University of Nebraska - Lincoln
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Publications from USDA-ARS / UNL Faculty
U.S. Department of Agriculture: Agricultural
Research Service, Lincoln, Nebraska
2002
Particulate Soil Organic Matter Carbon In Surface
Soils After 12 Years In No-Till Dryland Cropping
Systems
L.A. Sherrod
USDA-ARS Great Plains Systems Research
G.A. Peterson
Colorado State University - Fort Collins
D.G. Westfall
Colorado State University - Fort Collins
L.R. Ahuja
USDA-ARS Great Plains Systems Research
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Sherrod, L.A.; Peterson, G.A.; Westfall, D.G.; and Ahuja, L.R., "Particulate Soil Organic Matter Carbon In Surface Soils After 12 Years
In No-Till Dryland Cropping Systems" (2002). Publications from USDA-ARS / UNL Faculty. 1063.
http://digitalcommons.unl.edu/usdaarsfacpub/1063
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Proceedings of the Great Plains Soil Fertility Conference,
Denver, Colorado, March 5-6, 2002, ed. Alan J. Schlegel.
PARTICULATE SOIL ORGANIC MATTER CARBON IN SURFACE SOILS AFTER 12
YEARS IN NO-TILL DRYLAND CROPPING SYSTEMS
L.A.Sherrod!, G.A. Peterson2 , D.G. Westfall 2 , and L.R. Ahuja!
USDA-ARS Great Plains Systems Research, Fort Collins, COl
Department of Soil and Crop Sciences, Colorado State University, Fort Collins, C0 2
ABSTRACT
Soil organic carbon (SOC) in the surface soils has increased when summer fallow is reduced or
eliminated in the central Great Plains. We evaluated the effect of no-till cropping systems of WF,
wheat-com-fallow (WCF), wheat-corn-millet-fallow (WCMF), opportunity cropping (OPP), and
native grass species (G) on particulate organic matter (POM-C) and mineral associated C in the silt
and clay fractions. Soil organic carbon (SOC) has increased with increasing cropping intensity after
12 years, of no-till management. Particulate organic matter C accounted for 38 to 52 % of the total
SOC in the 0-2.5 cm and 24 to 48 % of the total SOC in the 2.5-5 cm depth depending on cropping
intensity. In the 5-10 cm depth, POM-C accounted for 22-35 % of the total SOC depending on
cropping intensity. In the 10-20 cm depth, however, POM-C accounted for only 0 to 12 % of the
total SOC depending on cropping intensity. In all depth increments however, G had the highest
POM-C followed by OPP. Overall, the increase in total SOC in surface soils with increasing
cropping intensity was due to increased C in the POM-C fraction.
INTRODUCTION
Soil organic matter degradation has occurred in the Great Plains soils with estimates of loss
up to 50 percent. The labile fraction represented by POM-C has been most affected by this
degradation. Particulate organic matter C is important for aggregate stability, nutrient cycling, and
water infiltration. Particulate organic matter is defined as material that passes through a 2 mm sieve
but is retained on a 53 um sieve minus the sand.
Production sustainability depends on management practices that promote the increase in
POM-C from primary production inputs. Impact of cropping system intensity as it relates to POM-C
has not been quantified We hypothesized that cropping systems that maximize production and reduce
and/or eliminate the practice of summer fallowing will provide the carbon inputs that will increase
POM-C.
bur objective was to evaluate the effect of site (ET gradient), slope position, and cropping
system intensity on the amount of POM-C and the more stable mineral associated C. Specifically,
we wanted to determine the POM-C and mineral soil C in surface soils ofWF, WCF, WCMF, OPP
(no summer fallow) and G after12 years in no-till across a ET gradient represented by three sites in
eastern Colorado and three slope positions.
MATERIALS AND METHODS
A no-till dryland cropping systems experiment was initiated in the fall of 1985 at 3 sites near
Sterling, Stratton, and Walsh Colorado located along a PET gradient from 1000 mm to 1900 mm
143
each with an average annual precipitation of 425 mm. Each site has a catenary sequence of soils
across which cropping system treatments were imposed. Cropping systems treatments are WF,
WCF, WCMF, and OPP. At the high PET site, Walsh, grain sorghum is substituted for corn. All
cropping system treatments have all phases of the rotation present each year. The fallow phase of
the WF, WCF, and WCMF systems along with OPP and G was sampled in the fall of 1997 in 0-2.5,
2.5-5, and 5-10cm depth increments. Bulk density was sampled at the same time for all depths.
