Showing papers in "European Journal of Soil Science in 2021"

Climate change impacts on soil salinity in agricultural areas

Abstract: Changes in climate patterns are dramatically influencing some agricultural areas. Arid, semi‐arid and coastal agricultural areas are especially vulnerable to climate change impacts on soil salinity. Inventorying and monitoring climate change impacts on salinity are crucial to evaluate the extent of the problem, to recognize trends and to formulate irrigation and crop management strategies that will maintain the agricultural productivity of these areas. Over the past three decades, Corwin and colleagues at the U.S. Salinity Laboratory (USSL) have developed proximal sensor and remote imagery methodologies for assessing soil salinity at multiple scales. The objective of this paper is to evaluate the impact climate change has had on selected agricultural areas experiencing weather pattern changes, with a focus on the use of proximal and satellite sensors to assess salinity development. Evidence presented in case studies for Californiaʼs San Joaquin Valley (SJV) and Minnesotaʼs Red River Valley (RRV) demonstrates the utility of these sensor approaches in assessing soil salinity changes due to changes in weather patterns. Agricultural areas are discussed where changes in weather patterns have increased root‐zone soil salinity, particularly in areas with shallow water tables (SJV and RRV), coastal areas with seawater intrusion (e.g., Bangladesh and the Gaza Strip) and water‐scarce areas potentially relying on degraded groundwater as an irrigation source (SJV and Murray‐Darling River Basin). Trends in salinization due to climate change indicate that the infrastructure and protocols to monitor soil salinity from field to regional to national to global scales are needed. HIGHLIGHTS: Climate change will have a negative impact on agriculture, particularly in arid regions. Proximal/remote sensors are useful to assess climate change impact on soil salinity across scales. Salt‐water intrusion, shallow water tables and degraded water reuse will increase soil salinity. Infrastructure and protocols to monitor soil salinity across multiple scales are needed.

Bypass and hyperbole in soil research: Worrisome practices critically reviewed through examples

Abstract: Almost 30 years ago, a distinguished soil physical‐chemist, Grant W. Thomas, voiced serious concern about what he saw in the soil science literature as more a preoccupation with style than with substance. The present article argues that, similarly, there are reasons to be worried at the moment because of a tendency in much of the literature on soils, both within and outwith soil science, to systematically ignore certain bodies of “old” literature, even when they are extremely relevant, and also to unduly inflate the potential significance of research achievements. These two practices, referred to as “bypass” and “hyperbole”, are illustrated by several examples dealing, respectively, with soil “aggregates”, soil quality/health, soil “contributions to ecosystem services” and whole‐soil metagenomics, in the case of bypass, and with biochar, the “4 per 1000” initiative, and the role of soils in achieving Sustainable Development Goals, in the case of hyperbole. It is hoped that the present review article will lead to a healthy debate on where our discipline stands at the moment in terms of how we build on the achievements of our predecessors and how accurately we describe the significance of our work. This debate should allow soil science to evolve to meet the daunting challenges it faces in the years ahead. HIGHLIGHTS: The literature on soils seems characterized by a significant amount of bypass and hyperbole Bypass is described, related to soil “aggregates”, soil quality/health, soil “contributions to ecosystem services” and whole‐soil metagenomics Hyperbole is described in connection with the research on biochar, the “4 per 1000” initiative, and the role of soils in achieving Sustainable Development Goals. The need to curb these deviances is stressed.

