2006 carbon contents and aggregation noellemeyer soil till res.pdf
TRANSCRIPT
+ Models
STILL-2486; No of Pages 12
Carbon contents and aggregation related to soil physical and
biological properties under a land-use sequence in the
semiarid region of central Argentina
Elke Noellemeyer *, Federico Frank, Cristian Alvarez,German Morazzo, Alberto Quiroga
Facultad de Agronomıa, Universidad Nacional de La Pampa, C.C. 300, RA-6300 Santa Rosa, La Pampa, Argentina
Received 25 June 2007; received in revised form 11 December 2007; accepted 8 February 2008
Abstract
Land-use change affects vast areas of the semiarid region of central Argentina, where agriculture becomes predominant over
mixed farming systems, and large areas of permanent pastures (PAS) are being converted to agricultural land. This land-use change
causes loss of soil structure, but very little is known about the effect of changes in aggregate size distribution on soil physical,
chemical and biological properties. We decided to use dry sieved aggregates since this technique is commonly used in semiarid
regions. The study was carried out at Anguil, La Pampa, Argentina. The soil was a sandy loam Entic Haplustoll with a carbonate-
free A-horizon. The PAS site had been under weeping love grass for more than 40 years. Parts of this PAS were turned to cultivation
in 1989 (CULT14) and in 2001 (CULT2). Sampling was carried out at 0.6 m intervals to 0.18 m depth. Bulk density (BD), organic
carbon (OC), and water holding capacity and infiltration were determined on these samples. Dry aggregate size distribution and OC
content of the size fractions were determined on large undisturbed samples. Samples of pooled aggregate size fractions>4, 1–4, and
<1 mm, as well as corresponding samples of non fractionated soil were incubated and respiration was measured by CO2 evolved.
The soil of CULT2 had 29% lower contents of large (>4 mm) and 37% higher contents of very small (<1 mm) aggregates than PAS.
The intermediate size aggregates were not affected by the short-term effect of tillage. OC loss in CULT2 was 16% regarding PAS.
Longer term effects of cultivation were characterized by 30% loss of intermediate size aggregates, 22% increase of bulk density, 74
and 19% decrease in water infiltration and water retention, respectively of CULT14 compared to PAS. A 32% decrease of OC was
observed after 14 years of cultivation. Intermediate size aggregates had highest OC contents and no difference between treatments
was found, except for a lower value of large aggregates in CULT14. Respiration rates and total CO2 evolved was related to OC
contents of fractions; however, PAS respired more from its small aggregates than expected from their OC content. The results
showed that OC turnover and loss of aggregation was very fast in this soil, but soil hydraulic properties were affected in the longer
term. Dry aggregates were found to useful for studying soil degradation, and they showed similar trends as those indicated in the
literature for water stable aggregates.
# 2008 Elsevier B.V. All rights reserved.
Keywords: Land-use change; Semiarid Argentina; OC turnover; Dry aggregate size changes; Physical properties; Respiration rates
www.elsevier.com/locate/still
Available online at www.sciencedirect.com
Soil & Tillage Research xxx (2008) xxx–xxx
* Corresponding author. Tel.: +54 2954 433093x104.
E-mail address: [email protected]
(E. Noellemeyer).
0167-1987/$ – see front matter # 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.still.2008.02.003
Please cite this article in press as: Noellemeyer, E., et al., Carbon co
properties under a land-use sequence in the semiarid . . ., Soil Ti
1. Introduction
In the semiarid region of central Argentina agriculture
becomes increasingly dominant over the traditional
mixed farming and animal husbandry system, as large
ntents and aggregation related to soil physical and biological
llage Res. (2008), doi:10.1016/j.still.2008.02.003
E. Noellemeyer et al. / Soil & Tillage Research xxx (2008) xxx–xxx2
+ Models
STILL-2486; No of Pages 12
areas of permanent pastures (PAS) are being converted to
cropland. Soil carbon losses due to cultivation and tillage
on virgin soils are reported to be in the order of 10–55%
(Brown and Lugo, 1990; Burke et al., 1989). This ample
range might be due to climate and texture differences,
with highest losses in sandy soils in semiarid arid regions
(Balesdent et al., 2000). Various authors reported soil C
losses in different semiarid regions ranging from 35 to
56% (Zach et al., 2006; Elberling et al., 2003) after 3–5
years of cultivation.
Cultivation also changes the soils’ aggregate size
distribution and stability, which has been related to soil
organic matter and microbial activity in numerous studies
(Balesdent et al., 2000; Paustian et al., 2000; Six et al.,
2000a, 2000b; Beare et al., 1994; Dinel et al., 1992). In
general, water stable aggregates smaller than 250 mm
obtained by wet sieving have been used in these studies,
and conceptual frameworks about aggregate hierarchy,
related pore sizes and the relationship between aggregate
turnover and C dynamics have been developed (Six et al.,
2004). However, the soil’s surface in its natural state is
formed by dry aggregates ranging in size from less than
1 mm to more than 8 mm. This is specifically true for
sandy loam and loam soils in semiarid regions that
developed under grassland vegetation. Pena Zubiate et al.
(1980) described the soil structure in the semiarid Pampa
as predominantly medium to large sub-angular blocks.
Dry sieved aggregates could therefore be considered to
represent more truly the actual state of aggregation and
soil structure, and differences in size of these aggregates
have been associated with the effect of different tillage
practices (Hevia et al., 2007). They are obtained by gentle
hand manipulation followed by sieving (Douglas and
Goss, 1982; Chepil, 1953) as in contrast to water stable
aggregates fractionated by suspension and wet sieving.
Dry sieved aggregates have mainly been used in wind
erosion studies (Diaz Zorita et al., 2002; Zobeck, 1991)
and few references exist about their use to evaluate the
effect of management on soil aggregate stability (Eynard
et al., 2004; Martens, 2000) and on C sequestration in
these aggregates (Holeplass et al., 2004).
