeze-thaw effects on pore space and hydraulic properties of compacted soil and potential consequences with climate change
- 2024
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Ingår i: Soil and Tillage Research. - 0167-1987 .- 1879-3444. ; 239
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Tidskriftsartikel (refereegranskat)abstract
- Freezing and thawing affect the pore -space structure in agricultural soils with implications for soil hydraulic properties and water flow. Previous studies have focused on the upper few centimeters of the tilled topsoil, where most freeze -thaw (FT) cycles occur, even though deeper soil layers are also subject to freezing and thawing in cold climates. Thus, little is known about how freezing and thawing affect untilled soil layers, which often show high bulk densities that restrict vertical water movement. Furthermore, it remains unclear how shifts in FT patterns with climate change may change the pore -space structure and water flow through these soil layers. Here we investigated the effects of freezing and thawing on X-ray imaged pore -space characteristics, water retention and near -saturated hydraulic conductivity (K) in untilled soil directly below plough depth. Intact cores were sampled at two sites in central Sweden under the same long-term reduced tillage management. The two soils, a silt loam and a silty clay loam, were subjected to three FT scenarios in a laboratory environment intended to represent FT patterns that are considered likely under current and future winter conditions for this region. The latter scenario was characterised by more FT cycles and a lower freezing temperature. Freezing and thawing increased K in the near -saturated range in both soils, which we attribute to observed small (<0.01 mm(3 )mm( -3)) increases in the volume of pores of diameters close to the X-ray resolution limit. Concomitant increases in pore network connectivity and critical pore diameter, especially in the denser silty clay loam soil, probably contributed to this increase in K. The water retention data suggested that changes in pore -space characteristics below X-ray resolution also occurred in both soils. Furthermore, our results indicate that both soils may show higher drainage rates due to shifts in FT patterns in the future, although longer -term changes in pore -space structure with an increasing number of FT cycles would mostly be limited to soils with relatively high clay contents. These soils are often more compacted below plough depth and, thus, benefits from improvements in soil structure such as improved root growth and plant water supply are also expected to be larger.
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| 5. |
- Klöffel, Tobias, et al.
(författare)
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Relative entropy as an index of soil structure
- 2022
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Ingår i: European Journal of Soil Science. - : Wiley. - 1351-0754 .- 1365-2389. ; 73
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Tidskriftsartikel (refereegranskat)abstract
- Soil structure controls key soil functions in both natural and agro-ecosystems. Thus, numerous attempts have been made to develop methods aiming at its characterization. Here we propose an index of soil structure that uses relative entropy to quantify differences in the porosity and pore(void)-size distribution (VSD) between a structured soil derived from soil water retention data and the same soil without structure (a so-called reference soil) estimated from its particle-size distribution (PSD). The difference between these VSDs, which is the result of soil structure, is quantified using the Kullback-Leibler Divergence (KL divergence). We applied the method to soil data from two Swedish field experiments that investigate the long-term effects of soil management (fallow vs. inorganic fertilizer vs. manure) and land use (afforested land vs. agricultural land dominated by grass/clover ley) on soil properties. The KL divergence was larger for the soil receiving regular addition of manure compared with the soils receiving no organic amendments. Furthermore, soils under afforested land showed significantly larger KL divergences compared to agricultural soils near the soil surface, but smaller KL divergences in deeper soil layers, which closely mirrored the distribution of organic matter in the soil profile. Indeed, a significant positive correlation (r = 0.374, p < 0.001) was found between soil organic carbon concentrations and KL divergences across all sites and treatments. Despite challenges related to modelling the VSD of the reference soil without structure, the proposed index proved useful for evaluating differences in soil structure in response to soil management and land-use change and reflected the expected effects of soil organic matter on soil structure. We conclude that relative entropy shows great potential to serve as an easy-to-use index of soil structure, as it only requires widely available data on soil physical and hydraulic properties. Highlights A new index of soil structure is proposed based on relative entropy A method is developed that separates the effects of soil texture and structure on the pore space The index identified soil structural differences in response to land use and soil organic carbon concentrations (SOC) The index shows the potential to serve as an easy-to-use metric of soil structure
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| 6. |
- Klöffel, Tobias, et al.
