Agriculture, Ecosystems and Environment 196 (2014) 59–68

Contents lists available at ScienceDirect

Agriculture, Ecosystems and Environment
journal homepage: www.elsevier.com/locate/agee

Soil tillage to reduce surface metal contamination – model
development and simulations of zinc and copper concentration proﬁlesin a pig slurry-amended soil
Fábio Joel Kochem Mallmann a, *, Danilo dos Santos Rheinheimer a ,Carlos Alberto Ceretta a , Cesar Cella a , Jean Paolo Gomes Minella a ,
c c , Folkert van Oort d, Jirka Šimunek e
Rosana Lamana Guma b , Vilim Filipovi
aDepartamento de Solos, Universidade Federal de Santa Maria, CEP 97.105-900, Santa Maria, Rio Grande do Sul, Brazil
Departamento de Ciências Florestais, Universidade Federal de Santa Maria, CEP 97.105-900, Santa Maria, Rio Grande do Sul, Brazil
Department of Soil Amelioration, Faculty of Agriculture, University of Zagreb, Svetošimunska 25, Zagreb 10000, CroatiadINRA, UR 251, Pessac, RD10, Cedex F-78026, FranceeDepartment of Environmental Sciences, University of California Riverside, Riverside, CA 92521, USAbc

A R T I C L E I N F O

A B S T R A C T

Article history:
Received 18 September 2013
Received in revised form 23 June 2014
Accepted 25 June 2014
Available online xxx

Long-term applications of organic amendments, such as pig slurry (PS), may represent environmental
risk of soil and water pollution by trace metals (TM). Our objective was to examine different soil andmanure management scenarios that enhance the long-term agricultural use of soils under repetitive PS
applications while avoiding environmental risk. Firstly, we developed a new module for simulating theimpacts of soil tillage frequencies in Hydrus-1D. Secondly, we used a previously validated modelingapproach to predict the surface accumulation and movement of the TM during the next 100-year in thesoil under different PS doses (80 and 40 m3 ha1 cultivation1) and tillage frequencies (no-tillage and 20,
10, and 5-year tillage). No-tillage simulations revealed consistent TM surface accumulations, reaching thesoil threshold value for Cu in the 0–20 cm layer after 86 years of PS amendments at high doses, but inlayers 0–5, 0–10, and 5–10 cm, this concentration was already reached after 17, 38, and 75 years,
respectively. While soil tillage reduced TM concentrations over the top 20 cm of the soil proﬁle, it
increased their transfer to deeper layers. Periodical soil tillage each 5, 10, and 20 years was found to allow
PS applications without reaching the Cu threshold value in soil during 100 years. However, soil solution
concentrations of Zn reached the threshold values for groundwater. Therefore, the best manure
management practice for the long-term PS disposal with respect to Zn and Cu concentrations in soil is theapplication of moderate PS rates.
ã 2014 Elsevier B.V. All rights reserved.

Keywords:
Hydrus-1D
Trace metals
Organic waste
Solute movement
Groundwater pollution
Surface accumulation

1. Introduction
Long-term applications of organic waste amendments on soils
may lead to a notable accumulation of mineral and organic
micropollutants in the soil’s surface layer. Hence, such practices
potentially represent environmental risk of soil and groundwaterpollution. Recently, we have carried out validating and prospectivemodeling work, using the Hydrus software package, to simulate
the movements of trace metals (TM) zinc (Zn) and lead (Pb),derived from past industrial metallurgical activities, in agricultural* Corresponding author. Tel.: +55 55 3220 8108; fax: +55 55 3220 8256.
E-mail address: fabiojkmallmann@gmail.com (F.J.K. Mallmann).
http://dx.doi.org/10.1016/j.agee.2014.06.024
0167-8809/ ã 2014 Elsevier B.V. All rights reserved.

soils under different long-term land uses in northern France(Rheinheimer et al., 2013; Mallmann et al., 2012a). Then we havesuccessfully applied the same modeling approach to simulate themovement of Zn and copper (Cu) in an Alﬁsol in Southern Brazil,
managed under repetitive applications of pig slurry (PS) (Mallmann et al., 2012b). In addition to major nutrients such as
phosphorus (P), nitrogen (N), and potassium (K) (Lourenzi et al.,2013), PS contains consistent amounts of oligo-nutrient elements
such as Zn and Cu that at high concentrations become contaminants (Girotto et al., 2010; Berenguer et al., 2008; L'Herroux et al.,1997). Both Zn and Cu are consistently present in pigs’ diet,representing mineral supplements or growing elements, aiming toincrease the productivity index of these animals (Li et al., 2005). A
large fraction of Zn and Cu, however, is not absorbed by the animal

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F.J.K. Mallmann et al. / Agriculture, Ecosystems and Environment 196 (2014) 59–68