In the context of the semiarid Pampa of central
Argentina the most common land-use change is the
cultivation of very old PASs (mainly Eragrostis
curvula) for cash cropping. The climatic variations
that occurred during the past three decades, character-
ized by higher rainfall during the summer (Sierra et al.,
2001), induced farmers to increase the area of summer
crops at the expense of these long established PASs.
Based on the concepts developed for water stable
aggregates we supposed that in the sandy to sandy loam
soils of this region, the conversion of PAS into
Please cite this article in press as: Noellemeyer, E., et al., Carbon co
properties under a land-use sequence in the semiarid . . ., Soil Ti
cultivated lands would cause rapid change of dry
aggregate size distribution, carbon loss and associated
deterioration of soil physical properties such as the
soil’s pore system, water dynamics and susceptibility to
erosion. We also hypothesized that C losses would
affect the biological activity of the soil. The objective of
the present study therefore was to evaluate short and
longer term effects of cultivation on soil structure and
related physical properties, carbon stocks and their
distribution in different size dry aggregates.
2. Materials and methods
2.1. Study area
The study was carried out in 2003 on three adjacent
fields at INTA (National Institute for Agricultural
Technology) Experimental Station in Anguil
(3683501900S and 6385704600W), in the center of the
semiarid Pampa of Argentina (Fig. 1). The soil was a
sandy loam Entic Haplustoll with a carbonate-free A-
horizon of approximately 25 cm depth.
The PAS site had been under weeping love grass for
more than 40 years. A 25-ha part of this PAS was
ploughed in 1989 (CULT14) and then cultivated with a
rotation of wheat (Triticum aestivum); oats (Avena
sativa); sunflower (Elianthus annuus) and alfalfa
(Medicago sativa) PAS with conventional tillage (disk
plough). This field had been under alfalfa PAS for the
last 3 years when the sites were sampled. Another 12 ha
part of the original PAS was ploughed in 2001 and
cultivated with one crop of forage oats and one crop of
sunflower, both with conventional tillage before
sampling (CULT2). The three treatments thus reflected
a land-use time sequence under the same soil and
climatic conditions. Soil properties of the three sites are
shown in Table 1.
2.2. Soil sampling and analysis
All soil samples were collected at six points at 20 m
distance each, along an N–S linear transect at each site.
This sampling method was chosen in order to create
pseudo-replicates of each treatment, since true repli-
cates were impossible to obtain given that only one field
represented each treatment. Sampling was carried out
with cylinders (471.24 cm3 volume) at 0–0.06, 0.06–
0.12 and 0.12–0.18 m depth, all within the limits of the
A-horizon and within the tillage depth of the disk plow.
Samples were air dried, passed through a 2 mm sieve
and weighed, and bulk density (BD) of the soil was
calculated. Organic carbon (OC) was determined by wet
ntents and aggregation related to soil physical and biological
llage Res. (2008), doi:10.1016/j.still.2008.02.003
E. Noellemeyer et al. / Soil & Tillage Research xxx (2008) xxx–xxx 3
+ Models
STILL-2486; No of Pages 12
Fig. 1. Map of La Pampa, Argentina.
oxidation with sodium dichromate and sulphuric acid at
120 8C and titration of the CO2 trapped in NaOH
(Snyder and Trofimov, 1984).
Water infiltration was also measured at the six
sampling points in each treatment using the double ring
method as described by Fernandez et al. (1971).
Infiltrated water was determined after 1, 10, 20, 30,
40, 50 and 60 min, and the results were expressed as
accumulated infiltration (mm h�1). Initial soil water
contents of the treatment sites were 10.5, 10.2 and
12.3% in the first 0.20 m for PAS, CULT2 and CULT14,
respectively. Water holding capacity was determined in
1 m2 plots in each treatment, at the same points where
Please cite this article in press as: Noellemeyer, E., et al., Carbon co
properties under a land-use sequence in the semiarid . . ., Soil Ti
Table 1
Basic soil properties of the A-horizon in the three adjacent fields
corresponding to the three treatments studied
CULT14 CULT2 PAS
C (g kg�1) 12.3 b 12.8 b 16.5 a
N (g kg�1) 0.86 b 0.93 b 1.1 a
P (mg kg�1) 10.4 a 4.8 b 6.7 b
Ca (mmol p+ kg�1 soil) 99 b 122 a 131 a
Mg (mmol p+ kg�1 soil) 30 a 23 a 30 a
K (mmol p+ kg�1 soil) 3.7 a 2.6 b 3.7 a
Na (mmol p+ kg�1 soil) 29 a 23 b 23 b
CEC (mmol p+ kg�1 soil) 191 b 200 a 203 a
Base saturation (%) 84.5 a 87.7 a 90.3 a
infiltration was measured. After the infiltration assay,
when the soils were saturated to at least 0.40 m depth,
the soil surface was covered with polyethylene to
prevent evaporation. Samples were collected after 3, 6,
8 and 12 days and their volumetric water content was
determined by weighing moist and oven-dried (60 8C)
samples.
Large undisturbed samples to a depth of 0.20 m
(1413.72 cm3 cylinders) were collected at six points
along the sampling transect for aggregate size
distribution determination. Air-dried samples were
manually disaggregated with very gentle pressure
through rupture across the natural planes of weakness
(Arshad et al., 1996). The same technician skilled in this
procedure processed all samples. Then the samples
were shaken through a battery of 8, 4, 3, 2 and 1 mm
diameter sieves during 30 min. Soil mass retained by
each sieve was weighed and C content of these
aggregate size fractions was determined by the same
method as for OC.
