Agriculture, Ecosystems and Environment 190 (2014) 52–59
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Agriculture, Ecosystems and Environment
journal homepage: www.elsevier.com/locate/agee
Soil carbon and nitrogen stocks and fractions in a long-term
integrated crop–livestock system under no-tillage in southern Brazil
Joice Mari Assmann a , Ibanor Anghinoni a , Amanda Posselt Martins a,∗ ,
Sérgio Ely Valadão Gigante de Andrade Costa a , Diego Cecagno a ,
Filipe Selau Carlos a , Paulo Cesar de Faccio Carvalho b
a
b
Department of Soil Science, Federal University of Rio Grande do Sul, Bento Gonçalves Avenue 7712, PO Box 15100, Porto Alegre 91 540-000, RS, Brazil
Department of Forage Plants and Agrometeorology, Federal University of Rio Grande do Sul, Porto Alegre 91 540-000, RS, Brazil
a r t i c l e
i n f o
Article history:
Received 19 February 2013
Received in revised form
27 November 2013
Accepted 2 December 2013
Available online 20 December 2013
Keywords:
Black oat + ryegrass
Carbon management indexes
Grazing intensities
a b s t r a c t
Managing grazing stocks in integrated crop–livestock (ICL) systems under no-tillage is a key variable for
reaching equilibrium in soil C and N budgets. Understanding how different plant and animal residues
affect soil C and N stocks in these systems goes beyond soil dynamics since these elements are crucial for
the functioning of the soil–plant–atmosphere system. The objective of this research was to determine
soil C and N fractions, stocks, budgets and the carbon management index as affected by nine years of ICL
with grazing intensities under no-tillage conditions. The experiment established in May 2001 in a Rhodic
Hapludult (Oxisol) of southern Brazil was composed of black oat (Avena sativa) plus ryegrass (Lolium
multiflorum) pasture in winter and soybean (Glycine max) crop in summer. Treatments were regulated by
grazing pressures to maintain forage at 10, 20, 30 and 40 cm high (G10, G20, G30 and G40, respectively).
Non-grazed (NG) treatment was the control. Changes in soil C and N stocks and fractions (particulate
and mineral-associated) were assessed in the ninth year of the experiment. Moderate and light grazing
intensities (G20, G30 and G40) resulted in similar increases in total organic C, particulate organic C,
total N, and particulate organic N compared with NG treatment. Soil C additions ranged from 0.54 to
8.68 Mg ha−1 from NG to the other grazing treatments. The G10 led to a soil N loss of 1.17 Mg ha−1 due
to soil organic matter degradation. The carbon management index (CMI) values, compared with native
forest (NF) as a reference, indicated soil quality loss and degradation under high grazing intensity (G10).
For a positive contribution to the soil system, ICL must be managed with moderate grazing intensities
and adjustment of N additions through N fixation or fertilization.
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
Integrated crop–livestock (ICL) systems have long been used
for food production with positive results since the Neolithic era,
when plant and animal domestication began (Carvalho et al., 2007).
According to Keulen and Schiere (2004), ICL reached 2.5 billion
hectares around the world, being responsible for more than 50% and
90% of cattle meat and milk production, respectively. Thus, these
systems became promising alternatives for sustainable agriculture,
with positive animal–plant interactions, allowing environmental
benefits and economic viability (Allen et al., 2007; Balbinot Junior
et al., 2009).
Benefits from ICL, if well managed, include yield optimization
reaching soil quality ameliorations along time (Entz et al., 2002).
∗ Corresponding author. Tel.: +55 5133087420; fax: +55 5133086852.
E-mail address: amandaposselt@gmail.com (A.P. Martins).
0167-8809/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.agee.2013.12.003
Grazing not only affects nutrient dynamics but also water fluxes
and microbial diversity and population (Descheemaeker et al.,
2010; Chávez et al., 2011). Thus, in ICL systems, grazing modifies
soil–plant–atmosphere feedbacks due to new processes and the
rate in which they occur. An example of such changes is the increase
in nutrient cycling (Carvalho et al., 2006) as a result of higher shoot
and root biomass production due to defoliation, resprouting and
tillering cycles.
Production systems that use grass species under no-tillage conditions are capable of maintaining or even increasing soil organic
matter (SOM) content in the superficial layers (Diekow et al., 2005;
Loss et al., 2009; Batlle-Bayer et al., 2010). The higher pasture root
production under grazing conditions (D’andréa et al., 2004) enables
higher soil C accumulation, becoming, thus, an important C sink
(Nicoloso et al., 2008). Pasture management according to stocking
rates results in different residue (plant and animal) additions and,
thus, nutrient recycling, affecting soil C and N (Nicoloso et al., 2006;
Lopes et al., 2008; Carvalho et al., 2010).
J.M. Assmann et al. / Agriculture, Ecosystems and Environment 190 (2014) 52–59
Decreases in soil C and N stocks in pastures under long-term
high grazing intensity have been observed by many researchers
(Cui et al., 2005; Han et al., 2008; Steffens et al., 2008). Ingram
et al. (2008) noted that high grazing intensity under mixed pasture results in soil C losses of approximately 30% in the 0 to 60 cm
layer. They explained such behavior as a consequence of changes in
plant morphological characteristics and biomass production and in
surface soil organic matter accumulation, becoming more vulnerable to C losses. He et al. (2011) observed decreases in soil C and N
stocks at 0 to 10 and 10 to 30 cm layers with an increase in sheep
grazing intensity under temperate climate in northern China; however, adequate grazing management results in soil C and N stock
increases.
Nicoloso et al. (2008) verified that Italian ryegrass (Lolium
multiflorum) + black oat (Avena sativa) mixed pastures without fertilization and a 28-day grazing interval during winter with corn
cropping during summer contribute to increases in residue production and, thus, in SOM accumulation in a Rhodic Paleudult soil
in Rio Grande do Sul state, Brazil. On the other hand, after four years
of ICL under high grazing frequency (14-day interval) and soybean
(Glycine max) cropping during summer, soil C stocks decreased due
to low residue addition.
Long-term ICL under no-tillage with different grazing intensities
can affect nutrient dynamics, especially C and N, since grazing itself
promotes modifications in biotic and abiotic conditions (Shariff
et al., 1994). Animal residues, due to their labilities, influence soil
nutrient concentration and microbial community (Mcnaughton,
1992; Chávez et al., 2011). Thus, the particulate soil organic matter
fraction, regarded as the most suitable fraction for evaluating soil
management impacts on soil quality, and, an important attribute
related to soil C and N budgets (Conceição et al., 2005), must be
approached. According to Franzluebbers and Stuedemann (2008),
after three years of ICL under no-tillage conditions, C and N stocks
and fractions were not affected by cattle grazing, resulting in total
N stocks of approximately 3.88 and 4.14 Mg ha−1 for grazed and
non-grazed areas, respectively, during winter.
