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Journal ArticleDOI

3D analysis of the soil porous architecture under long term contrasting management systems by X-ray computed tomography

01 Aug 2019-Soil & Tillage Research (Elsevier BV)-Vol. 191, pp 197-206

AbstractThe development of adequate soil structure is important for achieving good physical status, which influences the sustainability of agricultural areas. Different management systems lead to the development of a wide range of soil pore network characteristics. The objective of this research was to analyze the effect of three contrasting tillage systems (zero-tillage, ZT; reduced tillage, RT; conventional tillage, CT) in the soil porous system of an Oxisol. Samples were collected from the surface layer (0–10 cm). An area under secondary forest (F) was also assessed to provide an undisturbed reference. X-ray Computed Tomography (μCT) scanning of undisturbed soil samples and image analysis were employed for analysis of the pore network. The soil under ZT had the smallest porosity in comparison to the other management systems. The conventionally tilled soil had the largest porosity and the most connected pores. One large connected pore was responsible for around 90% of the porosity of the resolvable pores (>35 μm) studied for all the management systems. Pores of elongated shapes, which enhance water movement through the soil, were the most frequent pores in terms of shape.

Topics: Soil structure (62%), Soil test (58%), Porosity (55%), Conventional tillage (53%), Tillage (52%)

Summary (1 min read)

1. INTRODUCTION

  • The objective of this particular research was to apply the X-ray Computed Tomography technique to evaluate, in 3D and at the µm scale, the morphological properties of an Oxisol under contrasting soil management systems.
  • Experimental areas under long term zero-tillage and reduced and conventional tillage systems were investigated.
  • Samples were collected at the soil surface layer (0-10 cm).

2. MATERIALS AND METHODS

  • Differences in the soil morphological parameters due to the treatments were evaluated by a one-way analysis of variance followed by Tukey's HSD post hoc tests.
  • Results were classified as statistically significant at p<0.05.
  • Parameters such as the mean, standard deviation and coefficient of variations were also measured for each soil physical property analyzed.
  • Pearson correlations among each pair of variables were measured for some of the morphological properties.
  • The statistical analysis was carried out using PAST software (Hammer et al., 2001) .

3. RESULTS AND DISCUSSION

  • This type of pore system is related to soil structural development and it is indicative of structures that function well for water infiltration (Bullock and Thomasson, 1979) .
  • Garbout et al. (2013) determined that the volume of connected pores constituted 91% and 85% for drilling and ploughing areas, which indicates the great contribution of a main pore network to the overall porosity.
  • Dal Ferro et al. ( 2014) also observed a contribution of around 70% of macropores to porosity, which would contribute to water infiltration and potentially reduce erosion (Imhoff et al., 2010) .

CONCLUSIONS

  • The authors analyzed the structure of samples of an Oxisol under different management systems using X-ray Computed Tomography.
  • The results of pore connectivity, degree of anisotropy and tortuosity show that the soil structure under ZT was not negatively affected by the reduction in its porosity.
  • Similar to the 3D image visualizations, the largest contribution to porosity was due to the presence of a main pore network, which means the porous system was well connected in all the management systems.
  • The results of this study provided a detailed characterization of the soil porous system at the micrometric scale.

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1
3D analysis of the soil porous architecture under
long term contrasting management systems by X-ray
Computed Tomography
L.F. Pires
a
, W.L. Roque
b
, J.A. Rosa
c
, S.J. Mooney
d
a
Laboratory of Physics Applied to Soils and Environment, Department of Physics, State University of Ponta Grossa,
84.030-900, Ponta Grossa, PR, Brazil
b
Petroleum Engineering Modelling Laboratory, Department of Scientific Computation, Federal University of Paraíba,
58.051-900, João Pessoa, PB, Brazil
c
Laboratory of Soil Physics, Agricultural Research Institute of Paraná, 84.001-970, Ponta Grossa, PR, Brazil
d
Division of Agricultural and Environmental Sciences, School of Biosciences, University of Nottingham, Sutton
Bonington Campus, Leicestershire LE12 5RD, UK
Corresponding author:
Prof. Dr. Luiz F. Pires, Phone: (55) 42 3220 3044. Fax: (55) 42-3220-3042
E-mail: lfpires@uepg.br (Luiz F. Pires);
Proofs should be sent to:
Prof. Luiz Fernando Pires, Departamento de Física, Universidade Estadual de Ponta Grossa,
Campus de Uvaranas, Bloco L, Sala 15B; Av. Carlos Cavalcanti, 4748, CEP 84.030-900, Ponta
Grossa, PR, Brazil.

