Advancing the frontiers of soil science towards a geoscienceimartins/Wilding_Lin_2006.pdf · 2009-12-15 · Advancing the frontiers of soil science towards a geoscience Larry P. Wildinga,*,

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Geoderma 131 (2

Advancing the frontiers of soil science towards a geoscience

Larry P. Wildinga,*, Henry Linb

aDepartment of Soil and Crop Sciences, Texas A&M University, College Station, TX, United StatesbDepartment of Crop and Soil Sciences, The Pennsylvania State University, University Park, PA, United States

Available online 20 June 2005

Abstract

The visions, directions, and images of soil science are changing. Historically, soil science has followed a circuitous path in

its evolution from a discipline with foundational roots in geology, to an applied agricultural and environmental discipline, and

now to a bio- and geo-science through the Earth’s Critical Zone investigations. This closes the loop or spiral, but along the way,

soil science has become more comprehensive, extensive, integrative, analytical, and quantitative. In spite of the challenges

described in this paper, now is a golden era for soil science to integrate its expertise more closely with other bio- and geo-

sciences. This will significantly enhance the opportunity to obtain extramural funding and public support, as well as the

advancement of soil science. As such, soil science needs to vigorously become more interactive and extend its role beyond

traditional agriculture. The knowledge of spatial soil diversity and landscape dynamics is a fundamental underpinning critical to

the success of this venture. Pedology, as a unique subdiscipline of soil science, contributes inordinately to Earth science,

including, for example, elucidation of field variability, surficial weathering processes, Earth system dynamics, and vadose zone

flow and transport. With the blooming of hydrogeosciences, hydropedology is a timely addition in this era of interdisciplinary,

multidisciplinary, and systems approaches for developing comprehensive prioritization of science and applications in Earth

science. Hydropedology has a niche in this march with other bio- and geo-sciences in addressing global Earth science priorities.

Soil scientists support changing paradigms and favor closer linkages with the bio- and geo-sciences community. In this regard,

hydropedology has a unique role to play.

D 2005 Elsevier B.V. All rights reserved.

Keywords: The Critical Zone; Earth science; Pedosphere; Hydropedology; Pedology; Soil architecture; Soil function

1. Introduction

Soil is that invaluable, diverse, and fragile natural

resource at Earth’s terrestrial surface that provides for

life support. While best known for its role in provid-

0016-7061/$ - see front matter D 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.geoderma.2005.03.028

* Corresponding author. Tel.: +1 979 776 8832; fax: +1 979 862

1712.

E-mail address: [email protected] (L.P. Wilding).

ing nutrients and water to sustain agriculture and

ecosystems, soil resources are equally fundamental

for waste disposal, ground water recharge, climate

impact, and as raw materials for engineering construc-

tion/manufacturing activities. More generally, this bi-

ologically active, structured porous medium – called

the pedosphere – mediates most of the biogeophysical

and chemical interactions among the land, its surface

and ground waters, and the atmosphere. For example,

006) 257–274

L.P. Wilding, H. Lin / Geoderma 131 (2006) 257–274258

organic carbon is recycled to the atmosphere through

soils; about 25% of the atmospheric carbon dioxide

comes from biological oxidation reactions in the

pedosphere, which contains twice as much carbon as

the atmosphere and up to three times the carbon in all

vegetation (NRC, 2001; Drees et al., 2001; Lal, 2001,

2004). Soils have a major influence on the hydrologic

cycle as well. The water most people use comes from

ground water, streams, and lakes; regardless of its

pathway, the water quality and quantity are largely

governed by the nature of soils it passes through.

In most countries, the field of soil science has

developed primarily as a by-product of research in

agriculture. In the U.S., its recognition and support

through institutions such as the National Academy of

Sciences and the National Science Foundation have

been remarkably limited, because all too frequently,

soil science is viewed as an agricultural science; until

recently, its function, role, and contributions to the

basic bio- and geo-sciences have not been fully ap-

preciated within the Earth science community. New

thrusts in hydrology, composition and surface reac-

tions of organic/mineral colloids, fate and transport of

xenobiotics, bioremediation of wastes, detoxification

of soils, land use impacts on biodiversity, natural

hazards, fluxes of greenhouse gases, aqueous geo-

chemistry, and planetary explorations, have brought

opportunities for funding of soil science in the Earth

science agenda through multiagency and multidisci-

plinary consortia. A recent report of the U.S. National

Research Council, entitled Basic Research Opportu-

nities in Earth Science (NRC, 2001), identified sev-

eral unique roles for soil scientists to conduct

integrative basic research with other bio- and geo-

scientists in near-surface environments now called

the Critical Zone. The scope of this research would

involve the C-cycle (soil C sequestration), hydrology,

quantification of microbial and mineral interactions,

dynamics of land–ocean interface, encoding the Earth

history record, and new tools in biotechnology and

nanometrics. The report further identified opportuni-

ties for soil scientists to contribute to geobiology,

Earth and planetary systems, natural Earth science

laboratories, and education (K-12 education, field

training, and post-doctorate/sabbatical leaves) through

various partnerships and leveraging activities.

The purpose of this paper is to highlight the im-

portance of soil science in an Earth science context, to

briefly describe the evolution of soil science towards a

bio- and geo-science, and to illustrate hydropedology

opportunities in the geosciences.

2. Concepts and definitions

The Critical Zone (Fig. 1) is that portion of the

Earth’s surface that includes the atmosphere, bio-

sphere, pedosphere, and lithosphere interfaces (NRC,

2001). The Critical Zone is the thin, fragile envelope

of soil, rock, air, and water that includes the land

surface, and its canopy of vegetation, rivers, lakes,

and shallow seas. It extends through the pedosphere,

unsaturated vadose zone, and saturated ground water

zone. Interactions at these interfaces determine the

availability of nearly every life-sustaining resource.

The life-sustaining zone, the pedosphere itself, plays a

major role in recycling carbon, nitrogen, and other

chemicals to the atmosphere, hydrosphere, and litho-

sphere, as well as storing water and disposing of solid

and liquid wastes. Recent advances in the disciplines

of Earth surface processes, chemistry, and biology

provide the tools for integrative and systematic

approaches to the hydrogeobiological interactions in

the Critical Zone. For far too long, the biological

functions and weathering mechanisms in soils have

been too partitioned from abiotic inorganic processes.

The organic and inorganic components of soils are

intimately interlinked and as such need further atten-

tion by the geoscience community. The Critical Zone

concept provides a natural framework for cross-disci-

plinary fundamental research on soil, rock, air, water,

and biotic resources at the Earth’s surface.