The carbon management index (CMI) is a discerning tool for
evaluating the impact of long-term management systems on the
soil–plant–atmosphere equilibrium (Diekow et al., 2005). Evaluating a long-term ICL system, Souza et al. (2009) highlighted the
importance of this tool on soil management quality by observing
much lower value (65) for high grazing intensities in ICL in relation
to no grazing (reference), indicating soil organic matter degradation.
Therefore, under ICL conditions, different soil C and N stocks,
fractions, budgets and CMI values are expected, especially for the
particulate fraction, which is more susceptible to soil management.
The objective of this research was to determine soil C and N fractions, stocks, budgets and the CMI as affected by nine years of ICL
with grazing intensities under no-tillage conditions.
2. Material and methods
2.1. Experimental site
The experimental area of approximately 22 ha was split into
experimental plots ranging from 1.0 to 2.5 ha for treatments of
different pasture sward heights of 10, 20, 30, and 40 cm (G10, G20,
G30 and G40, respectively) and no-grazing (NG), representing
grazing intensities, distributed in a randomized block design
with three replicates. The grazing heights were controlled every
14 days by the sward stick method (Bircham, 1981) to control
steer grazing. Continuous grazing was used and grazing cycles
began when pasture reached 1500 kg ha−1 of dry matter (DM)
production. Usually, the grazing cycles were from mid-July to
mid-November. Steers of approximately 12 months of age were
53
used. After grazing, the pasture was desiccated with glyphosate
and soybean was sown and harvested in April–May of each year.
The experiment was established in May 2001 at Espinilho
Farm (Agropecuária Cerro Coroado), located in São Miguel das
Missões county in the Planalto Médio region of Rio Grande do
Sul state (Brazil) (29◦ 03 10 S latitude and 53◦ 50 44 W longitude).
The soil is a clayey Oxisol (Rhodic Hapludox—Soil Survey Staff,
1999). In the 0–20 cm layer, the amounts of clay (<0.002 mm), silt
(between 0.002 and 0.02 mm) and sand (>0.02 mm) were 540, 270,
and 190 g kg−1 , respectively. The amounts of dithionite-citratebicarbonate and ammonium oxalate-soluble iron were 110 and
5 g kg−1 , respectively (Silva Neto et al., 2008). According to these
authors, kaolinite and hematite were the predominant minerals
in the clay and iron oxide fractions, respectively. The climate is
subtropical with a warm humid summer (Cfa), according to the
Köeppen classification (Kottek et al., 2006).
Before the experiment, the area was cultivated under no-tillage
for seven years with black oat during the winter and soybean during the summer. Cattle grazing in the area began in the autumn
of 2000 with a black oat + Italian ryegrass mixed pasture followed
by soybean cultivation. In autumn 2001, after soybean harvest, the
experiment was established by seeding black oat + Italian ryegrass.
After soybean harvest, the soil was sampled for physical and chemical characterization (Table 1). After grazing cycle, in the autumn of
2001, superficial broadcast liming was applied in the whole area at a
rate of 4.5 Mg ha−1 with a total neutralization relative power (TNRP)
of 62%, which is recommended to elevate the soil pH in water to
5.5 in the 0- to 10-cm layer, according to CQFS RS/SC (2004) for
long-term no-tillage conditions.
2.2. Residue addition
To determine the amount of residues added to the soil in each
grazing system, shoot material was sampled after each ICL cycle
(soybean and pasture residual material), and shoot dry matter production was then calculated for the 10-year trial period. Pasture
was sampled at the end of each grazing cycle before desiccation
using an iron frame with an area of 0.25 cm2 . Root dry matter production was determined by Conte et al. (2007) and Souza et al.
(2008) in the 0 to 10 cm soil layer using an auger with a diameter of
6.5 cm (2007 and 2006). The samples were dispersed in water and
passed through a 1-mm sieve mesh for root-to-soil separation.
Manure dry matter production for each treatment was sampled
in two-year periods at the end of August and October in 2009 and
2010. Ten manure pats were randomly sampled per parcel, and
manure dry matter production was obtained using data gathered
by Silva (2012), which monitored (GPS) manure distribution and
accumulation during the grazing cycle.
Soybean shoot dry matter was sampled in 2009, 2010, and 2011
when plants achieved the full pod reproductive stage (R4). Soybean
plants were sampled at 10 points per meter (linear) in each parcel.
During flowering (R2), roots were evaluated to a 20-cm depth. Soil
monoliths (0.2 × 0.2 × 0.2 m) were sampled in soybean rows and
roots were washed and dried at 55 ± 5 ◦ C until reaching constant
weight. The same procedure was used for all dry matter estimations.
After drying, C additions via plant residues were calculated as a
function of shoot dry matter added to the soil (pasture + soybean),
considering an average C concentration of approximately 45%
(Schlesinger, 1991) in soybean grains, soybean shoots, pasture
shoots and manure. The average N content for pasture residue,
soybean residue, pasture roots, soybean roots and soybean grain
contribution were 19.3, 43.3, 10.0, 19.7, and 55.9 g kg−1 , respectively. For manure + urine N, the average manure N content was
24.7 g kg−1 . Urine N was a result of subtracting manure N and animal tissue N from the N intake (animal consumption was measured
54
J.M. Assmann et al. / Agriculture, Ecosystems and Environment 190 (2014) 52–59
Table 1
Soil chemical attributes before integrated crop–livestock system establishment in 2001 in a Brazilian Oxisol (Latosol).
Layer (cm)
pH (H2 O)
OM(1)
(g kg−1 )
Ca(2)
(cmolc dm−3 )
Mg(2)
(cmolc dm−3 )
Al(2)
(cmolc dm−3 )
H + Al
(cmolc dm−3 )
P(3)
(mg kg−1 )
K(3)
(mg kg−1 )
V(4) (%)
m(5)
0–5
5–10
10–15
15–20
4.9
4.6
4.6
4.6
42.2
34.8
25.5
25.5
6.2
4.8
4.1
4.0
1.3
1.8
2.2
1.1
0.3
0.6
0.7
0.1
8.7
9.7
9.7
10.1
13.4
9.8
5.2
3.7
240
119
88
55
48
41
40
34
4
9
11
17
(1)
(2)
(3)
(4)
(5)
Soil organic matter.
Exchangeable (KCl 1 mol L−1 ) Ca, Mg and Al.
Available P and K (Mehlich-1).
Base saturation.
Al saturation.
with grazing exclusion cages). All N contents were obtained by
Kjeldahl method.