2
3D analysis of the soil porous architecture under long1
term contrasting management systems by X-ray2
Computed Tomography3
L.F. Pires
a,1
, W.L. Roque
b
, J.A. Rosa
c
, S.J. Mooney
d
4
a
Laboratory of Physics Applied to Soils and Environment, Department of Physics, State5
University of Ponta Grossa, 84.030-900, Ponta Grossa, PR, Brazil6
b
Petroleum Engineering Modelling Laboratory, Department of Scientific Computation, Federal7
University of Paraíba, 58.051-900, João Pessoa, PB, Brazil8
c
Agricultural Research Institute of Paraná, 84.001-970, Ponta Grossa, PR, Brazil9
d
Division of Agricultural and Environmental Sciences, School of Biosciences, University of10
Nottingham, Sutton Bonington Campus, Leicestershire LE12 5RD, UK11
12
ABSTRACT13
The development of adequate soil structure is important for achieving good physical14
status, which influences the sustainability of agricultural areas. Different management15
systems lead to the development of a wide range of soil pore network characteristics.16
The objective of this research was to analyze the effect of three contrasting tillage17
systems (zero-tillage, ZT; reduced tillage, RT; conventional tillage, CT) in the soil18
porous system of an Oxisol. Samples were collected from the surface layer (0-10 cm).19
An area under secondary forest (F) was also assessed to provide an undisturbed20
reference. X-ray Computed Tomography (µCT) scanning of undisturbed soil samples21
and image analysis were employed for analysis of the pore network. The soil under ZT22
1
Corresponding author
Tel.: +55 42 3220-3044
E-mail addresses: luizfpires@gmail.com; lfpires@uepg.br (L.F. Pires)

3
had the smallest porosity in comparison to the other management systems. The23
conventionally tilled soil had the largest porosity and the most connected pores. One24
large connected pore was responsible for around 90% of the porosity of the resolvable25
pores (>35 µm) studied for all the management systems. Pores of elongated shapes,26
which enhance water movement through the soil, were the most frequent pores in27
terms of shape.28
Keywords: Minimum tillage; Zero-tillage; Conventional tillage; Morphological properties;29
X-ray microtomography; Soil structure.30
1. INTRODUCTION31
The use of tillage has been employed for centuries to improve soil structure for32
enhanced crop development. However, the choice of tillage systems can have a33
significant impact on a soil heath and quality. Sustainable farming systems greatly34
depend on soil quality (Bünemann et al., 2018). Soil tillage provokes substantial35
changes in several soil physical properties such as total porosity, bulk density, water36
retention and infiltration, penetration resistance, pore size distribution, connectivity and37
tortuosity (Imhoff et al., 2010; Daraghmeh et al., 2009; Blanco-Canqui et al., 2004;38
Katsvairo et al., 2002).39
In Brazil the adoption of minimum tillage systems such as reduced (RT) and40
zero tillage (ZT) is common. The total Brazilian area used in crop production is around41
66 million hectares and there are over 31 million hectares under ZT (FEBRAPDP,42
2013). Conventional tillage (CT) is characterized by the disruption of the top soil due to43
ploughing and harrowing operations employed to turn over and loosen the soil. As a44
result of these operations, macropores are created and pore continuity is disrupted,45
which directly affect the water movement (e.g. hydraulic conductivity and infiltration)46
and retention (Blanco-Canqui et al., 2017; Ogunwole et al., 2015; Cássaro et al., 2011;47
Imhoff et al., 2010). Minimum tillage systems such as RT and ZT do not usually lead to48