Revealing pore connectivity across scales and resolutions with X‐ray CT

Abstract: Connectivity is one of the most important parameters to quantify pore structure and link it to soil functions. One of the great challenges in quantifying connectivity with X‐ray microtomography (X‐ray μCT) is that high resolution, as required for small pores, can only be achieved in small samples in which the connectivity of larger pores can no longer be quantified in a meaningful way. The objective of this study was to investigate the changes in pore connectivity with changing sample size, covering a range of analysed pore diameters of more than three orders of magnitude. With this approach, we wanted to address whether pore types formed by different processes in an agricultural chronosequence leave characteristic traces in certain connectivity metrics. The Euler number, χ, and the connection probability of two random points within the pore system, that is, the Γ‐indicator, were determined as a function of minimum pore diameter. The results show that characteristic signatures of certain pore types overlap with scale artifacts in the connectivity functions. The Γ‐indicator, gives highly biased information in small samples. Therefore, we developed a new method for a joint‐Γ‐curve that merges information from three samples sizes. However, χ does not require such a scale fusion. It can be used to define characteristic size ranges for pore types and is very sensitive to the occurrence of bottle necks. Our findings suggest a joint evaluation of both connectivity metrics to disentangle different pore types with χ and to identify the contribution of different pore types to the overall pore connectivity with Γ. This evaluation on the chronosequence showed that biopores mainly connect pores of diameters between 0.5 and 0.1 mm. This was not coupled with an increase in pore volume. In contrast, tillage led to a shift of pores of diameter >0.05 mm towards pores of diameter >0.20 mm and thus increased connectivity of pores >0.20 mm. This work underlines the importance of accounting for the scale dependence of connectivity measures and provides a methodological approach for doing so. HIGHLIGHTS: Scale dependence of connectivity metrics needs to be accounted for. Connectivity metrics can be used to disentangle different pore types across scales. Roots mainly connect the pore system between 0.1 and 0.5 mm. A joint Γ‐connectivity function can be constructed that is free of scale artifacts.

The effects of straw incorporation with plastic film mulch on soil properties and bacterial community structure on the loess plateau

Abstract: The application of plastic film mulch and the return and incorporation of crop straw into topsoil as independent treatments affect soil physicochemical properties, including nutrient balance/cycling. It remains unclear whether combining straw incorporation and plastic film mulch significantly affects soil physicochemical properties and bacterial communities. We conducted a two‐factor (plastic film mulch application and maize straw incorporation) randomized block design experiment with four treatments: no plastic film mulch or straw incorporation (C), plastic film mulch (M), straw incorporation without mulch (CS) and straw incorporation with mulch (MS). Soil was sampled at the end of the growing cycle after 3 years of treatment. Soil organic carbon (SOC), total nitrogen (TN) and nitrate‐nitrogen (NO₃⁻‐N) concentrations significantly improved after straw incorporation. Plastic film mulch had a significant negative effect on soil bacterial richness, whereas straw incorporation had no effect. Straw incorporation had a significant positive effect on bacterial diversity, whereas plastic film mulch had no effect. The MS and M treatments had significantly more Proteobacteria than the C and CS treatments. Formation of the soil bacterial community structure was driven by soil TN, NO₃⁻‐N and SOC in the treatments with straw incorporation, and soil ammonium‐nitrogen (NH₄⁺‐N) in the treatments without straw incorporation. In conclusion, plastic film mulch coupled with straw incorporation can significantly change the taxonomical and functional composition of soil bacterial communities and enhance soil bacterial diversity by affecting carbon and nitrogen cycling in cropland soils of farmland, especially in arid and semiarid regions. HIGHLIGHTS: SOC, TN and NO₃⁻–N concentrations significantly improved after straw incorporation Straw incorporation had a greater effect on bacterial communities than plastic film mulch Soil bacterial community structure was driven by soil TN, NO₃⁻–N and SOC after straw incorporation Soil bacterial community structure was driven by soil NH₄⁺‐N without straw incorporation.

Influence of soil structure on the spread of Pseudomonas fluorescens in soil at microscale