2.3. Soil sampling and total C and N stocks
Soil was shovel sampled in May of 2010, nine years after the
experiment was established. Soil C and N contents were analyzed
in eight soil layers: 0 to 2.5; 2.5 to 5; 5 to 7.5; 7.5 to 10; 10 to 15; 15
to 20; 20 to 30; and 30 to 40 cm. The soil samples resulted in eight
sub-samples per experimental plot in all field replicates. Additionally, in May of 2010, a native forest (NF) area near the trial was
sampled for comparison. Soil samples were conditioned in plastic
bags and brought to the Federal University of Rio Grande do Sul
Soil Fertility Laboratory, air dried and sieved in a 2 mm mesh for
analysis.
For stock calculations, soil bulk density was estimated using
volumetric rings with 40 and 160 cm3 . Soil density values were
1.21 and 1.36 Mg m−3 for the 0- to 2.5- and 2.5- to 5.0-cm layers,
respectively, and 1.35 Mg m−3 for the remaining layers.
2.4. Carbon and nitrogen stocks, physical fractionation and
carbon management index
Soil organic matter physical fractionation was performed
according to Cambardella and Elliot (1992), where 20 g of soil was
weighed and put into 180 mL snap-caps, and 80 mL of sodium hexametaphosphate (5 g L−1 ) was added. Samples were horizontally
agitated for 16 h. The soil suspension was then passed through
a 53-␮m mesh with the aid of water. The soil that remained in
the sieve was dried to constant weight at 50 ◦ C and milled with
an agate stone, and the particulate organic carbon content (POMC) analyzed. The mineral-associated carbon (MAC) resulted from
the difference between total organic carbon (TOC) and particulate organic carbon (POM-C). A TruSpec-CHN element analyzer was
used for both the soil total and particulate N and N concentration
determinations.
Total soil organic carbon (TOC) and nitrogen (TN) stocks were
calculated using two procedures: (1) soil equivalent layers and (2)
soil equivalent mass. POM-C and POM-N stocks and MAC were
calculated using only the second procedure. The equivalent layer
method takes into consideration soil density and layer width (Bayer
et al., 2000); the equivalent mass method considers the relation
between the soil mass of each treatment and the one with the
higher soil mass, which is taken as a reference (Ellert and Bettany,
1995).
The carbon management index (CMI) and its components were
calculated according to Blair et al. (1995), with adaptations by
Diekow et al. (2005). The CMI considers POM-C as the labile fraction
and the MAC as the non-labile fraction. The CMI and its components,
carbon stock index (CSI) and carbon lability index (CLI) were calculated for the 0- to 20- and 20- to 40-cm layers, considering two
scenarios, one with no grazing treatment as reference and the other
with native forest soil as a reference (CMI = 100%),
CMI = CSI × CLI × 100, in which,
CSI = treatment TOC stock/reference TOC stock,
CLI = treatment CL/reference CL.
Carbon lability (CL) was calculated for the 0- to 20- and 20- to 40cm layers, being the ratio between the labile and non-labile carbon
fractions, according to the following equation:
CL = labile C/non-labile C, in which:
Labile C = particulate organic matter carbon stock;
Non labile C = mineral-associated carbon stock.
2.5. Statistical analysis
For the analysis of variance (ANOVA) of the soil variables, the
following model was used:
(a) Grazing effects
Yij = + Bi + Gj + error a(ij);
where = overall experimental average; B = blocks (i = 1,2,3);
G = grazing intensities (1,2,3,4,5,6); and error (a) = experimental
error.
(b) Grazing and depth effects
Yijk = + Bi + Gj + error a(ij) + Dk + error b(i, k)
+ GD(jk) + error c(i, j, k)
where = overall experimental average; B = blocks (i = 1,2,3);
G = grazing
intensities
(j = 1,2,3,4,5,6);
D = soil
layers
(k = 1,2,3,4,5,6) and a, b, and c = experimental errors.
When ANOVA was significant (p < 0.05), a Tukey test (p < 0.05)
or t test was applied to separate means.
3. Results and discussion
3.1. Carbon and nitrogen additions
Grazing intensities resulted in different levels of residue production (root and shoot) and, as a consequence, influenced soil C
and N addition (Table 2). Soybean contribution to soil C and N along
time was stable, with average C and N values of 1.90 Mg ha−1 year−1
and 103.7 kg ha−1 year−1 , respectively. In contrast, grazing intensities affected the pasture contribution to soil C and N. The highest
grazing intensity (G10), on average, resulted in 30% less C addition (pasture roots, shoots and manure) compared with the other
J.M. Assmann et al. / Agriculture, Ecosystems and Environment 190 (2014) 52–59
55
Table 2
Soil carbon and nitrogen addition rates in a Rhodic Hapludox with integrated crop–livestock system under no-tillage with grazing intensities.
Treatment(1)
G10
G20
G30
G40
NG
Plant and animal residue
Residue outputs
Pasture residue(2)
(Mg ha−1 year−1 )
Pasture root(3)
(Mg ha−1 year−1 )
Urine + manure(4)
(Mg ha−1 year−1 )
Total
(Mg ha−1 year−1 )
Soybean shoot(5)
(Mg ha−1 year−1 )
Soybean root(5)
(Mg ha−1 year−1 )
Total
(Mg ha−1 year−1 )
Soybean yield(2)
(Mg ha−1 year−1 )
1.40
2.98
4.74
5.80
5.50
1.40
1.30
1.20
1.00
0.70
1.22
0.81
0.61
0.46
...
4.02
5.09
6.54
7.26
6.20
5.13
5.06
5.56
5.04
5.37
1.72
1.91
1.70
1.69
2.22
6.85
6.97
7.26
6.73
7.59
2.75
2.78
2.73
3.02
2.97
Carbon addition (Mg ha−1 year−1 )
G10
G20
G30
G40
NG
0.63
1.34
2.13
2.61
2.48
0.63
0.59
0.54
0.45
0.32
0.55
0.36
0.27
0.21
1.81
2.29
2.94
3.27
2.79
2.31
2.28
2.50
2.27
2.42
0.77
0.86
0.77
0.76
1.00
3.08
3.14
3.27
3.03
3.42
Nitrogen addition (kg ha−1 year−1 )
G10
G20
G30
G40
NG
27
58
91
112
106
14
13
12
10
7
72
57
47
37
...
113
128
151
159
113
222
219
241
218
233
34
38
34
33
44
256
257
274
252
276
Carbon outputs (Mg ha−1 year−1 )
C annual addition (Mg ha−1 year−1 )
1.24
1.25
1.23
1.36
1.34
3.65
4.18
4.98
4.94
4.87
Nitrogen outputs (kg ha−1 year−1 )
N annual additions (kg ha−1 year−1 )
154
155
153
169
166
216
229
272
242
223
(1)
G10, G20, G30 and G40 represent the 10, 20, 30 and 40 cm sward pasture heights.
10 years average.
