Soil Physicists Research Articles

The role of hydropedology when aiming for the United Nations Sustainable Development Goals

AbstractSoil physics defines soil water, air, and temperature regimes that are crucial for agricultural production, the quality of water resources, and waste management. Positioning such activities in the context of the United Nations Sustainable Development Goals (SDGs) will provide a valuable link to the international policy arena and should also include consideration of other SDGs dealing with climate change, biodiversity preservation, and soil health, thereby covering aspects of SDG 2 (zero hunger), SDG3 (good health and wellbeing), SDG6 (clean water and sanitation), SDG13 (climate action), and SDG15 (life on land). Combined expertise of soil physicists and pedologists in hydropedology offers a basic soil package, to be completed by soil chemists and biologists, to interdisciplinary teams studying ecosystem services in line with SDGs. Soils not being isotropic and homogeneous, pedology offers descriptions of soil heterogeneity, requiring innovative measuring methods. Digital mapping significantly improves the quality of traditional soil maps by being more quantitative at lower cost. Socioeconomic conditions are important elements of sustainable development as is recognized by the soil security concept, distinguishing soil connectivity with users and soil codification, linking soil with the policy arena. The latter has been successfully achieved in South Africa. Innovative, “applied” interdisciplinary research is needed to develop operational methods, assessing ecosystem services that are relatively of low cost, simple, and transparent, allowing acceptance by critical stakeholders. Modern proximal sensing techniques offer a promising perspective. An exploratory case study of a Dutch: “Living Lab” is referred to as an example of such an “applied” interdisciplinary approach.

Profile of Jennifer Marshall Graves

“Sometimes when you ask a functional question, you get an evolutionary answer,” says Jennifer Marshall Graves, a leader in the field of epigenetics and comparative genomics. Her team’s vast body of research on Australian fauna has helped the distinguished professor at Melbourne’s La Trobe University (LTU) uncover fundamental insights into mammalian sex chromosomes and sex-determining genes. Elected as an International Member of the National Academy of Sciences in 2019, Graves compared DNA sequences across widely divergent animals and demonstrates in her Inaugural Article (1) that bird and reptile microchromosomes, once thought to be insignificant, are ancient and highly conserved and represent the original building blocks of vertebrate genomes. Graves was born in Adelaide, Australia. Her father, the soil physicist T. J. Marshall, formulated the Marshall equation, which describes the movement of fluids in soil. Her mother, Ann Marshall, was a geologist and urban geographer whose activism concerning overdevelopment in Adelaide left a mark on the city. Graves recalls being “turned onto genetics” when high school biology teacher Doreen McCarthy used colorful images of budgerigars to demonstrate Mendel’s laws of genetics. Graves says, “I was hooked and enrolled in science at Adelaide University in 1960.” Shortly thereafter, during her mother’s sabbatical, she spent a semester at the University of California, Berkeley, where she studied cell biology taught by Daniel Mazia. Returning to Adelaide, she received the Sir Ronald A. Fisher Award for Genetics in 1962 and conducted honors research on X chromosome inactivation in kangaroo females with advisor David Hayman. At Adelaide, she earned both an undergraduate degree in genetics and physical chemistry and a Master’s degree in genetics. Jennifer Marshall Graves. Image credit: GAMMA/Micheline Pelletier. The Fisher Award, a £10 book token, was followed by a Fulbright Travel Grant, which enabled doctoral studies at Berkeley under Mazia and cell geneticist …

Educator's Heart Leads to Legacy—the Kirkham Conference

Educator's Heart Leads to Legacy—the Kirkham Conference

Improving unsaturated hydraulic conductivity estimation in soils via percolation theory

Accurate estimation of unsaturated hydraulic conductivity K(Sw) in soils has been of great interest to soil physicists and hydrologists in the past several decades. Although various methods such as a “bundle of capillary tubes” conceptual approach were applied in the literature to theoretically model hydraulic conductivity in term of water saturation, in this study we invoke percolation theory, which quantifies the effect of the interconnectivity of pores on the macroscopic fluid flow. We incorporate the pore-solid interface roughness effect in the hydraulic conductance-pore radius (g-r) relationship, evaluate our K(Sw) model using 104 soil samples from the UNSODA database as well as another 20 soil samples from the Rijtema database, and compare it to the Ghanbarian-Alavijeh and Hunt (2012) model. Generally speaking, we experimentally demonstrate that K(Sw) estimations were improved over the entire range of water saturation when the surface roughness effect was incorporated. However, our model still underestimates the unsaturated hydraulic conductivity at low water saturations (corresponding to K(Sw)<10−4cm/day). We show that after eliminating the effect of non-equilibrium conditions in the measurements K(Sw) estimations were improved substantially. Other plausible sources for K(Sw) underestimation are also discussed.