Particulate organic matter was obtained by taking a 10 g 2-mm sieved sub-sample and
dispersing with 0.5 % sodium hexametaphosphate overnight and then washing this suspension
through a 53 urn sieve and collecting the mineral slurry going through. This mineral slurry was
oven dried at 70° C overnight, weighed and powder ground. A 0.2000 g sub-sample of this mineral
associated soil fraction along with a sub-sample from the whole soil was then analyzed by
combustion furnace. The mineral associated C was then subtracted from the whole soil carbon to
obtain the POM-C (Cambardella and Elliott, 1992). The C data from the LECO CHN-1000
combustion furnace was corrected for inorganic carbon by using the modified pressure-calcimeter
method (Sherrod et aI., 2002).
RESULTS AND DISCUSSION
The amount ofPOM-C found in the 0-2.5 cm depth was significantly increased by increasing
cropping intensity with OPP and G having the highest mass and WF having the lowest mass (Figure
1). The mineral associated C was not affected by cropping intensity at any depth. The amount of
POM-C found in the 2.5-5 cm depth also increased with increasing cropping intensity (Figure 2).
Cropping intensity also increased POM-C in the 5-10 cm depth with OPP and G significantly higher
than WF (Figure 3). The percent of POM-C found in the SOC decreased as profile depth increased
(Figure 5). Particulate organic matter C accounted for 38 to 52 % of the total SOC in the 0-2.5 cm
and 24 to 48 % of the total SOC in the 2.5-5 cm depth depending on cropping intensity. In the 5-10
cm depth, POM-C accounted for 22-35 % of the total SOC depending on cropping intensity. In the
10-20 cm depth, however, POM-C accounted for only 0 to 12 % of the total SOC depending on
cropping intensity. Mineral associated C was affected by interaction (P = 0.0064) with slope
position and cropping intensity in the 0-2.5 cm (Figure 6). As cropping intensity increased, so did
the mineral associated C in the toeslope position. However, the side and summit soil positions did
not change in mineral associated C with increased cropping intensity.
The ET gradient affected total POM -C in the 0-10 cm depth with levels decreasing as ET
increased. (Figure 7). Slope position also affected POM-C in the 0-10 cm depth with the toeslope
soil having approximately 1/3 more C than the side and summit soils (Figure 8). Cropping intensity,
averaged over sites and slopes, increased POM-C in the 0-10 cm depth (P=<.OOOl) which related
directly to the increase in cropping intensity (Figure 9). The G treatment and OPP was higher than
all other cropping systems but lower than the G system. The WF cropping system had 3000 kg ha~1
POM-C averaged over sites and slopes, whereas OPP cropping without any summer fallow, had
4800 kg ha ~I. If we look at all depths averaged over sites and slopes we can see that the first 0-2.5
cm is most impacted POM-C fraction followed by the 5-10 cm depth with the 10-20 cm depth
showing the most variability (Figure 10).
144
CONCLUSIONS
Particulate organic matter C was significantly affected by ET gradient and slope position
down to the a 10 cm soil depth. Cropping system intensity increased POM-C in the 0-10 cm
depth as well. There was however a interaction between cropping system and slope for the 0-2.5
cm depth. Cropping systems that intensify the frequency of cropping and reduce and/or eliminate
summer fallow maximized the amount ofPOM-C and this fraction represented approximately 50
% of the SOC in the OPP and G treatments in the 0-2.5cm depth. Particulate organic matter Cis
considered the active fraction of soil OM and is most susceptible to management effects. By
eliminating summer fallow and/or limiting the frequency by increasing cropping intensity with notill management, significant increases in the POM-C have occurred. These changes positively
impact aggregate stability, nutrient cycling, and water infiltration. The result of imposing no-till
management, which allowed for systems with greater cropping intensity, increased SOC levels
with increasing cropping intensity. These observed increases in SOC levels have been the result
of increases in the POM-C fraction.