(3)
Data from Conte et al. (2007) and Souza et al. (2008).
(4)
2009/2010 average.
(5)
2009, 2010 and 2011 average.
NG = No-grazing.
(2)
grazing intensities. Grazing decreased the annual carbon addition
by 17% and 33% for the G20 and G10, respectively, in relation to
the NG treatment, and for G30 and G40 there was no change. As
shown in Table 2, the major source of C was the forage residues
at the end of the grazing cycle. These results are consistent with
those found by Nicoloso et al. (2008), who observed smaller C additions (54% and 59%, respectively) in areas grazed every 14 and
28 days compared with a non-grazed area with soybean summer
cropping.
Soil N additions were also affected by grazing management, but
with less intensity since approximately 90% of N returns to the soil
as manure and urine (Haynes and Williams, 1993). According to
Oenema et al. (2005), 40% to 50% of urine N returns to the soil and is
used by pasture, and the remainder is lost through NH3 volatilization, denitrification, leaching, and surface runoff. By considering
that 60% of manure and urine are lost (Oenema et al., 2005), the
annual increment of N would range from 172 to 223 kg ha−1 year−1 ,
with soybeans residues being the major N source. Yet, two aspects
must be pointed out when approaching C and N dynamics in grazing systems: defoliation frequency and grazing method (rotational
or continuous). In continuous grazing systems with low sward
heights, represented by the G10 treatment in this trial, the high
defoliation rate limits adequate photosynthetic capacity (Lemaire
et al., 2009). Conversely, moderate grazing intensity (represented
by G20 and G30) is feasible to attain equilibrium between herbage
harvesting and development, contributing for total residue accumulation.
Although questioning may arise regarding the method used for
estimation of C input in the soil, the focus of this research remains in
how grazing may affect soil C and N stocks. Therefore, the extension
of C and N uncoupling, resulted from grazing, will not be detailed,
especially when considering ICL as a single complex ecosystem
through its eco-enzymatic stoichiometry, which is crucial for comprehending the responses of such systems to the environment
(Parsons et al., 2011). However, the importance of continuous flow
of leaf senescence and production of leaf litter will be highlighted
when needed even though such data was not used for this research.
3.2. Total and physical fractions of carbon and nitrogen stocks
After nine years of ICL adoption, the soil TOC and TN in both,
0 to 20 and 0 to 40-cm layer (1A and B and 2A and B) were lower
(p < 0.05) for the highest grazing intensity (G10) compared with the
remaining grazing treatments, which did not differ among themselves. The G10, however, led to a small increase in TOC, from
51 Mg C ha−1 in 2001 to 51.5 Mg C ha−1 while TN decreased from
2010. Soil TOC in native forest (NF) was, however, higher only for
0 to 40 cm layer (Fig. 1B).
On average, the TOC increase in the G20, G30, and G40 and NG
treatments in the last sampling (May 2010) was approximately
8.7 Mg ha−1 , representing an annual C addition from May 2001 of
0.96 Mg ha−1 year−1 .The most intensive grazing G10 resulted in no
increase (Table 2) as compared with that previously observed by
Souza et al. (2009) after three (2004) and six (2007) years of ICL.
Except for the G10, the annual C additions for the remaining treatments in the 0 to 20 cm layer also resulted in similar stock values
between grazing treatments and native forest (reference area), of
approximately 59 Mg ha−1 (Fig. 1A), and lower values in the 0 to
40 cm layer (Fig. 1B). According to Diekow et al. (2005), there is
a limit to soil organic matter accumulation due to biogeochemical factors. Such rate is higher than the value of 0.33 Mg ha year−1
previously found by Souza et al. (2009), six years after ICL adoption.
Results of the present study are somehow different to the
results from Carvalho (2010) in the 0 to 30 cm after four
years of ICL in a savannah biome with C stocks being higher
(62.8 Mg ha−1 ) with grazing than NG successive cropping area
(56.4 Mg ha−1 ). Piva (2012) also reported, after five years, higher
C stocks in crop–livestock–forest integration compared with nograzing tillage cropping systems. Increase of C stocks will depend
on a combination of soil–plant–animal–atmosphere conditions,
such as climate (i.e., rainfall distribution), soil type and residue
(plant + animal) amount and quality.
The POM-C stocks in the 0 to 20 cm layer (Fig. 1A) ranged from
4.1 Mg ha−1 , in the high grazing intensity (G10), to 9.0 Mg ha−1 , in
the NF (reference area). Lower POM-C stocks under G10 reflected
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J.M. Assmann et al. / Agriculture, Ecosystems and Environment 190 (2014) 52–59
120
Carbon stock, Mg ha-1
100
0 - 20 cm
POM-C
MAC
0 - 40 cm
A
A
B
B
B
B
B
b
ab
ab
ab
ab
c
b
b
b
b
G20
20
G30
30
G40
40
C
80
A
60
A
A
A
A
*
B
a
40
b
a
a
a
a
ab
c
b
b
b
ab
a
NG
NF
20
0
G10
10 G20
20 G30
30 G40
40
G10
10
2001
NG
a
NF
Treatments
Fig. 1. Total carbon, particulate organic matter carbon (POM-C) and mineral associated carbon (MAC) in the 0 to 20 cm (A) and 0 to 40 cm (B) layer in a Rhodic Hapludox
under integrated crop–livestock system in no-tillage with different grazing intensities. G10, G20, G30 and G40 represent the 10, 20, 30 and 40 cm sward pasture heights.
NG = No-grazing. NF = Native forest. Columns whit the same letter do not differ by Tukey test (p < 0.05).
4.5 Mg ha−1 year−1 in an ICL system under no-tillage conditions.
Such amounts of continuous dry matter addition are important
to support POM-C, as well as MAC. Greater POM-C guarantees a
positive C flux to the soil, there by maintaining or increasing soil
biological activity and quality (Salton et al., 2005). Conversely, low
labile C additions will result in organic matter oxidation, reducing
soil C stocks, triggering soil degradation and quality loss.
Carbon stocks in the 0 to 40 cm soil layer (Fig. 1B) followed the
same general pattern as for the 0 to 20 cm layer, with greater POMC in NF, followed by no (NG), low, and moderate grazing intensities
(G20, G30, G40), and finally high grazing intensity (G10). The TOC
stocks in this layer (110.6 Mg ha−1 ) in the native forest followed the
same patter as POM-C. The G10 was 25% lower than native forest
and, on average, 15% lower than the other grazing intensity treatments and the non-grazed area. In addition to lower grass residue
inputs, low accumulation of TOC can be also attributed to higher C
lower residue production, not sufficient for sustainable management. According to Assmann et al. (2003) and Cassol (2003), the
threshold value for pasture residue production that maintains longterm sustainable ICL systems ranges from 2 to 3 Mg ha1 . Therefore,
both the total and particulate C stocks (Fig. 1A) indicated that G10
did not represent long-term sustainable management. Such a pattern is highlighted by comparing the contribution of the C labile
fraction (POM-C) under NF (15%) and NG (11%) with that from the
high grazing (G10) intensity area (8%).