100 g samples of pooled aggregate size fractions>4,
1–4, and <1 mm, as well as corresponding samples of
non fractionated (entire) soil were incubated in closed
recipients in a growth chamber at 24 8C and at 80% of
their water holding capacity. The respired CO2 was
trapped in 1N NaOH and the excess was titrated with
0.1N HCl. Determination of CO2 was realized daily at
ntents and aggregation related to soil physical and biological
llage Res. (2008), doi:10.1016/j.still.2008.02.003
E. Noellemeyer et al. / Soil & Tillage Research xxx (2008) xxx–xxx4
+ Models
STILL-2486; No of Pages 12
Table 2
Dry aggregate size distribution
Size classes (mm) Dry aggregate size distribution (g kg�1 soil)
>8 4–8 3–4 2–3 1–2 <1
CULT14 281.4 a 156.4 a 85.8 b 68.4 b 76.9 b 331.1 b
CULT2 160.4 b 114.6 b 116.7 ab 84.1 ab 113.9 a 409.6 a
PAS 226.9 a 147.6 b 147.4 a 95.6 a 122.6 a 259.8 b
References: soil mass (g kg�1) in the aggregate size classes. Different letters indicate significant differences ( p <0.05) within a column (n = 6).
the beginning of the experiment and less frequently
when respiration rates slowed down. When rates had
stabilized no further measurements were taken.
2.3. Statistical analysis
Mean values of the six replicates of all variables
were compared using one-way analysis of variance
and separated by the Fisher LSD test at the 95%
confidence level. CO2 incubation data were log-
transformed when necessary, and regression lines
were compared according to the method proposed by
Sokal and Rohlf (1968).
3. Results
3.1. Soil physical properties
Dry aggregate size distribution (Table 2) differed
according to the history of land-use of the soil. The soil
with a short period of cultivation (CULT2) had lower
contents of large (>4 mm) and higher contents of very
small (<1 mm) aggregates than both the PAS and long-
term cultivated (CULT14) soil. The intermediate size
aggregates were very little affected by the short-term
Please cite this article in press as: Noellemeyer, E., et al., Carbon co
properties under a land-use sequence in the semiarid . . ., Soil Ti
Fig. 2. Accumulated water infiltration in the field (mm) after 1 h.
References: error bars represent standard error of means (n = 6).
effect of tillage, since values for CULT2 and PAS were
similar. However, CULT14 showed significantly lower
values, which might have been due to the longer term
effect of tillage on aggregate size distribution. The
decrease in medium size aggregates in this site was
considerably higher than that of CULT2, with losses of
42, 29 and 37% for the 3–4, 2–3 and 1–2 mm size
classes, respectively. The relatively high values of large
aggregates in CULT14 may be attributed the effect of
the alfalfa PAS, which covered this soil for the last 3
years.
The highest water infiltration rate was found in
CULT2, whereas CULT14 had a considerably lower
rate than both other treatments (Fig. 2), even during the
first 10 min. Accumulated infiltration of CULT14 was
74% lower than that of PAS, and CULT2 showed a 38%
increase (Table 3) with respect to the latter.
Soils reached steady state of water movement
between 8 and 12 days, when no further water drainage
occurred due to gravity forces. Soil water content at this
moment (Table 3) can be considered as the water
holding capacity as measured in field conditions
(Fuentes Yague, 1996). Water holding capacity was
22.5% (w/w) in CULT14, whereas both CULT2 and
PAS had significantly higher values of 25.5 and 27.6%,
respectively. However, when these values were con-
verted to volumetric water contents, due to the
differences in BD between CULT14 and both other
treatments, no significant difference was found (27.4%,
25.5% and 28.7% for CULT14, CULT2 and PAS
respectively).
ntents and aggregation related to soil physical and biological
llage Res. (2008), doi:10.1016/j.still.2008.02.003
Table 3
Soil physical properties
BD (Mg m�3) WC 12 (%, w/w) I (mm h�1)
CULT14 1.22 a 22.5 b 100.7 c
CULT2 1.00 b 25.5 a 540.5 a
PAS 1.04 b 27.6 a 391.3 b
References: bulk density (BD), water content 12 days after saturation
(WC 12) and infiltration (I). Different letters indicate significant
differences ( p < 0.05) within a column (n = 6).
E. Noellemeyer et al. / Soil & Tillage Research xxx (2008) xxx–xxx 5
+ Models
STILL-2486; No of Pages 12
Table 4
Organic carbon (C)
Depth (cm) C content (g kg�1) C mass (Mg ha�1)
0–6 6–12 12–18 0–6 6–12 12–18
CULT14 11.5 c 10.4 a 8.5 a 8.4 b 7.4 a 6.0 a
CULT2 14.3 b 12.0 a 9.4 a 8.6 b 7.6 a 6.2 a
PAS 17.0 a 12.8 a 9.7 a 10.6 a 9.1 a 6.4 a
References: total C content (g kg�1) and volumetric C mass (Mg ha�1) of the soil. Different letters indicate significant differences ( p < 0.05) within
a column (n = 6).
Table 5
Organic carbon (C) of different aggregate size fractions
Size classes (mm) C content (g kg�1) C mass (Mg ha�1)
>4 1–4 <1 >4 1–4 <1
CULT14 8.6 b 23.6 a 10.9 a 9.2 a 13.1 a 8.8 b
CULT2 11.7 a 16.9 a 12.3 a 6.4 b 10.6 b 10.1 a
PAS 12.1 a 20.7 a 12.4 a 9.2 a 15.4 a 6.6 a
References: total C content (g kg�1) and volumetric C mass to a depth of 20 cm (Mg ha�1) of the different aggregate size fractions. Different letters
indicate significant differences ( p < 0.05) within a column (n = 6).
Table 6
Accumulated CO2 production after 17 days
Aggregate size class Treatment CO2-17 (mg C kg�1 soil)
>4 mm CULT14 177.0 b
CULT2 178.2 b
PAS 302.3 a
1–4 mm CULT14 565.4 a
CULT2 377.8 b
PAS 479.5 ab
<1 mm CULT14 182.0 b
CULT2 211.0 b
PAS 466.1 a
Entire soil CULT14 351.4 a
CULT2 414.7 a
PAS 386.6 a
References: accumulated CO2 production after 17 days of incubation
(mg C kg�1 soil). Different letters indicate significant differences
( p < 0.05) within a column and within an aggregate size fraction
(n = 6).
