Influence of Organic Matter Content on Hydro-Structural Properties of Constructed Technosols

Abstract

Constructed Technosols may be an alternative for creating urban green spaces. However, the hydro-structural properties emerging from the assembly of artefacts have never been documented. The soil shrinkage curve (SSC) could provide relevant structural information about constructed Technosols, such as the water holding capacity of each pore system (macropores and micropores). The objectives of this study were (i) to evaluate the SSC and water retention curve (WRC) to describe the structure of constructed Technosols and (ii) to understand the influence of organic matter content on soil hydro-structural properties. In this study, Technosols were obtained by mixing green waste compost (GWC) with the material excavated from deep horizons of soil (EDH). The GWC was mixed with EDH in six different volumetric percentages from 0% to 50% (GWC/total). The GWC and EDH exhibited highly divergent hydro-structural properties: the SSC was hyperbolic for GWC and sigmoid for EDH. All six mixture treatments (0%, 10%, 20%, 30%, 40% and 50% GWC) exhibited the classical sigmoid shape, revealing two embedded levels of pore systems. The 20% GWC treatment was hydro-structurally similar to the 30% and 40% GWC treatments; so, a large quantity of expansive GWC is unnecessary. The relation with the GWC percentage was a second-degree equation for volumetric available water in micropores, but was linear for volumetric available water in macropores and total volumetric available water. Total volumetric available water in the 50% GWC treatment was twice as high as that in the 0% GWC treatment. By combining SSCs and WRCs, increasing the GWC percentage increased water holding capacity by decreasing the maximum equivalent size of water-saturated micropores at the shrinkage limit and increasing the maximum equivalent size of water-saturated macropores, resulting in an increased range of pore diameter able to retain available water.

Full text

Pedosphere 26(4): 486–498, 2016
doi:10.1016/S1002-0160(15)60059-5
ISSN 1002-0160/CN 32-1315/P
c
⃝2016 Soil Science Society of China
Published by Elsevier B.V. and Science Press
Influence of Organic Matter Content on Hydro-Structural
Properties of Constructed Technosols
Maha DEEB1,2,∗, Michel GRIMALDI2, Thomas Z. LERCH1, Anne PANDO1, Pascal PODWOJEWSKI2and
Manuel BLOUIN1
1UPEC, Institute of Ecology and Environmental Sciences of Paris (UMR 7618), 61 avenue du G´en´eral de Gaulle, Cr´eteil 94010
(France)
2IRD, Institute of Ecology and Environmental Sciences of Paris (UMR 242), 32 avenue Henri Varagnat, Bondy 93143 (France)
(Received December 29, 2015; revised March 30, 2016)
ABSTRACT
Constructed Technosols may be an alternative for creating urban green spaces. However, the hydro-structural properties emer-
ging from the assembly of artefacts have never been documented. The soil shrinkage curve (SSC) could provide relevant structural
information about constructed Technosols, such as the water holding capacity of each pore system (macropores and micropores). The
objectives of this study were (i) to evaluate the SSC and water retention curve (WRC) to describe the structure of constructed Tech-
nosols and (ii) to understand the influence of organic matter content on soil hydro-structural properties. In this study, Technosols
were obtained by mixing green waste compost (GWC) with the material excavated from deep horizons of soil (EDH). The GWC
was mixed with EDH in six different volumetric percentages from 0% to 50% (GWC/total). The GWC and EDH exhibited highly
divergent hydro-structural properties: the SSC was hyperbolic for GWC and sigmoid for EDH. All six mixture treatments (0%, 10%,
20%, 30%, 40% and 50% GWC) exhibited the classical sigmoid shape, revealing two embedded levels of pore systems. The 20% GWC
treatment was hydro-structurally similar to the 30% and 40% GWC treatments; so, a large quantity of expansive GWC is unnecessary.
The relation with the GWC percentage was a second-degree equation for volumetric available water in micropores, but was linear for
volumetric available water in macropores and total volumetric available water. Total volumetric available water in the 50% GWC
treatment was twice as high as that in the 0% GWC treatment. By combining SSCs and WRCs, increasing the GWC percentage
increased water holding capacity by decreasing the maximum equivalent size of water-saturated micropores at the shrinkage limit and
increasing the maximum equivalent size of water-saturated macropores, resulting in an increased range of pore diameter able to retain
available water.
Key Words: available water, soil shrinkage curve, soil water content, water holding capacity, water retention curve
Citation: Deeb M, Grimaldi M, Lerch T Z, Pando A, Podwojewski P, Blouin M. 2016. Influence of organic matter content on
hydro-structural properties of constructed Technosols. Pedosphere.26(4): 486–498.
INTRODUCTION
Technosols are soils that contain a significant
percentage of artefacts (at least 20% in the upper 100
cm), i.e., something in the soil recognizably made or
strongly altered by humans or extracted from greater
depths (WRB, 2014). Constructed Technosols are mix-
tures of anthropogenic materials used on purpose to
create a new soil dedicated to growing plants (Baize
and Girard, 2008). This kind of soil is a new solution
in ecological reclamation of degraded land. For exam-
ple, the addition of urban wastes has been used on
decontaminated soil to improve their quality (S´er´e et
al., 2008). In addition, it provides an alternative to u-
sing agricultural topsoil to create urban green spaces,
which is often necessary because urban soils can be
unfavorable for plant growth and development (Craul,
1999; De Kimpe and Morel, 2000).
Adding organic waste to degraded land in urban
or rural areas is a practice largely documented in the
literature as a way to improve water holding capaci-
ty (Epstein et al., 1976; Kelling et al., 1977), hy-
draulic conductivity (Kumar et al., 1985), aggregation
(Zhang, 1994), total porosity (Mathan, 1994), bulk
density (Arvidsson, 1998), ability to resist compaction
(Soane, 1990; Paradelo and Barral, 2013) and soil qua-
lity (Reeves, 1997). Understanding the influence of di-
fferent percentages of organic matter is essential for
improved plant production, since it is useful to identi-
fy the percentage of organic matter necessary to create
a Technosol with the desired properties without increa-
sing costs.
∗Corresponding author. E-mail: mahadeeb.y@gmail.com.