Assuming G20 has a minimum threshold annual addition of
4.18 Mg ha−1 year−1 of C (Table 2), total dry matter addition of about
9.0 Mg ha−1 year−1 (shoot, root and manure) would be necessary
to maintain C stocks with grazing compared with ungrazed condition. Bayer et al. (2006) highlighted the importance of adding
approximately 3.9 Mg ha−1 year−1 of C to the soil under no-tillage
conditions. Nicoloso et al. (2008) found values of approximately
Nitrogen stocks, Mg ha-1
10
8
0 - 20 cm
POM-N
MAN
A
0 - 40 cm
B
A
A
A
A
A
b
a
a
a
a
a
b
ab
ab
ab
a
a
G10
G20
NG
NF
6
4
2
0
AB
A
B
B
B
b
a
a
a
a
a
c
b
ab
ab
ab
a
G20 G30 G40
NG
NF
*
B
C
G10
2001
G30 G40
Treatments
Fig. 2. Total, particulate organic matter (POM-N) and mineral associated (MAN) nitrogen stocks in the 0 to 20 cm (A) and 0 to 40 cm (B) layer in a Rhodic Hapludox under
integrated crop–livestock system under no-tillage with different grazing intensities. G10, G20, G30 and G40 represent the 10, 20, 30 and 40 cm sward pasture heights.
NG = No-grazing. NF = Native forest. Columns with the same letter do not differ by Tukey test (p < 0.05).
J.M. Assmann et al. / Agriculture, Ecosystems and Environment 190 (2014) 52–59
losses by microbial respiration, as observed by Souza et al. (2010).
The highest TOC stock under NF was due to higher C values at depth.
Since this area was never tilled and had trees and shrubs with high
rooting capacity (depth and mass), higher C additions in deeper soil
layers are expected.
Total nitrogen (TN) in the 0 to 20 cm soil layer was not different than in 2001 except compared with intensive grazing of
G10 (Fig. 2A), that was smaller. The increments compared to
other grazing treatments were small and ranged from 0.21 to
0.56 Mg ha−1 , being related to small N additions (45 kg ha−1 year−1 )
along nine years. In fact, there was a decrease of 0.90 Mg ha−1
(100 kg ha−1 year−1 ) in TN in G10, which can be attributed to the
low grass residues (Table 2) and N losses, as NH3 volatilization,
desnitrification, leaching and surface runoff, as pointed out by
Haynes and Williams (1993). After eight years of ICL adoption, Silva
et al. (2011) also observed similar TN values between ICL and NF.
Nitrogen stocks in the 0 to 40 cm layer (Fig. 2B) followed the
same pattern as the 0 to 20 cm layer, with higher TN, POM-N, and
MAN values for NF as for moderate to light grazing intensities (G20,
G30, and G40) and NG, and the lowest values for high grazing intensity (G10).
3.3. Carbon and nitrogen distribution in soil profile
Carbon and N distribution in the soil profile (Figs. 3 and 4)
were greater in the most superficial layer (0 to 2.5 cm) for NF
(reference), TOC (Fig. 3A) and TN (Fig. 4A) with values of 47 and
4.3 g kg−1 , respectively. The main difference between treatments
was observed in the top layer, with lower values for G10, which
also resulted in lower C and N stocks (1A and 2A). The NG and G20
had similar intermediate values, and the highest values were from
G30 and G40, with TOC and TN contents of 39 and 36 g kg−1 and
3.6 and 3.3 g kg−1 , respectively. In the deeper layers, only the G10
resulted in lower C contents.
Soil organic matter increases in areas under ICL with soybean/corn summer rotation (Sulc and Tracy, 2007). Sartor (2012)
observed greater SOM in the 0 to 10 cm layer under ICL compared
with NG after 5 years of system adoption. ICL affects TOC accumulation over time due to continuous plant growth and soil coverage,
crop rotation, and increases in shoot production as a result of grazing and higher nutrient cycling (Tracy and Zhang, 2008).
By comparing the most contrasting treatments (Figs. 3 and 4),
MAC, MAN, POM-C, and POM-N were lower in G10 (p < 0.05) compared with NG, especially in the 0 to 10 cm layer. These results
indicate soil quality loss, with soil C and N losses to the atmosphere,
intensifying the greenhouse effect. On the other hand, the light and
moderate grazing intensities (G40, G30, and G20) did not differ
(p < 0.05) from NG, showing that well managed pastures under ICL
can promote soil C and N accumulation. Compared with the reference NF, soil C and N contents were usually lower under ICL, even
in the superficial layer (0 to 2.5 cm). Such conditions give reason
to believe that ICL under a no-tillage system can still evolve in a
positive manner.
3.4. Carbon management index
The carbon management index (CMI) allows the evaluation of
soil quality gain or loss processes since higher values mean higher
soil quality, and vice-versa. In one scenario, we used CMI of the
no grazed area as a reference area. In this case, light and moderate
grazing intensities (G20, G30, and G40) were able to maintain CMI
values similar to NG and greater than G10 in the 0 to 20 cm soil
layer (Table 3). The obtained value (57%) is even smaller than the
one observed (65%) by Souza et al. (2009), three years before, in the
same trial. According to the authors there is a cumulative effect of
lower POM-C (Fig. 1A) in such conditions (high grazing intensity),
57
Table 3
Carbon stock index (CSI), lability (L), lability index (LI) and carbon management
index (CMI) in soil layers from a Rhodic Hapludox under soybean–cattle integration
system in no-tillage with different grazing intensities using non-grazing area (NG)
as reference.
Treatment(1)
CSI
Fraction
L
CLI
CMI
%
0.08 B
0.12 A
0.12 A
0.12 A
0.13 A
0.68 B
0.92 A
0.95 A
0.99 A
–
57 B
89 A
93 A
96 A
100 A
0.07 A
0.07 A
0.08 A
0.08 A
0.09 A
0.77 A
0.75 A
0.88 A
0.95 A
–
60 C
71 BC
80 AB
88 AB
100 A
0–20 cm layer
G10
G20
G30
G40
NG(2)
G10
G20
G30
G40
NG(2)
0.84 B
0.98 A
0.98 A
0.96 A
–
20–40 cm layer
0.78 B
0.95 A
0.91 AB
0.93 AB
–
(1)
G10, G20, G30 and G40 represent the 10, 20, 30 and 40 cm sward pasture heights.
Reference, with CMI = 100.
NG = No-grazing. Values followed by the same letter in the columns do not differ by
Tukey test (p < 0.05).