Pedosphere is the thin semi-permeable membrane

at the Earth’s surface that serves as an interface be-

tween the solid and fluid envelopes (atmosphere,

hydrosphere, biosphere, and lithosphere) as schemat-

ically illustrated in Fig. 1. The Glossary of Geology

defines pedosphere as b. . .that shell or layer of the

Earth in which soil forming processes occur.Q (Jack-son, 1997) and dissipates the mass flux and energy

among Earth surface components (NRC, 2001). It is

commonly known as the global soil cover. It sustains

biomass productivity, serves as the reactor for organic/

mineral weathering, is the foundation of physical

structures, serves as a construction material, is the

living filter for water supplies and remediation/biore-

Fig. 1. A schematic of the Earth’s Critical Zone and the pedosphere: The pedosphere is the thin skin of soil on the Earth’s surface that represents

a geomembrane across which water and solutes, as well as energy, gases, solids, and organisms are actively exchanged with the atmosphere,

biosphere, hydrosphere, and lithosphere to create a life-sustaining environment. Soil–water interactions create the fundamental interface

between the biotic and abiotic and hence serve as a critical determinant of the state of the Earth system and its critical zone (drawing not to

scale) (modified after Lin et al., 2005).

L.P. Wilding, H. Lin / Geoderma 131 (2006) 257–274 259

mediation of waste products, and functions as the

organic-rich medium that determines the sustainability

and environmental quality of the ecosystem. It is a

highly dynamic solid/fluid envelope. For example,

reaction rates are often much faster at the pedo-

sphere/atmosphere interface than the heat exchange,

gas exchange, and biotic response at the lithosphere/

hydrosphere interface, such as the circulation of water

in deep lakes and oceans.

Soil Science is that component of Earth science

that quantifies the functions, behavior, and processes

of near-surface Earth environments. It includes, but is

not limited to, the quality, distribution, extent, spatial

diversity, use, and management of soil landscape bod-

ies from submicroscopic to megascopic scales (Sum-

ner, 2000). It deals with soils as very slowly

renewable natural resources or anthropogenically-

modified ecosystems. Soil science considers those

near-surface processes that determine the quality and

functions of the pedosphere relative to evolution,

geochemical environment, and organismal habitat. It

provides tools to help integrate the components of the

Earth systems, to understand the causes and conse-

quences of spatial and temporal diversity, and to

achieve a more holistic approach to dynamic process-

es effecting ecosystems. The current scope of this

science should be multifaceted, namely as an agro-

nomic, environmental, ecological, and as a bio- and


geo-science. It is the latter opportunity that soil sci-

ence has not well captured and is commonly less well

understood by the geoscience community. Soil sci-

ence as a bio- and geo-science partner, however,

offers major avenues of new growth potential for

investigations in the pedosphere and the Critical

Zone.

Hydropedology is the . . .binterwoven branch of

soil science and hydrology that embraces interdisci-

plinary and multiscale approaches to study interactive

pedological and hydrological processes in the Earth’s

Critical ZoneQ (Lin, 2003). It could also be considered

as the a subdiscipline of soil science and geoscience

that investigates gaseous and fluid fluxes through the

pedosphere as conditioned by pedogenesis and spatial

diversity in landscape settings. Lin et al. (2005) have

recently provided a comprehensive summary of the

role of hydropedology in bridging bio- and geo-

sciences at multiple scales and their links to the

integrative studies of the Earth’s Critical Zone. They

suggest that hydropedology contributes to a better

understanding of a wide variety of environmental,

ecological, geological, agricultural, and natural re-

source issues of social importance. As examples,

these include water quality and quantity, soil quality,

landscape processes, watershed management, nutrient

cycling, contaminate fate, waste disposal, precision

agriculture, climatic change, carbon sequestration,

and ecosystem functions.

3. History of soil science and a changing paradigm

It is interesting to trace the evolutionary history of

soil science over the past several centuries and note

changing paradigms in this discipline over recent time

(Landa, 2004). Soil science received its parentage

from geology, chemistry, and biology, but for the

past 100 years has been considered an independent

body of knowledge (Arnold, 1983; Sumner, 2000)

with strong underpinnings to agriculture. Because of

the unparalleled success that applied soil science

enjoyed in helping bring food, feed, fiber, and fuel

to the world, the development of basic soil science has

come primarily as a product of research in agriculture

(Sposito and Reginato, 1992).

For the past three decades, we have witnessed

major shifts of soil science to environmental and

ecological focus (e.g., Wild, 1989; Yaalon, 1993;

Miller, 1993; Gardner, 1993; Bouma, 1994; Warken-

tin, 1994; Wilding, 1994; Mermut and Eswaran,

1997, 2001; Sparks, 2000). Soil is the long-term

bcapitalQ on which a nation builds and grows. It is

the basic component of ecosystems. Much of the

change in emphasis has resulted from the negative

anthropogenic effects on soil, air, and water quality

(NRC, 1993). To better address these new research

opportunities, secure funding, and attract students,

there has been a push by the profession to seek

greater identity, visibility, and outreach for soil sci-

ence. Further, it was undergirded by the passion to

place soil scientists bat the tableQ with other leading

biological and physical scientists in global scientific

and outreach programs.

Historically, soil science has followed a circuitous

path in its evolution from a discipline with founda-

tional roots in geology, to an applied agricultural and

environmental discipline, and now to a bio- and geo-

science through the Critical Zone investigations. This

closes the loop, cycle, or spiral, but along the way soil

science has become more comprehensive, extensive,

integrative, analytical, and quantitative. Drivers of the

return of soil science towards an Earth science para-

digm in the U.S. have been activities and reports

commissioned by the Soil Science Society of America

(SSSA), National Research Council (NRC), and the

National Science Foundation (NSF) as a government

arm of basic research support. Important in this regard

were the documents such as Opportunities in Hydro-

logic Sciences (NRC, 1991), Opportunities in Basic

Soil Science Research (Sposito and Reginato, 1992),

Soil and Water Quality—An Agenda for Agriculture

(NRC, 1993), New Strategies for America’s Water-

sheds (NRC, 1999), and Basic Research Opportuni-

ties in Earth Science (NRC, 2001). The NSF-

commissioned report (NRC, 2001) provided impetus

to reorganize the NSF Division of Earth Science to

more effectively integrate soil science into basic re-

search programs of the geosciences. In all of the

above, soil scientists were either architects of the

reports or members of the NRC study committees. It

was through such engagement that the impacts of soil

science were felt in the derived products. While much

is yet to be done, the process has been set in motion

and soil science is becoming a partner in the Earth

science agenda.


The SSSA joined the American Geological Insti-

tute (AGI) in 1993 to further enhance its geoscience

role, especially in K-12 educational efforts (Landa,

2004). This has actively fostered soil science’s en-

gagement in geoscience programs and the senior au-

thor of this paper has had the pleasure to serve on the

AGI Executive Committee, Strategic Planning Com-

mittee, and AGI Foundation in this behalf. AGI is a

nonprofit federation of 45 scientific and professional

associations that represents over 100,000 geoscien-

tists. As such, AGI is the largest geoscience constit-

uency in the U.S. Soon after the SSSA became a

member society, two issues of Geotimes were dedi-

cated to soil science (AGI, 1996, 2002), and AGI

published its second Environmental Awareness Series

report Sustaining Our Soils and Society (Loynachan

et al., 1999). These publications highlighted the im-

portance of soil science to other geoscience disciplines

and served as a gateway to further joint endeavors.