ORGANIC MATTER EFFECT ON TECHNOSOL PROPERTIES 487
Many recent studies on Technosols focus on phy-
sical, physico-chemical and chemical parameters, such
as pH, available nutrients, bulk density (Rokia et al.,
2014), available water (Molineux et al., 2009), elec-
trical conductivity (Rowe et al., 2006), particle size
distribution (Olszewski et al., 2010), and water flow
(S´er´e et al., 2012), which can control the quality of
the substrate and, therefore, plant development. To
our knowledge, the hydro-structural properties of con-
structed Technosols have never been studied by com-
bining water retention curve (WRC) and soil shrinkage
curve (SSC). The WRC defines the relation between
soil water potential and water content, while the SSC
represents the concomitant decrease in soil volume and
water mass during drying (Haines, 1923). The shape
of the SSC depends on soil structure and composition
(organic and mineral). Peng and Horn (2013) distin-
guished six types of SSC, which depend on the pre-
sence or absence of one or two of the four SSC shrinkage
phases (interpedal/saturated (in), structural (st), basic
(ba) and residual (re) shrinkage phases) described by
Braudeau et al. (1999), Groenevelt and Grant (2001),
and Peng and Horn (2005). Recently, Leong and Wi-
jaya (2015) developed an empirical universal SSC equa-
tion for all types of soil. Braudeau et al. (2004) de-
veloped a conceptual model that defined quantitative
analysis of soil structure (arrangement of soil particles
and associated pores) by distinguishing two pore sys-
tems (elementary particle arrangement, defining pri-
mary peds and associated micropores; primary ped
arrangement, defining macropores) and characterizing
hydraulic properties for each of them (Braudeau et al.,
2004; Assi et al., 2014).
Other studies have combined WRC and SSC, such
as that by Braudeau et al. (2005), who characterized
soil structure of natural soils, and that by Boivin et
al. (2006), who used the van Genuchten equation to de-
scribe the two curves. Guimar˜aes Santos et al. (2011)
argued that these curves are indicators for evaluating
soil physical quality. Alaoui et al. (2011) relied on these
curves to discuss soil deformation, and Kechavarzi et
al. (2010) used them to explain the influence of long-
term changes in peat soils and characterize hydro-
structural properties.
A huge number of organic and mineral wastes can
be used for the construction of Technosols. For exam-
ple, Rokia et al. (2014) tested mixtures of 11 different
materials to evaluate the additivity of their physico-
chemical properties. Here, this study used two urban
wastes, known for their abundance, the financial in-
terest of recycling them, and their physico-chemical
and agronomic properties, to construct Technosols:
one mineral material excavated from deep horizons of
soil and one organic material, green waste compost
(GWC), with the latter added in six different volu-
metric percentages (from 0% to 50%). We then deter-
mined the SSC of constructed Technosols to describe
hydro-structural properties, as proposed by Assi et
al. (2014). The WRCs were also determined to pro-
vide complementary information about the pore size
distribution in constructed Technosols, as applied by
Milleret et al. (2009). The objectives of this study were
to evaluate the validity and relevance of WRC and
SSC for physically characterizing constructed Tech-
nosols and to understand how Technosol structure is
influenced by organic matter content.
MATERIALS AND METHODS
Technosol parent materials
The mineral material excavated from deep hori-
zons of soil (EDH) used in this study was provided
by the ECT Company (Villeneuve sous Dammartin,
France). This material is typically what is found when
foundations are dug in the Ile-de-France. It is mainly
the result of the weathering of carbonated rock frag-
ments of the Parisian Basin (France) from the Eocene.
In this study, 500 kg of EDH at eight locations were
collected from the base of urban waste dump of the
ECT company in order to have a composite sample
representative of what may be used to construct Tech-
nosols around Paris. The EDH is classified as a car-
bonated sandy soil (Nachtergaele, 2001). The material
was composed of 880 g kg−1sand, 100 g kg−1silt and
20 g kg−1clay after carbonate removal, which repre-
sents 431 g kg−1of total dry mass. Without carbonate
removal, the EDH was composed of 110 g kg−1parti-
cles of <2µm in size, 300 g kg−1particles of 2–50
µm, and 590 g kg−1particles of 50 µm–2 mm. The
X-ray diffraction performed with a Siemens D500 di-
ffractometer (CuKa, 40 kV, 30 mA) identified quartz,
calcite and dolomite as major minerals. The concen-
trations of organic carbon and nitrogen were measured
by elemental analysis (Vario EL III, Elementar, Hanau,
Germany). The GWC used in this study was composed
of cuttings from urban areas. Table I shows the main
chemical properties of the EDH and GWC materials.
Both materials were air-dried and sieved to 4 mm
before mixing by an electrical concrete mixer with a
100 L capacity and 690 W power, at 390 round min−1
for 10 min. Six different mixture treatments of 20 Leach
were prepared, with 0%, 10%, 20%, 30%, 40% and 50%
(GWC/total, volume/volume) of GWC, respectively.