REFERENCES
Cambardella, c.A. and E. T. Elliott. 1992. Particulate Soil Organic-Matter Changes across a
Grassland Cultivation Sequence. Soil Sci. Soc. Am. 1. 56:777-783.
Peterson, G.A., D.G. Westfall, and C.Y. Cole. 1993. Agroecosystem approach to soil and crop
management research. Soil Sci. Soc. Am. 1. 57: 1354-1360.
Sherrod, L.A., G. Dunn, G.A. Peterson, and R.L. Kolberg. 2002. Inorganic Carbon Analysis by
Modified Pressure-Calcimeter Method. Soil Sci. Soc. Am. 1. 66:299-305.
12000
10000
POM P=<.0001
mlPOM
.. Mineral
Mineral =0.2998
I
~
8000
6000
4000
2000
0
WF
WCF
WCMF
OPP
GRASS
Cropping Intensity
Figure l.Particulate organic matter carbon and mineral associated carbon as affected by
cropping intensity in the 0-2.5 cm depth.
145
12000
10000
I
PO M
• Mineral
+-------------------------jllll!ll
8000
POM P=<.0001
6000
~
Mineral P=O.2956
4000
2000
0
WF
WCF
WCMF
GRASS
OPP
Cropping Intensisy
Figure 2. Particulate organic matter carbon and mineral associated carbon as affected by
cropping intensity in the 2.5-5 cm depth.
12000
10000
j
~
j
..
a
8000
Mineral P=O.6721
6000
4000
2000
0
WF
WCF
opp
WCMF
GRASS
C roppi-ng Intensity
Figure 3. Particulate organic carbon and mineral associated carbon as affected by cropping
cropping intensity in the 5-10 cm depth.
12000
10000
8000
6000
4000
2000
o
WF
WCF
WCMF
opp
GRASS
Cropping Intensity
PO M·C P=O.0720
Mineral P=O.3276
Figure 4. Particulate organic matter carbon and mineral associated carbon as affected by
cropping intensity in the 10-20 cm depth.
146
'2
.c
g
U
-;
...
'"
=
~
3500
3000
2500
2000
1500
1000
500
0
WF
W CF
Opp
WCMF
GRASS
Cropping Intensisy
IDSide IIIIISummit IIIIlIToe I
Figure 5. Percent of POM-C found in soil organic carbon as affected by cropping intensity
and depth increment after 12 years in No-till dryland management.
j
)
'-"
U
";!
...
~
3500
3000
2500
2000
1500
1000
500
0
WF
WCF
WCMF
OPP
GRASS
Cropping Intensisy
IDSide "Summit .Toe I
Figure 6. Mineral associated C as affected by slope position and cropping system intensity
after 12 years under No-till management.
..
~
.c
~
=
.8...
..
U
7000
6000
5000
4000
3000
2000
1000
0
PO M
Fraction
I_Low
ET
IIIIIIM ed ET
WHigb ET
Figure 7. Particulate organic matter carbon in 0-10 cm as affect by ET site location after
12 years in No-till dryland management.
147
6000
5000
'OS'
.------------------- - ----- --------------------- --------
_____L_~~_=__9_76_______________________________~
P
..c
~
4000
U
3000
~
2000
= 0.0039
~
1000
0
Sid e
Toe
Summit
S 10 pe
Figure 8. Particulate organic matter carbon in the 0-10 cm depth as affect by slope position
after 12 years in No-till management.
7000
6000
.c
""'~
U
:>:
...0
~----------
--------
---- -C 5 0-,;-721--------- - - - - - - - - - - - -- ----
5000
4009
3000
2000
1000
0
WF
W C F
opp
WC:MF
Cropping System
G RA SS
Intensity
Figure 9. Particulate organic matter carbon in the 0-10 cm depth as affect by cropping
system intensity after 12 years in No-till dryland management.
1_10-20 em D 5-10 em 1m12.5-5 em III!II 0-2.5 em
10000
'OJ'
LSD 0 -2 0 c m
~
""
0'
~
=1 64 5
8000
..c
6000
---
- - -- - - - - - - - - - - - - - - - - - - - - - - - - - - - -
4000
2000
()
WF
WCF
WCMF
opp
GRASS
Cropping Intensity
Figure 10. Particulate organic matter carbon down to 20 cm depth, as affect by cropping
system intensity after 12 years in no-till dryland management.
148