AGI aggressively markets Geotimes to enhance public

awareness of the geosciences, and by doing so, also

enhances the service to soil science. Lastly, AGI’s

Government Affairs Program delivers critical geosci-

ence educational materials and services for state and

federal policy-makers to enlighten them to make more

rational decisions.

Another cornerstone of the changing image and

visibility of soil science was the formation in 1999

the U.S. National Committee of Soil Science (USNC/

SS) under the auspices of the NRC/National Academy

of Sciences (NAS). This was a critical step for soil

science because it enhanced the visibility and prestige

of the discipline in the U.S. through affiliation with

the NRC/NAS. It empowered soil scientists to become

engaged with other scientists in scientific programs,

and fostered membership of soil scientists in allied

Study Committees and Boards of the NRC/NAS. The

senior author of this paper had several opportunities to

provide services in this behalf. The formation of the

USNC/SS also was timely because through this Com-

mittee, the NAS was the official adhering member for

the U.S. soil science community to the International

Union of Soil Sciences (IUSS). By such action, the

NAS provides financial support for the IUSS, makes

all individual soil scientists in the U.S. members of the

IUSS by virtue of country membership in the IUSS,

and gives soil scientists access to international activ-

ities of the International Council of Scientific Unions

(ICSU). ICSU mobilizes the knowledge and resources

of the international scientific community to: (i) iden-

tify and address major issues of importance to science

and society, and (ii) facilitate interaction of scientists

across disciplines and among nations. Here, soil scien-

tists have an opportunity to contribute their expertise

to international conventions and programs such as

biodiversity, climatic change, food security, human

health, land carrying capacity, and land degradation

and desertification.

In a presentation to the IUSS Inter-Congress meet-

ing in Philadelphia on April 26, 2004, Dr. Thomas

Rosswall, Executive Director of the ICSU, suggested

emerging issues to which the IUSS and, thus, soil

scientists might contribute:

! Genetically modified materials in soil systems

! Salt affected soils

! Survival of pests and diseases in the soil system

! Biodiversity of soils

! Soil resource survey and monitoring

! Communication between science and society

! Bioremediation

! Water cycling

! Carbon sequestration

! Soils in climatic models

He further suggested that the IUSS could help

identify other emerging issues, collaborate with

other Unions, contribute expertise to ongoing ICSU

programs (e.g., global change), and make soil science

more policy-relevant. He noted that science is neces-

sary but not sufficient for sustainable development.

Science must become more policy-relevant if it is

going to help integrate the environmental, social,

and ecological components of sustainable develop-

ment. Science must become more participatory with

stakeholders and the indigenous populous.

In summary, there are encouraging signs that soil

scientists are extending their expertise and contribu-

tions more effectively with other bio- and geo-

sciences in an Earth science context. This is not

intended to narrow the discipline’s scope but rather

to make it more inclusive. This process will likely

enhance the visibility, image, and outreach of the soil

science community worldwide. It should result in

further employment of soil scientists within the bio-

and geo-science community in academic units of


higher learning, government institutions, agencies

such as the National Aeronautics and Space Admin-

istration (NASA) and the U.S. Geological Survey

(USGS), and non-governmental organizations. Joint

professional meetings among geoscience societies and

cross participations will further these goals.

4. Soil science as a basic Earth science

Brown (1996) illustrates how soil science is an

Earth science and shares the commonalities of field-

based orientation, process focus, database uncertain-

ty, interdisciplinary character, and importance of un-

derstanding landscape models to predict functions

and behavior of near-surface environments. He

notes that boundaries between the various disciplines

of Earth sciences have historically worked against

interdisciplinary cooperation. These boundaries have

included legal, institutional, and intellectual separa-

tions. For example, soil scientists are commonly

housed in colleges of agriculture, institutes or schools

of natural resources, and in agencies of the U.S.

Department of Agriculture, while geologists typically

are employed in colleges of liberal arts and sciences

and in agencies of the U.S. Department of Interior.

Legal boundaries include different licensures, boards

of certification, and regulations giving rise to varying

degrees and types of recognition for different disci-

plines. These constraints and opportunities are chal-

lenges for Earth science disciplines in the future if

full impacts of their interdisciplinary endeavors are to

be realized. Landa (2004) emphasizes many of these

same points as he traces the developmental history of

the geological and soil sciences. He further elaborates

on connects, disconnects, and opportunities for these

disciplines to work collaboratively across disciplinary

boundaries.

National imperatives identified for Earth science

include the discovery, conservation, and use of natural

resources; mitigation and characterization of natural

resources; geotechnical and materials engineering;

stewardship of the environment; and global security

and national defense (NRC, 2001). Expertise from soil

science and allied bio- and geo-science disciplines is

necessary to address these imperatives successfully,

including developing technologies to enhance and

conserve renewable natural resources—soil, air,

water, and biotic quality; quantifying climatic change

and consequent impacts on complex natural and man-

aged ecosystems; protecting and restoring critical

wildlife and wetland habitats; and developing early

warning systems of land degradation. The time is ripe

for multidisciplinary collaboration. Research activities

of the past century have been largely single-

disciplined. The efforts of individual disciplines

have given rise to an extensive body of knowledge

and research and technological infrastructure capabil-

ity that now make it possible to begin studying the

numerous interactions of a holistic Earth system. For

example, contributions are already prominent in the

soil science literature on foundational research in

pedology, biology, chemistry, mineralogy, physics,

and pedometrics as subdisciplines of soil science

with bio- and geo-science overtones. Specifically,

contributions in the following areas are directly ger-

mane to the geosciences (Sposito and Reginato, 1992;

Wilding, 1994):

! Elucidate pedogenic and weathering processes to

quantify, model, and reconstruct present and past

Earth-surface environments using state-of-science

tools;

! Reconstruct environmental conditions, natural re-

source bases, occupational activities, and con-

straints of ancient civilizations via soil archeology

inferences;

! Establish organic carbon pools and C/N dynamics

in soils as components of the global C cycle and

their impact on global climatic change;

! Employ biotechnology to encode genetic microbial

materials as unique markers of organismal identity,

functionality, and biodegradation products;

! Unravel the complex chemical environments in soil

systems to quantify the dynamics of mineral and

organic transformations, to identify new natural

and xenobiotic compounds, to verify surface

charge characteristics and sorption–desorption ki-

netics, and to model transport processes of chemi-

cals within soil and geological systems; and

! Develop quantitative physical measurements and

model descriptions of soils to predict and verify

flow and transport pathways of solutes, liquids and

gases, mechanisms of mass movement and energy

fluxes within the system, and movement of

microbes in the environment.