488 M. DEEB et al.
TABLE I
Main agronomic properties of technogenic materialsa) used to
make the constructed Technosols in this study
Property EDH GWC
pH (H2O) 8.3 ±0.0b) 7.9 ±0.1
pH (KCl) 8.1 ±0.1 7.5 ±0.1
Organic carbon (g kg−1) 0.38 ±0.0 210.41 ±4.2
Total nitrogen (g kg−1) 0.03 ±0.0 1.47 ±0.0
Particle density (g cm−3) 2.75 ±0.2 2.06 ±0.1
Bulk density (g cm−3) 1.33 ±0.0 0.61 ±0.0
Residual water content (g kg−1) 65.8 ±4.0 87.9 ±2.3
a)EDH = mineral material excavated from deep horizons of soil;
GWC = green waste compost.
b)Means ±standard errors (n= 4).
Organic carbon content was 0.38 g kg−1for the
0% GWC mixture and 70.67 g kg−1for the 50% GWC
mixture. Thus, the lower limit of the organic carbon
gradient corresponded to a soil with depleted organic
carbon; however, the upper limit was kept below 109.5
g kg−1, which is considered the maximum value for
French soils (statistics from the French soil-monitoring
network (RMQS) (Jolivet et al., 2006). One liter of
each mixture was placed in 1.2-L containers (13 cm ×
13 cm ×12.5 cm). Each mixture (from 0% to 50%)
was replicated four times, for a total of 24 containers.
All samples were then kept at 80% of the water hol-
ding capacity with deionized water (MilliQ) over 24 h.
The water holding capacity for every sample was mea-
sured at the beginning of the experiment by using a
pressure-plate apparatus (Richards, 1948) with a wa-
ter potential of −31 kPa.
Soil shrinkage curve measurement
Constructed Technosol samples were collected from
the surface of each container using a cylinder of 5
cm tall and 5 cm diameter (one per container, n=
24). The cylinder was pressed delicately into the mix-
ture far enough to fill the inner cylinder without com-
pacting the soil. To facilitate sample manipulation,
permeable fabric was placed at the base of each cylin-
der and held in place by a rubber band. Cylinders
were then placed on a wet porous plate for saturation
with deionized water at 18 ◦C in the dark, according
to manufacturer instructions (Sandbox, Eijkelkamp,
Netherlands), for 7 d by applying a water potential
of 0 kPa at the base of the sample. The experimen-
tal procedure to measure the SSC consisted of simul-
taneous and continuous measurements of the height,
diameter, and weight of the saturated soil cores du-
ring water removal by evaporation in an experimen-
tal retractometer c
⃝(Braudeau et al., 1999). Water-
saturated Technosol samples were placed in an oven
at a constant temperature (30 ◦C) to provide conti-
nuous and rapid evaporation. An electronic scale (0.01
g precision) ensured the accurate measurement of wa-
ter loss during drying. Each sample volume (diameter,
height) was determined with vertical and lateral laser
beams (resolution of 10 µm) and recorded along with
its mass (nominal precision of 0.01 g) every 10 min.
The experiment was stopped when the mass of the soil
sample after water loss remained constant. This oc-
curred generally after 3–4 d and a minimum of 400
measurements. At the end of measurements, samples
were dried in an oven at 105 ◦C for 48 h to measure
their dry mass. These data were converted into soil
specific volume (V, m3kg−1), expressed as the soil vo-
lume divided by mass of dry soil, and gravimetric soil
water content (W, kg kg−1).
The shrinkage data measured were fitted according
to the SSC model (Braudeau et al., 2004). In this mo-
del, the SSC is subdivided into a maximum of four
shrinkage phases (interpedal/saturated (in), structural
(st), basic (ba) and residual (re) shrinkage phases) that
are due to four types of water pools (Win ,Wst,Wba and
Wre) (Fig. 1). The pedostructure is considered an as-
sembly of primary peds (aggregates made of the clayey
particles) that determines two nested levels of organi-
zation: the macropore level containing Wma (Wma =
Win +Wst) and the micropore level containing Wmi
(Wmi =Wre +Wba). The three transition points sepa-
rating the four pseudo linear shrinkage phases (Fig.1)
are Points L, M and N, which are at the intersec-
tion of the tangent straight lines of the linear pha-
ses. According to this model of the SSC (Braudeau
et al., 1999, 2004), the value of the gravimetric water
content at each point (WL,WMand WNfor Points
L, M and N, respectively) is equal to the value of
max(Wst) for WL, max(Wmi ) (max(Wmi) = max(Wre )
+ max(Wba)) for WM, and max(Wre) for WN. The
other hydro-structural parameters are: slope of the
interpedal/saturated shrinkage phase (Kin), slope of
the structural shrinkage phase (Kst), slope of the basic
shrinkage phase (Kba), slope of the residual shrinkage
phase (Kre), and three parameters, kL,kMand kN,
related to the SSC shape at Points L, M and N, re-
spectively. Finally, V0is the specific volume at the end
of the SSC when no further change in water content is
observed. In addition, macropore (Vma ) and micropore
(Vmi) volumes are calculated as follows (Braudeau et
al., 2001):
Vma = (WL−WM)/ρw(1)
max(Vmi) = WM/ρw(2)
Vmi =V−Vs−Wma/ρw(3)

ORGANIC MATTER EFFECT ON TECHNOSOL PROPERTIES 489
Fig. 1 Configurations of water partitioning in soil macropores and micropores related to the shrinkage phases (interpedal/saturated
(in), structural (st), basic (ba) and residual (re) shrinkage phases) that are due to four types of water pools (Win,Wst ,Wba and Wre , re-
spectively) of a standard shrinkage curve (adapted from Braudeau et al., 2004). Points F, L, M and N are the three transition points
separating the four pseudo linear shrinkage phases. Kin,Kst,Kba and Kre are the slopes of the in, st, ba and re shrinkage phases in the
shrinkage curve, respectively.
where ρwis the water density, assuming ρw= 1 ×103
kg m−3and Vsis the solid specific volume (m3kg−1).
Water retention curve measurement
The analysis that is complementary to that of the
SSC for characterizing the influence of organic ma-
tter on pore size distribution is WRC (Grimaldi et al.,
2002), which was measured separately on samples tak-
en from each of the 24 experimental units, as for SSC.
Technosol samples were collected using cylinders of 3
cm tall and 5 cm diameter, gently pressed down across
the surface of the same containers used previously for
SSC. Each cylinder was then placed on a wet porous
plate for saturation. A range of matric potentials be-
tween water saturation (0 kPa) and permanent wilting
point (−1 554 kPa) were applied to the same cylin-
der using a sand box (high matric potentials: −0.2,
−0.98 and −3.1 kPa) and a pressure-plate apparatus
(Richards, 1948) (lower ones: −31, −98, −155, −491
and −1 554 kPa). The matric potential applied by the
pressure-plate apparatus was corrected using the ther-
modynamically based equation (Eq. 4) to calculate the
water potential pressure (h, kPa) according to the air
pressure equilibrium applied in the Richards appara-
tus, π(kPa) (Braudeau et al., 2014):
h= 137.72ln(π/100 + 1) (4)
Then, soil WRC was fitted according to the van
Genuchten equation (van Genuchten, 1980):
θ(ψ) = θr+ (θs−θr)/[1 + (α|ψ|)]1−1/n (5)
where θis the volumetric water content (m3m−3),
ψis the matric potential (kPa), θsis the saturated
volumetric water content (m3m−3), θris the residual
volumetric water content (m3m−3), αis related to the
inverse of the air entry suction (m−1), and nis a shape
parameter.
After WRCs were calculated, the Jurin-Laplace e-
quation (Eq. 6) was used to convert the water poten-
tial at Points L, M and N into maximum equivalent
size (considering cylindrical tubes) of water-saturated
pores (Grimaldi et al., 2002).
Pc=Pw−P0= (4Tscosβ)/deq =−h(6)
where Pcis the capillary pressure (Pa), P0is the atmo-
spheric pressure (Pa), Pwis the water pressure (Pa),
Tsis the surface tension of water (75 ×10−3N m−1), β
is the contact angle of water with the pore walls (0◦, if
the water completely moistens the solid particles), deq
is the equivalent size of the pore, corresponding to the
diameter of a cylindrical capillary (therefore, also “e-
quivalent diameter”) or twice the distance between the
two walls of a fissure (m), and, his the water potential
pressure (Pa).