gastrointestinal tract and is released via pig manure (Nicholson
et al., 2003). In the work of Mallmann et al. (2012b), we showed
how a continuous application of PS on the Alﬁsol for 50 years
would lead to large Zn and Cu contents in the 0–5 cm soil layer.
Particularly for Cu, the simulated soil concentrations in this layer
exceeded the Brazilian guideline intervention value for agriculturalareas of 200 mg kg1, established by the Conselho Nacional do
Meio Ambiente (CONAMA, 2009).
Such strong accumulation of TMs at the soil’s surface is directly
related to agricultural land management practices of no-tillage,
currently widely used in Brazil. More than 60% of cultivated land
(23.6 million hectares) is farmed as a no-till system, maintaining
the soil covered and unplowed, sowing is performed directly on thesoil surface without its previous preparation and crop rotation isused (Mello and van Raij, 2006). Therefore, no-tillage practices inagricultural lands under long-term PS amendments will favor theaccumulation of Zn and Cu within the ﬁrst few centimeters of thesoil proﬁle, and reduce the movement of these TMs to layers below
the depth of 20 cm. In this view, the no-tillage management
represent a disadvantage in comparison to the conventional tillage
management, where the surface layer is annually mixed byplowing and, consequently, the concentrations of added micropollutants are mechanically homogenized over the entire plowdepth (about 20 cm). Therefore, introducing periodical soil tillage,
as a sustainable land management practice, represents an original
solution for reducing the strong surface accumulation of the TMs
by mixing them over a greater depth. It also represents a solution tocomply with Brazilian environmental guidelines on maximum TM
values (CONAMA, 2009), which may be restrictive for long-term
organic amendments on no-tillage farming systems.
Soil tillage practices, however, by homogenizing the plow layer
and thus reducing the soil solution metal concentrations in theuppermost soil layer and increasing them at the bottom of thetilled layer, favor the downward movement of the TMs via the soil
solution to depths below the plow layer. They may then propagate
down to the bottom of the soil proﬁle and require a more detailed
examination, especially at depths close to the groundwater table.
Therefore, the threshold values for groundwater established by theBrazilian legislation (CONAMA, 2009), i.e. 1.05 and 2.0 mg L1 forZn and Cu, respectively, should not be reached at deeper soil depths
to avoid risks of groundwater pollution.
The aims of the present work were to examine current andadapted soil and manure management practices for a sustainableagricultural land use of soils under repetitive PS applications, while
avoiding environmental pollution risks. For that, we used Hydrus1D to model the future movement of Zn and Cu in an Alﬁsol
contaminated by repetitive applications of PS. First, we developed
a new module that simulates the effects of soil tillage at different
time intervals and implemented it in Hydrus-1D. Second, we usedthe validated modeling approach of Mallmann et al. (2012a,b) topredict the surface accumulation, soils solution concentrations,and redistribution of TMs in the Alﬁsol proﬁle for different PS doses
and varying soil tillage frequencies during the next 100 years.
Simulated soil and solution concentrations of Zn and Cu were thencompared with current Brazilian guideline values.
2. Materials and methods
2.1. General and site characteristics, soil sampling and analysis
The studied soil proﬁle, a typic Hapludalf (USDA, 2003), is
located at the experimental ﬁelds of Federal University of Santa
Maria, Rio Grande do Sul State, Brazil (29 420 5200 S and 53 4201000 W,
90 m altitude). An experiment that was conducted during eight
years (01/2000–01/2008) under the no-tillage management andthat received applications of different PS doses (0, 20, 40, and80 m3 ha1) serves as the basis of this study. The PS doses wereapplied at the soil’s surface before each cultivation; one time in2007, two times in 2000, 2004, and 2005, and three times in 2001–
2003, and 2006.
Soil samples from a plot with the 80 m3 ha1 PS treatment werecollected in January 2008 from soil layers of 0–5, 5–10, 10–25, 25–
35, 35–50, and 50–60 cm depths, with three subsamples per layer.
We determined the soil’s particle density, water retention curve(SWRC), particle size distribution, saturated soil hydraulicconductivity (Ks), bulk density, total porosity, pHH2O, total content
and desorption curves of Zn and Cu, and organic carbon. Analyticalmethods and procedures used for the determination of theseparameters are extensively described in Mallmann et al. (2012b).
The results are shown in Table 1.
2.2. Model parameterization and solute transport simulations
Hydrus-1D (Šimunek et al., 2008) was used to simulate onedimensional unsaturated water ﬂow and Zn and Cu transport in a
vertical domain for a one century period. The analytical models of
van Genuchten and van Genuchten–Mualem were used to describewater retention curves and unsaturated hydraulic conductivity
functions (van Genuchten, 1980), respectively. This software also
requires additional hydro-physical and chemical parameters to run
all desired simulations. For Brazilian climatic conditions with highintensity rainfalls, the most important physical parameter is thesaturated hydraulic conductivity (Ks), since it determines waterinﬁltration and percolation through the soil proﬁle, the transportof dissolved solutes, and their transfer to greater depths. Additional
key parameters include the soil residual (ur) and saturated (u s)water contents, the shape parameters aVG and n1 obtained from
SWRC, and the pore connectivity/tortuosity factor (L).
Mallmann et al. (2012a,b) and Rheinheimer et al. (2013) used
the TM proﬁle concentrations collected in ﬁeld experiments toshow that the two-site sorption model reproduced better the TM
movement in the soil compared to the equilibrium sorption model.
Similar conclusions were obtained by many other researchers whocollected metal breakthrough curves from soil column studies. For
example, Chotpantarat et al. (2012) showed that the two-site
sorption model ﬁtted both rising and declining branches ofbreakthrough curves of heavy metals much better than theequilibrium sorption model. Pang et al. (2002) showed that metalinteractions with the soil indicate the presence of chemical nonequilibrium in the system, due to the presence of long tailing in
breakthrough curves. Moreover, according to Pang and Close(1999), non-equilibrium sorption models describe better thetransport of heavy metals and provide better explanations forthe spreading and asymmetry of breakthrough curves.
In this way, the chemical parameters required by the two-site
model include the initial Zn and Cu solution concentrations, andthe Freundlich’s n and KF parameters, describing the equilibrium
adsorption/desorption process. The most important parameterscharacterizing the sorption kinetics are b and l . The b parameterdeﬁnes the amounts of sorption sites in chemical equilibrium withthe soil solution. In our conditions, this parameter decreases withdepth. The lower the value of this parameter, the more important
are the sorption sites that react slower with the dissolved heavy
metals. These sites are sometimes called kinetic sorption sites. As
the fraction of kinetic sorption sites increases, the l parameter,
describing the sorption rate, becomes more important. The lower
its value, the slower the adsorption to the soil sorption sites, and,
consequently, the higher the solute concentration in the soil
solution and the faster the transport to deeper layers. However,during the desorption phase, the low value of the l parameter

F.J.K. Mallmann et al. / Agriculture, Ecosystems and Environment 196 (2014) 59–68

61

Table 1
Hydro-physical and chemical soil parameters, and initial values required for simulations with Hydrus-1D.
Parameter a

SoilpH
Clay, g kg1
Silt, g kg1
Sand, g kg1
OC , g kg1
Bd , g cm3
Ks, cm dia1
us, cm3 cm3
ur, cm3 cm3
aVG, cm1
n1
L
D, cm
Zinc
Total, mg kg1
Solution, mg L1bl, 105 day1
KF
n

CopperTotal, mg kg1
Solution, mg L1bl, 105 day1
KFn

Soil layer (cm)
1 (0–5)2 (5–10)

3 (10–25)

4 (25–35)

5 (35–50)