Integrative studies of the Critical Zone have been

proposed to enhance the soil science knowledge base

into the Earth science research agenda (NRC, 2001).

This integration would foster interdisciplinary efforts

in geobiology, Earth and planetary materials, and

planetary science, and extend our purview beyond

terrestrial environments. Several soil scientists are

currently employed by the NASA and have provided

soils expertise to extraterrestrial space exploration and

planetary materials science for nearly two decades.

Other soil scientists have been leaders in remote

sensing providing education, research, and applica-

tions of this tool for integrated Earth science studies.

Perhaps soil scientists, and especially those with

broad expertise such as hydropedologists, can best

contribute to opportunities in the Critical Zone stud-

ies. Research niches here include soil quality, food

security, resource sustainability and management,

global climatic change, natural disasters, steward-

ship/conservation/utilization and enhancement of

land resources, and public literacy in Earth sciences

(e.g., K-12 educational agenda). For example, under-

standing the relationship of the terrestrial C cycle to

global climatic change, spatial soil diversity, and

sources and sinks of C is heavily dependent upon

soil organic and inorganic carbon pools, hydrological

influences, gaseous fluxes, C/N dynamics, and micro-

bial degradation kinetics. Quantification of microbial

interactions that influence mineral weathering, soil

formation, mobilization of nutrients, and fate of che-

micals and toxins in the environment is closely tied to

the terrestrial C cycle and hydropedology in the Crit-

ical Zone. While it is generally recognized that ped-

ogenic processes are governed by microbial

dynamics, too little attention was given to this matter

in the past; most soil genesis models were heavily

focused on abiotic processes and it is now well rec-

ognized that this was a significant oversight.

Equally important to the Critical Zone studies is

the dynamics of the land–ocean interface. Here, coast-

al ocean processes (tides, waves, and currents) inter-

acting with river drainage, ground water flow, and

sediment flux largely control geomorphic erosion pro-

cesses and the geometry of the land surface. This

geometry in turn governs soil erosion, soil parent

materials, pedogenesis, terrestrial geochemical pro-

cesses, spatial diversity of soils, hydrology, and

biota. With new tools of radiometric dating, stable

isotope analysis, and soil/paleosol reconstructions,

soil scientists, stratigraphers, sedimentologists, and

geochemists interactively are able to begin recon-

structing portions of Earth’s history in the Critical

Zone. For example, the evolution of our planet can

be tracked by determining how the physical, chemical,

and biological characteristics of the Critical Zone have

changed throughout its history. Topographic relief,

length of day, solar influx, and composition of the

atmosphere are some of the aspects of the Earth’s

surface that have varied significantly over time. The

quality of the paleo record in the Critical Zone, and

thus the ability to derive accurate reconstructions,

vary depending on the extent of time averaging of

the data set, erosion, diagenesis, and tectonism.

New facilities and instrumentation allow for some

exciting possibilities to quantify environments in the

Critical Zone. For example, 3-D and 4-D visualiza-

tions allow stratigraphy and fluid attributes of terres-

trial systems to be visualized as they are examined in

different vertical, oblique, and horizontal geometric

orientations. In the petroleum engineering exploration

industry, 4-D visualizations allow for one to find oil-

bearing strata with a high degree of certainty from

computer synthesis of prior bore holes and seismic

logs in off-shore Gulf Coast regions (Anderson et al.,

1995). Similar approaches could be explored with the

comprehensive soil survey databases in the USDA-

NRCS National Soil Information Systems (NASIS) to

portray soil stratigraphy, soil physical/chemical/bio-

logical attributes, and hydrology of soils in 3-D or

4-D geometry. Synchrotron-based X-ray spectroscopy

permits soil features and mineral/organic constituents

to be examined at atomic scales to understand surface

colloidal reactions, complex interactive compositions,

and fate and transport of chemicals. Nanophase bio-

geochemistry is in its infancy and offers a very prom-

ising future to differentiate organic and inorganic for

observed soil properties (Lower et al., 2002).

Major research opportunities have been opened by

the development of remote sensing observation plat-

forms and instruments, largely space-borne, capable

of recording features of the surface and near near-

surface states and fluxes of the Critical Zone. Devel-

opment of improved in situ instrumentation and the

capability of recording, and accessing prodigious

amounts of data in ground-based networks provide

opportunities for intensive temporal and spatial sam-


pling of the spectrum of fluxes and states. Digital

elevation models (DEM), ground penetrating radar

(GPR), high resolution electromagnetic and acoustic

imaging, sonar, and integrative geographic informa-

tion systems (GIS) are tools of the present and future.

For example, estimation of precipitation fluxes with

radar calibrated against ground-based measurements

at scales of 1-km pixels may provide unprecedented

opportunities for developing distributed hydrologic

models. Measurements of surface energy fluxes com-

bined with future refined radar measurements at the

scale of 100 m pixels or better would open the way for

modeling and describing hillslope hydrology and en-

ergy fluxes at a scale needed for accurate representa-

tions of biogeochemical interactions in the Critical

Zone. Refined digital terrain data have been used

with coupled soil distribution models to provide new

insights in hillslope mass wasting and identification of

landslide hazard zones (Drees et al., 2003). Significant

advances could be made in the fluid mechanics and

characterization of flow paths and residence times in

heterogeneous porous media, both partially saturated

and saturated domains, at the micropore and macro

pore scales that are crucial for understanding transport

processes and biogeochemical interactions.

Isotope geochemistry and molecular biology have

added new dimensions to the Critical Zone studies.

For example, stable C and O isotopes offer opportu-

nities for reconstruction of hydrological, vegetative,

and climatic paleoenvironments (Driese and Mora,

2002). They also allow differentiation of lithogenic

versus pedogenic weathering products, such as pedo-

genic carbonates in soil systems (West et al., 1988).

Development and use of cosmogenic isotopes (radio-

nuclides 10Be, 26Al, and 36Cl, and stable 3He and21Ne) could revolutionize understanding of geomor-

phic processes and climate timing in high-latitude and

arid landscapes. Nucleic acids of known sequences

can be arranged through computer chips known as

microarrays. Microarrays are miniature, ordered, high-

density distributions of genes, gene fragments, or

other nucleic acid sequences that could be interrogat-

ed to indicate whole cell physiological response to

chemical exposure or other environmental stressors.

Complete, whole-organism response to chemical ex-

posure or environmental stress is theoretically possi-

ble. The potential for microarrays to serve as early

warning signals of land degradation is a new molec-

ular biology novelty (Staub et al., 2002; Zhou and

Thompson, 2004). However, the potential of micro-

arrays under the wide diversity of environmental con-

ditions in the Critical Zone has not yet been verified.