Abstract: For over a half a century, researchers have been aware of the fact that the physical and chemical characteristics of microenvironments in soils strongly influence the activity, growth and metabolism of microorganisms. However, many aspects of the effect of soil physical characteristics, such as the pore geometry, remain poorly understood. Therefore, the objective of the present research was to determine the influence of soil pore characteristics on the spread of bacteria, observed at the scale relevant to microbes. Pseudomonas fluorescens was introduced in columns filled with 1–2 mm soil aggregates, packed at different bulk densities. Soil microcosms were scanned at 10.87 μm voxel resolution using X‐ray computed tomography (CT) to characterize the geometry of pores. Thin sections were prepared to determine the spread and colonization of bacteria. The results showed that average bacterial cell density was 174 cells mm⁻² in soil with bulk density of 1.3 g cm⁻³ and 99 cells mm⁻² in soil with bulk density of 1.5 g cm⁻³. Soil porosity and solid‐pore interfaces influence the spread of bacteria and their colonization of the pore space at lower bulk density, resulting in relatively higher bacterial densities in larger pore spaces. The study also demonstrates that thin sectioning of resin‐impregnated soil samples can be combined with X‐ray CT to visualize bacterial colonization of a 3D pore volume. This research therefore represents a significant step towards understanding how environmental change and soil management impact bacterial diversity in soils. HIGHLIGHTS: We used a quantitative approach to study bacterial spread in soil at scales relevant to microbes. The rate of pseudomonas spread decreased with increased bulk density of soil. Soil porosity and soil‐pore interface influence Pseudomonas in lower bulk density soil. Soil structure with different pore characteristics effects spread and activity of bacteria in soil.

Soil multifunctionality: Synergies and trade-offs across European climatic zones and land uses

Abstract: With increasing societal demands for food security and environmental sustainability on land, the question arises: to what extent do synergies and trade-offs exist between soil functions and how can they be measured across Europe? To address this challenge, we followed the functional land management approach and assessed five soil functions: primary productivity, water regulation and purification, climate regulation, soil biodiversity and nutrient cycling. Soil, management and climate data were collected from 94 sites covering 13 countries, five climatic zones and two land-use types (arable and grassland). This dataset was analysed using the Soil Navigator, a multicriteria decision support system developed to assess the supply of the five soil functions simultaneously. Most sites scored high for two to three soil functions, demonstrating that managing for multifunctionality in soil is possible but that local constraints and trade-offs do exist. Nutrient cycling, biodiversity and climate regulation were less frequently delivered at high capacity than the other two soil functions. Using correlation and co-occurrence analyses, we also found that synergies and trade-offs between soil functions vary among climatic zones and land-use types. This study provides a new framework for monitoring soil quality at the European scale where both the supply of soil functions and their interactions are considered. Highlights: Managing and monitoring soil multifunctionality across Europe is possible. Synergies and trade-offs between soil functions exist, making it difficult to maximize the supply of all five soil functions simultaneously. Synergies and trade-offs between soil functions vary by climatic zone and land-use type. Climate regulation, biodiversity and nutrient cycling are less frequently delivered at high capacity.

Comparing two theories about the nature of soil phosphate

Abstract: Two theories about the nature of phosphate in soil are current. One holds that soil phosphate is mostly present as particles of iron, aluminium and calcium phosphates: the precipitate‐particulate theory. The other holds that phosphate is mostly adsorbed and penetrates heterogeneous, variable‐charge particles: the adsorption‐penetration theory. This is the only theory that is consistent with and can be deduced from observations. It is my contention that the persistence of the precipitate‐particulate theory leads to: wasted research effort in trying to identify the supposed phosphate fractions; failure to recognize the long‐term changes in soil phosphate due to repeated applications, and thus to over‐fertilisation; and misapprehension about the effects of pH on phosphate availability.

Statistical approaches for spatial sample survey: Persistent misconceptions and new developments

Abstract: Several misconceptions about the design-based approach for sampling and statistical inference, based on classical sampling theory, seem to be quite persistent. These misconceptions are the result of confusion about basic statistical concepts such as independence, expectation, and bias and variance of estimators or predictors. These concepts have a different meaning in the design-based and model-based approach, because they consider different sources of randomness. Also, a population mean is still often confused with a model mean, and a population variance with a model-variance, leading to invalid formulas for the variance of an estimator of the population mean. In this paper the fundamental differences between these two approaches are illustrated with simulations, so that hopefully more pedometricians get a better understanding of this subject. An overview is presented of how in the design-based approach we can make use of knowledge of the spatial structure of the study variable. In the second part, new developments in both the design-based and model-based approach are described that try to combine the strengths of the two approaches.

