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Journal of African Earth Sciences 39 (2004) 441–445

Soil physics: a Moroccan perspective

Sabah Lahlou a,*, Rachid Mrabet b, Mohamed Ouadia a

a Department of Geology, UFR. Geoscience and Environment, Faculty of Sciences, Chouaib Doukkali University,

P.O. Box 20, El Jadida 24000, Moroccob Institut National de la Recherche Agronomique (INRA), Aridoculture Center, Soil Physics Laboratory, P.O. Box 589, Settat 26000, Morocco

Available online 18 September 2004

Abstract

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 interpre-

tation 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 (contami-

nation 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 prop-

erties and to revise developed models to meet our conditions. Large, but special, investment is required to promote research pro-

grams in soil physics, which consider developments in this discipline and respect Moroccan needs. These programs will be

highlighted herein.

� 2004 Elsevier Ltd. All rights reserved.

Keywords: Soil physics; Instrumentation; Environment; Morocco; Degradation; Soil quality

1. Introduction

Soil physics is a relatively young science, which meas-

ures, predicts and controls the physical processes taking

place in and through the soil. It uses theories, models,

technologies and instruments, and benefits from labora-

tory and field experiments for a perpetual evolution and

0899-5362/$ - see front matter � 2004 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jafrearsci.2004.07.021

* Corresponding author.

E-mail address: sabah_26@hotmail.com (S. Lahlou).

better fulfilling the future requirements. Kutilek and

Rieu (1998) reported that soil physics followed two

paths during its development. The first is the empirical

one characterized by countless numbers of laboratory

and field experiments where the results were only quali-

tatively interpreted. The second path is characterized by

the real application of physical theories to the solutionof transport processes in soil, to tillage and compaction

of soil and many other processes and phenomena. By

providing a description of these processes, soil physics

constitutes an instrument essential for a sustainable

442 S. Lahlou et al. / Journal of African Earth Sciences 39 (2004) 441–445

management of soils, not only as a bridge for improving

plant production, but also with regard to their protec-

tion and conservation. However, until recently, the

knowledge of the soil physical system as a whole was

recognized to be still fragmentary, because of the space

and time variation of soil properties. In order to deter-mine this variability, there has been a great evolution

of measurement techniques. This evolution in instru-

mentation, coupled with modeling, has contributed to

a thorough understanding of some processes linked to

environmental pollution and degradation of soil and

water resources. Most of these developments were car-

ried out in industrialized countries, but are not yet well

exploited by research programs in developing countries.Consequently, Moroccan soil physicists, when focusing

their research on environmental problems and agricul-

tural applications, should benefit from former work to

implement permanent working tools to develop their

proper database, and models to meet specific conditions

of the country (climate, soil, topography, vegetation,

groundwater resources, etc). Since soil physics has not

yet acquired it proper place in Morocco, this paper isa first contribution for providing this branch of soil sci-

ence the status of a primary discipline for education and

research purposes. The objectives of this paper 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.

2. History of soil physics

During the 17th and 18th centuries, the research of

some physicists was focused on the vital role of pores

and pore geometry in the expansion of roots and in

the exchanges of nutritive solutions especially in clay

soils (Philip, 1974). This same author reported that DeLahire was the first person in the 17th century, to study

the soil–water relationship, and published a treatise on

percolation of water through lysimeters (cited in Philip,

1974). The first systematic study of a wide variety of soil

physical properties was particularly formed on those

properties that might affect crop yields (Kohnke,

1968). The concept of capillary and non-capillary poros-

ity of soils was introduced in different research (Kohnke,1968). In the 19th century, the soil physics study ex-

tended in various scientific directions and mechanical

analysis was developed for the physical characterization

of soils, especially for determination of particle size dis-

tribution. The majority of soil physical analysis was

done on sieved samples because the importance of natu-

ral soil structure had not yet been recognized.

After intensive experimentation and quantitativephysical theory, Buckingham had developed the concep-

tual basis for modern physical studies of water in

unsaturated soils and Darcy�s law was used to under-

stand the water movement in unsaturated soils. Changes

during the evolution of soil physics were directed from

the laboratory to the field regime, either through gener-

alization of Darcy�s law (Richards, 1931) or in situ

measurements. In the early 1950s, soil physicists startedproducing new equipment for in situ measurement of

soil hydraulic properties (Gardner, 1958). Water infiltra-

tion in soils was studied and modeled in the early 1900s

(Green and Ampt, 1911) and the most recent infiltration

models date back to the 1960s (Philip, 1957). Because of

the need to study macropore flow (preferential flow),

new tentative models were proposed to explain this flow.