(författare)
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Soil, climate, time and site factors as drivers of soil structure evolution in agricultural soils from a temperate-boreal region
- 2024
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Ingår i: Geoderma. - 0016-7061 .- 1872-6259. ; 442
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of soil structure in agricultural soils is driven by natural and anthropogenic factors including inherent soil properties, climate and soil management interventions, all acting at different spatial and temporal scales. Although the causal relationships between soil structure and these individual factors are increasingly understood, their relative importance and complex interactive effects on soil structure have so far not been investigated across a geo-climatic region. Here we present the first attempt to identify the relative importance of factors that drive the evolution of soil structure in agricultural soils as well as their direction of effect with a focus on the temperate-boreal zone. This was done using a random forest (RF) approach including soil, climate, time, and site factors as covariates. Relative entropy, as quantified by the Kullback-Leibler (KL) divergence, was used as a quantitative index of soil structure, which is derived from the particle-size distribution and soil water retention data, and integrates the effects of soil structure on pores from the micrometre-scale to large macropores. Our dataset includes 431 intact topsoil and subsoil samples from 89 agricultural sites across Sweden and Norway, which were sampled between 1953 and 2017. The relative importance of covariates for the evolution of soil structure was identified and their non-linear and non-monotonic effects on the KL divergence were investigated through partial dependence analysis. To reveal any differences between topsoils (0-30 cm; n = 174) and subsoils (30-100 cm; n = 257), the same analysis was repeated separately on these two subsets. The covariates were able to explain on average more than 50% of the variation in KL divergence for all soil samples and when only subsoil samples were included. However, the predictions were poorer for topsoil samples (approximate to 35%), underlining the complex dynamics of soil structure in agricultural topsoils. Parent material was the most important predictor for the KL divergence, followed by clay content for all soil samples and sampling year for only subsoil samples. Mean annual air temperature ranked third and annual precipitation ranked fourth for subsoil samples. However, it remains unclear whether the effects of climate factors are direct (e.g., freezing and thawing, wetting and drying, rainfall impact) or indirectly expressed through interactions with soil management. The partial dependence analysis revealed a soil organic carbon threshold of around 3% below which soil structure starts to deteriorate. Besides this, our results suggest that subsoil structure in the agricultural land of Sweden deteriorated steadily during the 1950 ' s to 1970 ' s, which we attribute to traffic compaction as a consequence of agricultural intensification. We discuss our findings in the light of data bias, laboratory methods and multicollinearity and conclude that the approach followed here gave valuable insights into the drivers of soil structure evolution in agricultural soils of the temperate-boreal zone. Theses insights will be of use to inform soil management interventions that address soil structure or soil properties and functions related to it.
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| 7. |
- Klöffel, Tobias
(författare)
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Soil structure and water functions in agricultural soils of the temperate-boreal zone in a changing climate
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Climate change may affect the productivity of cropping systems in the temperateboreal zone by increasing the frequency of periods with water excess and shortage. Soils have the capacity to buffer such extreme weather events by regulating water storage and fluxes, which are mainly a function of soil structure. However, climate itself is linked to the evolution of soil structure through a multitude of processes (e.g., freezing and thawing, soil management). The main objective of this thesis was to improve our understanding of the effects of climate-driven processes on the porespace structure of agricultural soils in order to identify potential implications for soil water functions in the context of climate change. This was done using a wide range of approaches including a meta-analysis, a laboratory experiment, and the application of machine learning to a newly developed index of soil structure based on relative entropy. It was revealed that climate is an important driver of the structural pore space of arable soils in Sweden and Norway. Warmer and wetter regions showed a less developed structure compared to cooler and drier regions, in particular in the subsoil, although it remains unclear whether this was the result of direct or indirect climate-driven processes. With climate change, the number and intensity of freeze-thaw cycles is expected to increase in some parts of the temperateboreal zone. Results from this thesis show that this may lead to increased drainage rates in compacted soil layers under near-saturated conditions as well as improved pore connectivity, especially in fine-textured soils. Furthermore, most changes in pore-space structure induced by freezing and thawing were found for pores of diameters <200 μm. The findings are discussed in the context of wetter soil conditions, early summer droughts, and an intensification of agricultural practices expected for different parts of the temperate-boreal zone in the future.