Wet sieving versus dry crushing: Soil microaggregates reveal different physical structure, bacterial diversity and organic matter composition in a clay gradient

Abstract: Soil microaggregates contain particles of different sizes, which may affect their potential to store organic carbon (OC). A variety of methods can be used to isolate microaggregates from the larger soil structures, among which wet sieving approaches are widely employed. We developed a novel dry crushing method that isolates microaggregates along failure planes due to mechanical stresses rather than hydraulic pressures and compared the mechanical stability, OC contents and microbial community composition between dry‐crushed and wet‐sieved samples with contrasting clay contents. Dry‐crushed samples exhibited a higher stability and bacterial diversity compared to wet‐sieved samples. As a result, the dry‐crushed microaggregates had different size distributions when analysed dry and after wetting. In the dry state, dry‐crushed microaggregates were larger and contained more sand‐sized primary particles within the aggregate structures. The wetting of dry‐crushed aggregates caused a disintegration of larger microaggregates and sand‐sized primary particles into smaller microaggregates that contained finer particles. In the soils with lower clay contents, the diameter of dry‐crushed microaggregates was 40 μm larger due to more sand‐sized primary particles remaining within the aggregates. Depending on how much volume in microaggregates is occupied by large primary particles, the OC concentration increased in the soil with higher clay content. Wet‐sieved size fractions also showed a similar pattern of OC distribution, whereas more primary particles were observed outside of aggregates. Wet sieving approaches disperse the soil into OC‐rich aggregates and might be preferable if OC dynamics are investigated. Differences in bacterial community composition in dependence on clay content were more pronounced in dry‐crushed microaggregates. If intact aggregate architectures are of interest for the isolation of soil structural units, the presented dry crushing method might provide an advantageous alternative that also better preserves bacterial diversity.

Inconsistent effects of agricultural practices on soil fungal communities across twelve European long-term experiments

Abstract: Cropping practices have a great potential to improve soil quality through changes in soil biota. Yet the effects of these soil improving cropping systems on soil fungal communities are not well known. Here, we analysed soil fungal communities using standardized measurements in 12 long‐term experiments and 20 agricultural treatments across Europe. We were interested in whether the same practices (i.e. tillage, fertilization, organic amendments and cover crops) applied across different sites have predictable and repeatable effects on soil fungal communities and guilds. The fungal communities were very variable across sites located in different soil types and climatic regions. The arbuscular mycorrhizal fungi (AMF) were the fungal guild with most unique species in individual sites while plant pathogenic fungi were most shared between the sites. The fungal communities responded to the cropping practices differently in different sites and only fertilization showed a consistent effect on AMF and plant pathogenic fungi while the response to tillage, cover crops and organic amendments were site, soil and crop species specific. We further show that the crop yield is negatively affected by cropping practices aimed at improving soil health. Yet, we show that these practices have the potential to change the fungal communities and that change in plant pathogenic fungi and in AMF is linked to the yield. We further link the soil fungal community and guilds to soil abiotic characteristics and reveal that especially Mn, K, Mg and pH affect the composition of fungi across sites. In summary, we show that fungal communities vary considerably between sites and that there are no clear directional responses in fungi or fungal guilds across sites to soil improving cropping systems but that the responses vary based on soil abiotic conditions, crop type, and climatic conditions. Details on experiments related to the data is provided in supplementary materials of the related article,Fungi: DNA was extracted using the modified Power Soil protocol (Harkes et al., ), with 0.25 g soil per sample and Lysing matrix E beads tubes (MP Biomedicals). Fungal DNA was amplified using primers ITS4ngs and ITS3mix1‐5 (Tedersoo et al., , ) and purified using AMPure magnetic beads (Beckman Coulter). Polymerase chain reactions (PCRs) were performed with 12.5‐μL Hotstart ready mix (Fisher scientific) and approximately 50 ng of DNA per reaction. Dual tags were added to samples (Illumina dual indexing kits v1‐3) using seven cycles of PCR. PCR products were further purified using magnetic beads. The DNA was quantified using a Qubit fluorometer and equimolar pooled into libraries of 285 and 250 samples each. Mock community samples with eight fungal strains were sequenced along with the experimental samples. Sequencing was performed using Illumina MiSeq pair‐end 2x300bp. Here we give the OTU table and taxa files as well as report all OTUs unique to one site. Soil Chemistry: Chemical soil properties were determined by AgroCares BV (Wageningen, the Netherlands). Soils for chemical analysis were dried at 50°C using fruit dryers, crushed and sieved (2 mm sieve). One part of the soil sample was homogenized and pulverized (<0.2 mm) using a planetary micro mill with 10 clean metal balls for 3 min with speed 500 rpm. This sample was used to measure the total C and N by heating it to 900°C in the presence of O2, forming CO2 and N2, which were quantitatively measured with a thermal conductivity detector. Peak areas are correlated with validated calibration curves, to obtain element weight for C and N, which is recalculated to percentage by considering the sample mass. Total organic carbon (TOC) was measured using the Elementar Rapid CS cube (Elementar Analysensysteme, Germany) after removal and quantification of the total inorganic carbon (TIC) fraction as carbonates through acid (1 M HCl) treatment. Samples for soil texture were weighed and treated with 30% H2O2 for the removal of organic material, treated with dithionite solution (40 g/L Na2S2O4 in 0.3 M NaOAc, pH 3.8) for the removal of iron oxide, and treated with 1 M HCl for the removal of carbonates. After this sample treatment, the samples were measured with the Mastersizer 3,000 (Malvern Panalytical B.V., Almelo, the Netherlands) to determine the particle size distribution using laser diffraction. Soil pH (KCl) was determined using a pH electrode. The procedure for the extraction of soils using Mehlich‐3 solution as extractant was validated and executed according to Wolf and Beegle (), with one exception, the shaking time was increased from 5 to 10 min. The measurement of samples for the determination of bulk multi‐element concentrations in dry soil samples (RT: Real Totals) was carried out using the PANalytical Epsilon 3 ED‐XRF (Malvern Panalytical B.V., Almelo, the Netherlands). The procedure is in accordance with ISO18227:2014 and validated. The samples were prepared as pellets with a soil to wax ratio of 9:1. Lastly, cation exchange capacity (CEC) and the content of exchangeable cations (Al3+, Ca2+, Fe2+, K+, Mg2+, Mn2+, Na+, B+, Cu2+, Mo2+, Ni2+ and Zn2++) and anions (S2−, P3−) in soils were determined after extraction with hexamminecobalt trichloride solution. The procedure was validated and is in accordance with ISO 23470:2007.