3.2. Organic matter
Organic C in the uppermost depth layer (0.00–
0.06 m) decreased from 17.0 g kg�1 in PAS to
14.3 g kg�1 in CULT2 and 11.5 g kg�1 in CULT14
(Table 4). Carbon losses in this layer due to cultivation
were 16% for CULT2 and 32% for CULT14. However,
there were no significant differences among treatments
in the two deeper layers (0.06–0.12 and 0.12–0.18 m).
When these values were transformed to mass per
hectare, OC losses were 4.3 and 3.7 Mg ha�1 for
CULT14 and CULT2, respectively.
The OC content of aggregate size fractions ranged
from 8.6 to 12.1 g kg�1 in>4 mm aggregates; from 16.9
to 23.6 g kg�1 in 1–4 mm aggregates, and from 10.9 to
12.4 g kg�1 in<1 mm aggregates (Table 5). There were
no significant differences in OC content of aggregate size
fractions among treatments, with the exception of the
lower value of >4 mm aggregates in CULT14. The
highest OC contents were found in the 1–4 mm size class
in all treatments, with an average value of 20.4 g kg�1.
The two other size classes had very similar averagevalues
of 11.9 and 10.8 g kg�1 for<1 and>4 mm, respectively.
We then calculated OC mass per hectare contained in
these aggregate fractions by multiplying the OC
concentration in each fraction by its weight proportion,
considering the sampling depth of 0.20 m and the average
bulk density: OC (kg Mg�1) � weight of aggregate frac-
tion (kg Mg�1) � 2000 m3 ha�1 � average bulk density
(Mg m�3). Theresultsarealso shown inTable 5. This way
Please cite this article in press as: Noellemeyer, E., et al., Carbon co
properties under a land-use sequence in the semiarid . . ., Soil Ti
of expressing the data made long- and short-term effects
more evident: CULT2 had the highest amount of OC in
the<1 mm fraction and least in the largest aggregates. On
the other hand, CULT14, showed a similar distribution of
aggregate size classes as PAS.
3.3. Biological properties
In order to characterize the biological activity and
availability of C pools contained in the different size
ntents and aggregation related to soil physical and biological
llage Res. (2008), doi:10.1016/j.still.2008.02.003
E. Noellemeyer et al. / Soil & Tillage Research xxx (2008) xxx–xxx6
+ Models
STILL-2486; No of Pages 12
Fig. 3. Respiration of different aggregate size classes and entire soil. References: values represent the average of six replicates.
fractions incubation assays for pooled fractions of
large (>4 mm), intermediate (1–4 mm) and small
(<1 mm) aggregates were carried out. We expected
that soil fragments would show different respiration
rates according to their difference in C contents. The
total amounts of CO2-C evolved after 17 days of
incubation (Table 6) confirmed this hypothesis. The
intermediate (1–4 mm) aggregate size fraction showed
the highest values with an average of 474.2 mg C kg�1
soil for all three treatments, while >4 and <1 mm size
classes had averages of nearly half that value (219.2
and 286.4 mg C kg�1 soil, respectively). CULT2 had
the lowest CO2-C production (377.8 g C kg�1 soil) in
the intermediate aggregate size fraction while both
CULT14 and PAS had similar and higher values.
This trend coincided with the respective aggregate
size OC contents of the treatments. No such trend
was observed in the largest size fraction where
PAS had significantly higher CO2-C production
(302.3 mg kg�1) than CULT14 (177.0 mg kg�1) and
Please cite this article in press as: Noellemeyer, E., et al., Carbon co
properties under a land-use sequence in the semiarid . . ., Soil Ti
CULT2 (178.2 mg kg�1), whereas the OC contents of
this fraction were similar between PAS and CULT2. In
the <1 mm fraction PAS also produced significantly
more CO2-C (466.1 mg kg�1) than both other treat-
ments, which also could not be predicted from its OC
contents. Accumulated CO2 respiration from the
entire soil did not differ among treatments, and the
values were considerably lower compared to the sum
of aggregate size fraction CO2-C respiration for each
treatment. These sums were 924, 766 and
1247 mg C kg�1 for CULT14, CULT2, and PAS,
respectively, while the values for entire soil of these
treatments were 351, 414, and 386 mg C kg�1,
respectively.
Within each site, the aggregate size fractions also
differed in their respiration rates (Fig. 3). A steep curve
and very rapid depletion of evolved CO2 was observed
in the>4 mm class. On the contrary,<1 mm aggregates
showed the lowest slope and also the longest period of
respiration.
ntents and aggregation related to soil physical and biological
llage Res. (2008), doi:10.1016/j.still.2008.02.003
E. Noellemeyer et al. / Soil & Tillage Research xxx (2008) xxx–xxx 7
+ Models
STILL-2486; No of Pages 12
Please cite this article in press as: Noellemeyer, E., et al., Carbon contents and aggregation related to soil physical and biological
properties under a land-use sequence in the semiarid . . ., Soil Tillage Res. (2008), doi:10.1016/j.still.2008.02.003
Fig. 4. Regression lines for CO2 production of entire soil and different aggregate size fractions.
E. Noellemeyer et al. / Soil & Tillage Research xxx (2008) xxx–xxx8
+ Models
STILL-2486; No of Pages 12
Within each fraction, we also found different slopes
for PAS, CULT2 and CULT14 (Fig. 4). With the
exception of >4 mm aggregates of CULT2 and
CULT14, all data sets had to be log-transformed in
order to obtain regression lines that adjusted to a linear
model with R2 ranging from 0.85 to 0.96. Statistical
comparison of these regression lines revealed that only
>4 mm aggregates of CULT2 and CULT14 had
comparable regression lines ( p = 0.60), with similar
slopes ( p = 0.87) that could be considered superposed
( p = 0.85). All other regression lines were different
between treatments.