490 M. DEEB et al.
Expression of results of void and moisture ratios
Soil specific volume V(m3kg−1), as a function of
the gravimetric soil water content W(kg kg−1) ob-
tained from the Braudeau model, was converted into a
void ratio (the ratio of the volume of voids to the volu-
me of solids, e, m3m−3), as a function of the moisture
ratio (the ratio of the volume of water to the volume of
solids, ν, m3m−3). This step makes it easier to com-
pare Technosols that have different compositions and
thus different particle densities, considering Eqs.7 and
8:
ν= (ρs/ρw)W(7)
e=Vρs−1 (8)
where ρwis the water density (g cm−3) and ρsis the
particle density (g cm−3) calculated for all mixtures of
GWC and EDH from the measurements on materials
sieved at 2 mm with a pycnometer (ISO 17892-3:2004).
All hydro-structural parameters were transformed
with Eqs. 7 and 8 and thus became the moisture ra-
tio at macropore saturation (νL), the moisture ratio
at micropore saturation (νM), the moisture ratio at
the shrinkage limit (νN), the four slopes (KL,Kst,Kba
and Kre), parameters related to the SSC shape (kL,kM
and kN) and the void ratio at the end of the shrinkage
period (e0). The other parameters calculated were the
macropore ratio (ema ) and micropore ratio (emi).
Based on the hydro-structural parameters, volu-
metric available water content (θ′, m3m−3) was
calculated to compare available water reservoirs (hol-
ding capacities) for plants in the mixtures:
θ′=ν/(V ρs) (9)
The volumetric available water contents in macro-
pores (θ′
ma) and micropores (θ′
mi) were obtained u-
sing the following equations: θ′
ma =θ′
L−θ′
Mand
θ′
mi =θ′
M−θ′
N, where θ′
L,θ′
Mand θ′
Nare the maxi-
mum volumetric available water contents at Points L,
M, N of SSC, respectively (m3m−3), and the sum of
both was the total volumetric available water content
for plants (θ′
total) (Braudeau et al., 2004, 2005).
The van Genuchten equation was expressed as a
function of the moisture ratio (ν) by replacing θwith
νin Eq. 5:
ν(ψ) = νr+ (νs−νr)/[1 + (α|ψ|)]1−1/n (10)
where νrand νsare the moisture ratios under resi-
dual and saturated conditions, respectively (m3m−3).
The Van Genuchten model parameters were calcula-
ted directly after fitting by linear regression, using the
method of least squares in SigmaPlot software version
13.0 (Systat Software, Inc., San Jose, USA).
Statistical analysis
Means and standard errors of hydro-structural pa-
rameters were calculated for all treatments by fit-
ting the curves with the hydro-structural model. The
hydro-structural parameters representing the slope of
the interpedal/saturated shrinkage phase (Kip) and
the shape of the SSC at Point M (kM) were not inclu-
ded because they were constant for all mixture treat-
ments (Kip = 1) and (kM=−53).
The statistical analysis was performed with R 3.0.3
software (R Development Core Team, 2014) using
MASS and ade4 packages for principal component ana-
lysis (PCA) (Venables and Ripley, 2002) and for li-
near discriminant analysis (LDA). The LDA was used
to identify which hydro-structural parameters sepa-
rate the influence of GWC on constructed Technosols
(Huberty and Olejnik, 2006). Treatment separation
based on hydro-structural parameters was tested with
Wils and Pillai tests. Hydro-structural parameters and
macropore, micropore and total volumetric available
water were statistically analyzed by analysis of vari-
ance (ANOVA). The influence of GWC was considered
significant at P < 0.05. When a significant influence
of GWC was observed in volumetric available water
contents and pore sizes, both linear and non-linear re-
gressions were calculated, and the simpler and more
efficient model was selected.
RESULTS
Hydro-structural properties of parent materials
The EDH showed the classic sigmoid shape of
the SSC observed most often in the literature (Lau-
ritzen, 1948; Boivin et al., 2004; Peng and Horn, 2005;
Braudeau et al., 2014), whereas the compost SSC had
a different shape (Fig. 2). A large difference was ob-
served in void ratio between EDH (0.8–1.6 m3m−3)
and GWC (4.6–5.5 m3m−3). The maximum moisture
ratio was 1.09 m3m−3for EDH and 3.01 m3m−3for
GWC.
Ignoring the saturated shrinkage phase, the GWC
SSCs showed that the void ratio decreased slowly until
a moisture ratio of 1.0 m3m−3. Then, starting from 5.1
±0.1 m3m−3, the void ratio decreased more rapidly
until the point of complete water removal. Comparing
the SSC of EDH, at a moisture ratio of 0.4, the void
ratio did not change (0 or close to 0.01).