(2)
with lower C budgets due to lower residue additions, as well as
greater C exportation (meat and soybean) ratio and losses from
microbial respiration (Souza et al., 2010). In the 20 to 40 cm layer,
CMI increased as grazing intensity decreased with values for G10,
G20, G30 and G40 of 60%, 71%, 80% and 88%, respectively (Table 3).
The low CMI values in the 20 to 40 cm layer resulted from a longterm no-tillage condition that tends to preferentially accumulate C
in the superficial soil layers (Fig. 3).
In the second scenario, to verify how pasture management
relates to natural edaphoclimatic conditions, the CMI values were
compared with NF (Table 4). No grazing treatment reached CMI values close to NF. Furthermore, high grazing intensity (G10) resulted
in very low CMI values (42% and 54% for the 0 to 20 and 20 to
40 cm, respectively). The greater CMI values in the 20 to 40 cm
layer in relation to G10 can be attributed to management dilution
effects on soil C in the most superficial layer (Fig. 3). The CMI values
were closely related to pasture residue production, since POM-C
contents were greater for the reference area in the soil profile. The
evolution of soil quality under ICL is time-dependent, such that
Table 4
Carbon stock index (CSI), lability (L), lability index (LI) and carbon management
index (CMI), in soil layers from a Rhodic Hapludox under soybean-cattle integration system under no-tillage with different grazing intensities using native forest as
reference.
Treatment(1)
CSI
Fraction
L
CLI
CMI
%
0.47 B
0.64 AB
0.67 AB
0.70 A
0.72 A
–
42 C
65 B
68 B
69 B
73 B
100 A
0.89 A
0.87 A
1.02 A
1.10 A
1.19 A
–
54 D
64 CD
72 BCD
79 ABC
90 AB
100 A
0–20 cm layer
G10
G20
G30
G40
NG
NF(2)
G10
G20
G30
G40
NG
NF(2)
(1)
0.87 B
0.09 C
1.01 A
0.12 BC
1.02 A
0.12 B
1.00 A
0.13 B
1.02 A
0.13 B
–
0.18 A
20–40 cm layer
0.60 A
0.07 A
0.74 A
0.07 A
0.71 A
0.08 A
0.72 A
0.09 A
0.78 A
0.09 A
–
0.08 A
G10, G20, G30 and G40 represent the 10, 20, 30 and 40 cm sward pasture heights.
Reference, with CMI = 100.
NG = No-grazing. NF = native forest. Values followed by the same letter in the
columns do not differ by Tukey test (p < 0.05).
(2)
J.M. Assmann et al. / Agriculture, Ecosystems and Environment 190 (2014) 52–59
0
5
20
30
40
50
60
5
A
Tukey
(p < 0.05)
10
5
10
15
Depth, cm
Depth, cm
10
Particulate organic carbon, g kg-1
Mineral associated organic carbon, g kg-1
Total organic carbon, g kg-1
20
25
10
15
20
25
30
35
0
40
B
2
4
6
8
10
12
20
25
16
Tukey
(p < 0.05)
10
15
14
C
5
Tukey
(p < 0.05)
Depth, cm
58
15
20
25
30
30
30
35
35
35
40
40
40
G-10 cm
G-20 cm
G-30 cm
G-40 cm
NG
NF
Fig. 3. Soil organic carbon contents in soil profile from a Rhodic Hapludox under integrated crop–livestock system under no-tillage with different grazing intensities: total
organic carbon (A), mineral associated organic carbon (B) and particulate organic carbon (C). Horizontal bars compare grazing intensities for each layer by Tukey test (p < 0.05).
G10, G20, G30 and G40 represents the 10, 20, 30 and 40 cm sward pasture heights. NG = No-grazing. NF = Native forest.
Total nitrogen, g kg-1
Depth, cm
10
2
3
4
5
0
A
5
Tukey
(p < 0.05)
15
20
25
10
Depth, cm
5
1
1
2
3
4
Particulate organic matter nitrogen, g kg-1
0,0
0.0
5
B
15
20
25
0,2
0.2
0,4
0.4
0,6
0.6
0,8
0.8
1,0
1.0
C
5
Tukey
(p < 0.05)
Tukey
(p < 0.05)
10
Depth, cm
0
Mineral associated nitrogen, g kg-1
15
20
25
30
30
30
35
35
35
40
40
40
G-10
G-20
G-30
G-40
NG
NF
Fig. 4. Soil organic nitrogen contents in soil profile from a Rhodic Hapludox under integrated crop–livestock system under no-tillage with different grazing intensities: total
nitrogen (A), mineral associated nitrogen (B) and particulate organic matter nitrogen (C). Horizontal bars compare grazing intensities for each layer by Tukey test (p < 0.05).
G10, G20, G30 and G40 represents the 10, 20, 30 and 40 cm sward pasture heights. NG = No-grazing. NF = Native forest.
reaching, equilibrium with the NT in nine years is possible. Yet, as
highlighted before, ICL adoption with moderate grazing intensities
seem to be a promising food production system, with continuous
improvements in the soil–plant–animal–atmosphere continuum,
evolving to higher levels of organization, with positive feedbacks
and source–sink relations.
4. Conclusions
Moderate grazing intensities, with sward pasture heights
between 20 and 40 cm, and a long period of a crop–livestock
integration under no-tillage promoted total, particulate, and
mineral-associated organic carbon and nitrogen stocks similar to
non-grazed areas (no-tillage). Compared, with native forest, carbon management index (CMI) indicates that cropping decreased
soil quality, especially with high grazing intensity. Moderate grazing intensities led to a soil quality similar to that of non-grazed
areas.
References
Allen, V.G., Baker, M.T., Segarra, E., Brown, C.P., 2007. Integrated irrigated
crop–livestock systems in dry climates. Agron. J. 99, 346–360.
Assmann, T.S., Ronzelli, P.J., Moraes, A., Assmann, A.L., Koehler, H.S., Sandini, I., 2003.
Rendimento de milho em área de integração lavoura-pecuária sob o sistema
plantio direto, em presença e ausência de trevo branco, pastejo e nitrogênio.
Rev. Bras. Cienc. Solo 27, 675–683.
Balbinot Junior, A.A., Moraes, A., Veiga, M., Pelissari, A., Dieckow, J., 2009. Integração
lavoura-pecuária: intensificação de uso de áreas agrícolas. Cienc. RuralV 39,
1925–1933.
Batlle-Bayer, L., Batjes, N.H., Bi’ndraban, P.S., 2010. Changes in organic carbon stocks
upon land use conversion in the Brazilian Cerrado: a review. Agric. Ecosyst.
Environ. 137, 47–58.
Bayer, C., Lovato, T., Diekow, J., Zanatta, J.A., Mielniczuk, J., 2006. A method for
estimating coefficients of soil organic matter dynamics based on long-term
experiments. Soil Tillage Res. 91, 217–236.