The contribution of total CO2-C produced in 17 days
by each aggregate fraction was calculated considering
their weight proportion and CO2-C evolved during
incubation (Fig. 5). The 1–4 mm aggregate fraction
contributed most to respiration in all treatments, ranging
from 42% in PAS to 49% in CULT14. Larger aggregates
contributed similar amounts in PAS and CULT14 (28
and 29%, respectively) while in CULT2 this fraction
made up only 19%. These trends were expected
considering the OC content and weight proportion of
these fractions. On the other hand, smaller than 1 mm
aggregates decreased in their contribution according to
land use from 30% in PAS to 22% in CULT14. This was
not related to their OC content and aggregate size
distribution.
The total CO2-C production was calculated by the
sum of aggregates’ contributions (Fig. 5), considering
the partial contributions of each class, and it showed
great differences among treatments. PAS had signifi-
cantly higher values than both cultivated soils, and there
were no significant differences between the latter. When
compared to the entire soil, only PAS had similar values
of aggregates’ sum and undisturbed (entire) sample. On
the other hand, the CO2-C released by CULT14 and
Please cite this article in press as: Noellemeyer, E., et al., Carbon co
properties under a land-use sequence in the semiarid . . ., Soil Ti
Fig. 5. Contribution of different aggregate size classes to total CO2
(mg C kg�1 soil) produced in 17 days, compared to the entire soil
sample.
CULT2’s entire soil was higher than their sum of
aggregates’ respiration.
4. Discussion
Land-use change from a permanent PAS to cultiva-
tion caused important changes in the size distribution of
aggregates. After 2 years of tillage, large aggregates had
decreased by 29% compared to the PAS. At the same
time, small aggregates (<1 mm) increased by 37%. The
losses of aggregates in the intermediate size classes
ranged from 21, 12 and 7% for 3–4, 2–3 and 1–2 mm
aggregates, respectively. This suggested that larger soil
fragments contributed more to the loss of soil structure,
and that cultivation produced an immediate increase of
small soil particles, especially those that are susceptible
to wind erosion (<0.84 mm). The longer term effect of
cultivation on this soil was more related to intermediate
size aggregates in the 1 to 4 mm size classes, which
were significantly lower in CULT14 than in the
permanent PAS, whereas the proportion of largest
and smallest aggregates was similar between these
treatments. The relatively high values of large
aggregates in CULT14 may be attributed the effect of
the alfalfa PAS, which covered this soil for the last 3
years. A recuperation of soil structure under PAS and
under no-till agriculture has often been observed. For
instance, Paustian et al. (2000) and Six et al. (2000b)
found increases in water stable aggregates and soil OC
in soils that were not tilled. Our data indicated that the
same might hold true for dry sieved aggregates. The
distribution of aggregate size classes among our land-
use sequence treatments was very different since the
size fraction which represented the smallest amount of
soil mass was different in each treatment: PAS had 26%
of small aggregates, CULT2 had 28% of large
aggregates and 23% of the soil under CULT14 was
found in intermediate ones.
It has been reported by various authors that tillage
destroys water stable aggregates and specifically affects
the larger soil aggregates, which are considered to be
less stable (Beare et al., 1994; Kay, 1990; Elliott, 1986;
Tisdall and Oades, 1982; Van Veen and Paul, 1981).
This could be applied to our results as a short-term
consequence of cultivation. However, the longer term
effect on intermediate size aggregates we observed
could not be compared with results obtained with water
stable aggregates. There are few studies on the
dynamics of dry sieved aggregates to be found in the
literature. For instance, Eynard et al. (2004) found
smaller mean weight diameters in dry aggregates of
perennial PASs on Ustolls and Uderts of South Dakota
ntents and aggregation related to soil physical and biological
llage Res. (2008), doi:10.1016/j.still.2008.02.003
E. Noellemeyer et al. / Soil & Tillage Research xxx (2008) xxx–xxx 9
+ Models
STILL-2486; No of Pages 12
than in corresponding no-till and tilled plots. Drury
et al. (2004) also found higher proportion of larger
aggregates in continuous corn than under rotation corn
in a clay loam, typic Argiaquoll. The apparent
contradiction with our results might be explained by
the climatic regime and clay contents that favor high
carbon stocks and corresponding fine granular struc-
tures in Ustolls and Argiaquolls under land-use systems
that have relatively high inputs of plant residues. In
Udolls of the semiarid Pampa large sub-angular blocks
are formed as predominant structural units under PASs
and native vegetation, while carbon losses due to
cultivation lead to predominance of smaller less stable
aggregates and soil compaction (Quiroga et al., 1998).
Thus, the effect of texture and environmentally
determined carbon stocks of the soil have to be
considered when comparing the results of dry sieved
aggregate size distributions and these have to be related
to the structure type conditioned by soil genesis. Drury
et al. (2004) already suggested that their results showed
that indigenous soil properties exerted a greater
influence on aggregate size distribution than cropping
history.
After 14 years of cultivation, soil water holding
capacity decreased by nearly 19%. This change
considerably affects the soils potential for crop
productivity, especially in a semiarid region where
long drought periods are common. The loss of water
retention might be related to the significantly lower
proportion of aggregates in the 1–4 mm size class in
CULT14. Following Elliott and Coleman’s (1988)
theory of hierarchical pore categories that correspond
to aggregate size classes as their mirror images, this
would indicate that the intermediate size aggregates
have associated pore sizes which play an important role
in defining water retention. Dexter (2004) showed that
soil microstructure is responsible for most physical soil
properties and that structural porosity is directly related
to water holding capacity. In the case of the sandy loams
of the semiarid Pampa, water holding structural porosity
is apparently more related to medium size aggregates
(1–4 mm). The decrease of structural porosity under
cultivation (CULT14) was also confirmed by a 22%
increase of bulk density in CULT14 relative to PAS and
CULT2.