However, by-pass infiltration is still empirically modeled(Bevan and German, 1982). This transition from labora-

tory to field measurement has given rise to new areas of

research: field spatial and temporal variations of soil

properties (Jury et al., 1991). Soil physics research was

then oriented to agricultural aspects (including tillage,

soil structure, drainage, irrigation, etc.) (Mahboubi

and Lal, 1998). Only recently has research in soil physics

expanded its scope to include problems related to envi-ronmental pollution and degradation. To monitor and

assess these problems, there was an important emer-

gence of new instruments, which were gradually im-

proved and became more sophisticated (Hanks and

Brown, 1987; Topp et al., 1992).

3. Soil physics: development in measurement techniques

Development in instrumentation helped to explain

simultaneously processes, satisfy theories and orient

management decisions in agriculture (irrigation, drain-

age), environment (waste management and disposal,

erosion, salinity control, etc.), and industry (remediation

and clean-up). The measurement techniques presented

in this article relate to the principal parameters involvedin the characterization of the physical soil properties,

mainly soil moisture, hydraulic conductivity and soil

structure. In fact, remarkable progress has been made

on instruments for measuring most soil physical proper-

ties (particle-size distribution (PSD), gas diffusivity,

thermal conductivity, salinity, alkalinity, etc.). For all

soil scientists, PSD constitutes a fundamental soil prop-

erty correlated to most other soil properties. PSD can bemeasured either with simple apparatus (hydrometer and

pipette) or with advanced equipment (sedigraph, laser,

gamma- or X-ray) (Gee and Bauder, 1986; Ketteler

et al., 2001). These instrumental developments are due

to needed precision in data collection for accurate inter-

pretation of space and time variation of soil properties.

The satisfaction of these goals prompted the emergence

of advanced theories and comprehensive mechanisms ofmost natural processes, the development of new mathe-

matical tools (modeling and computer simulation, frac-

S. Lahlou et al. / Journal of African Earth Sciences 39 (2004) 441–445 443

tals, geostatistics, transformations), the creation of high

precision instrumentation (computer assisted, less time

constraint, increased number of measured parameters)

and the scale sharpening of physical measurements,

which range, from the micro-scale to the watershed

(Vandenbygaart et al., 1999).Knowledge of the soil water status is of primary

importance in soil physics. The standard method for

measuring water content is the gravimetric method. This

method becomes difficult when measurements are re-

quired in dry climates because significant water losses

can occur rapidly during handling and weighing. In

the field, the neutron probe provides a non-destructive

method for monitoring water content in the subsoil(Dexter, 1996). Its main disadvantages are the high ini-

tial cost of the instrument, low degree of spatial resolu-

tion, difficulty of measuring moisture in the soil surface

zone and the health hazard associated with exposure to

neutron radiation (Hillel, 1998). Dexter (1996) reported

that for accurate work, the probe needs to be calibrated

for each horizon of each soil, which is not always

practiced. In recent years, electromagnetic or dielectricmethods have been used increasingly. These include

time-domain reflectometry or TDR (Whalley, 1993).

TDR has been applied to measure soil water content

and/or salt concentration directly in the field through a

calibration curve relating the dielectric constant of the

soil material as a function of water content and/or salt

concentration (Topp et al., 1992). This instrument is still

a subject of research and development (Skaling, 1992;Wraith and Dani, 1999; Siddiqui et al., 2000). However,

other measurement techniques have not achieved much

technical improvement and are used largely as originally

developed. This is the case for matric potential, a critical

variable in water management and agriculture, meas-

ured with tensiometer and porous pressure plate (Phene

et al., 1992). Hydrodynamic properties (conductivity,

diffusivity, sorptivity) are parameters of water flow the-ories. Hence, field measurements were required to vali-

date these theories. Various instruments and devices

were designed accordingly. Among recently developed

equipment, Guelph, disk permeameter and tension infil-

trometer are the most commonly used. Early conductiv-

ity and sorptivity instruments were proposed by

Bouwer, 1966 (single and double ring infiltrometer).

