Estimating soil porosity and pore size distribution changes due to wetting-drying cycles by morphometric image analysis

https://doi.org/10.1016/j.still.2020.104814Get rights and content

Highlights

  • Microtomography showed modifications in soil structutre due to wet and dry cycles.

  • Wet-dry cycles promoted different changes in soil structure according to management.

  • Wet and dry cycles produced strong impacts in pore functionality.

Abstract

Porous systems such as soils tend to present great complexity when analyzed at the micrometer-scale. Processes such as tillage and repeated wetting and drying (W-D) cycles tend to continuously alter the structure of the soil. X-ray computed microtomography (μCT) is one of the techniques that can be utilized for quantifying changes in the soil micrometer-scale structure. The objective of this study was to analyze the effect of W-D cycles in the soil porous system of core samples submitted to contrasting management practices (conventional tillage – CT, minimum tillage – MT, no-tillage – NT). An algorithm based on the Mercury intrusion porosimetry method (MIP) was utilized for this purpose. An area of secondary forest (F) was used as a reference. The results of the porosity and functionality of the pores showed that the W-D cycles altered the pore distribution in all management systems. MT was the management that showed the most significant changes in the soil physical properties, where the application of W-D cycles caused fractions of transmission pores to become fissures. In CT, a significant reduction of transmission pores was observed, which indicates the effect of harrowing and plowing operations. Our results show that, depending on the management system adopted, the soil will respond differently to the action of W-D cycles with a direct influence on water retention and movement due to the induced changes in the soil porous system.

Introduction

Soils in natural conditions such as those found in areas under native forest are generally characterized by complex pore arrangements, mainly in the top layers, where the flora and the fauna have a direct impact. Soils submitted to different management practices tend to present modifications in their porous spaces due to the action of the machinery used to prepare it and the crop introduction (Bodner et al., 2013a, 2013b; Boyle and Powers, 2013).

Contrasting management practices can cause continuous changes in the physical properties of the soil, thus resulting in modifications mainly in its porous system with impacts in soil functionality and sustainability (de Andrade Bonetti et al. 2017; de Moraes et al., 2016; Bavoso et al., 2012). After these changes, the action of natural or artificial processes can contribute to soil recovering its functional and structural characteristics. According to de Moraes et al. (2016) and de Andrade Bonetti et al. (2017), soils under long-term no-tillage or with high contents of organic matter have a great ability to return to its original state or as close as possible to it. However, Bavoso et al. (2012) stated that the soil capacity to recover its quality is strongly dynamic and influenced by several different factors.

Wetting and drying (W-D) cycles represent an important process of modification of the soil structure and, consequently, of its porous system. Several physical properties, such as soil bulk density, total porosity, macroporosity, pore size, and shape distributions, are affected by the W-D cycles (Diel and Vogel, 2019; Yiping et al., 2016; Bodner et al., 2013a; Pires et al., 2009, 2008). Soils usually are submitted to W-D cycles as the effect of irrigation practices and the natural water regime processes (e.g., rain and evapotranspiration). Also, measurements of water retention properties such as the soil water retention curve involve the application of several W-D cycles to the soil samples, depending on the method employed (Pires et al., 2009; Bacchi et al., 1998). Jayanth et al. (2012) and Al-Kayssi (2016) reported that water retention properties are strongly influenced and can even be altered by intensive W-D cycles. Thereby, the application of W-D cycles can cause different responses in the porous system of soils under contrasting management systems during water retention properties evaluation, with impacts on the quality of -the acquired data. Thus, the use of techniques such as computed microtomography (μCT) makes it possible to complement the information regarding such modifications at a different scale of measurement, in general, few micrometers.

Methodologies that apply image analysis such as μCT have been widely used in the micromorphological analysis of porous systems such as soils (Pires et al., 2020, 2017a; Diel and Vogel, 2019; Galdos et al., 2019; Borges and Pires, 2012). This technique has enabled the quantification and estimation of image-based porosity, pore size distribution curves, and the characterization of the porous system based on porous functionality (Ferreira et al., 2019; Borges and Pires, 2012; Peth et al., 2008; Vogel and Roth, 2001; Capowiez et al., 1998).