Bayer, C., Mielniczuk, J., Amado, T.J.C., Martin Neto, L., 2000. Organic matter storage
in a sandy clay loam Acrisol affected by tillage and cropping systems in southern
Brazil. Soil Tillage Res. 54, 101–109.
Bircham, J.S., 1981. Herbage growth and utilization under continuous stocking management. In: Ph.D. Thesis. University of Edinburgh, Edinburgh, Ireland.
Blair, G.J., Lefroy, R.D.B., Lisle, L., 1995. Soil carbon fractions based on their degree of
oxidation, and the development of a carbon management index for agricultural
systems. Aust. J. Agric. Res. 46, 1459–1466.
Cambardella, C.A., Elliot, E.T., 1992. Particulate soil organic matter changes across a
grassland cultivation sequence. Soil Sci. Soc. Am. J. 56, 777–783.
Carvalho, J.L.N., 2010. Dinâmica do carbono e fluxo de gases do efeito estufa em
sistemas de integração lavoura-pecuária na Amazônia e no Cerrado. In: Ph.D.
Thesis. University of São Paulo, Piracicaba, Brazil.
Carvalho, P.C.F., Moraes, A., Anghinoni, I., Lang, C.R., Silva, J.L.S., Sulc, R.M., Tracy, B.F.,
2006. Manejo da integração lavoura-pecuária em sistema de plantio direto na
região de clima subtropical. In: Encontro Nacional de Plantio Direto na Palha,
Uberaba, pp. 77–184, Resumos.
Carvalho, P.C.F., Silva, J.L.S., Moraes, A., Fontanelli, R.S., Macari, S., Bremm, C.,
Trindade, J., 2007. Manejo de animais em pastejo em sistemas de integração
lavoura pecuária. In: International Symposium on International Crop–livestock
Systems, Curitiba, CD-ROM.
J.M. Assmann et al. / Agriculture, Ecosystems and Environment 190 (2014) 52–59
Carvalho, P.C.F., Anghinoni, I., Moraes, A., Souza, E.D., Sulc, R.M., Lang, C.R., Flores, J.P.C., Lopes, M.L.T., Silva, J.L.S., Conte, O., Wesp, C.L., Levien, R., Fontaneli,
R.S., Bayer, C., 2010. Managing grazing animals to achieve nutrient cycling and
soil improvement in no-till integrated systems. Nutr. Cycling Agroecosyst. 88,
259–273.
Cassol, L.C., 2003. Relação solo-planta-animal num sistema de integração lavourapecuária em semeadura direta com calcário na superfície. In: Ph.D. Thesis.
Federal University of Rio Grande do Sul, Porto Alegre, Brazil.
Chávez, L.F., Escobar, L.F., Anghinoni, I., Carvalho, P.C.F., Meurer, E.J., 2011.
Diversidade metabólica e atividade microbiana em sistema de integração
lavoura-pecuária em plantio direto sob intensidades de cultivo. Pesqui.
Agropecu. Bras. 46, 1254–1261.
Comissão de Química e Fertilidade do Solo—RS/SC (CQFS RS/SC), 2004. Manual de
adubação e de calagem para os estados do Rio Grande do Sul e Santa Catarina. In:
Liming and Fertilizing Manual for Rio Grande do Sul and Santa Catarina States,
10th ed. Sociedade Brasileira de Ciência do Solo—Núcleo Regional Sul, Porto
Alegre.
Conceição, P.C., Amado, T.J.C., Mielniczuk, J., Spagnollo, E., 2005. Qualidade do solo
em sistemas de manejo avaliada pela dinâmica da matéria orgânica e atributos
relacionados. Rev. Bras. Cienc. Solo 29, 777–788.
Conte, O., Levien, R., Trein, C.R., 2007. Demanda de tração em haste sulcadora na
integração lavoura-pecuária com diferentes pressões de pastejo e a sua relação
com o estado de compactação do solo. Eng. Agríc. 27, 222–228.
Cui, X.Y., Wang, Y.F., Niu, H.S., Wu, J., Wang, S.P., Schnug, E., Rogasik, J., Fleckenstein,
J., Tang, Y.H., 2005. Effect of long-term grazing on soil organic carbon content in
semiarid steppes in Inner Mongolia. Ecol. Res. 20, 519–527.
D’andréa, A.F., Silva, M.L.N., Curi, N., Guilherme, L.R.G., 2004. Estoque de carbono e
nitrogênio e formas de nitrogênio mineral em um solo submetido a diferentes
sistemas de manejo. Pesqui. Agropecu. Bras. 39, 179–186.
Descheemaeker, K., Amede, T., Haileslassie, A., 2010. Improving water productivity
in mixed crop–livestock farming systems of sub-Saharan Africa. Agric. Water
Manage. 97, 579–586.
Diekow, J., Mielniczuk, J., Knicker, H., Bayer, C., Dick, D.P., Kögel-Knabner, I., 2005.
Soil C and N stocks as affected by cropping systems and nitrogen fertilization in
a southern Brazil Acrisol managed under no-tillage for 17 years. Soil Tillage Res.
81, 87–95.
Ellert, B.H., Bettany, J.R., 1995. Calculation of organic matter and nutrients stored in
soils under contrasting management regimes. Can. J. Soil Sci. 75, 529–538.
Entz, M.H., Baron, V.S., Carr, P.M., Meyer, D.W., Smith Jr., R.S., Mccaughey, W.P., 2002.
Potential of forages to diversify cropping systems in the northern Great Plains.
Agron. J. 94, 240–250.
Franzluebbers, A.J., Stuedemann, J.A., 2008. Early response of soil organic fractions
to tillage and integrated crop–livestock production. Soil Sci. Soc. Am. J. 72,
613–625.
Han, G.D., Hao, X.Y., Zhao, M.L., Wang, M.J., Ellert, B.H., Willms, W., Wang, M.J., 2008.
Effect of grazing intensity on carbon and nitrogen in soil and vegetation in a
meadow steppe in Inner Mongolia. Agric. Ecosyst. Environ. 125, 21–32.
Haynes, R.J., Williams, P.H., 1993. Nutrient cycling and soil fertility in the grazed
pasture ecosystem. Adv. Agron. 49, 119–199.
He, N.P., Zhang, Y.H., Yu, Q., Chen, Q.S., Pan, Q.M., Zhang, G.M., Han, X.G., 2011. Grazing intensity impacts soil carbon and nitrogen storage of continental steppe.
Ecosphere 2, 1–8.
Ingram, L.J., Schuman, G.E., Buyer, J.S., Vance, G.F., Ganjegunte, G.K., Welker, J.M.,
Derner, J.D., 2008. Grazing impacts on soil carbon and microbial communities
in a mixed-grass ecosystem. Soil Sci. Soc. Am. J. 72, 939–948.