Extraterrestrial Soils and Space Agriculture

Extraterrestrial Soils and Space Agriculture

Hydropedology and the Societal Challenge of Realizing the 2015 United Nations Sustainable Development Goals

Core Ideas The UN Sustainable Development Goals present a guiding principle for hydropedology. Hydropedology is potentially more effective than the separate disciplines. Pedologists should better support their observations with physical measurements. Measuring and interpreting bypass flow may be more effective than developing new theory. Existing soil databases can't provide a full picture of soil behavior in the field. The UN Sustainable Development Goals (SDGs) offer a major challenge for both society and the science community. Hydropedology, combining the expertise of soil physicists and pedologists, plays a key role in realizing goals focused on food, water, climate, and ecology, requiring interdisciplinary research. This update explores emerging trends and future work, focusing on examples of contributions by pedology to measuring and modeling in hydropedological studies. Many soil types create heterogeneous flow patterns that are difficult to characterize using current soil databases and physical flow models. The clear potential of hydropedology to produce better modeling results than those obtained from separate contributions by the two subdisciplines can, however, only be established by field validation of modeling results using different types of data and models. Overall soil input in interdisciplinary SDG‐oriented research includes chemical and biological aspects that become more representative by considering hydropedological conditions.

The holistic rhizosphere: integrating zones, processes, and semantics in the soil influenced by roots.

Despite often being conceptualized as a thin layer of soil around roots, the rhizosphere is actually a dynamic system of interacting processes. Hiltner originally defined the rhizosphere as the soil influenced by plant roots. However, soil physicists, chemists, microbiologists, and plant physiologists have studied the rhizosphere independently, and therefore conceptualized the rhizosphere in different ways and using contrasting terminology. Rather than research-specific conceptions of the rhizosphere, the authors propose a holistic rhizosphere encapsulating the following components: microbial community gradients, macroorganisms, mucigel, volumes of soil structure modification, and depletion or accumulation zones of nutrients, water, root exudates, volatiles, and gases. These rhizosphere components are the result of dynamic processes and understanding the integration of these processes will be necessary for future contributions to rhizosphere science based upon interdisciplinary collaborations. In this review, current knowledge of the rhizosphere is synthesized using this holistic perspective with a focus on integrating traditionally separated rhizosphere studies. The temporal dynamics of rhizosphere activities will also be considered, from annual fine root turnover to diurnal fluctuations of water and nutrient uptake. The latest empirical and computational methods are discussed in the context of rhizosphere integration. Clarification of rhizosphere semantics, a holistic model of the rhizosphere, examples of integration of rhizosphere studies across disciplines, and review of the latest rhizosphere methods will empower rhizosphere scientists from different disciplines to engage in the interdisciplinary collaborations needed to break new ground in truly understanding the rhizosphere and to apply this knowledge for practical guidance.

Spatio‐temporal scaling of Vegetation Growth and Soil Formation from Percolation Theory

Spatio‐temporal scaling of Vegetation Growth and Soil Formation from Percolation Theory

Is Soil Moisture Related to Wildfire?

Is Soil Moisture Related to Wildfire?

Canopeo: a new tool to measure green canopy cover

Canopeo: a new tool to measure green canopy cover

BEYOND THE “LEAST LIMITING WATER RANGE”: RETHINKING SOIL PHYSICS RESEARCH IN BRAZIL

As opposed to objective definitions in soil physics, the subjective term “soil physical quality” is increasingly found in publications in the soil physics area. A supposed indicator of soil physical quality that has been the focus of attention, especially in the Brazilian literature, is the Least Limiting Water Range (RLL), translated in Portuguese as "Intervalo Hídrico Ótimo" or IHO. In this paper the four limiting water contents that define RLLare discussed in the light of objectively determinable soil physical properties, pointing to inconsistencies in the RLLdefinition and calculation. It also discusses the interpretation of RLL as an indicator of crop productivity or soil physical quality, showing its inability to consider common phenological and pedological boundary conditions. It is shown that so-called “critical densities” found by the RLL through a commonly applied calculation method are questionable. Considering the availability of robust models for agronomy, ecology, hydrology, meteorology and other related areas, the attractiveness of RLL as an indicator to Brazilian soil physicists is not related to its (never proven) effectiveness, but rather to the simplicity with which it is dealt. Determining the respective limiting contents in a simplified manner, relegating the study or concern on the actual functioning of the system to a lower priority, goes against scientific construction and systemic understanding. This study suggests a realignment of the research in soil physics in Brazil with scientific precepts, towards mechanistic soil physics, to replace the currently predominant search for empirical correlations below the state of the art of soil physics.

Rooted in Field Research: A Day in the Life of Betty Klepper

Rooted in Field Research: A Day in the Life of Betty Klepper

Why is the influence of soil macrofauna on soil structure only considered by soil ecologists?