5. Unique contributions of pedology to Earth

science

Pedology is a branch of soil science that integrates

and quantifies the morphology, formation, distribu-

tion, and classification of soils as natural or anthro-

pogenically-modified landscape entities. It has many

unique contributions to Earth science. For instance,

soil mapping provides the classical foundation for our

understanding of soil–landform relationships and soil

variability over the landscape; soil profile descriptions

have been the major source of in situ soil morpholog-

ical information and various soil hydromorphological

features that are signatures of hydrology in the unsat-

urated zone; soil survey databases provide a wealth of

information that bio- and geo-sciences could utilize

for various applications; soil classification offers a

hierarchical system for organizing, modeling, and

transferring our knowledge about different soils across

broad climo-geographic regions that are needed in

Earth system modeling; and soil genesis provides

insights regarding weathering processes and soil-geo-

morphology evolution over time. Here we highlight

some Earth science research needs that expertise in

pedology could make significant contributions:

! Soil spatial variability and geomorphology: Pedol-

ogy plays a unique role in understanding the dis-

tribution, mechanisms, and magnitudes of soil

variability across landscapes and geographic

regions. Soil surveyors with pedological expertise

map and quantify soil spatial diversity based on

predictive soil-landscape models, augmented by

soil genesis theory and verified (or negated) by

ground truth observations. Pedological expertise

provides insights into how landscapes may be par-

titioned into geomorphic components according to

landform erosional/constructional processes with

corresponding spatial diversity of soil properties.

This provides a powerful basis for statistical anal-

ysis by stratified random sampling or transect anal-

ysis that is oriented transverse to maximum


differentials in landform/soil gradients. Improved

understanding of how scale influences the diversity

and function of soils is crucial if we are to move

towards more sustainable land use and better mod-

els of soil ecosystems (McSweeney and Norman,

1996). Modern research has increasingly demon-

strated the close dependence of soils, landforms,

and geomorphological processes. Patterns of land-

forms are matched, often on a one-to-one corre-

spondence with soil patterns (Gerrard, 1981; Hall,

1983, Wysocki et al., 2000).

! Surficial weathering processes and biogeochemis-

try: The relationship of soil composition, soil

weathering, and pedogenesis has been comprehen-

sively summarized by Allen and Fanning (1983).

Pedogenesis is essentially an integrated weathering

phenomenon resulting from a series of physical,

chemical, and biological processes. It provides a

holistic view of the processes that have occurred,

or are occurring, in the Critical Zone. The recent

formation of the Weathering System Science Con-

sortium within the biogeochemistry community

demonstrates the need to answer a fundamental

scientific question: bHow does the Earth’s weath-

ering engine transforms the protolith into soils and

solutes in response to climatic, tectonic, and an-

Fig. 2. Contaminant hydrogeology and the role of the vadose zone: The fat

moves through the soil and over the landscape (Modified after Fetter, 199

thropogenic forcing?Q (Anderson et al., 2004).

Quantitative models that describe the impact of

environmental variables on rock weathering and

soil formations are lacking.

! Global change and Earth system science: One

reason that pedology has received continued atten-

tion over the years by bio- and geo-scientists, land

use planners, land owners, and regulatory agencies

is the success of the pedologically-based soil sur-

vey information and interpretations. While the po-

tential of soil surveys is largely untapped,

considerable attention is currently being devoted

to better marketing strategies to achieve more ef-

fective utilizations by decision makers and other

stakeholders. Digital soil maps and databases at

various geographical scales provided by soil sur-

veys, in conjunct with other bio- and geo-science

databases, are important for modeling the Earth

system, the Critical Zone, and global change. In

addition, palepedology provides valuable tools to

reconstruct past Earth environment from soil

records (Retallack, 1996; Driese and Mora, 2002).

! Vadose zone hydrology and hydrogeology: Much

like bone cannot ignore the role of ground water in

performing geologic workQ (Domenico and

Schwartz, 1998), water in the unsaturated zone

e of contaminants in the environment has a lot to do with how water

3 and Lin, 2003).


cannot be ignored in soil formation and dynamic

changes in soil systems (Lin et al., 2005). One

common question hydrogeologists often ask when

dealing with ground water quality and quantity is

bWhere, when, how much, and how fast water and

contaminants come from the overlying vadose

zone?Q Because many releases of contaminants to

the subsurface occur within or above the vadose

zone (Fig. 2), including xenobiotic materials ap-

plied deliberately (e.g., agricultural chemicals,

landfill leachate, or toxic waste dumps) and those

released accidentally (e.g., leaking septic tanks,

chemical spills, or leaking petroleum tanks), it is

imperative that we understand thoroughly the

impacts of in situ soils on water movement and

chemical transport through various types and

thicknesses of soils and near-surface geological

materials (Brown, 1996; Wagenet, 1996). Hydro-

pedology, in combination with hydrogeology, sug-

gests a more integrated and holistic approach to

study water–soil–rock interactions (Figs. 1 and 2).

The emphasis of pedology is now shifting from

classification and inventory to understanding and

quantifying spatially and temporally variable process-

es upon which the water cycle and ecosystems de-

pend. The next section of this paper highlights the

need for hydropedology that suggests a shift of geol-

ogy-rooted classical pedology to a hydrology-driven

approach, reflecting the crucial role of water in many

environmental, ecological, and geological processes

and functions.

6. Hydropedology and the blooming of

hydrogeosciences

The area of hydrogeosciences has emerged as a

compelling discipline given its links to a broad area of

environmental, ecological, geological, agricultural,

and natural resource issues of societal importance.

This area has substantial potential of growth (Lin et

al., 2005). Hydrogeoscientists are encountering a new

intellectual paradigm that emphasizes connections be-

tween the hydrosphere and other components of the

Earth system (Fig. 1). While hydroclimatology, hydro-

geology, and ecohydrology are now well recognized,

an important missing piece of puzzle is hydropedol-

ogy that focuses on the interface between the hydro-

sphere and the pedosphere. Hydropedology closes this

gap and emphasizes flow and transport processes in in

situ soil systems as landscape bodies (i.e., soils that

have distinct characteristics of pedogenic features,

structure, layering, and soil–landscape relationship).

Hydropedology is a timely addition in this exciting

era of interdisciplinary and systems approaches for

developing comprehensive prioritization of science

and applications in the Earth science. Seizing this

opportunity requires that we further the vision of

hydropedology and explore its unique contributions

to the overall Earth science. We believe that hydro-

pedology can contribute significantly to the study of

the pedosphere, the hydrologic cycle, the Earth’s Crit-

ical Zone, and the Earth system as a whole. For a

comprehensive review on the advances in hydrope-

dology, readers are referred to Lin et al. (2005).