Keulen, H., Schiere, H., 2004. Crop–livestock system: old wine in new bottles? In:
Fisher, T., et al. (Eds.), New Directions for a Diverse Planet. Proceedings of the IV
International Crop Science Congress. Australia.
Kottek, M., Grieser, J., Beck, C., Rudolf, B., Rubel, F., 2006. World map of the
Köppen–Geiger climate classification updated. Meteorol. Z. 15, 259–263.
Lemaire, G., Silva, S.C., Agnusdei, M., Wade, M., Hodgson, J., 2009. Interactions
between leaf lifespan and defoliation frequency in temperate and tropical pastures: a review. Grass Forage Sci. 64, 341–353.
Lopes, M.L.T., Carvalho, P.C.F., Anghinoni, I., Santos, D.T., Kuss, F., Freitas, F.K., Flores,
J.P.C., 2008. Sistema de integração lavoura-pecuária: desempenho e qualidade da
carcaça de novilhos superprecoces terminados em pastagem de aveia e azevém
manejada sob diferentes alturas. Cienc. Rural 38, 1765–1773.
59
Loss, A., Pereira, M.G., Schultz, N., Anjos, L.H.C., Silva, E.M.R., 2009. Carbono e frações
granulométricas da matéria orgânica do solo sob sistemas de produção orgânica.
Cienc. Rural 39, 1067–1072.
Mcnaughton, S.J., 1992. Ecology of a grazing ecosystem: the Serengeti. Ecol. Monogr.
55, 259–295.
Nicoloso, R.S., Lanzanova, M.E., Lovato, T., 2006. Manejo das pastagens de inverno
e potencial produtivo de sistemas de integração lavoura-pecuária no Estado do
Rio Grande do Sul. Cienc. Rural 36, 1799–1805.
Nicoloso, R.S., Lovato, T., Amado, T.J.C., Bayer, C., Lanzanova, M.E., 2008. Balanço de
carbono orgânico no solo sob integração lavoura-pecuária no sul do Brasil. Rev.
Bras. Cienc. Solo 32, 2425–2433.
Oenema, O., Wrage, N., Velthof, G.L., van Groeningen, J.W., Dolfing, J., Kuikman, P.J.,
2005. Trends in global nitrous oxide emissions from animal production systems.
Nutr. Cycling Agroecosyst. 72, 51–65.
Parsons, A., Rowarth, J., Thornley, J., Newton, P., 2011. Primary production of grasslands, herbage accumulation and use impacts of climate change. In: Lemaire, G.,
Hodgson, J., Chabbi, A. (Eds.), Grassland Productivity and Ecosystem Services.
CAB Int., Wallingford, pp. 3–18.
Piva, J.T., 2012. Fluxo de gases de efeito estufa e estoque de carbono do solo em sistemas integrados de produção no sub trópico brasileiro. In: Ph.D. Thesis. Federal
University of Paraná, Curitiba, Brazil.
Salton, J.C., Mielniczuk, J., Bayer, C., Fabricio, A.C., Macedo, M.C.M., Broch, D.L.,
Boeni, M., Conceição, P.C., 2005. Matéria Orgânica do Solo na Interação LavouraPecuária em Mato Grosso do Sul. Embrapa Agropecuária Oeste, Dourados.
Sartor, L.R., 2012. Atributos químicos e biológicos do solo, rendimento e valor nutritivo de grãos de milho em sistema de integração lavoura-pecuária em resposta
ao nitrogênio. In: Ph.D. Thesis. Federal University of Paraná, Curitiba, Brazil.
Schlesinger, W.H., 1991. Biogeochemistry, an Analysis of Global Change. Academic
Press, New York, NY.
Silva, F.D., 2012. Distribuição espacial e temporal de placas de esterco e produtividade da soja em sistema de integração soja-bovinos de corte. In: M.Sc.
Dissertation. Federal University of Rio Grande do Sul, Porto Alegre, Brazil.
Silva Neto, L.F., Inda, A.V., Bayer, C., Dick, D.P., Tonin, A.T., 2008. Óxidos de ferro em
latossolos tropicais e subtropicais brasileiros em plantio direto. Rev. Bras. Cienc.
Solo 32, 1873–1881.
Silva, E.F., Lourente, E.P.R., Marchetti, M.E., Mercante, F.M., Ferreira, A.K.T., Fujii, G.C.,
2011. Frações lábeis e recalcitrantes da matéria orgânica em solos sob integração
lavoura-pecuária. Pesqui. Agropecu. Bras. 46, 1321–1331.
Shariff, A.R., Biondini, M.E., Grygiel, C.E., 1994. Grazing intensity effects on litter
decomposition and soil nitrogen mineralization. J. Range Manage. 47, 444–449.
Soil Survey Staff, 1999. Soil taxonomy: a basic system of soil classification for making
and interpreting soil surveys. In: USDA Natural Resource Conservation Service
Agriculture Handbook No. 436. U.S. Government Printing Office, Washington,
DC.
Souza, E.D., Costa, S.E.V.G.A., Lima, C.V.S., Anghinoni, I., Meurer, E.J., Carvalho,
P.C.F., 2008. Carbono orgânico e fósforo microbiano em sistemas de integração
agricultura-pecuária submetidos a intensidades de pastejo em plantio direto.
Rev. Bras. Cienc. Solo 32, 1273–1282.
Souza, E.D., Costa, S.E.V.G.A., Anghinoni, I., Carvalho, P.C.F., Andrighetti, M.H., Cao,
E.G., 2009. Estoques de carbono orgânico e de nitrogênio no solo em sistema
de integração lavoura-pecuária em plantio direto, submetido a intensidades de
pastejo. Rev. Bras. Cienc. Solo 33, 1829–1836.
Souza, E.D., Costa, S.E.V.G.A., Anghinoni, I., Lima, C.V.S., Carvalho, P.C.F., Martins, A.P.,
2010. Biomassa microbiana do solo em sistema de integração lavoura-pecuária
em plantio direto, submetido a intensidades de pastejo. Rev. Bras. Cienc. Solo
34, 79–88.
Steffens, M., Kölbl, A., Totsche, K.U., Kögelknabner, I., 2008. Grazing effects on soil
chemical and physical properties in a semiarid steppe of Inner Mongolia (PR
China). Geoderma 143, 63–72.
Sulc, R.M., Tracy, B.F., 2007. Integrated crop–livestock systems in the U.S. corn belt.
Agron. J. 99, 335–345.
Tracy, B.F., Zhang, Y., 2008. Soil compaction, corn yield response, and soil nutrient
pool dynamics within an integrated crop livestock system in Illinois. Crop Sci.
48, 1211–1218.