ORGANIC MATTER EFFECT ON TECHNOSOL PROPERTIES 491
Fig. 2 Comparison of soil shrinkage curves and their phases (interpedal/saturated (ip), structural (st), basic (ba) and residual (re)
shrinkage phases) of (a) mineral material excavated from deep horizons of soil (EDH), (b) a mixture of green waste compost (GWC)
and EDH (30% GWC, GWC volume/total volume) and (c) GWC. n= 4.
The GWC SSC also differed from the mixtures’
SSCs, for example at the 30% GWC treatment (Fig.
2b). GWC had only three shrinkage phases: saturated,
structural and basic (Fig. 2c). This behavior is similar
to that observed in soils rich in organic matter (Geb-
hardt et al., 2010). The pedostructural model did not
fit well for GWC. The relation between the void ratio
(e, m3m−3) and moisture ratio (ν, m3m−3) could be
fitted by a hyperbolic equation (ignoring the specific
gravity of water):
e=e0+aν/(b+ν) (11)
where aand bare shape parameters, with r2= 0.97,
standard deviation = 0.01 and P < 0.001.
Hydro-structural properties of constructed Technosols
Mean SSCs and WRCs for all mixture treatments
after modeling are shown in Fig. 3. The four SSC pha-
ses are recognizable for all Technosol mixtures (Fig. 3).
High percentages of organic matter were associated
with increases in the maximum moisture and void ra-
tios measured at the beginning and end of each curve
(Fig. 3). The void ratio for all mixture treatments var-
ied from 1.35 to 2.50 m3m−3, whereas the moisture
ratio ranged from 1.1 to 2.0 m3m−3.
The WRCs also had a sigmoid shape for the sec-
tion between −0.1 and −300 kPa. This shape form was
emphasized for low percentages of GWC. The maxi-
mum and minimum moisture ratios also gradually in-
creased with the GWC percentage. Table II provides
an overview of the shrinkage parameters for the con-
structed Technosols in this study.
Statistical analysis of hydro-structural parameters
From the PCA (not shown) performed on hydro-
structural parameters (Table II), the GWC percen-
tage had an influence on hydro-structural parameters
(P= 0.001) and explained 65% of their variance. The
LDA applied after the PCA revealed a significant influ-
ence of GWC percentage on hydro-structural parame-
ters (P < 0.000 1; Wilks and Pillali tests), explaining
95% of their variance (Fig.4). Mixture treatments were
separated into three groups: (i) 0% and 10% GWC, (ii)
20%, 30% and 40% GWC, and (iii) 50% GWC. The
first and second axes explained 70% and 25% of the
variance, respectively. The hydro-structural variables
that best separated the 50% GWC treatment were νL,
νMand e0.Kst was discriminant for the 20%, 30%,
40% and 50% GWC treatments. Finally, KLand νN
discriminated the 0% and 10% GWC treatments.
The ANOVA results showed that the percentage
of GWC had a positive significant influence on νL,
νM,νN,e0,KLand Kst, but a negative influence on
Kre (Table II). However, it revealed that GWC had
no significant influence on Kba (P= 0.13) and KN
(P= 0.06). The ANOVA results also showed that the
percentage of GWC had a positive influence on the
macropore ratio (ema ) and the micropore ratio (emi).
Variations in water types with the percentage of GWC
The behaviors of different types of water pools were
not similar. For example, the influence of GWC was not
additive for θ′
mi, which ranged from 0.10 to 0.15 m3
m−3for all mixture treatments except the 50% GWC
treatment, which had a higher value of θ′
mi: 0.23 ±0.02
m3m−3(Fig. 5a). The mean value of θ′
ma was similar

492 M. DEEB et al.
Fig. 3 Soil shrinkage curves (SSCs) and water retention curves (WRCs) for the constructed Technosols at six different volumetric
percentages of green waste compost (GWC)(GWC/total, from 0% to 50%), which express the void ratio (right axis) and water potential
(left axis) as functions of the moisture ratio, respectively. Means ±standard deviations (n= 4) at Points F, L, M and N and the end
of the shrinkage period from the highest to the lowest point in the SSCs are marked by the bars. Means ±standard deviations (n= 4)
at matric potential |ψ|= 0.24, 0.98, 3.10, 12.88, 37.19, 94.12, 129.14, 244.79 and 386.42 kPa from the lowest to the highest point in
the WRCs are also marked by the bars. A third axis was added on the left to determine the maximum equivalent size of water-saturated
pores at each water potential according to the Jurin-Laplace equation. For example, at 30% GWC, Point N in the SSC corresponds to a
water potential of approximately −750 kPa, which corresponds to a maximum equivalent size of water-saturated pores of 0.1 µm.
Fig. 4 Linear discriminant analysis of the influence of green waste compost (GWC) on hydro-structural parameters for the constructed
Technosols at six different volumetric percentages of GWC (GWC/total, from 0% to 50%): (a) correlations between the parameters and
(b) projection of the six mixture treatments (0%, 10%, 20%, 30%, 40%, 50% GWC, showing as 0, 10, 20, 30, 40, and 50, respectively)
onto discriminant axes (X1and X2). The first and second axes explained 70% and 25% of the variance, respectively. νL= moisture
ratio at macropore saturation; νM= moisture ratio at micropore saturation; νN= moisture ratio at the shrinkage limit; e0= void
ratio at the end of the shrinkage period; Kst = slope of the structural phase; Kbs = slope of the basic phase; Kre = slope of the residual
phase; KLand KN= parameters related to shape form of soil shrinkage curve.