Besides pedology, soil physics, and hydrology (as

bcornerstonesQ of hydropedology), hydropedology is

also linked to other bio- and geo-sciences such as

geomorphology, geology, geography, hydrogeology,

hydroclimatology, ecohydrology, biology, and other

branches of soil science (Lin, 2003). Hydropedology

suggests a renewed perspective and a more integrated

way to study soil–water interactions across spatial and

temporal scales. Taking a holistic view of the land-

scape, with the roots in pedology and a focus on water

as a driving force, hydropedology emphasizes the

system linkages, the state and pattern of its component

storages, interfacial fluxes, and dynamic changes, in-

cluding those caused by anthropogenic activities (Lin

et al., 2005). Hydropedology attempts to characterize

integrated physical, chemical, and biological process-

es of soil–water interactions at all scales, including the

mass and energy transport by the water flow, and the

interrelationships between soil distributions/functions

and hydrologic and geomorphic processes. Soil hy-

drology is a major driving force behind pedogenesis,

soil morphology, and soil distribution patterns and

extent. It controls a variety of soil physical, chemical,

and biological processes that lead to the formation of

different soils and diverse land uses. Soil moisture

regimes play a critical role in classifying soils, and the

spatial-temporal distribution of water provides clues

regarding soil variability and mapping. Furthermore,

with increasing emphasis on human impacts and land

management practices, the arising interest in dynamic


soil properties would require more attention to soil

physical and hydraulic properties and their relations to

soil taxonomic constructs and cartographic map units.

Hence, many knowledge gaps could be better

addressed from an integration of classical pedology

with hydrology through hydropedological studies.

Some examples include:

! Soil structure quantification and modeling

! Preferential flow prediction, and determination of

flow mechanism and pattern

! Soil hydromorphology quantification and modeling

! Water movement as recharge, discharge, and inter-

flow controlled by soil landscape attributes

! Soil spatial and temporal variability and its un-

derlying causes; pattern identification and predic-

tions of various soil and hydrologic properties and

processes

! Scale-bridging from laboratory to field, landscape,

region, and globe

! Data-bridging through approaches such as pedo-

transfer functions, including the fundamental

mechanisms and practical enhancements to im-

prove the values of soil survey databases

7. Soil architecture and soil function

For over a century, pedologists have used soil

architecture (soil horizonation and structure) as an

index to separate soils with different qualities, poten-

tials, and constraints for land management. Soil

structure is the physical constitution of solid particles

and voids into secondary polyhedral assemblages

(Brewer, 1964). Peds are aggregates of those assem-

blages separated by natural surfaces of weakness

(e.g., coatings of sesquioxides, clays, organic-clay

assemblages, carbonates, and physical rearrangement

of in situ clay plasma by stress, etc.) (Figs. 3 and 4).

Structure and various micromorphic features at struc-

tural interfaces have been used to differentiate and

classify soils at all categorical levels within the U.S.

Soil Taxonomy (Douglas and Thompson, 1985;

Wilding and Flach, 1985; Soil Survey Staff, 1998).

In addition, soil structure has been used as a marker

of soil age, a predictor of soil stability, an indicator

of long-term redox state, an archive of polygenetic

history, and a determinant of infiltration and chem-

ical transport paths (Figs. 3 and 4). Macromorphic

observations of soil structure by pedologists empha-

size pedality—the size, shape, and grade (durability)

of polyhedral units (Fig. 3).

From a hydrological and biophysical perspective,

the porosity associated with peds – location, size,

shape, continuity, orientation, and origin of conduc-

tive voids – is of equal or greater importance than

pedality in developing hydrological pedotransfer

functions for modeling of water movement (Lin et

al., 1999a,b). For example, in strongly-structured Ver-

tisols and Alfisols, Lin et al. (1996) determined that

effective porosity in water flux was associated primar-

ily with macro- and mesopores greater than 0.06 mm

in diameter. They observed that nearly all (99%) of

the near-saturated water flow occurred through about

5% of the total porosity (i.e., meso- and macropores).

Slickenside fissures accounted for 30%, root channels

28%, and vertical fissures 25% of the flow pathways.

More recent work by Nobles et al. (2003, 2004) has

emphasized the importance of roots and slickensides

in transfer of water to subsurface horizons. It is pos-

tulated that with increasing soil depth, the structure/

porosity/water flux relationships would display the

following general trends: increasing ped size, decreas-

ing ped grade, decreasing equidimensional ped shape,

decreasing effective porosity, increasing preferential

porosity, increasing by-pass flow, increasing spatial

flux concentration, and increasing heterogeneity.

These uncertainties have made classical approaches

of modeling water flow and chemical transport in

structured soils a challenge (Schwartz et al., 1999;

Lin, 2003). To date, few models have fully taken

into account the above relationships (Brown, 1996;

Wagenet, 1996; Lin et al., 2005).

The importance of structure and associated macro-

voids in transport of water and solutes, and chemical

weathering is evident from numerous macromorphic

and micromorphic studies of soil architecture at mul-

tiple levels of scale resolution (pedons, soil horizons,

pedality, porosity, and microfabric zonation of organic

and inorganic constituents) (Figs. 3 and 4). It is said

that a crushed or pulverized sample of the soil is

related to the soil formed by nature like a pile of

debris to a demolished building (Kubiena, 1938).

Neither the structure nor behavior of a soil can be

determined from a crushed sample any more than the

architecture of a building from a pile of bricks; this is

Fig. 3. Diversity of field-scale soil macromorphological features with consequent impacts on water flow through the unsaturated soil zone: (A)

Carbonate coating (white zones) along ped structural interfaces and biopores of a Btk horizon in an Ustalf. These coatings provide evidence of

by-pass flow and long-term water and solute transport along macropores. (B) An Udalf exhibiting an E horizon with platy structure (light gray

color) superposed over an Fe-rich (plinthic), reticulate-colored subsoil where iron oxides have precipitated along interpedal macropores. This

has resulted in macropore plugging, root restriction, decreased permeability, and evidence of seasonal reduction/oxidation environments. (C)

Dye-stained hand specimen of a structural Bt horizon in an Ustalf. Blue dye traces water movement from natural rainfall events along blocky

ped interfaces. Peds are 2–5 cm in diameter and illustrate strong preferential flow along ped interfaces. (D) Columnar structure in an Ustalf with

a natric (Btn) horizon. The columnar peds are indicative of restricted vertical movement of roots, water, and solutes into this zone because of

chemical dispersion of clay/organic colloids with Na. (E) Granular porous structure of a surface horizon of a Vertisol. This structure is indicative

of chemical flocculation of clay/organic colloids by Ca and Mg. This structural condition is favorable for air/water/chemical transport and

biological activity. (F) A slickenside in the Bss subsoil of an Ustert. The slickenside illustrates the propensity of these clayey shrink-swell soil

matrixes to fail along shear planes set at 10–808 to the horizontal. Slickenside surfaces bounding wedge-shaped peds are dense and ped

interfaces serve as preferential root and water pathways. The physical activity along slickensides causes flattening and shearing of root systems.

(G) Iron zonation along a ped interface (dark clay-rich trace) in the Bt horizon of an Ustalf. This is indicative of seasonal changes in oxidation/

reduction environments and temporal Eh conditions. Note gray eluvial materials near exterior of ped and redder interior (Fe-enriched) zone that

becomes less red with radial distance into ped matrix. Iron oxides at ped surface have become reduced by seasonal saturation at ped surface.