Mechanical analysis of soil structure can produceuseful information for agronomical soil classification

and guidelines for soil management (Chisci et al.,

1989). However, quantification of stable aggregates in

soils is still largely dependant at early-developed method

of Henin et al., 1958, Chepil (1962) and Kemper and

Chepil (1965). Even though soil structure and aggrega-

tion are important parameters and are processes occur-

ring under continuous changes in the environment, theirmeasurement has been modified only slightly (Amez-

keta, 1999). The dry method developed by Chepil

(1962) consisted of separation of aggregates in a rotary

sieve with several sizes. In the high portion of the aggre-

gate diameter (>0.83 mm), it is less likely that wind ero-

sion will occur. The wet method developed by Kemper

and Chepil (1965) was modified in 1986 by Kemper

and Rosenau. It was meant to reflect the occurrence ofwater erosion. In order to quantify more precisely the

soil structure, several attempts were made in the applica-

tion of image analysis or using the computed tomogra-

phy method. This latter related porosity and pore size

distribution to soil management (Gantzer and Ander-

son, 2002). Other methods exist, and the treatment con-

sists in wetting the samples in liquids other than distilled

water, such as ethanol (Le Bissonnais, 1996).

4. Relationship to other disciplines

One would not study soil physics without carrying

out frequent incursions into the other related disciplines

(agronomy, hydrology, geology, mathematics, pedol-

ogy, physics, sedimentology, etc.). For successful treat-ment of all classical and new environmental problems,

soil physics completes its traditional theories with re-

cently developed approaches in applied mathematics

and instrumentation physics and its interaction with

other scientific branches (Kutilek and Rieu, 1998). Espe-

cially, hydrologists are concerned with water regime and

water flow through the soil, while soil physics can ex-

plain the greenhouse effect that interests climatologists.Additionally, the environmental industry has contrib-

uted to a better understanding of many facets of soil

physics. In other words, research demand in soil physics

has increased considerably to satisfy specific and envi-

ronmental problems (contamination of water resources,

global warming, etc.).

5. Soil physics research in Morocco: highlights

The developments in the field of soil physics world-

wide have also helped the establishment of new research

topics (global warming, point vs non-point contamina-

tion, waste management, etc.). However, in Morocco

soil physics is still at an embryonic stage. Soil physics re-

search has been directed to study processes (infiltration,erosion, runoff, etc.) and phenomena (salinity, compac-

tion, water and soil conservation, etc.). Mrabet (1989)

studied preferential flow of water in vertisols of two re-

gions of Morocco using rainfall simulation and double

ring infiltrometer. He is also studying runoff generation,

crack networks and soil bulk density evolution with

water content. This relationship was detailed by Faraji

in 1990. Merzouk (1985) studied erodability of Moroc-can soils with a rainfall simulator. This technique for

studying hydrodynamic and physical processes was well

444 S. Lahlou et al. / Journal of African Earth Sciences 39 (2004) 441–445

used in Morocco. Soil and water conservation measures

are known elsewhere to prevent degradation; results

from soil physics research confirmed their applicability

to the local conditions of Morocco. In fact, Lahlou

(1999), when measuring soil physical properties (bulk

density, structure) and hydraulic properties (conductiv-ity, sorptivity using Guelph permeameter), confirmed

the positive impact of no-tillage practices in improving

these properties of a Mollisol. Research on salinity in

Morocco dates back to the pioneering work by Bryssine

in 1961. Basic modeling of water retention was carried

out by Merzouk et al. (1987a,b).

This lack of intensive soil physics research in Moroc-

co explains the difference in approaches to problems ofenvironment and to soil related phenomena and proc-

esses. Consequently, research programs should aim to

favour development of soil physics laboratories at the

regional level (university, research and industry institu-

tions). These same programs should consider building

teams specialised in important research areas (contami-

nation, erosion, salinity, global warming, etc.). These

teams also should work within other concerned groupsin order to carry out multidisciplinary research. Soil

physics should be included in education curricula of sci-

ence faculties as it is already at agronomic institutes.

6. Conclusion

Upon our ability to measure soil physical properties,depends our understanding and prediction of natural

processes. Thus, soil physicists should be able to synthe-

size these processes and put them to work in maintain-

ing the quality of our environment, while producing

the needed food and fibre for growing populations. Even

though soil physics is a recent science, it has contributed

to improving our lifestyle. This paper also points to the

need for more intensive research to contribute improveto understanding of human environmental impacts.

However, soil physics research in Morocco is still frag-

mentary. To strengthen soil physics research, a national

program needs to be implemented to coordinate educa-

tion, research and industry sectors. This program should

use existing knowledge and respect our requirements.

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