4
drastic soil structure changes. These systems, known as conservation techniques,49
have been utilized as a means of reducing tillage and field costs as well as for50
conserving soil structure due to reduced disturbance (Aziz et al., 2013; Cavalieri et al.,51
2009). The residues of the previous crop are left intact and the absence of harrowing in52
ZT and RT can increase soil organic carbon and aggregate stability, reduce CO
2
53
emissions and moderate fluxes of water, air and heat through the soil (Aziz et al., 2013;54
Daraghmeh et al., 2009; Zibilske and Bradford, 2007).55
The fluxes of water and air, organic matter decomposition, plant-available water56
and soil resistance to erosion are directly linked to the architecture of the soil porous57
system. Mesopores and macropores play an important role in these processes (Imhoff58
et al., 2010; Fuentes et al., 2004; Cameira et al., 2003). In CT, the soil porous system59
is affected by operations such as ploughing and harrowing, which can increase porosity60
and loosen soil (Mangalassery et al., 2014). This operation allows good root growth61
and air exchange, while the exposition of the soil to rain in tropical regions can62
sometimes lead to erosion (Alvarez et al., 2009). On the other hand, the activity of63
earthworms and root decay help to create channels and burrows under RT and ZT,64
which facilitate drainage and gaseous diffusion (Soto-Gómez et al., 2018; Carducci et65
al., 2017; Pires et al., 2017; Pierret et al., 2002).66
Based on the important functions that mesopores and macropores fulfill for a67
healthy soil, techniques to image and measure key properties such as X-ray Computed68
Tomography (µCT) are very important (Tseng et al., 2018; Yang et al., 2018; Ferreira69
et al., 2018; Pagenkemper et al., 2014). The spatial distribution of pores can be non-70
destructively imaged at high resolutions and in three dimensions (3D) by µCT (e.g.71
Galdos et al. 2018; Helliwell et al., 2013; Peth et al., 2008). µCT has been previously72
applied with success to study the size, shape, number, connectivity, degree of73
anisotropy, macropore thickness, fractal dimension and tortuosity of the soil porous74
system (Wang et al., 2016; Dal Ferro et al., 2014; Garbout et al., 2013; Vogel, 1997).75

5
This provides vital information to characterize the physical structure of the porous76
system, which allows a better understanding of key processes (i.e. mass and energy77
transport, nutrient cycling, root development) within the soil (Hillel, 2004).78
Previous studies on evaluating the influence of tillage systems at the µm scale79
in 3D in tropical soils are still scarce. In Brazil, one of the largest food and agricultural80
producers of the world, previous studies have characterized the soil porous system at81
µm to measure the porosity and pore size distribution of Brazilian Oxisols (Vaz et al.,82
2011), assessed the effect of tillage systems on the percentage of macropores83
(Beraldo et al., 2014) and explored the spatial and morphological configuration of the84
pore space of Oxisols under CT (Carducci et al., 2017, 2014). Other studies have85
determined the influence of ZT on the pore size and shape distribution of macropores86
(Passoni et al., 2015), tested the capacity of soil recovering under different87
management strategies (Marchini et al., 2015) and measured the impact of ZT and CT88
on the pore size and shape distribution and water retention (Pires et al., 2017). Recent89
work has analyzed the soil structure utilizing the geometrical parameters of the soil90
porous system (Tseng et al., 2018), considered the influence of liming on the structure91
of aggregates under ZT (Ferreira et al., 2018) and revealed the structural development92
associated with long term (>30 years) ZT (Galdos et al., 2018).93
The objective of this particular research was to apply the X-ray Computed94
Tomography technique to evaluate, in 3D and at the µm scale, the morphological95
properties of an Oxisol under contrasting soil management systems. Experimental96
areas under long term zero-tillage and reduced and conventional tillage systems were97
investigated. Samples were collected at the soil surface layer (0-10 cm).98
2. MATERIALS AND METHODS99
The experimental field plots of this study were located in Ponta Grossa, in a100
humid mesothermal Cfb-subtropical region in southern Brazil (25°09’S, 50°09’W, 875 m101

Figures (8)
Citations
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Journal ArticleDOI
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.

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Cites background from "3D analysis of the soil porous arch..."

  • ...…examined the influence of tillage on the connectivity of macropores, showed both that tillage increases (Pihlap et al., 2019; Pires et al., 2017; Pires et al., 2019; Schlüter et al., 2018) or decreases (Dal Ferro et al., 2014; Lucas et al., 2019; Zhao et al., 2017) the connectivity of the pore…...

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Abstract: Conservation agriculture promotes as one of its three key principles the reduction of tillage intensity to minimize soil physical disturbances. The choice of tillage system alters hydraulic conductivity at (Ks) and near saturation. Drier regions of the hydraulic conductivity characteristic (HCC) may be affected as well. Temporal variations of the HCC along with water retention characteristics of tilled soils have come into the focus of researchers in recent years. It was shown that it may be preferable to account for such variations in soil water modelling. Here, the effects of a conventional tillage (CT), reduced tillage (RT) and no tillage (NT) system on the HCC were investigated on an experimental field with a Haplic Luvisol in Eastern Germany throughout part of a winter wheat growing season. This included changes following agricultural management such as stubble breaking and seedbed preparation. Hood infiltrometer measurements were conducted in the field and transient evaporation experiments in the laboratory were performed on undisturbed soil cores to describe the HCC over a wide range of pressure heads (h) from saturation to −1000 cm (pF 3). On tilled plots, Ks and hydraulic conductivity at h = −2 cm (K−2 cm) were more variable with time than observed spatial variability. Overall, Ks was significantly (p