6 (50–60)

Mixed (0–20)

5.51
158
376
466
24.5
1.33
190.490.386
0.142
0.1834
1.3696
0.5
2.5

5.43
174
354
472
12.4
1.51
93.85
0.393
0.139
0.12481.4095
0.5
2.5

5.41
182
350
468
9.3
1.56
65.93
0.406
0.142
0.2834
1.367
0.5
2.5

5.12
188
322
490
8.6
1.46
58.78
0.380
0.122
0.127
1.4092
0.5
2.5

5.01
176
345
478
7.8
1.46
216.8
0.322
0.109
0.092
1.4891
0.5
2.5

5.06
173
393
434
6.3
1.41
301.8
0.324
0.117
0.15641.3632
0.5
2.5

5.44
174
357
469
13.9
1.49
104.050.398
0.141
0.21681.3714
0.5
2.5

69.36
177.02
0.56
4.29
4.41
0.65

39.91
146.71
0.29
4.13
2.87
0.65

22.74
98.11
0.14
3.04
2.12
0.65

16.33
106.95
0.04
1.82
1.44
0.65

18.97
145.78
0.04
1.44
1.37
0.65

21.47
164.56
0.02
2.82
1.43
0.65

38.69
129.99
0.36
3.97
2.88
0.65

59.38
80.34
0.61
6.87
96.38
0.85

22.77
36.92
0.46
4.17
71.57
0.85

12.02
20.93
0.21
2.61
61.22
0.85

7.73
15.77
0.13
2.49
50.07
0.85

12.02
26.35
0.07
1.83
50.34
0.85

12.02
26.85
0.06
3.10
49.53
0.85

26.55
39.78
0.49
5.33
72.60
0.85

a
OC: organic carbon; Bd: bulk density; Ks: saturated hydraulic conductivity; us: saturated water content; ur: residual water content; aVG and n1: retention parameters; L:
pore-connectivity factor; D: longitudinal dispersivity; b: fraction of sorption sites with instantaneous sorption of the heavy metals; l: kinetic constant for sorption sites 1  b;
KF and n: parameters of the Freundlich isotherm for the b sites, calculated with total and solution concentrations in mol g1 and mol L1, respectively.

produces a slow rate of desorption from the soil sorption sites tothe soil solution and, consequently, the slower transport of theheavy metals to deeper soil layers.
As shown in Table 1, the b values vary signiﬁcantly between
different soil layers. This is because these values do not depend
only on soil texture, which is very similar throughout the soil
proﬁle. Both Zn and Cu total concentrations in the soil affectsigniﬁcantly the value of this parameter. As their concentrations
increase, the saturation of soil sorption sites increases as well,resulting in weaker bonds between the soil functional groups andthe chemical, and higher amounts of the early extractable metal(in percentage value). Consequently, the fraction of easily
extractable metals tends to be much higher in soil layers withhigher metal concentrations (i.e., in the surface soil layer). Other
soil characteristics that can strongly affect the b values are theorganic carbon contents and soil pH (Carrillo-González et al.,2006). The organic carbon in the soil can bond to Cu or Zn andincrease or decrease their solubility, depending on the type andamount of the compound. With respect to soil pH, the higher its
value, the weaker the metal binding, which favors the desorption
from the soil. It is also important to emphasize that the bparameter is related to Q1/Qtotal, where Q1 is the fraction of themetal easily extractable with EDTA and Qtotal is the total content of
the metal in soil (Mallmann et al., 2012a,b). As the natural content
of Zn and Cu in our soil is low (and has very low desorbed values
with EDTA) and the concentration of metal in the surface layer ofthe soil under PS applications is high (exogenous contents ofmetals have high desorption when extracted with EDTA), the bparameter tends to be high at the surface and very low at deeper
layers, especially in places with low downward movement ofmetals, as in our study.

Hydro-physical and chemical parameters were determined forall soil layers from the experiment with the 80 m3 ha1 PS dose,
following the procedure described by Mallmann et al. (2012b), andare presented in Table 1.
Numerical solutions of the Richards equation describing
variably-saturated water ﬂow, and the convection–dispersion
equation describing solute transport, require the speciﬁcation of
initial and boundary conditions. The initial concentration proﬁlesof Zn and Cu were deﬁned based on the analysis of soil samples
collected at the experimental site, as described in Section 2.1. The
atmospheric and free drainage boundary conditions were considered in Hydrus-1D simulations at the soil surface and bottom,
respectively. Daily precipitation and evapotranspiration data from
01/01/2000–01/01/2008 used by Mallmann et al. (2012b) (Fig. 1)
were used repeatedly 12.5 times to cover the entire simulated
period of one century. Average annual rainfall and evapotranspiration were 1678 and 921 mm, respectively.
The total amounts of TMs added to the soil during the simulated
100-year period, considering a PS dose of 80 m3 ha1 cultivation1,
were 954 and 704 kg ha1 of Zn and Cu, respectively. For
simulations that considered the 40 m3 ha1 doses, corresponding
amounts were half, i.e., 477 and 352 kg ha1, respectively. Moredetails about the temporal distribution of TMs during thesimulation and their amounts added to the soil at each time canbe found in Mallmann et al. (2012b). This dataset was also repeated
12.5 times and formed our base plan for the TMs introduction at
the soil surface.
We simulated the vertical movement of Zn and Cu in soil using
Hydrus-1D, for 100 years (2008–2108), using a two-site sorption
chemical model validated by Mallmann et al. (2012a,b), which
considers that the total TM concentration in the soil is partitioned

100

10000

80

8000

60

6000

40

4000

20

2000

0

0

10

10000

8

8000

6

6000

4

4000

2

2000

0
2000

2001

2002

2003

2004

2005

2006

2007

0
2008

Cumulative precipitation, mm

F.J.K. Mallmann et al. / Agriculture, Ecosystems and Environment 196 (2014) 59–68

Cumulative evapotranspiration, mm

Daily evapotranspiration, mm

Daily precipitation, mm

62Time, year
Fig. 1. Daily (bars) and cumulative (line) precipitation (top) and crop evapotranspiration (bottom) at the experimental site in Santa Maria, Rio Grande do Sul State,
Brazil, from 2000 to 2008. Constant evapotranspiration values of 1.98 mm day1
correspond to fallow periods and represent average values from places close to theexperimental site.Source: Sistema Irriga1–UFSM.