For the case of water infiltration, the short-term
effect of cultivation was positive, facilitating water
capture and translocation in the soil. The longer term
effect of agricultural use however, greatly diminished
the soil’s capacity to infiltrate water and could lead to
runoff losses and decreased water use efficiency. Thus,
water retention, aggregate size class, bulk density and
Please cite this article in press as: Noellemeyer, E., et al., Carbon co
properties under a land-use sequence in the semiarid . . ., Soil Ti
water infiltration data revealed significant reduction of
structural porosity due to 14 years of cultivation. On the
other hand, the short-term effect of cultivation on
structural porosity and soil hydraulic properties was
very small, despite the considerable loss of large and
increase of very small aggregates that are most
susceptible to wind erosion.
Organic C losses were 4.3 and 3.7 Mg ha�1 for
CULT14 and CULT2, respectively. About half of this
decrease was due to the OC loss in the uppermost 0.06 m
soil layer (2.2 and 2.0 Mg ha�1 for CULT14 and CULT2,
respectively). The apparent OC loss rate during the first 2
years of cultivation was 1.85 Mg C ha�1 year�1, while
the average rate after 14 years of cultivation under a
rotation with alfalfa PAS was 0.31 Mg C ha�1 year�1.
Considering 26.1 Mg ha�1 as a stable OC content in this
soil its average half life would be approximately 42 years,
but during the first few years of cultivation a significantly
lower half life of 7 years was found. These data confirmed
that OC turnover rates in soils of the semiarid Pampa are
high, with half lives of approximately 10 years and no
evidence of long-term stabilized C (Zach et al., 2006).
Apparently, most of the C was lost during a short period
following cultivation of the PAS, and even under
rotations that include alfalfa (as in CULT14) a further
decrease was observed. Angers et al. (1992) reported an
increase in OC content upon conversion of continuous
corn to alfalfa PAS, which might indicate that under
continuous cropping, C degradation would have been
even more severe than that observed in CULT14.
Carbon contents in aggregates size fractions were
very similar among treatments, and only CULT14 had
significantly lower OC contents in the largest aggregate
fraction. While our results did not show a clear effect of
land use on OC contents of aggregate fractions, Drury
et al. (2004) reported higher OC contents in all
>0.25 mm aggregate fractions under rotation, com-
pared with corn monoculture, and Holeplass et al.
(2004) also found higher OC concentration in these
aggregate sizes under grain – PAS rotation than under
all – grain production systems.
The highest OC content among aggregate fractions
was found in the pooled 1–4 mm size class in all
treatments. For water stable aggregates, Holeplass et al.
(2004) found a trend of increasing OC concentration
with decreasing aggregate size, while Saroa and Lal
(2003) reported that OC increased with increasing
aggregate size. This trend reflects the concept of
aggregate hierarchy proposed by Tisdall and Oades
(1982). Our results, however, did not agree with this
theory, since intermediate size aggregates had higher
OC contents than both other fractions. Zotarelli et al.
ntents and aggregation related to soil physical and biological
llage Res. (2008), doi:10.1016/j.still.2008.02.003
E. Noellemeyer et al. / Soil & Tillage Research xxx (2008) xxx–xxx10
+ Models
STILL-2486; No of Pages 12
(2005) explained the lack of aggregate hierarchy as
shown by a similar OC content across aggregate size
fractions as the effect of principal binding agents
other than organic matter. In their study on water
stable aggregates in low activity clay oxisols under
different cropping systems, these authors conclude
that the OC loss from natural vegetation to conven-
tional tillage can only partly be explained by the loss
of C-rich macroaggregates and an increase in C-poor
microaggregates, since both fractions did not differ in
their OC concentrations. Thus, several authors
reported divergences from the aggregate hierarchy
model under different soil conditions even for
aggregates separated by wet sieving. Our data
suggested that for the dry sieved aggregate size
classes we studied, the most important fraction for
OC stabilization would be the intermediate class
(1–4 mm), due to its higher OC concentration and the
observed decrease of this aggregate size fraction after
prolonged agricultural use.
The lower OC contents of >4 and <1 mm fractions
(not significant) in CULT14 would suggest that in these
dry sieved aggregate classes the conceptual model of
Six et al. (1998), which states that in tillage agro-
ecosystems less C is sequestered due to higher macro
aggregate turnover that lowers the rate of micro
aggregate formation within macro aggregates also
could be valid.
Incubation assays showed that on the average the OC
content of the aggregate size fraction was related to the
amount of CO2-C evolved by the fraction. The
intermediate size class had highest OC contents and
also produced most CO2-C. Both for OC contents and
CO2-C production this fraction showed values almost
twice as high as both >4 and <1 mm fraction. These
results do not agree with those of Drury et al. (2004),
who also used dry sieved aggregates to evaluate the
impact of aggregation on biological processes under
rotation and continuous cropping. They found an
increase of CO2 production with decreasing aggregate
size, but they also reported a strong relation between
CO2 respiration and POC contents, especially under
rotation. Our results however did not show a clear effect
of treatment on the OC content of the aggregate size
fractions, nor on respiration. Whereas the low CO2-C
production of CULT2 in the 1–4 mm fraction could be
associated to its low OC content, this was not true for
CO2-C in the >4 and <1 mm fractions. In both cases
OC contents were similar between CULT2 and PAS,
while CO2-C production was similar for CULT14 and
CULT2. This might indicate a similar nature of OC in
these fractions between CULT14 and CULT2. Short and
Please cite this article in press as: Noellemeyer, E., et al., Carbon co
properties under a land-use sequence in the semiarid . . ., Soil Ti
longer term effects of cultivation on the biological
behavior of the aggregate size fractions therefore could
not be distinguished.
The comparison between the CO2-C production of
the entire soil and the sum of the aggregate size
fractions revealed that size fractions produced far more
CO2-C. The smallest difference was found in CULT2
(414.7 and 767.0 mg kg�1, for entire soil and aggregate
sum, respectively, which represents 1.85 times the
amount), while in the case of CULT14, CO2-C
production of aggregate sum was 2.63 times that of
the entire soil; and for PAS this values was 3.23 times.