ORGANIC MATTER EFFECT ON TECHNOSOL PROPERTIES 493
TABLE II
Hydro-structural parameters for the constructed Technosols at six different volumetric percentages of green waste compost (GWC)
(GWC/total, from 0% to 50%) with analysis of variance (ANOVA) results (Fand Pvalues) showing the influence of GWC percentages
on the parameters
Parametera) Treatment Fvalue Pvalue
0% GWC 10% GWC 20% GWC 30% GWC 40% GWC 50% GWC
Kst 0.00 ±0.0b) 0.02 ±0.0 0.11 ±0.0 0.13 ±0.0 0.11 ±0.0 0.11 ±0.0 27.8 <0.001
Kbs 0.31 ±0.0 0.30 ±0.0 0.32 ±0.0 0.32 ±0.0 0.28 ±0.0 0.23 ±0.0 2.0 0.13
Kre 0.03 ±0.0 0.02 ±0.0 0.05 ±0.0 0.06 ±0.0 0.06 ±0.0 0.02 ±0.0 4.8 <0.05
νL(m3m−3) 0.93 ±0.0 1.02 ±0.0 1.17 ±0.0 1.26 ±0.0 1.33 ±0.0 1.63 ±0.1 19.4 <0.001
νM(m3m−3) 0.77 ±0.0 0.81 ±0.0 0.79 ±0.0 0.81 ±0.0 0.85 ±0.0 1.10 ±0.1 5.4 <0.05
νN(m3m−3) 0.46 ±0.0 0.45 ±0.0 0.53 ±0.0 0.53 ±0.0 0.46 ±0.0 0.28 ±0.1 7.3 <0.001
e0(m3m−3) 1.20 ±0.1 1.25 ±0.1 1.51 ±0.1 1.42 ±0.1 1.87 ±0.2 2.25 ±0.1 12.8 <0.001
KL2.25 ±0.2 2.25 ±0.5 3.00 ±0.0 2.04 ±0.4 1.09 ±0.1 1.07 ±0.2 6.4 <0.05
KN0.75 ±0.2 1.00 ±0.0 0.45 ±0.1 0.46 ±0.2 0.42 ±0.1 0.46 ±0.1 2.1 0.06
ema (m3m−3) 0.16 ±0.0 0.21 ±0.0 0.38 ±0.0 0.45 ±0.0 0.48 ±0.0 0.54 ±0.0 20.6 <0.001
emi (m3m−3) 0.31 ±0.0 0.36 ±0.0 0.26 ±0.1 0.27 ±0.0 0.39 ±0.0 0.81 ±0.1 27.0 <0.001
θ′
ma (m3m−3) 0.07 ±0.0 0.08 ±0.0 0.14 ±0.0 0.17 ±0.0 0.16 ±0.0 0.15 ±0.0 19.2 <0.001
θ′
mi (m3m−3) 0.12 ±0.0 0.15 ±0.0 0.09 ±0.0 0.10 ±0.0 0.13 ±0.0 0.24 ±0.0 10.0 <0.001
θ′
total (m3m−3) 0.19 ±0.0 0.22 ±0.0 0.23 ±0.0 0.27 ±0.0 0.29 ±0.0 0.39 ±0.0 39.3 <0.001
Maximum equivalent size of water-saturated poresc)
Pore size at L (µm) 32.06 ±2.8 34.72 ±3.8 69.06 ±6.5 66.46 ±7.0 56.93 ±5.9 120.40 ±34.0 4.8 <0.05
Pore size at M (µm) 10.14 ±1.9 9.84 ±1.1 6.49 ±1.7 4.93 ±0.8 3.28 ±0.8 5.85 ±1.7 3.8 <0.05
Pore size at N (µm) 0.66 ±0.2 0.43 ±0.1 0.52 ±0.2 0.49 ±0.2 0.10 ±0.0 0.09 ±0.0 8.9 <0.001
a)Kst = slope of the structural phase; Kbs = slope of the basic shrinkage phase; Kre = slope of the residual phase; νL= moisture
ratio at macropore saturation; νM= moisture ratio at micropore saturation; νN= moisture ratio at the shrinkage limit; e0= void
ratio at the end of the shrinkage period; KLand KN= parameters related to the shrinkage curve shape; ema = macropore ratio; emi
= micropore ratio; θ′
ma and θ′
mi = volumetric available water contents in macropores and micropores, respectively; θ′
Total = total
volumetric available water content.
b)Mean ±standard error (n= 4).
c)The maximum equivalent size of water-saturated pores calculated by the Jurin-Laplace equation at Points L, M, and N.
Fig. 5 Relationships between green waste compost (GWC) percentage and (a) volumetric available water content in micropores (θ′
mi),
(b) volumetric available water content in macropores (θ′
ma), and (c) total volumetric available water content (θ′
total) for the constructed
Technosols at six different volumetric percentages (GWC/total, from 0% to 50%) of GWC. Lines represent regressions.
for the 0% and 10% GWC treatments (0.08 ±0.02
m3m−3), began to rise with the 20% GWC treatment
and decreasesd to a constant value (0.15 ±0.04 m3
m−3) for the 30%, 40% and 50% GWC treatments
(Fig. 5b). The sum of both types of water pools (θ′
total)
increased at higher percentages of GWC. θ′
total for the
50% GWC treatment was the highest because of the
high value of θ′
mi (Fig. 5c).
The influence of the GWC percentage on volumet-
ric available water contents, θ′
ma,θ′
mi and θ′
total, was
analyzed by ANOVA. All the three types were signifi-
cantly and positively influenced by the GWC percen-
tage (P < 0.001) (Fig. 5). The best regressions between
GWC percentage and volumetric available water were