between soil water and instantaneous and kinetic sorption sites.
Our simulations included estimations of TM quantities transported
to soil layers below a depth of 60 cm. Eight tested scenarios
included different PS doses applied on the soil’s surface before each
cultivation and different frequencies of soil tillage. Scenarios A
through D were ran for 80 m3 ha1 PS doses (a high dose) and soil
management practices with no-tillage (A) or tillage of the upper 0–
20 cm layer every 20 (B), 10 (C), and 5 (D) years. These scenarios are
hereafter referred to as 80 m3 no-till, 80 m3 20y-till, 80 m3 10y-till,and 80 m3 5y-till, respectively. Scenarios E through H involved
40 m3 ha1 PS doses (a moderate dose) and the same sequence ofsoil tillage frequencies, hereafter referred to as 40 m3 no-till, 40 m3
20y-till, 40 m3 10y-till, and 40 m3 5y-till, respectively. Scenarios inwhich soil tillage was considered every year are not presented
here, because they did not show any signiﬁcant differencescompared to scenarios with soil tillage every 5 years. Moreover,such a one-year tillage frequency would be in contradiction withthe actual no-tillage conservative soil management policies
promoted in Brazil, a concept we kept in mind in our work since
it is of great interest for practical agricultural applications.
For simulations of scenarios that used periodical soil tillage (B–D and F–H), we changed the soil characteristics for the upper
20 cm. This 0–20 cm layer was referred to as a mixed layer, forwhich we used weighted average values of soil characteristics fromthe layers 1, 2, and 3 (Table 1). Indeed, the ﬁrst soil tillage in thesimulations was performed on the ﬁrst day, and then repeatedaccording to particular frequencies of each scenario.
2.3. Development of a soil tillage module for Hydrus-1D
To be able to perform simulations for scenarios with periodicalsoil tillage, we have developed a new module for Hydrus-1D. This
module allowed us to select different depths and frequencies(dates) of soil tillage. At the time of speciﬁed tillage, Hydrus-1D

simply homogenizes the surface layer subject to tillage. It ﬁrst
integrates water over the tillage depth and then assigns theaverage water content to this entire soil layer as follows:RuðzÞdzu¼(1)
Ltillagewhere u (z) is the water content (cm3 cm3) at a depth z at time oftillage, Ltillage is the depth (cm) of tillage, and u is the average watercontent (cm3 cm3) over the tillage depth after tillage.
Similar homogenization (averaging) is done for solutes. For anonreactive solute, the averaging would be done as follows:RuðzÞcðzÞdz
c¼(2)
u Ltillage
where c (z) is the liquid phase concentration (mmol cm3) at a
depth z at time of tillage and cis the average liquid phase
concentration (mmol cm3) over the tillage depth after tillage.
Since the solute transport model adopted in this study
considers a reactive solute, which is present in the liquid phaseas well as instantaneously and kinetically sorbed to the solid phase,the tillage routine of Hydrus-1D needs to consider all these phases.
The code ﬁrst integrates the solute mass, which is present in theequilibrium and nonequilibrium states as follows:Z
se ¼ ½uðzÞcðzÞ þ f rse ðzÞdz
(3)
Z
sk ¼

½ð1  f Þrsk ðzÞdz(4)

where se and sk are solid phase concentrations at equilibrium(mmol cm3) and kinetic sorption sites (mmol g1), respectively,
and Se and Sk are solute masses in equilibrium (mmol cm2) andnonequilibrium (mmol cm2) states over the tillage depth,
respectively. The average solid phase concentration in thenonequilibrium state is calculated similarly as shown above fora nonreactive solute:R½ð1  f Þrsk ðzÞdz
sk
sk ¼
¼
(5)
ð1  f ÞrLtillage
ð1  f ÞrLtillage
However, since the solid phase concentration at equilibriumsites is calculated using the Freundlich isotherm, which is anonlinear equation, a root ﬁnding routine needs to be adopted to
calculate the average liquid phase concentration from the solute
mass in equilibrium state in the tillage depth, Se.
The two main input parameters into the tillage module, apartfrom water content and concentration distributions in the tillage
soil layer, are the frequency of tillage (e.g., no-tillage and/or tillage
each 5, 10, and 20 years) and the thickness of the tilled soil layer. It
is one of the objectives of this study to evaluate the effects of thefrequency of tillage on the transport of heavy metals.
There are several limitations of this new tillage module. The
module neglects any possible changes in soil hydraulic properties,
which are likely to occur during tillage. In our simulations, we
assumed that as a result of tillage, the soil hydraulic properties inthe tilled layer were constant over time and equal to average
properties of the top three layers (Table 1).
Another source of uncertainty is the extent of mixing during
tillage. Limiting examples of mixing may be deﬁned as (a) no
mixing, (b) complete mixing, and (c) a complete turnover of thetilled soil layer, when material (including moisture and solutes)
from the top will be moved to the bottom and vice versa. Since the
new tillage module assumes complete mixing, in simulations
presented in this study we account for scenarios without mixing(no-tillage scenario) and with complete mixing (scenarios withtillage each 5, 10 and 20 years).

F.J.K. Mallmann et al. / Agriculture, Ecosystems and Environment 196 (2014) 59–68