These last twenty years have seen the development of an abundant literature on the influence of soil macrofauna on soil structure. Amongst these organisms, earthworms, termites and ants are considered to play a key role in regulating the physical, chemical and microbiological properties of soils. Due to these influential impacts, soil ecologists consider these soil macro-invertebrates as ‘soil engineers’ and their diversity and abundance are nowadays considered as relevant bioindicators of soil quality by many scientists and policy makers. Despite this abundant literature, the soil engineering concept remains a ‘preach to the choir’ and bioturbation only perceived as important for soil ecologists.We discussed in this article the main mechanisms by which soil engineers impact soil structure and proposed to classify soil engineers with respect to their capacity to produce biostructures and modify them. We underlined the lack of studies considering biostructure dynamics and presented recent techniques in this purpose. We discussed why soil engineering concept is mainly considered by soil ecologists and call for a better collaboration between soil ecologists and soil physicists. Finally, we summarized main challenges and questions that need to be answered to integrate soil engineers activities in soil structure studies.

Comparison of Methods to Estimate Saturated Hydraulic Conductivity in Texas Soils with Grass

AbstractOne of the primary objectives for irrigation and drainage engineers, soil physicists, and hydrologists is to develop effective methods to estimate soil saturated hydraulic conductivity on the basis of readily available soil survey data. Although a few models have been derived from large ranges of soil texture data and successfully applied to many kinds of hydrologic analysis of agricultural lands and watershed for many years, there are few efforts to specifically investigate these models in soils with healthy grass growing. A field study was conducted to investigate and compare the performance of three readily applied models, including the Campbell model, Smettem and Bristow model, and Saxton et al. model, in Texas soils with established grass from September 2009 to May 2010. The results showed that two-parameter models, Campbell and Saxton et al. models, had better performance than the one-parameter model, Smettem and Bristow model. All three models need to be calibrated with local knowledge and ...

Evaluation of soil compaction effects on soil biota and soil biological processes in soils

Investigations on soil compaction focused mainly on effects on soil physical parameters and on plant growth. Nevertheless, a substantial number of papers deal with effects of soil compaction on soil organisms (soil fauna, soil microorganisms) and biologically driven processes in soils (e.g., macropore formation, respiration rates, N-mineralisation). In view of soil and soil functions protection, there is an essential need to identify soil compaction threshold values with respect to soil biota and soil biological processes. No such values are currently available. Thus the aim of our study was to evaluate literature on the effects of soil compaction mainly in agricultural soils on soil organisms and soil biological processes (e.g., respiration, nitrification); to identify relevant parameters which are helpful for assessing soil compaction from the soil biological point of view; and to find out whether threshold values of soil structure parameters proposed by soil physicists correspond to harmful impacts on soil organisms and biological processes in soils. Our literature review showed that due to the high variability of experimental situations and conditions in the evaluated papers, especially in papers describing field investigations, no general effect of soil compaction was found. Negative and positive effects occurred with slight compaction as well as with strong compaction. A verification of the thresholds published to date for soil compaction was not possible based on the data evaluated. However, the fact that above an effective bulk density of 1.7 g cm −3, only negative effects on microbial biomass and C-mineralisation were found confirms this value, proposed by soil physicists, also from the soil biological point of view. In order to provide a scientifically meaningful data base for the assessment of soil compaction, effects on soil biodiversity, related functions and processes, we recommend considering the following site and soil properties as essentials: land use, climate, soil type, texture, bulk density; soil organic matter content; pH value; soil moisture (water content/water tension); pore volume; macroporosity and air and/or water conductivity.

Trans‐Disciplinary Soil Physics Research Critical to Synthesis and Modeling of Agricultural Systems

Synthesis and quantification of disciplinary knowledge at the whole system level, via the process models of agricultural systems, are critical to achieving improved and dynamic management and production systems that address the environmental concerns and global issues of the 21st century. Soil physicists have made significant contributions in this area in the past, and are uniquely capable of making the much‐needed and exciting new contributions. Most of the exciting new research opportunities are trans‐disciplinary, that is, lie on the interfacial boundaries of soil physics and other disciplines, especially in quantifying interactions among soil physical processes, plant and atmospheric processes, and agricultural management practices. Some important knowledge‐gap and cutting‐edge areas of such research are: (1) quantification and modeling the effects of various management practices (e.g., tillage, no‐tillage, crop residues, and rooting patterns) on soil properties and soil–plant–atmosphere processes; (2) the dynamics of soil structure, especially soil cracks and biochannels, and their effects on surface runoff of water and mass, and preferential water and chemical transport to subsurface waters; (3) biophysics of changes in properties and processes at the soil–plant and plant–atmosphere interfaces; (4) modeling contributions of agricultural soils to climate change and effects of climate change on soil environment and agriculture; and (5) physical (cause‐effect) quantification of spatial variability of soil properties and their outcomes, new methods of parameterizing a variable field for field‐scale modeling, and new innovative methods of aggregating output results from plots to fields to larger scales. The current status of the various aspects of these research areas is reviewed briefly. The future challenges are identified that will require both experimental research and development of new concepts, theories, and models.

