Agriculture Reference
In-Depth Information
rather than increased erosion in these well-drained soils. With continued erosion
and the projected further increase in global temperature, the adoption of no-till
management or the inclusion of cover crops in the crop rotation (Willson et al.
2001) may be necessary to sustain present soil C levels.
Results from KBS show that C losses in near surface soils can be slowed or even
reversed with no-till and biologically based farming practices. Rates of SOC accu-
mulation in the top 5-7 cm of no-till relative to conventional tillage are ~22-30 g C
m
−2
yr
−1
(Robertson et al. 2000, Grandy and Robertson 2007) and are similar to those
for the entire Ap horizon (33 g C m
−2
yr
−1
, Syswerda et al. 2011), indicating that most
change occurs in the upper few centimeters. This is consistent with other estimates for
U.S. Midwestern cropping systems (West and Marland 2002). There is no evidence
for C change in deeper horizons of no-till soils at KBS (to 1 m; Syswerda et al. 2011),
which means that whole-profile C change is dominated by changes in surface soils.
That coefficients of variation for soil C increase from 7% in Ap to 29% in B/Bt to 92%
in Bt2/C horizons (Syswerda et al. 2011) underscores the difficulty with which subsur-
face soil C change can be detected if it occurs at all (Kravchenko and Robertson 2011).
Table 5.3. Baseline and contemporary SOC content and changes in SOC in the
MCSE and Interactions Experiment.
†
System
SOC
‡
(g kg
−1
soil)*
Change in SOC (g kg
−1
soil)
††
MCSE
1988
2006
From 1988 to 2006
Conventional
9.3 (0.7)
a
8.2 (0.3)
a
-1.15 (0.27)
a
No-till
10.6 (0.5)
a
9.9 (0.5)
b
-0.71 (0.48)
ab
NS
Biologically Based
10.0 (0.5)
a
9.8 (0.3)
b
-0.16 (0.29)
b
NS
P
value
0.13
0.002
0.06
Interactions Experiment
1986
2007
From 1986 to 2007
Conventional tillage
N-fertilized
9.8 (1.4)
a
9.5 (0.5)
a
-0.22 (0.46)
ab
NS
Not N-fertilized
9.8 (1.4)
a
8.2 (0.5)
b
-1.54 (0.51)
a
No-till
N-fertilized
7.4 (1.4)
a
8.3 (0.5)
ab
0.31 (0.48)
b
NS
Not N-fertilized
8.7 (1.4)
a
8.9 (0.5)
ab
0.19 (0.51)
b
NS
P
value
0.11
0.07
0.07
Mown Grassland (never tilled)
23.0 (0.9)
15.3 (0.6)
-7.7 (1.0)
†
Mean SOC content (±SE) in 1988 and 2006 for the MCSE (see Table 5.1) and in 1986 and 2007 for the Interactions
Experiment and Mown Grassland. Interactions Experiment systems are also corn-soybean-wheat rotations, but
either tilled or no-till and N-fertilized or not N-fertilized in a full factorial design (see
http://lter.kbs.msu.edu
for
a description). The Mown Grassland (never tilled) system is part of the MCSE (Table 5.1) and is adjacent to the
Interactions Experiment.
P
values are from an ANCOVA for testing the significance of the factor effects.
‡
Sampled to 15-cm depth in the MCSE and to 20 cm in the Interactions Experiment.
*Within the same column, values followed by the same letter for a given experiment are not significantly different at
α
= 0.1.
††
Within this column, values followed by the same letter for a given experiment are not significantly different at
α
= 0.05.
Note
: NS = the mean value is not significantly different from zero (
P
< 0.05).
Source:
Senthilkumar et al. (2009a).