3. Results
3.1. Water mass balance in soil
Simulations of scenarios without soil tillage displayed anaverage water storage in the soil proﬁle (60 cm deep) of 14.5 cm.
Moreover, during these 100-year simulations, water evapotranspiration and drainage reached cumulative amounts of 5364 and5944 cm, respectively. Scenarios with periodical soil tillage,
compared to the no-tilled soil, had a similar average water storageof 14.7 cm. However, evapotranspiration was 16.7% lower anddrainage was 15.2% higher. The frequency of soil tillage did notchange noticeably the water balance among different tilled
scenarios. The differences among various scenarios did not result
from the soil tillage practices simulated by the new module, butfrom different soil hydraulic parameters used for the tilled layer(0–20 cm) in scenarios with soil tillage (Table 1), as explained in
Section 2.2.
3.2. Prospective modeling of 100 years of Zn and Cu movement without
tillage
Simulations of scenarios without soil tillage produced a highTM retention in the soil surface layer (0–5 cm). After 100 years, thetotal Zn concentration in the ﬁrst soil layer increased from an initialvalue of 69.4 to 247.0 mg kg1 in scenario A (80 m3 no-till) (Fig. 2A)
and to 160.0 mg kg1 in scenario E (40 m3 no-till) (Fig. 2E). For thesame scenarios, the Cu increases were even higher, i.e., from an
initial value of 59.4 to 445.0 and to 246.0 mg kg1, respectively(Fig. 3A and 3E). Moreover, continuous PS applications with bothdoses increased Zn concentrations in the entire soil proﬁle (up to
60 cm depth). At the soil bottom, the initial Zn concentration(21.5 mg kg1) increased substantially and reached 47.9 and32.9 mg kg1 after one century for PS doses of 80 and 40 m3 ha1,respectively (Fig. 4). On the other hand, the Cu concentrations at
the 60 cm depth almost did not change during the simulation

No-tillage
300

period, and the Cu concentration proﬁle showed a consistentincrease only in the 0–40 cm soil layer in scenario A and in the 0–
30 cm soil layer in scenario E (Fig. 5).
No-tillage scenarios also showed a great increase of TM solution
concentrations in the soil proﬁle. The Zn concentration in the soil
solution increased in the entire soil proﬁle, and the maximum
values at the end of simulations were observed approximately at
depths of 7–10 cm, reaching 1.50 and 0.75 mg L1 for PS doses of 80
and 40 m3 ha1, respectively (Fig. 4). Furthermore, Zn solution
concentrations at the bottom of the soil proﬁle were 1.20 and
0.60 mg L1 in scenarios A and E, respectively. These concentrations slowly increased during the simulations, leading to anincrease in Zn transfer to soil layers deeper than 60 cm, reaching up
to 473.0 kg ha1 (scenario A) and 231.0 kg ha1 (scenario E) after
100 years (Fig. 6). The Cu solution concentrations also increased in
the whole proﬁle, but more consistently in the upper 30 cm of thesoil. The maximum (at the 1–3 cm depth) and bottom solution
concentrations at the end of the 100-year simulation period were0.97 and 0.08 mg L1 for scenario A, and 0.48 and 0.05 mg L1 forscenario E, respectively. These small bottom solution concentrations explain small transfers of Cu to soil depths below 60 cm:
21.4 and 17.3 kg ha1 for scenarios with 80 and 40 m3 ha1 PS doses,
respectively.
3.3. Future Zn and Cu movement under different scenarios of soil
tillage
The introduction of soil tillage data in simulations of Hydrus-1D
showed that after 100 years, scenarios with soil tillage each 20, 10,
and 5 years with PS doses of 80 m3 ha1 (scenarios B, C, and D) had Zn
surface concentrations in the 0–5 cm soil layer of 132.9, 131.6, and127.7 mg kg1, respectively. For scenarios with 40 m3 ha1 doses(scenarios F, G, and H), these concentrations were 87.3, 86.0, and83.4 mg kg1, respectively (Fig. 2). For Cu, the surface concentrations
reached 230.5, 210.6, and 189.4 mg kg1 when using 80 m3 ha1 PS
doses (scenarios B, C and D), and 128.3, 116.3, and 107.2 mg kg1

Tillage each 20 years

Tillage each 10 years

Tillage each 5 years

A

B

C

D

E

F

G

H

0

20 40 60 80 100 0
Time, year

20 40 60 80 100 0
Time, year

-1

250
Zn total, mg kg

63

200

0-5 cm5-10 cm
10-15 cm
15-20 cm
20-25 cm
25-30 cm

150
100
50
0
300

Zn total, mg kg

-1

250
200
150
100
50
0
20 40 60 80 100 0
Time, year

20 40 60 80 100
Time, year

Fig. 2. Total zinc concentrations in six layers of the soil proﬁle during one century simulations, considering scenarios with different pig slurry doses and soil tillage
frequencies. Upper and lower graphs were simulated under 80 and 40 m3 ha1 cultivation1 doses, respectively. Letters A and E represent scenarios under no-tillage soil
management. Vertical lines indicate soil tillage, performed with frequencies of each 20 (B and F), 10 (C and G), and 5 (D and H) years.

64

F.J.K. Mallmann et al. / Agriculture, Ecosystems and Environment 196 (2014) 59–68

No-tillage
500

Tillage each 20 years

Tillage each 10 years

Tillage each 5 years

A

B

C

D

E

F

G

H

0

20 40 60 80 100 0
Time, year

20 40 60 80 100 0
Time, year

0-5 cm5-10 cm
10-15 cm
15-20 cm
20-25 cm
25-30 cmCu total, mg kg

-1

400
300
200
100
0
500

Cu total, mg kg

-1

400
300
200
100
0
20 40 60 80 100 0
Time, year

20 40 60 80 100
Time, year

Fig. 3. Total copper concentrations in six layers of the soil proﬁle during one century simulations, considering scenarios with different pig slurry doses and soil tillage
frequencies. Upper and lower graphs were simulated under 80 and 40 m3 ha1 cultivation1 doses, respectively. Letters A and E represent scenarios under no-tillage soil
management. Vertical lines indicate soil tillage, performed with frequencies of each 20 (B and F), 10 (C and G), and 5 (D and H) years.

3

DOSE 80 m ha

-10

Depth, cm

10
20
30
40
50
60
0.0

0.4
0.8
1.2
Zn solution, mg L-1

1.6

0

3

DOSE 40 m ha

50

100
150
200
Zn total, mg kg-1

250

-1

0

Depth, cm

10
20
30
time 0no-tillage
tillage each 20 years
tillage each 10 years
tillage each 5 years

40
50
60
0.0

0.4
0.8
1.2
Zn solution, mg L-1

1.6

0

50

100
150
200
Zn total, mg kg-1

250

Fig. 4. Solution (left) and total (right) zinc concentrations in the soil proﬁle under continued pig slurry applications after 100 years, considering scenarios involving two
manure doses (80 and 40 m3 ha1 cultivation1) and different soil tillage frequencies (no-tillage and tillage each 20, 10, and 5 years).