Ferrous Fe has moved by diffusion into higher redox (Eh) zones of ped interior where it has precipitated as ferric oxyhydroxides. Diameter of

ped is 6 cm. (H) Platy soil structure at the base of a tillage pan indicative of compaction, root restriction, and reduced vertical water and chemical

transport. Ped is about 10 cm in diameter.


Fig. 4. Various soil micromorphological features that are significant in pedogenesis and hydropedology: (A) Micrograph of surface horizon of an

Ustert that has been in long-term (30 years) pasture after continuous cultivation for row-crops for 65 years. Fabric illustrates well-developed

subangular blocky peds (black), numerous pores (white) around peds, and high biologic activity consisting of worm casts and roots (root are

circular, yellowish bodies associated with voids). Frame length is 4 mm taken in plane-polarized light mode. (B) A banded clay coating (right

side) along a prismatic ped surface of a fragipan horizon in an Udalf. This micrograph illustrates the remarkable change in clay content and

inferred chemical and physical properties between the ped interior (left side) and sand/silt-free clay coating bordering root channel. Frame length

is 2.5 mm taken in cross-polarized light mode. (C) Scanning electron microscopy (SEM) of a clay coating (clay membrane) illustrating

remarkable change in clay orientation and porosity between clay coating at ped surface and ped interior. Clay membrane is only 5–10 Am thick

but serves as an interface between the bulk soil and root environment. (D) A calcite coating or calcan (white zone) along a planar ped structural

pore (black) in a Bk horizon. This illustrates remarkable differences in carbonate concentration between root environment and ped interior.

Frame length is 3.5 mm taken in cross-polarized light mode. (E) Micrograph of a crusted (sealed) surface of an Ustalf. Light colored seal is clay

and fine silt (upper half) with lower half illustrating porous nature of unsealed sandy matrix. Seal decreases water infiltration by several orders of

magnitude. Frame length is 1 mm taken with backscatter SEM mode. (F) A micrograph of an illuvial clay-rich band (seal) in the sandy surface

layer of an Ustalf. The illuvial clay filling packing voids between sand grains is a layer less than 1 mm thick but reduces infiltration significantly.

Frame length is 3 mm taken in plane-polarized light mode. (G) Micrograph of long-term (65 years) cultivated Ustert within 20 m of the pasture

site illustrated in panel (A). Surface Ap horizon illustrates compaction, decreased pedality, decreased macroporosity, reorientation of

macrospores horizontal to the soil surface, and loss of most of the biological activity (roots and worm casts). Frame length is 4 mm taken

in plane-polarized light mode. (H) An oxyhydroxide of Fe and Mn (black) surrounding a root macropore (white) containing a root cross-section.

The gray ped matrix is associated with a Btg horizon of an Aqualf that has been seasonally saturated and reduced. High Eh conditions upon

drainage of the macropore has resulted in precipitation of Fe and Mn that moved to the surface of the macropore by diffusion. Frame length is

2.5 mm taken in plane-polarized light mode. (I) Colonization of soil bacteria in a microvoid; frame length is about 2 Am.



a serious indictment for some applications of physical

and chemical measurements that use ground or

crushed soil samples.

Early microfabric studies of ped surfaces were

conducted to document their composition, thickness,

and continuity as related to pedogenesis (e.g., Frei and

Cline, 1949; Cady, 1950; Buol and Hole, 1959, 1961;

Flach, 1960; Heil and Buntley, 1965; Grossman et al.,

1964; Khalifa and Buol, 1968; Miller et al., 1971;

Gerber et al., 1974). These studies helped verify origin

and function of these features. Examples were coatings

and matrix segregations or zonations (clay, carbonates,

silica, salts, organic matter), Fe-oxide depleted zones,

microcrusts (or seals), and changes in macroporosity

with land use and management (Fig. 4). Many of these

micromorphic features could be traced directly to

water movement and consequent effects on preferen-

tial flow, suspension, diffusion, dissolution, and oxi-

dation/reduction processes. Others were markers of the

propensity for soils to degrade upon intensive man-

agement, population pressures, or wind/water erosion

causing surface crusts and tillage pans. While coatings

may comprise a small proportion of the total ped

volume, they have inordinate impact on biophysical

soil attributes, flow pathways, chemical dynamics at

the ped/macrovoid interfaces. Examples would in-

clude biotic activity (root and other biopore distribu-

tion patterns), sorption/desorption kinetics, diffusion

rates, mass flow, gas transport, and biomass produc-

tivity (e.g., Miller et al., 1971; Soileau et al., 1964;

Khalifa and Buol, 1969; Gerber et al., 1974; Sexstone

et al., 1985; Asady and Smucker, 1989).

Measurements of soil quality assess the capacity of

soils to function within ecosystems, sustain plant and

animal productivity, maintain or enhance air and water

quality, and support human health and habitation

(Karlen et al., 1997). Soil architecture (structure) via

its influence on infiltration rates, water transport, sol-

ute movement, aeration capacity, biological diversity,

and root proliferation heavily impacts soil quality.

Structural degradation results in decreased macropor-

osity, loss of biopores, soil compaction, horizontal

reorientation of planar voids, and enhanced surface

runoff and erosion from reduced infiltration (Fig. 4)

(e.g., Puentes and Wilding, 1990; Coulombe et al.,

1996).

The above accounts illustrate the multiple-scale

role pedology plays in understanding pedogenesis,

morphology, spatial diversity, and function of soils

in terms of hydropedology. It is this profession, linked

with other bio- and geo-scientists, that has the exper-

tise to qualitatively and quantitatively translate land-

scape knowledge of soils in terms of hydrological

functions. Using the vast database of pedology (such

as that in the U.S. National Cooperative Soil Survey

Program) to develop pedotransfer functions suitable

for modeling continues to be a growing area of re-

search (Lin, 2003; Lin et al., 2005; Pachepsky and

Rawls, 2005). It is critical to soil science, and espe-

cially to the subdiscipline of hydropedology, that the

expertise of pedology continues to be an important

component of our research and education. Otherwise,

the knowledge of spatial soil diversity and its land-

scape functions will be lost to future generations.

Consequently, the ability to derive meaningful hydro-

logical models will be constrained because of the lack

of suitable real-world representation of spatially var-

iable and temporally dynamic soil systems.

8. Philosophy and the future

The supporting disciplines of Earth surface process

research are data- and observational-intensive. The

extraordinary developments in data acquisition, man-

agement, and interpretation made possible with

advances in observing and recording instruments,

and computer systems permit high-resolution descrip-

tion and prediction. Recent technological advances

illuminate the cross-disciplinary opportunities. The

focus on the Earth’s surface can be applied to a variety

of spatial scales (atomic, global, interstellar) and tem-

poral scales (past, present, and future) for selected

time slices in the Earth’s history. Insights into very

early periods of the Earth, or other planets, can be

gleaned from this approach.