494 M. DEEB et al.
linear for macropore and total volumetric available wa-
ter contents (r2= 0.54 and 0.81, respectively), whereas
it was a second-degree equation for volumetric availa-
ble water in micropores (r2= 0.67) (Fig. 5). The values
of θ′
ma,θ′
mi and θ′
Total at 50% GWC were twice as high
as those at 0% GWC.
Water retention curve and pore sizes at Points L, M
and N
Increasing GWC percentage was responsible for an
increase in mean moisture ratio of all treatments re-
gardless of the matric potential (Table III). The maxi-
mum equivalent size of water-saturated macropores at
Point L increased by a factor of 4, from 32 µm at 0%
GWC to 120 µm at 50% GWC, whereas the maximum
equivalent size of water-saturated micropores at Point
M decreased by half from 0% GWC to 50% GWC. The
maximum equivalent size of water-saturated micro-
pores at Point N decreased from 0.65 µm at 0% GWC
to only 0.09 µm at 50% GWC.
The ANOVA results showed that the GWC percen-
tage had a significant influence on the maximum
equivalent size of water-saturated pores at Points L,
M and N (Table II). The correlation between GWC
percentage and maximum equivalent size of water-
saturated pores was positive and high at Point L
(r2= 0.82), but the correlations were negative at Point
M (r2= 0.69) and Point N (r2= 0.77) (Fig.6). As a
consequence, the difference in the maximum equiva-
lent size of water-saturated pores between Point L and
Point N (i.e., the range of pore sizes) increased as the
percentage of GWC increased.
Fig. 6 Relationships between green waste compost (GWC)
percentage and maximum equivalent size of water-saturated
pores at Points L, M and N in the soil shrinkage curve for the
constructed Technosols at six different volumetric percentages
(GWC/total, from 0% to 50%) of GWC. Straight lines repre-
sent linear regressions. Vertical bars are standard deviations of
means (n= 4).
DISCUSSION
Hydro-structural properties derived from the mixtures
Parent materials exhibited highly different beha-
viors: the GWC SSC had a hyperbolic shape (Fig. 2c),
whereas the EDH SSC had a sigmoid shape (presence
of both macro- and micropore levels) (Fig. 2a). The di-
fference in the SSC shape for GWC can be explained
by it being composed of a fraction of fine pores, which
may cause high capillary forces, and a higher fraction
of coarser pores. Thus, internal tensions during desic-
cation first result in low shrinkage, but when the GWC
moisture ratio decreases below 1 m3m−3, the change
in the void ratio is more noticeable and does not reach
the residual phase. This result is in agreement with
Peng and Horn (2007a).
For all GWC and EDH mixture treatments, we
found a SSC with a sigmoid shape, similar to the EDH
SSC. The hyperbolic shape was not observed, as that
for the GWC SSC (three phases), even in the 50%
GWC treatment, but it was noticed that the slope
of the residual shrinkage phase decreased with a high
percentage of organic matter (Table II). As this sig-
moid shape (macro- and micropore levels) is typical-
ly found in most natural soils, it seems that from
a hydro-structural viewpoint, constructed Technosols
have the same properties as those observed in natu-
ral soils. These results showed that fine particles from
primary particles (Fig. 1) may not be only clay; in this
case, they are organic material.
The EDH material used in this study exhibited a
high level of carbonates and a high pH. This can be ex-
plained by the calcareous materials of the parent rock
in Ile-de-France (Gis Sol, 2013) and also by the fact
that calcium carbonates are an important component
of gravel, cement and concrete (Scharenbroch et al.,
2005). As a consequence, the leaching of surface runoff
waters, previously in contact with concrete buildings,
generally impacts the nature of deep horizons in ur-
ban areas by increasing the level of carbonates and the
pH (Messenger, 1986). This kind of mineral material
is thus likely to be abundant in many cities. More-
over, every city has green spaces of vegetated areas in
which plants need to be trimmed. The GWC is thus
a potentially abundant material that can be produced
easily in many urban areas. With the need to mitigate
climate change, more and more communities have be-
gun to compost their organic wastes. This would also
increase the quantity of GWC that could be used for
Technosol construction. It is believed that the mate-
rials used in this study can be chosen for Technosol
construction in a wide variety of urban systems.

ORGANIC MATTER EFFECT ON TECHNOSOL PROPERTIES 495
TABLE III
Given pF before and after correction by the method of Braudeau et al. (2014), the measurement methods (1: wet porous plate; 2: pressure-plate apparatus (Richards, 1948)), pressure
applied, corrected water retention, maximum water-saturated pore size after correction and moisture ratio for the constructed Technosols at different volumetric percentages of green
waste compost (GWC) (GWC/total, from 0% to 100%)
Given Given Pressure Measure- Corrected Maximum Moisture ratio
pF pF applied ment water water-
before after method retention saturated 0% GWC 10% GWC 20% GWC 30% GWC 40% GWC 50% GWC 100% GWC
corre- corre- pore size
ction ction
kPa kPa µm m3m−3
Satura- Satura- 0 1 0 1.278 ±0.03 1.381 ±0.04 1.674 ±0.05 1.701 ±0.07 1.950 ±0.06 2.125 ±0.12 4.429 ±0.04
tion tion
0.4 0.4 0.24 1 0.24 609.10 1.201 ±0.03 1.310 ±0.03 1.406 ±0.01 1.532 ±0.04 1.744 ±0.04 1.870 ±0.06 4.049 ±0.06
1 1 0.98 1 0.98 153.00 1.093 ±0.03 1.209 ±0.03 1.293 ±0.03 1.410 ±0.03 1.597 ±0.02 1.627 ±0.03 3.534 ±0.06
1.5 1.5 3.1 1 3.10 48.38 1.008 ±0.03 1.107 ±0.03 1.134 ±0.02 1.233 ±0.03 1.311 ±0.01 1.408 ±0.01 2.328 ±0.06
2 2.11 9.8 2 12.88 11.87 0.779 ±0.04 0.813 ±0.03 0.917 ±0.03 0.922 ±0.03 1.037 ±0.02 1.140 ±0.02 1.888 ±0.11
2.5 2.57 31.01 2 37.19 4.11 0.671 ±0.03 0.713 ±0.02 0.796 ±0.03 0.803 ±0.02 0.906 ±0.02 1.003 ±0.03 1.805 ±0.07
3 2.97 98.06 2 94.12 1.62 0.623 ±0.03 0.642 ±0.02 0.712 ±0.03 0.730 ±0.02 0.818 ±0.03 0.929 ±0.04 1.739 ±0.07
3.2 3.11 155.42 2 129.14 1.18 0.565 ±0.04 0.587 ±0.02 0.625 ±0.02 0.648 ±0.02 0.746 ±0.04 0.815 ±0.05 1.657 ±0.07
3.7 3.38 491.48 2 244.79 0.62 0.459 ±0.05 0.483 ±0.05 0.506 ±0.04 0.535 ±0.05 0.637 ±0.03 0.705 ±0.07 1.439 ±0.04
4.2 3.58 1554.21 2 386.42 0.39 0.334 ±0.04 0.371 ±0.04 0.390 ±0.04 0.452 ±0.04 0.566 ±0.06 0.676 ±0.06 1.416 ±0.05