F.J.K. Mallmann et al. / Agriculture, Ecosystems and Environment 196 (2014) 59–68

65

DOSE 80 m3 ha-10Depth, cm

10
20
30
40
50
60
0.0

0.2

0.4
0.6
0.8
-1
Cu solution, mg L

1.0

0

100

3

DOSE 40 m ha

200
300
400
-1
Cu total, mg kg

500

-1

0

Depth, cm

10
20
30
time 0no-tillage
tillage each 20 years
tillage each 10 years
tillage each 5 years

40
50
60
0.0

0.2

0.4
0.6
0.8
-1
Cu solution, mg L

1.0

0

100

200
300
400
-1
Cu total, mg kg

500

Fig. 5. Solution (left) and total (right) copper concentrations in the soil proﬁle under continued pig slurry applications after 100 years, considering scenarios involving two
manure doses (80 and 40 m3 ha1 cultivation1) and different soil tillage frequencies (no-tillage and tillage each 20, 10, and 5 years).

when using 40 m3 ha1 PS doses (scenarios F, G and H, Fig. 3).
Although surface accumulation of Zn and Cu decreased when soil
tillage was used, their concentrations in the 10–20 cm layer
increased substantially, and independently of the tillage frequency.
For scenarios B and F, the concentrations in this soil layer increased
after 100 years to approximately 139 and 89 mg kg1 for Zn (Fig. 4)
and to 172 and 97 mg kg1 for Cu (Fig. 5), respectively.
After 100 years, the Zn solution concentrations simulated for
scenarios with periodical soil tillage were lower than for no-tillage
scenarios at all soil depths. For 80 m3 ha1 PS doses, the maximum
values reached were 1.30, 1.28, and 1.21 mg L1 for scenarios B, C,

50

400

40

80 m³, no-tillage
80 m³, tillage each 20 years
80 m³, tillage each 10 years
80 m³, tillage each 5 years
40 m³, no-tillage
40 m³, tillage each 20 years
40 m³, tillage each 10 years
40 m³, tillage each 5 years

-1

500

Cu loss, kg ha-1

Zn loss, kg ha

and D, respectively, and bottom values (60 cm depth) were 1.04,
1.01, and 1.09 mg L1 (Fig. 4). For moderate PS doses (40 m3 ha1),
the Zn maximum and bottom solution concentrations were lower
and equal to 0.65 and 0.51 mg L1, respectively, for scenario B, 0.63
and 0.50 mg L1 for scenario C, and 0.60 and 0.53 mg L1 forscenario D (Fig. 4). The transfers of Zn to depths below 60 cm wereslightly higher at all times in scenarios with soil tillage than
without tillage. The total amounts of transferred Zn reached 498,
506, and 513 kg ha1 for the high PS dose scenarios B, C, and D,
respectively, and 250, 252, and 256 kg ha1 for scenarios F, G, and H
with 40 m3 ha1 PS doses, respectively (Fig. 6).

300

200

100

30

20

10

0

0
0

20

40
60
Time, year

80

100

0

20

40
60
Time, year

80

100

Fig. 6. Zinc (left) and copper (right) amounts transferred in the soil proﬁle under continued pig slurry applications to depths greater than 60 cm, during future one century
simulations using different manure doses (80 and 40 m3 ha1 cultivation1) and soil tillage frequencies (no-tillage and tillage each 20, 10, and 5 years).

66

F.J.K. Mallmann et al. / Agriculture, Ecosystems and Environment 196 (2014) 59–68

0–5 cm surface layer exceeded 200 mg kg1 after 17 years (Fig. 3),
in the 0–10 cm layer after 38 years, in the 5–10 cm layer after 75
years, and in the entire 0–20 cm layer after 86 years (Fig. 7). This Cu
concentration (i.e., 200 mg kg1) refers to the Brazilian thresholdvalue, also deﬁned as an intervention value for agricultural soils(CONAMA, 2009). However, the law establishes that the entire 0–
20 cm layer needs to be considered to evaluate the concentration
limits of a soil. In this way, the threshold value for Cu in scenario A
was reached only after 86 years and even at the end of thesimulation the Cu concentration was only slightly higher, i.e.,
216 mg kg1 (Fig. 7).
When the PS doses of 40 m3 ha1 were used, the average Cu
concentration in the surface 0–5 cm layer exceeded 200 mg kg1 38
years later than when the 80 m3 ha1 PS doses were used (Fig. 3). In
this case (in scenario E), the soil threshold value of CONAMA (2009)(200 mg kg1 in the 0–20 cm soil layer) was not reached during the
100-year simulation. The ﬁnal average Cu concentration in the 0–
20 cm soil layer reached only 120 mg kg1 (Fig. 7). For Zn, although
its surface concentrations under no-tillage scenarios also strongly
increased, they did not exceed the maximum guideline concentrations (450 mg kg1) of CONAMA (2009) in either of PS doses
scenarios.
The main effect of considering soil tillage was related to a
reduction of the surface accumulation of TMs. This effect was more
pronounced for Cu; the scenarios with a 20, 10, and 5-year soil
tillage frequencies lowered the surface Cu concentrations below

The ﬁnal Cu solution concentrations in scenarios considering
periodical soil tillage were lower than in the no-tillage scenarios
only in the plow layer (0–20 cm), reaching maximum values at a 1–
2 cm depth of 0.77, 0.70, 0.60, 0.38, 0.34, and 0.30 mg L1 inscenarios B, C, D, F, G, and H, respectively (Fig. 5). Below the plowlayer, the Cu solution concentrations in soil tillage scenarios werehigher than in scenarios without tillage (A and E). The bottom
values of Cu solution concentrations were 0.128, 0.136, 0.141, 0.068,
0.071, and 0.075 mg L1, respectively, for scenarios B, C, D, F, G, andH (Fig. 5). Thus, the cumulative amounts of Cu loss to depths below
60 cm when using PS doses of 80 m3 ha1 were 38.1, 42.3, and44.3 kg ha1 for scenarios B, C, and D, respectively, and using PS
doses of 40 m3 ha1, they were 26.4, 27.9, and 29.4 kg ha1 forscenarios F, G and H, respectively (Fig. 6).
4. Discussion
4.1. Effects of soil tillage on Zn and Cu in the top soil
The assessment of risks related to Zn and Cu accumulations insoils requires a comparison between measured or simulated TM
concentrations and those established by regulatory bodies(Mantovi et al., 2003). Considering no-tillage scenarios, the Zn
and Cu concentrations in the soil surface layer increased
signiﬁcantly during 100 years, especially for the 80 m3 ha1 PS
dose applications. For this scenario, the Cu concentration in the