The lower CO2-C production of entire soil could be
attributed to protection of OC due to the undisturbed
soil matrix, while aggregate fractionation by dry sieving
might have released otherwise protected organic
material. Similarly, Drury et al. (2004) found that
grinding the aggregates reduced the differences of CO2
production between aggregate size classes and gen-
erally enhanced CO2 production.
In an attempt to evaluate the contribution of each
aggregate size fraction to soil respiration we
calculated these amounts pondered by the aggregates’
size fraction’s weight proportion and found that only
PAS had similar values between the sum of pondered
aggregate contribution and entire soil CO2 produc-
tion. Both cultivated treatments had higher entire soil
CO2 production than the pondered sum of aggregates
production. This result was astonishing, since the sum
of CO2 production of separate aggregate fractions was
considerably higher than entire soil respiration.
However, taking into account their contribution to
total soil mass this trend is reversed and no
explication for this apparent contradiction could be
adventured.
A steep curve and very rapid depletion of evolved
CO2 was observed in the >4 mm class, which might be
related to a more labile nature of C. On the contrary,
<1 mm aggregates showed the lowest slope and also the
longest period of respiration. Zhang et al. (2007) studied
the respiration rates of different OC fractions and found
that labile fractions showed steeper slopes than heavy C
fraction and whole soil OC. The difference of
respiration rates of aggregate size fractions among
treatments that became evident in the comparison of
regression lines therefore could indicate differential
substrate availability and/or differences in microbial
community. The major differences were between PAS
and both cultivated treatments, suggesting that despite
the positive effect of the alfalfa PAS on OC contents and
aggregate size distribution in CULT14, the biological
activity had not been recovered.
ntents and aggregation related to soil physical and biological
llage Res. (2008), doi:10.1016/j.still.2008.02.003
E. Noellemeyer et al. / Soil & Tillage Research xxx (2008) xxx–xxx 11
+ Models
STILL-2486; No of Pages 12
5. Conclusions
Land-use change from permanent PAS to arable
agriculture greatly affected OC stocks and all tested
physical and biological soil properties. Cultivation
caused a decrease of structural porosity, which was
related to higher bulk density and decreased infiltra-
tion rate. This process might be divided into a short-
term disruption of large aggregates, while the long-
term effect appeared to be the decrease of inter-
mediate size ones. The latter was reflected in an
important reduction of soil’s water retention and
infiltration, which could have a negative impact on
soil quality and productivity. OC losses were similar
between short- and long-term cultivation, which
indicated a very fast rate of C turnover in the studied
soil. The intermediate size aggregates had the highest
OC contents, and also contributed most to total
respiration. Differences in land-use history only
became evident in aggregate size fractions, while
entire soil samples did not show different respiration
rates or total CO2 production. Our results showed that
dry sieved aggregates provide meaningful fractions
for studies of the impact of land use on soil physical
and biological properties.
Acknowledgement
This work was financed by the Interamerican
Institute for Global Change Research (IAI) within the
collaborative research networks CRN 001 and 2031.
References
Angers, D., Peasent, A., Vigneux, J., 1992. Early cropping-induced
changes in soil aggregation, organic matter, and microbial bio-
mass. Soil Sci. Soc. Am. J. 56, 115–119.
Arshad, M.A., Lowery, B., Grossman, B., 1996. Physical test for
monitoring soil quality. In: Doran, J.W., Jones, A.J. (Eds.),
Methods for Assessing Soil Quality. Soil Science Society of
America, Madison, WI, pp. 123–141.
Balesdent, J., Chenu, C., Balabane, M., 2000. Relationships of soil
organic matter dynamics to physical protection and tillage. Soil
Till. Res. 53, 215–230.
Beare, M., Cabrera, M., Hendrix, P., Coleman, D., 1994. Aggregate-
protected and unprotected organic matter pools in conventional
and no-tillage soils. Soil Sci. Soc. Am. J. 58, 787–795.
Brown, S., Lugo, A., 1990. Effects of forest clearing and succession of
the carbon and nitrogen content of soils in Puerto Rico and US
Virgin Islands. Plant Soil 124, 53–64.
Burke, I., Yonker, C., Parton, W., Cole, C., Flach, K., Schimel, D.,
1989. Texture, climate and cultivation effects on soil organic
matter content in US Grassland soils. Soil Sci. Soc. Am. J. 53,
800–805.
Please cite this article in press as: Noellemeyer, E., et al., Carbon co
properties under a land-use sequence in the semiarid . . ., Soil Ti
Chepil, W.S., 1953. Field structure of cultivated soils with special
reference to erodibility by wind. Soil Sci. Soc. Am. Proc. 26, 4–6.
Dexter, A.R., 2004. Soil physical quality Part I. Theory, effects of soil
texture, density and organic matter and effects on root growth.
Geoderma 120, 201–214.
Diaz Zorita, M., Perfect, E., Grove, J.H., 2002. Disruptive methods for
assessing soil structure. Soil Till. Res. 64, 3–22.
Dinel, H., Levesque, P., Jambu, P., Righi, D., 1992. Microbial activity
and long-chain aliphatics in the formation of stable soil aggre-
gates. Soil Sci. Soc. Am. J. 56, 1455–1463.
Douglas, J.T., Goss, M.J., 1982. Stability and organic matter content of
surface soil aggregates under different methods of cultivation and
in grassland. Soil Till. Res. 2, 155–175.
Drury, C.F., Yang, X.M., Reynolds, W.D., Tan, C.S., 2004. Influence
of crop rotation and aggregate size on carbon dioxide production
and denitrification. Soil Till. Res. 79, 87–100.
Elberling, B., Toure, A., Rasmussen, K., 2003. Changes in soil
organic matter following groundnut-millet cropping at three
locations in semi-arid Senegal, West Africa. Agric., Ecosyst.