What is needed is a more effective way to scale

observations and data sets from the micro- to mega-

levels of resolution. Uncertainties in models become

particularly acute when projecting research informa-

tion from microlevels to megascales (e.g., from nano-

metrics to interstellar). No single method is universal

or a panacea. For example, geostatistics appears to be

a powerful interpolative tool but may have limited

extrapolative capability (Wilding et al., 1994; Lin et

al., 2005). Fractals serve as a mathematical tool to


determine the multiplicity of observational patterns

but it is not clear at this point how to apply this

knowledge in a meaningful way to scale soil observa-

tions from site-specific to more general inferences

(Baveye et al., 1999). Soil surveys serve as a useful

means to stratify data sets based on landform, geolo-

gy, hydrology, and biotic attributes, but often the

intensity of observations is insufficient for either geos-

tatistical or fractal analysis. Classical statistical

approaches often ignore the spatial domain of soils

in which soil scientists now know that random sam-

pling strategies are inappropriate (Wilding and Drees,

1983; Nielsen and Wendroth, 2003).

Modeling soil processes and spatial distribution

patterns continues to be a challenge, but clearly has

a role in future Critical Zone studies. In all of the

above approaches, vigorous ground truthing and val-

idation of models are a prerequisite. What is critical is

to plan for concurrent in situ and remote observations,

and to develop methodologies for making optimal use

of both kinds of data sets to increase the understand-

ing of the interactions and exchanges within the Crit-

ical Zone and other solid and fluid envelopes of the

Earth. Such efforts will be essential for addressing the

connections between water and biogeochemical

cycles; pedosphere, vegetation, and geological pro-

cesses; and understanding the long-term vitality of

these portions of the planet so critical to life.

Hydropedology offers a promising opportunity to

educate multiple Earth science clientele about soil

science principles and functions. However, its effec-

tiveness will be limited if the knowledge of pedology

in educational entities continues to be institutionally

eroded and/or de-emphasized. Without academic

training of future soil scientists in the unique subdis-

cipline of pedology, the knowledge of soil–landform

relationships and soil spatial diversity will be lost to

more theoretical modeling considerations. The danger

here is that insufficient ground truth and logic will

undergird these efforts.

Visualization models serve as excellent opportunity

to communicate knowledge to ancillary bio- and geo-

science disciplines and the public at large. For exam-

ple, illustrating water flow in soils using visuals of

dye tracers is much more effective than descriptive

models. Illustrating the architecture of soil attributes

macromorphically or micromorpically or with submi-

croscopy (e.g., zonation of constituents, clay/organic

coatings, soil structure, porosity heterogeneity, root

distribution patterns, and microbial habitats) (see illus-

trations in Figs. 3 and 4) provides much better knowl-

edge transfer than attempts to simply describe these

phenomena or use pure mathematical representations.

Understanding the architecture of the soil across

scales may provide insights into the physical, chem-

ical, and biological behavior of the soil including

water flow, movement of chemicals and colloids,

toxic and pathogenic habitats, activity of microorgan-

isms, and root growth. Likewise, it is much easier and

more effective to visualize how soil architecture may

influence the functionality of soils. Too little use of

soil micromorphology or other in situ visualization

methods is being used in teaching or research, espe-

cially in instruction at introductory levels (e.g., K-12

and undergraduates). This situation is not likely to

improve in the near future because research and teach-

ing using soil micromorphology as a tool are not

being widely practiced, and thus, may be lost to future

generations of bio- and geo-scientists.

Earth science education in many primary- and

middle-school systems is being de-emphasized, and

hence, teaching our future citizens about Earth science

is at risk. This is unfortunate because it will not only

jeopardize the number of students who are likely to

choose specific fields of Earth science for future

career pursuits, but it results in an uninformed public.

The AGI and other professional societies are vigor-

ously addressing this matter through publication of

geoscience educational materials, legislative hearings,

children’s books, television series, instruction of pri-

mary and middle school teachers in Earth science,

development of the Earth Science Week program,

and utilization of web-based outreach materials

(Landa, 2004). This is a future challenge to be

addressed by all professional soil scientists and alike

to help insure the viability of the discipline.

9. Closing remarks

Understanding near-surface Earth properties, pro-

cesses, and functions is essential to sustaining global

habitats. Bio- and geo-sciences provide the tools to

integrate the components of Earth systems, to under-

stand causes and consequences of spatial and temporal

variability, and to take a more holistic approach to the


dynamic processes affecting ecosystems. However,

the role of scientists as contributors to society’s

goals is challenged. Research and development in

public and private sectors have decreased. Science is

under public scrutiny; our mission and contributions

are subject to review. Research must have societal

benefits for public support; commonly fundamental

research is challenged for lack of apparent relevancy.

Soil science, as one of the bio- and geo-science

components, shares the same opportunities and chal-

lenges as other disciplines of Earth science. The world

is undergoing the greatest changes in science, tech-

nology, and institutional structure ever recorded in

history. As a discipline and profession, soil science

has tremendous opportunities, but must position itself

as a partner with other bio- and geo-sciences to take

advantage of these new developments. Soil science

can be a key partner in expanding the Earth science’s

agenda, with aggressive outreach, education, public

service, and cutting-edge science and technology. To

become a bio- and geo-science leader, however, soil

science must broaden its purview, become more

encompassing, sharpen its tools, enhance communi-

cation skills, deepen its knowledge base, and effec-

tively bridge with other bio- and geo-science

disciplines.

Bio- and geo-sciences and soil science in the 21st

century share a common agenda. That agenda is to: (i)

broaden constituencies beyond traditional partners;

(ii) expand focus in the near-surface bCritical ZoneQto include food security, food safety, ecosystem man-

agement, biosphere sustainability, environmental pro-

tection, and urban environment; (iii) enhance

fundamental knowledge of Earth systems that is

more systematic, interdisciplinary, dynamic, and pro-

cess-oriented; (iv) identify early warning systems of

natural hazards and resource degradations; and (v)

develop joint research and education partnerships

that attract coupling of public and private support.

Soil science is a major stakeholder in this agenda

and has the opportunity to contribute inordinately to

the success of these bio- and geo-science goals.

The current blooming of hydrogeosciences empha-

sizes the connections between the hydrosphere and

other components of the Earth system. Hydropedol-

ogy is emerging as a unique subdiscipline of soil

science and hydrology that focuses on the interface

between the hydrosphere and the pedosphere, with an

emphasis on flow and transport processes in soil-

landscape systems in situ. We believe that hydrope-

dology is a timely addition in this exciting era of

interdisciplinary multiscale integration that should be

characteristics of modern Earth science. Hydropedol-

ogy plays a unique role in advancing the frontiers of

soil science towards a bio- and geo-science.

Acknowledgements

We thank Drs. Edward R. Landa and Randy B.

Brown for their helpful reviews of this manuscript.

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