496 M. DEEB et al.
Influence of organic matter on hydro-structural pro-
perties
Organic matter had no influence on the slope of
the basic shrinkage phase (Table II), which was in
agreement with previous observations (Boivin et al.,
2009), but the increased slope in the structural shrin-
kage phase with the increase in organic matter differs
from the results obtained by Boivin et al. (2009). One
possible explanation was that the particles or aggre-
gates were not consolidated (i.e., without cohesion),
regardless of the amount of GWC, since these soils
had not yet experienced a complete cycle of swelling-
shrinkage.
Soil water holding capacity estimated from the SSC
was sensitive to GWC percentages, varying from 0.19
m3m−3in the 0% GWC treatment to 0.39 m3m−3
in the 50% GWC treatment (Table II, Fig. 5). The in-
crease in organic matter content along with available
water capacity is similar to that observed in natural
soils (Hudson, 1994; Emerson, 1995). The GWC had a
positive influence on the void ratio (Fig. 3), which was
also observed in natural soils (Giusquiani et al., 1995),
as well as on the moisture ratio for both macro- and
micropores. The LDA separated the treatments into
three groups: (i) 0% and 10% GWC, (ii) 20%, 30%
and 40% GWC and (iii) 50% GWC (Fig.4). This split
means that the 20%, 30% and 40% GWC treatments
behaved in a similar manner. This is an important
aspect for technical applications of constructed Tech-
nosols, because adding more than 20% of GWC, the
most expensive parent material in the mixture of this
study, can be avoided without losing the main bene-
ficial hydro-structural properties.
Combining data from soil shrinkage and water reten-
tion curves
The SSC provides a functional characterization of
soil hydro-structural properties, and Points L, M and N
correspond to thresholds of these properties. When the
amount of organic matter varies, the breaking Points
L, M and N do not correspond to fixed pore sizes.
For example, in the 0% GWC treatment, micropores
(Points N–M) ranged from 0.7 to 10 µm and macro-
pores (Points M–L) ranged from 10 to 32 µm, whereas
in the 50% GWC treatment, the micropores ranged
from 0.09 to 6 µm and the macropores ranged from
6 to 120 µm (Table II). The correspondence estab-
lished between hydro-structural domains and pore size
(Fig. 3) indicates that an increase in the percentage of
GWC induces a large increase in the range of macro-
pore size involved in retaining available water. For
organic-rich soils, Peng et al. (2007b) also observed
an increase in the maximum equivalent size of water-
saturated macropores, corresponding to an increase in
pore size at Point L. In this study, an increase in the
percentage of GWC induced a small decrease in the
range of micropore size involved in retaining available
water. The result of this large increase in macropore
range and small decrease in micropore range is a global
increase in the range of the size of pores retaining total
available water.
Despite the reduced range of the size of pores in-
volved in micropore when the percentage of GWC in-
creased (Fig. 6), we observed an increase in available
water in micropores (Fig. 5) when the percentage of
GWC increased from 20% to 50%. A possible expla-
nation for this apparent contradiction is that the nu-
mber of pores present in the micropore domain increa-
ses when the GWC percentage increases.
Constructed Technosols as a tool for studying the in-
fluence of specific soil components on shrinkage
Previous studies on SSCs of natural soils have
shown that organic matter and clay influence hydro-
structural properties (Shaykewich and Zwarich, 1968;
Boivin et al., 2004, 2009). However, in natural soils, or-
ganic matter content is correlated with other physico-
chemical soil properties such as the type of clay (Boivin
et al., 2004), cation exchange capacity (Tessier, 1990),
and ionic concentration in the soil solution (Emerson,
1962), which could influence the shape of the SSC. This
makes it difficult to attribute changes in SSC shape to
the amount of organic matter. With constructed Tech-
nosols, it is easy to manipulate the percentage of a
given kind of organic matter through the percentage of
different materials. The EDH was poor in organic car-
bon (0.38 g kg−1), whereas GWC was much richer in
it (210.4 g kg−1); the GWC can thus be considered the
only source of organic carbon in mixtures. Therefore,
organic carbon content can be changed by manipula-
ting the percentage of GWC.
CONCLUSIONS
Soil shrinkage and water retention curves have been
successfully used to characterize hydro-structural pro-
perties of natural soils. Here, the results of this study
showed that these two approaches can also be used for
studying constructed Technosols. Surprisingly, direct-
ly after mixing, mineral and organic materials showed
a shrinkage behavior similar to that found in more na-
tural soils, even though the EDH contained a negligible
quantity of clay. Combining soil shrinkage and water

ORGANIC MATTER EFFECT ON TECHNOSOL PROPERTIES 497
retention curve approaches allowed the influence of or-
ganic matter content on hydro-structural properties of
Technosols to be measured. Also, an increase in the
percentage of compost in the constructed Technosols
induced a large increase in macropore range and a
small decrease in micropore range, resulting in an ove-
rall increase in the range of the size of pores retaining
total available water. This study dealed with recently
mixed materials that underwent their first humecta-
tion/desiccation cycle. Further studies should be con-
ducted, since hydro-structural properties will likely di-
ffer after several humectation/desiccation cycles due
to consolidation of soil structure. Another perspective
would be to consider not only the percentage of ma-
terial in the mixture but its quality or composition.
Finally, the influence of organisms such as plants, fau-
na or microorganisms should be also investigated since
they drive the evolution of hydro-structural properties
of Technosols.
ACKNOWLEDGEMENTS
This study was conducted in collaboration with the
Departmental Council of Seine-Saint-Denis, France,
and the company Enviro Conseil et Travaux, France.
The authors thank the University of Damascus, Syria,
for financial support of the Ph.D. (No. 1473). The au-
thors also thank Dr. Gaghik Hovhannissian and Dr.
Erik Braudeau from the Institute of Research for De-
velopment (IRD), France for their scientific advices,
and Dr. Michael Corson (USA) from Soil, Agro- and
Hydro-Systems, Spatialization Research Unit (Rennes,
France), for proofreading the English.
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