Environ. 96, 37–47.
Elliott, E.T., 1986. Aggregate structure and carbon, nitrogen and
phosphorus in native soils and cultivated soils. Soil Sci. Soc.
Am. J. 50, 627–633.
Elliott, E.T., Coleman, D.C., 1988. Let the soil work for us. Ecol. Bull.
39, 23–32.
Eynard, A., Schumacher, T.E., Lindstrom, M.J., Malo, D.D., 2004.
Aggregate sizes and stability in cultivated South Dakota
prairie Ustolls and Usterts. Soil Sci. Soc. Am. J. 68, 1360–
1365.
Fernandez, P., Luque, J., Paoloni, J., 1971. Analisis de la infiltracion y
su aplicacion para disenos de riego en el valle inferior del Rıo
Colorado. Revista de Investigaciones Agrarias (Argentina), serie
3, vol. 8, pp. 1–29.
Fuentes Yague, J.L., 1996. Tecnicas de Riego. Mundi Prensa Madrid,
p. 471.
Hevia, G.G., Mendez, M., Buschiazzo, D.E., 2007. Tillage affects soil
aggregation parameters linked with wind erosion. Geoderma 140,
90–96.
Holeplass, H., Singh, B.R., Lal, R., 2004. Carbon sequestration in soil
aggregates under different crop rotations and nitrogen fertilization
in an inceptisol in southeastern Norway. Nutr. Cycl. Agroecosys.
70, 167–177.
Kay, B., 1990. Rates of change of soil structure under different
cropping systems. Adv. Soil Sci. 12, 1–52.
Martens, D.A., 2000. Management and crop residue influence soil
aggregate stability. J. Environ. Qual. 29, 723–727.
Pena Zubiate, C., Maldonado Pinedo, D., Martinez, H., Hevia, R.,
1980. Suelos. In: Inventario Integrado de los Recursos Naturales
de la Provincia de La Pampa. INTA – UNLPam – Gobierno de La
Pampa. Santa Rosa, L.P., Argentina.
Paustian, K., Six, J., Elliott, E.T., Hunt, H., 2000. Management options
for reducing CO2 emissions from agricultural soils. Biogeochem-
istry 48, 147–163.
Quiroga, A.R., Buschiazzo, D.E., Peinemann, N., 1998. Manage-
ment discriminant properties in semiarid soils. Soil Sci. 163,
591–597.
Saroa, G.S., Lal, R., 2003. Mulching effects on aggregation and
carbon sequestration in a Miamian soil in central Ohio. Land
Degrad. Dev. 14, 481–493.
Sierra, E., Perez, S., Casagrande, G., Vergara, G., 2001. Efectos del
ENSO sobre las precipitaciones del trimestre noviembre-enero
(1921/1998) en el centro-este de la provincia de La Pampa
ntents and aggregation related to soil physical and biological
llage Res. (2008), doi:10.1016/j.still.2008.02.003
E. Noellemeyer et al. / Soil & Tillage Research xxx (2008) xxx–xxx12
+ Models
STILL-2486; No of Pages 12
(Argentina). Revista Argentina De Agrometeorologıa (Argentina)
1, 83–87.
Six, J., Elliott, E.T., Paustian, K., Doran, J.W., 1998. Aggregation and
soil organic matter accumulation in cultivated and native grassland
soils. Soil Sci. Soc. Am. J. 62, 1367–1377.
Six, J., Elliott, E., Paustian, K., 2000a. Soil macroaggregate
turnover and microaggregate formation: a mechanism for C
sequestration under no-tillage agriculture. Soil Biol. Biochem.
32, 1099–2103.
Six, J., Elliott, E.T., Paustian, K., Combrink, C., 2000b. Soil
structure and soil organic matter: I. Distribution of aggregate
size classes and aggregate associated carbon. Soil Sci. Soc. Am.
J. 64, 681–689.
Six, J., Bossuyt, H., Degryze, S., Denef, K., 2004. A history of
research on the link between (micro) aggregates, soil biota, and
soil organic matter dynamics. Soil Till. Res. 79, 7–31.
Snyder, J.D., Trofimov, J.A., 1984. A rapid accurate wet oxidation
diffusion procedure for determining organic and inorganic car-
bon in plant and soil samples. Commun. Soil Sci. Plant Anal. 15,
587–597.
Please cite this article in press as: Noellemeyer, E., et al., Carbon co
properties under a land-use sequence in the semiarid . . ., Soil Ti
Sokal, R., Rohlf, F., 1968. Biometrıa. Principios y metodos estadıs-
ticos en la investigacion biologica. H. Blume Ediciones, Madrid,
Espana.
Tisdall, J., Oades, M., 1982. Organic matter and water stable aggre-
gates in soils. Soil Sci. 33, 141–161.
Van Veen, J., Paul, E., 1981. Organic carbon dynamics in grasslands
soils. Background information and computer simulation. Can. J.
Soil Sci. 61, 185–201.
Zach, A., Noellemeyer, E., Tiessen, H., 2006. Carbon turnover and 13C
natural abundance under landuse change in the semiarid La
Pampa, Argentina. Soil Sci. Soc. Am. J. 70, 1541–1546.
Zhang, J., Song, C., Wenyan, Y., 2007. Tillage effects on soil carbon
fractions in the Sanjiang Plain, Northeast China. Soil Till. Res. 93,
102–108.
Zobeck, T.M., 1991. Soil properties affecting wind erosion. J. Soil
Water Conserv. 46, 112–118.
Zotarelli, L., Alves, B.J.R., Urquiaga, S., Torres, E., Santos, H.P.,
Paustian, K., Boddey, R.M., Six, J., 2005. Impact of tillage and
crop rotation on aggregate-associated carbon in two oxisols. Soil
Sci. Soc. Am. J. 69, 482–491.
ntents and aggregation related to soil physical and biological
llage Res. (2008), doi:10.1016/j.still.2008.02.003