Sustainable futures over the next decade are rooted in soil science

Abstract: The importance of soils to society has gained increasing recognition over the past decade, with the potential to contribute to most of the United Nations’ Sustainable Development Goals (SDGs). With unprecedented and growing demands for food, water and energy, there is an urgent need for a global effort to address the challenges of climate change and land degradation, whilst protecting soil as a natural resource. In this paper, we identify the contribution of soil science over the past decade to addressing gaps in our knowledge regarding major environmental challenges: climate change, food security, water security, urban development, and ecosystem functioning and biodiversity. Continuing to address knowledge gaps in soil science is essential for the achievement of the SDGs. However, with limited time and budget, it is also pertinent to identify effective methods of working that ensure the research carried out leads to real-world impact. Here, we suggest three strategies for the next decade of soil science, comprising a greater implementation of research into policy, interdisciplinary partnerships to evaluate function trade-offs and synergies between soils and other environmental domains, and integrating monitoring and modelling methods to ensure soil-based policies can withstand the uncertainties of the future. Highlights: We highlight the contributions of soil science to five major environmental challenges since 2010. Researchers have contributed to recommendation reports, but work is rarely translated into policy. Interdisciplinary work should assess trade-offs and synergies between soils and other domains. Integrating monitoring and modelling is key for robust and sustainable soils-based policymaking.

