Agriculture Reference
In-Depth Information
Table 12.6. Nitrous oxide (N 2 O) and methane (CH 4 ) fluxes and GWIs from 1991
to 2010 of the MCSE. *
System
GHG Flux
GWI
N 2 O-N
CH 4 -C
N 2 O
CH 4
(g ha −1 d −1 )
(g CO 2 e m −2 y −1 )
Annual Crops (corn-soybean-wheat rotation)
Conventional
2.15 (0.33) a
-0.69 (0.09) a
36.6 (5.6)
-0.8 (0.1)
No-till
2.27 (0.15) a
-0.65 (0.06) a
38.6 (2.5)
-0.7 (0.1)
Reduced Input
2.06 (0.13) a
-0.57 (0.05) a
35.0 (2.3)
-0.6 (0.1)
Biologically Based
1.91 (0.15) a
-0.85 (0.03) b
32.5 (2.6)
-1.0 (0.0)
Perennial Crops
Alfalfa
2.72 (0.24) a
-0.87 (0.08) b
46.16 (4.2)
-1.0 (0.1)
Poplar
0.38 (0.04) b
-0.81 (0.05) a,b
6.4 (0.6)
-0.9 (0.1)
Successional Community
Early Successional
0.66 (0.05) c
-0.89 (0.05) b
11.2 (0.9)
-1.0 (0.1)
* Statistically significant differences (ANOVA repeated measures, p < 0.05) are indicated by different letters within
columns. GHG fluxes are based on untransformed values and GWIs are carbon dioxide equivalents (CO 2 e), calculated
using a 100-year time horizon (IPCC 2007), and all are expressed as mean (±SE, n  = 4 replicates).
Soil GHG fluxes were sampled April-December, 1991-2010. Positive values indicate emission to the atmosphere;
negative values are uptake.
Source: Gelfand et al. (2013).
(Syswerda et  al. 2012). After 20  years of abandonment, however, CH 4 oxidation
does begin to recover slightly in these systems (Table 12.6; Gelfand et al. 2013).
Measurements in our Mid-successional community suggest that it takes 50 years
or more for CH 4 oxidation to exceed 50% of preconversion rates (Robertson et al.
2000, Suwanwaree and Robertson 2005).
Why does CH 4 consumption take so long to recover to preconversion levels?
Part of the explanation may be related to methanotroph community composi-
tion and, in particular, methanotroph diversity (Gulledge et al. 1997). Levine et
al. (2011) found substantially higher methanotroph diversity in MCSE systems
with higher oxidation rates, suggesting that microbial community composition
(see Schmidt and Waldron 2015, Chapter 6 in this volume) may matter for CH 4
oxidation in the same way that it matters for N 2 O production via denitrification
(Cavigelli and Robertson 2000, 2001; Schmidt and Waldron 2015, Chapter 6 in
this volume).
Soil CH 4 oxidation is not known to be affected by any existing agronomic prac-
tice; it is as low in the MCSE No-till and Reduced Input systems and in various
organic systems of the Living Field Lab Experiment (Robertson and Hamilton
2015, Chapter 1 in this volume; Snapp et al. 2015, Chapter 15 in this volume) as it
is in the fertilized Conventional system (Suwanwaree 2003). Alternative agronomic
practices that increase the capacity for CH 4 oxidation could have the potential for
significant GWI mitigation (Gelfand et al. 2013).
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