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| 8. |
- Klöffel, Tobias
(författare)
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The challenges fraught opportunity of agriculture expansion into boreal and Arctic regions
- 2022
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Ingår i: Agricultural Systems. - : Elsevier BV. - 0308-521X .- 1873-2267. ; 203
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Tidskriftsartikel (refereegranskat)abstract
- Accelerated global warming in the cold-climate boreal and Arctic regions facilitates intensification and expansion of agriculture. However, current boreal and Arctic governmental policies targeting agricultural development differ among regions creating the risk for serious consequences for provision of goods and ecosystem services. On June 29th, 2021 we organized a United Nations Summit dialogue on "Local and global food security shaped by northern agriculture" to complement a 2019 survey of the scientific community on boreal and Arctic agriculture. The 33 attendees concluded that while climate change might offer significant agricultural opportunities in boreal and Arctic communities such as increased food security, sovereignty, and economic development, this should not be considered lightly and without strong support for environmental sustainability as carbon and biodiversity losses are main risks. Attendees expressed that using existing agricultural lands more efficiently is likely a better option than converting forest to new agricultural lands. It was also confirmed by the attendees that consistent policies are needed across northern jurisdictions that, above all else, consider environmental consequencesfollowed by local food needs and interests. We and the attendees propose that this can only be ensured through further research and effective dialogues which reflect the needs and concerns of all members of the northern communities, including farmers.
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| 9. |
- Klöffel, Tobias
(författare)
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Visualizing the transfer of organic matter from decaying plant residues to soil mineral surfaces controlled by microorganisms
- 2021
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 160
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Tidskriftsartikel (refereegranskat)abstract
- The interface between decaying plant residues and soil minerals represents an essential soil microenvironment at which soil organic matter forms. The high amount of microbial products and residues within this hot spot of microbial activity fosters the formation of mineral-associated organic matter. Besides classical quantitative analyses, our understanding of processes controlling soil organic matter formation greatly benefits from microscopic observations and measurements, which provide spatially resolved information at a meaningful scale for microbial processes and for the association between organic and mineral particles. We studied carbon and nitrogen transfer from fresh-plant residues to the mineral soil, through a litter decomposition experiment in an artificial soil mixture. Needles of Norway spruce (Picea abies L.) were placed in microbatch containers filled with an artificial soil mixture free of soil organic matter. Containers were buried in fresh organic layer material from a Norway spruce stand and incubated for 14 and 42 days. We applied nanoscale secondary ion mass spectroscopy (NanoSIMS) to investigate the spatial distribution of mineral and organic compounds at the needle vicinity and into the mineral soil (0-550 mu m from the needle). After 14 days, we depicted the formation of mineral-associated organic matter in the surrounding of the decaying needles. After 42 days, we observed substantial colonization of the needles and the detritusphere by saprotrophic fungi. The fungal hyphae extended into the mineral matrix of the artificial soil acting as vectors for the transfer of litter-derived carbon and nitrogen into the bulk soil. This resulted in an increase of the area covered by organic matter in the detritusphere, with up to 10% of the total investigated area classified as organic matter closely associated with mineral surfaces. Our results provide evidence that the carbon and nitrogen derived from litter decomposition transformed by microorganisms is transferred as mineral-associated organic matter, heterogeneously distributed from the litter source, and still detected 550 mu m away from the latter. The close association of newly formed soil organic matter and fine sized minerals suggests that the formation of mineral-associated OM and likely also microaggregates is directly driven by microbial activity in the vicinity of hot spots for plant carbon input (e.g. the detritusphere).
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