0-20 cm SOIL LAYER
450

200

Zn total, mg kg

-1

350
300
250
200
150

175
-1

80 m³, no-tillage
80 m³, tillage each 20 years
80 m³, tillage each 10 years
80 m³, tillage each 5 years
40 m³, no-tillage
40 m³, tillage each 20 years
40 m³, tillage each 10 years
40 m³, tillage each 5 years
Threshold value

Cu total, mg kg

400

150
125
100
75

100

50

50

25

0

0
0

20

40
60
Time, year

80

0

100

20

40
60
Time, year

80

100

20

40
60
Time, year

80

100

2.00

1.05

1.75

0.90

1.50

-1

1.20

Cu solution, mg L

Zn solution, mg L

-1

BOTTOM OF PROFILE

0.75
0.60
0.45

1.25
1.00
0.75

0.30

0.50

0.15

0.25

0.00

0.00
0

20

40
60
Time, year

80

100

0

Fig. 7. Zinc (left) and copper (right) total concentrations at the top 0–20 cm soil layer and solution concentrations at the bottom of the soil proﬁle (60 cm depth) undercontinued pig slurry applications during future one century simulations using different manure doses (80 and 40 m3 ha1 cultivation1) and soil tillage frequencies (no-tillage
and tillage each 20, 10, and 5 years).

F.J.K. Mallmann et al. / Agriculture, Ecosystems and Environment 196 (2014) 59–68

the Brazilian threshold value for agricultural soils when the
80 m3 ha1 PS doses were used (scenarios B, C, and D). However, forsoil tillage to be effective, it needs to be done down to a depth of
20 cm, and not only its shallow version for the upper 5 or 10 cm. As
shown in Scenario A, the high Cu concentrations of 0–5 and 5–
10 cm layers need to be distributed over the entire 0–20 cm layer.
Lowering of Cu surface concentrations by soil tillage not only
allows for the continuous use of PS applications in conformity withnational regulations, but also reduces potential risks of TM
transfers by surface runoff to surface waters, such as rivers orlakes, as related by Xue et al. (2003).
Soil tillage also resulted in an increase of Zn and Cu
concentrations in the 10–20 cm soil layer, promoting a larger
transfer of these TMs below the plow layer. In scenario D, 70.6% of
Zn and 34.5% of Cu added to the soil during the one-century
simulation period were moved from the upper 20 cm to deeper soil
layers, while in scenario A (no-tillage), these amounts were 67.7
and 19.2%, respectively.
Our simulations of Zn and Cu movements in the soil proﬁlewere in good agreement with the general biogeochemical cycling
dynamics of these two TMs in soil, with Zn showing higher
mobility than Cu (McBride, 1994) and, consequently, generally
observed higher transfers of Zn to deeper layers. Moreover, when
TM additions to soil are accompanied by organic compost
amendments, the difference between Zn and Cu mobility is evengreater, due to the higher afﬁnity of Cu to sorption sites in theorganic matter (Díaz-Barrientos, 2003).
After one century of PS applications on soils, the soil solution
concentrations of Zn and Cu in the 0–20 cm layer were lower inscenarios that considered periodical tillage than in corresponding
no-tillage scenarios. One of the soil chemistry laws of Barrow(1999) indicates that the adsorption process between chemicals
and soil functional groups depends to a large extent on theaccessibility of these sites. Accordingly, soil tillage and corresponding breaking of soil aggregates may facilitate the access of
TMs to adsorption sites in the plow layer, and thus reduce theirsolution concentrations.
4.2. Effects of tillage on Zn and Cu distribution at depth
Contrary to the effects observed in the upper 20 cm of the soil
proﬁle, the one century simulations did not show great differencesin TM concentrations in soil layers deeper than 20 cm between
scenarios with and without soil tillage. The quantities of Zn and Cu
in the 20–60 cm layers at the end of simulations with comparable
PS doses were very similar in all scenarios. Indeed, the total TM
concentrations in these subsurface layers remained much lower
than the Brazilian threshold values (CONAMA, 2009) during the
100-year simulations. Similar ﬁndings were mentioned by
Seuntjens (2002) for 100-year simulations of TM movements in
soil, with mean Cd concentrations in the subsoil of the plowed
scenario being not signiﬁcantly greater than in the “no-action”
scenario, and remaining close to the background value.
The higher TM transfers from the plow layer (0–20 cm) in
scenarios with soil tillage coincide with greater transfers of Zn and Cu
to soil layers below 60 cm. The results presented in Fig. 6 indicate agreater loss of Zn and Cu from the upper 60 cm soil proﬁle when soil
tillage is performed. For Zn when PS doses of 80 m3 ha1 were used,such losses were 5.4, 7.0, and 8.5% greater in scenarios B, C, and D,
respectively, than in no-tillage scenario A. For Cu, these percentages
were much greater than for Zn, reaching 78.3, 97.7, and 107.3%,
respectively, although the absolute amounts were smaller. Obviously, the 20–60 cm soil layer acts as a bypass layer for the excess TMs
coming from the top soil due to soil tillage, probably because its lower
Zn and Cu KF values indicate lower adsorption capabilities whencompared to the surface or mixed layers (Table 1).