Contrasting effects of different pH‐raising materials on N2O emissions in acidic upland soils

Abstract: Acidic soils, occupying ca. 40% of the world's arable soils, often need to be managed (e.g., to raise their pH and to improve crop productivity); however, the environmental impact of raising soil pH is often difficult to assess. Increasing soil pH stimulates the reduction of N₂O to N₂, thus lowering N₂O emissions associated with denitrification, but can also increase autotrophic nitrification rates and related N₂O emission. Using a ¹⁵N tracing technique, we provide process‐based insights into the effects of two acid‐neutralizing materials (quicklime [CaO] vs. pig manure) on N₂O emissions in an acidified upland soil that had experienced excessive N application. Without pH adjustments we found that N₂O emissions, stimulated by supply of reactive N, were related to denitrification‐ and heterotrophic nitrification‐derived N₂O emissions, whereas autotrophic nitrification‐derived N₂O emissions declined with decreasing soil pH. These effects were reversed by increasing soil pH via liming. However, increasing the soil pH via application of pig manure significantly increased soil N₂O emissions from both nitrification and denitrification. Our study highlights that pH‐amelioration practices may enhance N₂O emissions depending on the type of material applied to the soil. Therefore, both pH remediation and greenhouse gas mitigation options need to be considered together to avoid adverse environmental effects. The effect of different acid‐neutralizing materials on soil N₂O emissions should be incorporated into ecosystem models to better estimate global N₂O emissions when pH amelioration is practised. HIGHLIGHTS: Enhanced N₂O emission by N input was from denitrification and heterotrophic nitrification. Chemical N input and liming have reversible effects on N₂O emission. Soil N₂O emission was decreased by liming but increased by animal manure input. Careful consideration of pH raising substrates is needed to avoid adverse effects.

Grassland management effects on earthworm communities under ambient and future climatic conditions

Abstract: The impacts of climate change on biodiversity can be modulated by other changing environmental conditions (e.g. induced by land‐use change). The potential interactive effects of climate change and land use have rarely been studied for soil organisms. To test the effects of changing climatic conditions and land use on soil invertebrates, we examined earthworm communities across different seasons in different grassland‐use types (intensively managed grassland, extensively managed meadow and extensively managed sheep pasture). We predicted that the strength of climate change effects would vary with season and land use. Overall, extracted earthworm populations showed the strongest variations in response to the season, indicating major differences in activity patterns and extraction efficiency, whereas climate change and different grassland‐use types had fewer and weaker effects. Future climate, characterized by slightly higher precipitation in spring and autumn but a strong reduction during the summer, had positive effects on the abundance of extracted adult earthworms in spring but then reduced the abundance of active earthworms across the remaining seasons. In contrast, the total biomass of juveniles tended to be consistently lower under future climate conditions. Earthworm species responded differently to the climate change and different grassland management types, and these species‐specific responses further varied strongly across seasons. Intensive grassland management had negative effects, due to plant community composition, whereas sheep grazing favoured earthworm populations, due to dung deposition. There were only limited interactive effects between climate and land use, which thus did not support our main hypothesis. Nevertheless, these results highlight the complex and context‐dependent responses of earthworm communities and activity patterns to climate change, with potential consequences for long‐term population dynamics and crucial ecosystem functions. HIGHLIGHTS: We explored earthworm communities in response to climate change, different grassland‐use types and seasons Climate had species‐specific effects on active earthworms, but few interactions with land‐use type Intensive grassland management decreased, but sheep grazing favoured, active earthworm populations Strong seasonal variations in earthworm activity periods will be modulated by climate change

Seasonal patterns of greenhouse gas emissions from a forest‐to‐bog restored site in northern Scotland: Influence of microtopography and vegetation on carbon dioxide and methane dynamics

Abstract: Funding information Scottish Forestry; University of Aberdeen Abstract Northern peatlands play an important role in the regulation of the atmospheric greenhouse gas (GHG) balance, functioning as a net carbon sink with low rates of organic decomposition. However, perturbations such as drainage increase peat oxidation, which may lead to enhanced gaseous release of carbon. For this reason, the number of restoration projects that aim to rewet blanket bogs has increased in the last few years, but there is still a lack of understanding of the impact of restoration on emissions of greenhouse gases, such as methane, particularly in sites restored from forestry. In this paper, we investigate the seasonal greenhouse gas dynamics in a forest-to-bog restoration site in Scotland. We analyse the effects of restoration on both carbon dioxide and methane fluxes, and investigate which site factors (microtopography, vegetation type, soil moisture and temperature) drive the processes of gaseous exchange between the bog surface and the atmosphere. Our results show that the original surface is near greenhouse gase equilibrium at −0.28 gCO2eq m day and that microtopographic features act as a net greenhouse gas sink (ridges = −0.94 gCO2eq m day and furrows = −0.86 gCO2eq m day), whereas the bog pool is a net source of greenhouse gases (0.98 gCO2eq m day). We found different vegetation species play a key role in greenhouse gas flux dynamics, especially in forestry-derived microtopographical features, and their presence and influence on greenhouse gas dynamics should be accounted for to provide a more comprehensive understanding of emissions associated with restoration management practices.