The size of a soil pore determines its role in water transport and retention characteristics. The distribution of pores based on their sizes (i.e., the percentage of pores related to its equivalent diameter) defines what is known as the soil pore size distribution (PSD). The PSD is frequently used to follow and investigate modifications caused by climatic or anthropogenic interventions in the soil porous system (Chandrasekhar et al., 2019). It essentially allows the distinction between the distribution of micro and macro pores and somehow reflects the heterogeneity of the soil porous system. Heterogeneous porous media are frequently characterized by having pores distributed in a wide range of characteristic diameters and vice versa.

This kind of analysis is relevant due to the importance of the PSD considering the physical quality of any porous system. Image analysis methods based on three-dimensional (3-D) μCT data also enabled the proposition of models for the study of distribution, pore morphology, movement and fluid retention (liquid/gas) inside the soil, and porous system complexity (tortuosity and connectivity), among other studies (Diel and Vogel, 2019; Calistru and Jităreanu, 2015; Pires et al., 2013; Yang et al., 2014; Yang et al., 2009).

Researchers worldwide have worked on computer simulations based on μCT images aiming at quantifying the physical properties of different porous media (Yang et al., 2014; Khan et al., 2012; Garboczi and Bentz, 1990). The algorithms used in such simulations are usually based on experimental techniques, for example, Mercury intrusion porosimetry (MIP) (Dong et al., 2018; Do et al., 2013; Yang et al., 2009; Garboczi and Bentz, 1990). One of the advantages of these simulations is the preservation of the structure of the samples investigated, enabling the collection of valuable morphological information and the observation of the physical properties of such media (Dong et al., 2018; Calistru and Jităreanu, 2015; Khan et al., 2012; Yang et al., 2009; Peth et al., 2008).

The soil porous media is a dynamic system influenced by natural or artificial external processes. Among them, wetting and drying cycles are responsible for important changes in the soil structure. Laboratory and field studies have demonstrated that W-D cycles can greatly influence the soil bulk density and, consequently, the soil total porosity. Some studies have reported that the first W-D cycle usually causes the most important modifications on the soil structure (Kong et al., 2018; Tripathy et al., 2002; Leij et al., 2002). Nonetheless, studies that evaluate changes in the porous system of soils under contrasting management systems submitted to W-D cycles at the micrometric scale and in a 3-D perspective are still scarce in the literature.

Thus, this work aims to help researches to fill this gap by analyzing the modifications that W-D cycles can introduce in the structure of core samples submitted to contrasting management practices at the microscopic level of investigation. This was achieved by analyzing PSDs generated by computer simulations performed on 3-D μCT images. The computer program developed by Yang et al. (2009) was used to obtain the PSD. The soil pores were analyzed regarding their characteristic sizes and the modifications due to W-D cycles could be determined. Therefore, the work sought to relate the modifications observed in the porous system regarding the functionality of the soil pores and their size distribution.

Section snippets

Soil sampling

Soil samples were collected from areas submitted to different management practices located in an experimental station belonging to the “Instituto Agronômico do Paraná” (Agronomic Institute of Parana) at Ponta Grossa, in the southern region of Brazil (25° 09’ S, 50° 09’ W, 875 m a.s.l). The soil studied was a Rhodic Hapludox according to the Soil Survey Staff (2013). The soil was classified as a clay texture with 578 g kg-1 clay, 280 g kg-1 silt, and 142 g kg-1 sand. The management practices

Results and discussion

The PSDs of the samples for the different management practices investigated and for the soil under secondary forest submitted to the W-D cycles are shown in Fig. 2.

The application of W-D cycles caused distinct modifications to both the PSD characteristic amplitudes and the most frequent equivalent diameter of the pores in the different management practices under study. Regarding F and MT, the 12 W-D cycles resulted in a reduction in the amplitude associated with the characteristic pore diameter

Conclusions

The algorithm based on Mercury Intrusion Porosimetry showed to be efficient to quantify the changes caused by W-D cycles in the porous system of the soil samples submitted to different managements. PSDs indicated that the intense application of the cycles produced a decrease in the accessed porosity in the soil core samples under CT and F and an increase under NT and MT.

Such results evidence that the soil cores, even having the same textural characteristics, will respond differently when

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

Luiz F. Pires would like to acknowledge the financial support provided by the Brazilian National Council for Scientific and Technological Development (CNPq)and the Coordination for the Improvement of Higher Education Personnel (Capes)through the Grants 303726/2015-6 (Productivity in Research) and 88881.119578/2016-01 (Visiting Scholar). Special thanks to Prof. Sacha Mooney from the Division of Agricultural and Environmental Sciences, School of Biosciences, University of Nottingham, Sutton

References (60)

  • J. Hussein et al.