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Abstract: Soil structure is an indicator of soil quality and its alterations following cropping system conversion or fertilization change evolve slowly. How such alterations vary with scale remains elusive. We investigated this based on the Rothamsted long-term wheat experiment (since 1843) in the UK. Triplicate cores 7 cm high and 10 cm in diameter were taken from plots that have been under different fertilizations or returned to natural woodland for more than one century for imaging using X-ray computed tomography with the voxel size being 40 µm. We then broke each core and sampled three aggregates from it to scan with the voxel size being 1.5 µm. For each core and aggregate sample, we calculated its pore size distribution, permeability and tortuosity. The results showed that the fertilization change >170 years ago reshaped the soil structure differently between the core scale and the aggregate scale. Macro-porosity of the pores (>40 µm) in the cores unfertilized or fertilized with inorganic fertilizers was low and the pores were poorly connected in the top 10 cm of soil, compared to those given farmyard manure or in the woodland. In all treatments, the pores in the core images were hydraulically anisotropic with their permeability in the horizontal direction being higher than that in the vertical direction, whereas the aggregates were comparatively isotropic. The fertilization affected image porosity and permeability at core scale more significantly than at aggregate scale, and the aggregates fertilized with farmyard manure and in the woodland were more permeable than the aggregates in other treatments. It was also found that compared to no-fertilization or fertilization with complete fertilizers, fertilizing without phosphorus over the past 20 years increased the porosity and permeability of the aggregates but not of the cores. Fertilization with inorganic fertilizers increased the tortuosity of the macropores in the cores but not of the intra-aggregate pores, compared to no-fertilization. Porosity-permeability relationship for aggregates unfertilized or fertilized with inorganic fertilisers followed a power law with R2 > 0.8. In contrast, the permeability of the aggregates in farmyard manure and in the woodland trended differently as their porosity increased. The results also revealed that the transport ability of the aggregates and cores responded differently to carbon in that with soil carbon increasing, the permeability of the aggregates increased asymptotically while the permeability of the cores, especially its horizontal component, increased exponentially.

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DissertationDOI
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Abstract: During soil formation, the interaction of different biota (plants, soil fauna, microbes) with weathered mineral material shape unique structures depending on the parental material and the site specific climatic conditions. We here explore soil structure formation on a chronosequence in Rheinisch lignite mining area. In this area loess material from a depth of 4-10 m is used for reclamation in a standardized procedure since 24 years. Thus, it is an ideal site for studying soil structure formation as a function of time. Changes in soil pore system are characterised by parameters such as tortuosity, connectivity and pore size distribution. To derive these, undisturbed soil columns with a diameter of 10 cm were taken from two different depths (0-20 cm and 40-60 cm) with sites ranging in age from 0 to 24 years. X-ray CT is used for scanning the original columns as well as undisturbed subsamples of 3 and 1 cm diameter. This hierarchical sampling scheme was developed to overcome the trade-off between sample size and resolution – starting with an effective resolution of 57 µm for 10 cm cores via 19 µm for 3 cm columns to 6 µm for the smallest samples size of 1 cm. Subsamples therefore reveal information on micropores and small roots. The importance of roots for soil structure / pore system development in not only investigated in the CT images but also by destructive analyses and determination of root length with WinRHIZO The dataset is complemented by HYPROP measurements of water retention curves and unsaturated hydraulic conductivities; both functions of the pore system. In cooperation with project partners, VisNIR images from different slices of the soil columns will be taken to combine information about the local distribution of chemical features (iron oxides and organic compounds) with structural information of pores and roots. The current study is part of the DFG-Project Soil Structure (AOBJ: 628683).

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Cites background or result from "3D analysis of the soil porous arch..."

  • ...…µCT studies, which examined the influence of tillage on the connectivity of macropores, showed both, that tillage increases (Pihlap et al., 2019; Pires et al., 2019; Pires et al., 2017; Schlüter et al., 2018b) or decreases (Dal Ferro et al., 2014; Lucas et al., 2019; Zhao et al., 2017) the…...

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  • ...This is in line with several studies on conventional vs. no-tillage (Kravchenko et al., 2011; Pires et al., 2019; Rasmussen, 1999)....

    [...]

  • ...Also different tillage system lead to characteristically formed pores (Pires et al., 2019; Pires et al., 2017)....

    [...]


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