Compressing soil structural information into parameterized correlation functions

Abstract: Soil structure is highly interconnected to all of its properties and functions. The structure for most soils is very complex and hierarchical in nature. Considering the fact that a truly multiscale digital 3D soil structure model for a single genetic horizon, even with the resolution not finer than 1 μm, will contain an enormous amount (approx. up to 10¹⁵ voxels or even more) of data, it is an appealing idea to compress this structural information. Effective management and pore‐scale simulations based on such datasets do not seem feasible at the moment. Another approach would be to reduce the complexity to a limited but meaningful set of characteristics/parameters, for example using universal correlation functions (CFs). In this study, we successfully compressed the soil structural information in the form of 3D binary images into a set of correlation functions, each of which is described using only six parameters. We used four different correlation functions (two‐point probability, lineal, cluster and surface‐surface functions) computed in three orthogonal directions for the pores. The methodology was applied to 16 different soil 3D images obtained using X‐ray microtomography (XCT) and segmented into pores and solids. All computed CFs were fitted using a superposition of three basis functions. In other words, we reduced 900–1300³ voxel images into sets of 72 parameters. Fitting of computed correlation functions and reducing them to a number of parameters is a powerful way of compressing soil structural information. However, the analysis based on parameters alone is different from the one where correlation functions are used. This problem can be negated by uncompressing the correlation functions back from these parameters before any application. This way, correlation functions are not only a way to compress the soil structural information with minimal loss, but also may be used to solve a number of additional problems, including the comparison and differentiation of soil samples, location of elementary volumes, effective physical property prediction using machine learning, and fusion of hierarchical soil structures. HIGHLIGHTS: The 900–1300³ voxels soil XCT scans were compressed into sets of 72 parameters The use of fitted parameters alone may result in the inconsistent analysis of the soil structures Each soil structure was uniquely described by a set of directional correlation functions Correlation functions were found to be sensitive to the structural difference of all the studied soils

Long‐term zero‐tillage enhances the protection of soil carbon in tropical agriculture

Abstract: Contrasting tillage strategies not only affect the stability and formation of soil aggregates but also modify the concentration and thermostability of soil organic matter associated with soil aggregates. Understanding the thermostability and carbon retention ability of aggregates under different tillage systems is essential to ascertain potential terrestrial carbon storage. We characterised the concentration and thermostability of soil organic carbon within various aggregate size classes under both zero and conventional tillage using novel Rock-Eval pyrolysis. The nature of the pore systems was visualised and quantified by X-ray Computed Tomography to link soil structure to organic carbon preservation and thermostability. Soil samples were collected from experimental fields in Botucatu, Brazil, which had been under zero-tillage for 2, 15 and 31 years, along with adjacent fields under conventional tillage. Soils under zero-tillage significantly increased pore connectivity whilst simultaneously decreasing inter-aggregate porosity (10% compared to 4% in conventional and zero-tilled macroaggregates respectively), providing a potential physical mechanism for protection of soil organic carbon in the 0-20 cm soil layer. Changes in the soil physical characteristics associated with the adoption of zero-tillage resulted in improved aggregate formation compared to conventionally tilled soils, especially when implemented for at least 15 years, with the mean weight diameter of aggregates increasing by 74% in zero-tilled surface soils). In addition, we identified a chemical change in composition of organic carbon to a more recalcitrant fraction following conversion to zero-tillage, suggesting aggregates were accumulating soil organic carbon, rather than being exposed to mineralisation by the soil microbial community. These data reveal profound effects of different tillage systems upon soil structural modification, with important implications for the potential of zero-tillage to increase carbon sequestration compared to conventional tillage.