Identification of Naturally Occurring and Anthropogenic Sources of Perchlorate

†Dr. Robert D. Morrison is a Soil Physicist with DPRA, Inc. He has a BS in Geology, a MS in Environmental Studies, a MS in Environmental Engineering and a Ph.D. in Soil Physics from the University of Wisconsin at Madison. Dr. Morrison has been working for 30 years in the environmental field on issues related to soil and groundwater contamination. Dr. Morrison specializes in the forensic review and interpretation of scientific data for the purpose of identifying the source and age of a contaminant release. Emily A.Vavricka is an Environmental Scientist with DPRA, Inc. She possesses a BS in Environmental Science from the University of California, Riverside, and specializes in the use of environmental forensics for use in litigation matters.

The Soil Physics Contributions of Edgar Buckingham

During 1902 to 1906 as a soil physicist at the USDA Bureau of Soils (BOS), Edgar Buckingham originated the concepts of matric potential, soil–water retention curves, specific water capacity, and unsaturated hydraulic conductivity (K) as a distinct property of a soil. He applied a formula equivalent to Darcy's law (though without specific mention of Darcy's work) to unsaturated flow. He also contributed significant research on quasi‐empirical formulas for K as a function of water content, water flow in capillary crevices and in thin films, and scaling. Buckingham's work on gas flow in soils produced paradigms that are consistent with our current understanding. His work on evaporation elucidated the concept of self‐mulching and produced sound and sometimes paradoxical generalizations concerning conditions that favor or retard evaporation. Largely overshadowing those achievements, however, is that he launched a theory, still accepted today, that could predict transient water content as a function of time and space. Recently discovered documents reveal some of the arguments Buckingham had with BOS officials, including the text of a two‐paragraph conclusion of his famous 1907 report on soil water, and the official letter documenting rejection of that text. Strained interpersonal relations motivated the departure of Buckingham and other brilliant physicists (N.E. Dorsey, F.H. King, and Lyman Briggs) from the BOS during 1903 to 1906. Given that Buckingham and his BOS colleagues had been rapidly developing the means of quantifying unsaturated flow, these strained relations probably slowed the advancement of unsaturated flow theory.

Soil physics: a Moroccan perspective

Research on environmental pollution and degradation of soil and water resources is now of highest priority worldwide. To address these problems, soil physics should be conceived as a central core to this research. This paper objectives are to: (1) address the role and importance of soil physics, (2) demonstrate progress in this discipline, and (3) present various uses of soil physics in research, environment and industry. The study of dynamic processes at and within the soil vadose zone (flow, dispersion, transport, sedimentation, etc.), and ephemeral phenomena (deformation, compaction, etc.), form an area of particular interest in soil physics. Soil physics has changed considerably over time. These changes are due to needed precision in data collection for accurate interpretation of space and time variation of soil properties. Soil physics interacts with other disciplines and sciences such as hydro(geo)logy, agronomy, environment, micro-meteorology, pedology, mathematics, physics, water sciences, etc. These interactions prompted the emergence of advanced theories and comprehensive mechanisms of most natural processes, development of new mathematical tools (modeling and computer simulation, fractals, geostatistics, transformations), creation of high precision instrumentation (computer assisted, less time constraint, increased number of measured parameters) and the scale sharpening of physical measurements which ranges from micro to watershed. The environment industry has contributed to an enlargement of many facets of soil physics. In other words, research demand in soil physics has increased considerably to satisfy specific and environmental problems (contamination of water resources, global warming, etc.). Soil physics research is still at an embryonic stage in Morocco. Consequently, soil physicists can take advantage of developments occurring overseas, and need to build up a database of soil static and dynamic properties and to revise developed models to meet our conditions. Large, but special, investment is required to promote research programs in soil physics, which consider developments in this discipline and respect Moroccan needs. These programs will be highlighted herein.

A parameterised equation to estimate soil hydraulic conductivity in the field

The description of soil water dynamics using the Darcy–Buckingham approach involves the determination and use of soil hydraulic conductivity K v. soil water content θ functions. Many of the methods developed for the measurement of K are based on simplifying assumptions, such as the unit gradient and the choice of fixed models for the K(θ) relation. The need of quick, simple, and inexpensive methods to measure K(θ) in the field using a large number of replicates has also led soil physicists to develop simple methods. This paper presents a procedure that makes use of parameters of equations used to explain the internal water drainage process, and that naturally leads to the exponential character of the K(θ) relation. Results show that the parameterised equation represents a more rigorous estimation of K(θ), compared with the methods that assume unit gradient.