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9.3 Off-Field Straw Management Effects on GHGEs
9.3.1 Composting
Straw composting with manure can be an effective option to reduce CH 4 emissions
associated with in-field straw incorporation along with CH 4 and N 2 O emissions
from manure management. Manure management accounts for 11% of global agricultural emissions, thus is an equally important GHG source as lowland rice.
Emissions from manure are mainly in the form of CH 4 from anaerobic settling
ponds (23%) and N 2 O from manure applied to soils and dry storage (77%)
(FAO 2017).
Aerobic composting is an effective method to reduce methanogenesis of CH 4
from anaerobic manure storage in settling ponds. Studies suggest aerated manure
with straw can reduce CH 4 emissions up to 90% compared to anaerobic storage
(Petersen et al. 2013). The effects of composting on N 2 O emissions from manure
are, however, more complex than CH 4 . N 2 O is emitted indirectly from manure
mainly by NH 3 volatilization, which converts to N 2 O in the atmosphere. Smaller,
but additional N losses can occur from NO 3 leaching/erosion, which also convert
to N 2 O. Improper field application of manure or composting can cause an almost
100% loss of manure N to the atmosphere affecting both GHGEs and N supply
value if used for fertilizer. This often occurs when manure is applied to soils
with high pH and low CEC, and without injection/incorporation. In this scenario, composting manure with rice straw could provide substantial emissions
mitigation.
Rice straw is an ideal bulking agent for manure compost due to its high C:N
ratio, which can help maintain the ideal 25:1 of the compost. This C:N ratio maximizes N immobilization and substrate adsorption, which minimizes losses by volatilization and leaching. N losses from proper composting may be as low as 13% of
the original feedstock N (Chadwick et al. 2011). The opportunity to mitigate N 2 O
from composting, however, may be fairly small given many farms can avoid 100%
N loss by injecting/incorporating manure or applying it directly to soils with high
CEC, clay, or low pH. In this case, the mitigation opportunity of straw/manure
compost may be primarily through avoiding CH 4 emissions from anaerobic manure
storage and in-field rice straw incorporation, along with the potential indirect
abatement of emissions from N fertilizer production (Chen et al. 2011). An additional, yet understudied, effect of rice straw composting vs. in-field incorporation
may come from increased SOC sequestration. Although studies are limited, some
suggest composting increases the stabilized fraction of SOC and sequesters more
carbon compared to in-field aerobic decomposition of residue (Spaccini and
Piccolo 2017).
9 Rice Straw Management Effects on Greenhouse Gas Emissions and Mitigation…
9.3 Off-Field Straw Management Effects on GHGEs
9.3.1 Composting
Straw composting with manure can be an effective option to reduce CH 4 emissions
associated with in-field straw incorporation along with CH 4 and N 2 O emissions
from manure management. Manure management accounts for 11% of global agricultural emissions, thus is an equally important GHG source as lowland rice.
Emissions from manure are mainly in the form of CH 4 from anaerobic settling
ponds (23%) and N 2 O from manure applied to soils and dry storage (77%)
(FAO 2017).
Aerobic composting is an effective method to reduce methanogenesis of CH 4
from anaerobic manure storage in settling ponds. Studies suggest aerated manure
with straw can reduce CH 4 emissions up to 90% compared to anaerobic storage
(Petersen et al. 2013). The effects of composting on N 2 O emissions from manure
are, however, more complex than CH 4 . N 2 O is emitted indirectly from manure
mainly by NH 3 volatilization, which converts to N 2 O in the atmosphere. Smaller,
but additional N losses can occur from NO 3 leaching/erosion, which also convert
to N 2 O. Improper field application of manure or composting can cause an almost
100% loss of manure N to the atmosphere affecting both GHGEs and N supply
value if used for fertilizer. This often occurs when manure is applied to soils
with high pH and low CEC, and without injection/incorporation. In this scenario, composting manure with rice straw could provide substantial emissions
mitigation.
Rice straw is an ideal bulking agent for manure compost due to its high C:N
ratio, which can help maintain the ideal 25:1 of the compost. This C:N ratio maximizes N immobilization and substrate adsorption, which minimizes losses by volatilization and leaching. N losses from proper composting may be as low as 13% of
the original feedstock N (Chadwick et al. 2011). The opportunity to mitigate N 2 O
from composting, however, may be fairly small given many farms can avoid 100%
N loss by injecting/incorporating manure or applying it directly to soils with high
CEC, clay, or low pH. In this case, the mitigation opportunity of straw/manure
compost may be primarily through avoiding CH 4 emissions from anaerobic manure
storage and in-field rice straw incorporation, along with the potential indirect
abatement of emissions from N fertilizer production (Chen et al. 2011). An additional, yet understudied, effect of rice straw composting vs. in-field incorporation
may come from increased SOC sequestration. Although studies are limited, some
suggest composting increases the stabilized fraction of SOC and sequesters more
carbon compared to in-field aerobic decomposition of residue (Spaccini and
Piccolo 2017).
9 Rice Straw Management Effects on Greenhouse Gas Emissions and Mitigation…