    Changes in microstructure, voids and b-fabric of surface samples of a vertisol caused by wet/dry cycles

    Geoderma

    (1998)
  • F.J. Leij et al.

    Modeling the dynamics of the soil pore-size distribution

    Soil Tillage Res.

    (2002)
  • W.H. Moreira et al.

    Seasonal changes in soil physical properties under long-term no-tillage

    Soil Tillage Res.

    (2016)
  • M. Pagliai et al.

    Soil structure and the effect of management practices

    Soil Tillage Res.

    (2004)
  • L.F. Pires et al.

    Soil porous system changes quantified by analyzing soil water retention curve modifications

    Soil Tillage Res.

    (2008)
  • L.F. Pires et al.

    Soil pore characterization using free software and a portable optical microscope

    Pedosphere

    (2013)
  • L.F. Pires et al.

    Soil structure changes induced by tillage systems

    Soil Tillage Res.

    (2017)
  • L.F. Pires et al.

    Soil physico-hydrical properties changes induced by weed control methods in coffee plantation

    Agric. Ecosyst. Environ.

    (2017)
  • L.F. Pires et al.

    X-ray microtomography analysis of soil pore structure dynamics under wetting and drying cycles

    Geoderma

    (2020)
  • H.J. Vogel et al.

    Quantitative morphology and network representation of soil pore structure

    Adv. Water Resourc.

    (2001)
  • B.H. Yang et al.

    3D characterization and analysis of pore structure of packed ore particle beds based on computed tomography images

    Trans. Nonferrous Met. Soc. China

    (2014)
  • A.W. Al-Kayssi

    Impact of successive wetting and drying cycles on some physical properties of gypsifereous soils

    J. Agric. Food Dev.

    (2016)
  • F. Albregtsen

    Non-parametric histogram thresholding methods-error versus relative object area

    Proc. Scand. Conf. Image Anal.

    (1993)
  • C.F. Araujo-Junior et al.

    Sistema poroso e capacidade de retenção de água em Latossolo submetido a diferentes manejos de plantas invasoras em lavoura cafeeira

    Planta Daninha

    (2011)
  • O.O.S. Bacchi et al.

    Gamma-ray beam attenuation as an auxiliary technique for the evaluation of the soil water retention curve

    Scientia Agricola

    (1998)
  • M.A. Bavoso et al.

    Resiliência física de dois latossolos vermelhos sob plantio direto

    Revista Brasileira de Ciência do Solo

    (2012)
  • J.R. Boyle et al.

    Forest Soils, Reference Module in Earth Systems and Environmental Sciences

    (2013)
  • R. Brewer

    Fabric and Mineral Analysis Of Soils

    (1964)
  • A.E. Calistru et al.

    Applications of X-ray computed tomography for examining soil structure: a review

    Bull. Univ. Agric. Sci. Vet. Med. Cluj-Napoca Agriculture

    (2015)
  • Y. Capowiez et al.

    3D skeleton reconstructions of natural earthworm burrow systems using CAT scan images of soil cores

    Biol. Fertil Soils

    (1998)
  • Cited by (33)

    • Investigation on microstructure evolution of clayey soils: A review focusing on wetting/drying process

      2023, Journal of Rock Mechanics and Geotechnical Engineering
      Citation Excerpt :

      Besides, the porosity at the bottom of the sample increased and the pore connectivity improved. The soil submitted to contrasting management practices would respond differently to the action of wetting/drying cycles with a direct influence on water retention and movement due to the induced changes in the soil porous system (De Oliveira et al., 2021). In general, wetting/drying cycles leads to increase in the volume of macro-pores.

    • Radon attenuation characteristics of compacted soil layer for uranium mill tailings pond subjected to drying-wetting cycles

      2022, Science of the Total Environment
      Citation Excerpt :

      Notably, the normalized apparent porosity distribution curve of the CSL surface has two or three peaks in each experimental group, and the peak always occurs in spring or summer. The overall soil apparent porosity decreased in the medium drying-wetting environmental stress group (group 2), which might be associated with processes of recombination or reorganization of aggregates during the drying-wetting cycles (de Oliveira et al., 2021). Moreover, with successive drying-wetting cycles and progressive drying-wetting stress, the pore size is enlarged, which affects radon release from the topsoil to the atmosphere and water transport.

    View all citing articles on Scopus
    View full text