67

4.3. Risks of Zn and Cu output from soil
Soil tillage did not lead to signiﬁcant changes in the Zn and Cu
solution concentrations at greater depths, as shown in Fig. 7. The
TM solution concentrations at the bottom of the soil proﬁle (60 cm
depth) varied only little during the entire simulation period for
scenarios with the same PS dose (Fig. 7). However, the continued
PS disposal at the soil's surface notably increased TM solution
concentrations in the entire soil proﬁle, especially when applying
doses of 80 m3 ha1. This increase was so high that the Zn solution
concentrations at the bottom of the soil proﬁle at the end of
simulations in scenarios A and D reached values higher than theBrazilian threshold value for groundwater (1.05 mg L1) (CONAMA,
2009), and were not very different in comparison to scenarios B
and C (Fig. 4). For Cu solution concentrations, a similar effect wasobserved, but the increase at the proﬁle's bottom did not reach inany simulation the threshold value, which is higher for Cu(2.0 mg L1) than for Zn (CONAMA, 2009).
Comparing simulated results of the solution Zn concentrations
with a threshold value of the Brazilian Health Ministry, that ishigher than that of CONAMA (2009), the proﬁle bottom concentrations, as well as those in the whole proﬁle, remained below
5.0 mg L1, the maximum value of Zn for drinking water (BRAZIL,
2004). Although these solution concentrations were not exceeding
guideline values with respect to human health, we need toconsider the environmental guidelines that indicate reference
values for groundwater, and that are directly linked to effects
induced by a long-term PS disposal on soils.
In the view of the goal of keeping the TM solution concentrations below the threshold values, the best strategy for managing
soils during one century of PS applications is to adopt the use ofmoderate doses, i.e., 40 m3 ha1 cultivation1. In that case, thesolution concentrations at the proﬁle's bottom after 100 years areapproximately half of those found for high dose PS applications,
independently of whether the soil was frequently plowed or not(Fig. 7). Reduction of PS doses implies a reduction of TM inputs andconsequently, lowering of the surface TM accumulation. This was
also discussed by Novak et al. (2004); who showed a positive
impact of reducing manure application rates on declining topsoil
total Zn and Cu accumulation.
Moreover, if soils are used for a PS disposal during a shorter
time, i.e., 50 years, as previously studied by Mallmann et al.
(2012b); Zn solution concentrations will not reach the thresholdvalue. Consequently, 80 m3 ha1 PS doses will not present risk forenvironment if PS amendments are combined with periodical soil
tillage, thus solving the problem of excessive surface accumulationof Cu, as previously highlighted by Mallmann et al. (2012b).
According to Carrillo-González et al. (2006) and Koo et al.
(2005) the presence of plant roots may modify the soil environment in the rhizosphere. Plants may utilize various strategies tomobilize nutrients, such as modiﬁcation of the chemical composition or association of roots with micro-organisms (Neumann andRomheld, 2002). Consequently, plant roots may play an importantrole in the transformation and chemical speciation of TMs in soils,
which may affect their accumulation and solubility in the soil
(especially in the upper layers). Additionally, plant roots can also
act as biosorbents. However, it was not possible to consider theseeffects in our simulations with Hydrus-1D, which does not accountfor these processes. However, since Hydrus-1D was calibratedusing experimental ﬁeld data, the effects of these “non-accounted”
processes should be reﬂected in the calibrated model, and thus thesimulated results should not be signiﬁcantly different, if theseprocesses were considered directly.
Finally, it is important to emphasize that, if soil tillage is appliedin the ﬁeld, other soil conservation practices such as soil cover withcrops and residues, and appropriate terracing must be more

68

F.J.K. Mallmann et al. / Agriculture, Ecosystems and Environment 196 (2014) 59–68

carefully used. These latter practices reduce the losses of soil andchemicals due to erosion, which may be induced by soil tillage, andtherefore reduce the loss of TMs by surface runoff and consequenttransfer to, and contamination of, surface water bodies (Avalos
et al., 2009; Blanco and Lal, 2008; Bertol et al., 2003).
5. Conclusion
We used Hydrus-1D to predict vertical movements of Zn and Cu
over a period of 100 years in a pig slurry amended soil. We used a
two-site sorption and transport model, previously validated by
Mallmann et al. (2012a,b) and complemented it in this work with a
new soil tillage module. Simulations that did not consider tillage
showed a great surface accumulation of TMs, especially for Cu andfor PS doses of 80 m3 ha1 cultivation1. In this scenario, the total
Cu concentrations in the 0–20 cm soil layer reached the Brazilian
maximum threshold value after 86 years. When PS doses of
40 m3 ha1 cultivation1 were considered, the Cu threshold limit
for agricultural soils was not reached during 100 years, similarly as
predicted for Zn under both PS doses in no-tillage scenarios.
We also simulated scenarios considering soil tillage of the 0–
20 cm soil layer every 20, 10, and 5 years for the two PS application
doses. Soil tillage promoted dilution of TMs over the ﬁrst 20 cm
depth, but increased the amounts of Zn and Cu transferred todeeper layers. If prolonged PS applications to soil should remain in
conformity with Brazilian regulations, the slowest increases on
TMs concentrations in the 0–20 cm soil layer were obtained using
the scenario with tillage every 5 years. Indeed, scenarios withapplications of 80 m3 ha1 PS doses indicated that the total Cu
concentrations in soil remained under the threshold value during
the 100-year simulation period for the 20, 10, and 5-year tillage
frequencies. However, soil tillage was found less effective in
reducing surface accumulation of TMs in areas with high PS doses
than reducing the PS dose by half.
Moreover, in addition to decreasing the TM concentrations at the
soil's surface, soil tillage also affected TM concentrations in the soil
solution. Soil tillage slightly increased the transfer of Zn and Cu in thesoil proﬁle to depths larger than 60 cm. For the PS dose of 80 m3 ha1,
the Zn solution concentrations at the soil depth of 60 cm were close,
or exceeded, the threshold value after 100 years, presenting risk forgroundwater pollution. Yet when the considered duration of PS
applications was shortened, or when PS doses were reduced, the Zn
solution concentrations at larger depths were no longer anenvironmental problem with regards to guideline values.
Hydrus-1D proved to be a very useful tool for supporting the
agricultural and environmental planning, and in evaluating theimpacts of modifying soil and manure management practices.
Periodical soil tillage may be an efﬁcient practice to reduce TM
surface concentrations in PS-contaminated soils and to extend
their agricultural use when under manure applications. However,depending on desired duration of PS disposal and requirement tomeet environmental guidelines related to Zn and Cu, soil tillage
must be accompanied by a reduction in PS doses applied to soil.
Acknowledgements
F.J.K. Mallmann acknowledges CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brazil) and CNPq
(Conselho Nacional de Desenvolvimento Cientíﬁco e Tecnológico –Brazil) for postgraduate scholarships.

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