150
9.2.2.4 Soil Type
Emissions and mitigation from rice straw management are highly dependent on soil
type (Badagliacca et al. 2017). A meta-analysis of GHGE studies across Japan
showed that CH 4 emissions significantly varied by soil type by as much as 200%
(Kajiura et al. 2018). Still, the soil properties that stimulate CH 4 emissions from
straw incorporation are not well understood. Conditions known to stimulate methanogenesis are a soil redox potential below −200 mV and neutral pH. It can be
assumed that the variability in CH 4 production by soil type may be related to differences in soil nutrients. Some studies suggest that high levels of ammonia and sulfates are known to inhibit methanogenesis (Sánchez et al. 2015).
The ability of straw incorporation to improve SOC sequestration is also affected
by soil type. Generally, soils which have been depleted of SOC and contain high
clay or oxygen-reduced conditions can store more C. It is estimated that returning
crop residues to these soils along with proper CSA management could help sequester enough SOC to offset the current increase in emissions from all anthropogenic
sources (White 2017).
9.2.2.5 Fertilizer
Studies suggest there is a significant interaction effect of rice straw management
and fertilizer on GHGEs. Yet, the degree of this effect is complex and thus difficult
to form conclusions on management recommendations. N 2 O emissions from the
application of organic and inorganic fertilizers are, however, an important topic as
they represent 5% of global anthropogenic emissions (IPCC 2007). Although N 2 O
is considered negligible during most rice production, which is flooded or kept saturated, trends towards more aerobic rice systems due to water limitations and increasing upland crop rotation make N 2 O a concern. A meta-analysis on 112 assessments
showed that straw incorporation can reduce N 2 O emissions from fertilizer by 27%
in rice, although straw incorporation alone generally increased N 2 O due to the
inherent N content of straw (Shan and Yan 2013). There is also evidence that CH 4
emissions from straw incorporation are affected by fertilizer. A meta-analysis of
155 data pairs showed that N fertilizer stimulated CH 4 emissions in 64% of cases
and the stimulatory effect of N fertilizer on CH 4 was two to threefold greater with
urea than with ammonium sulphate (Banger et al. 2012).
J. Allen et al.
9.2.2.4 Soil Type
Emissions and mitigation from rice straw management are highly dependent on soil
type (Badagliacca et al. 2017). A meta-analysis of GHGE studies across Japan
showed that CH 4 emissions significantly varied by soil type by as much as 200%
(Kajiura et al. 2018). Still, the soil properties that stimulate CH 4 emissions from
straw incorporation are not well understood. Conditions known to stimulate methanogenesis are a soil redox potential below −200 mV and neutral pH. It can be
assumed that the variability in CH 4 production by soil type may be related to differences in soil nutrients. Some studies suggest that high levels of ammonia and sulfates are known to inhibit methanogenesis (Sánchez et al. 2015).
The ability of straw incorporation to improve SOC sequestration is also affected
by soil type. Generally, soils which have been depleted of SOC and contain high
clay or oxygen-reduced conditions can store more C. It is estimated that returning
crop residues to these soils along with proper CSA management could help sequester enough SOC to offset the current increase in emissions from all anthropogenic
sources (White 2017).
9.2.2.5 Fertilizer
Studies suggest there is a significant interaction effect of rice straw management
and fertilizer on GHGEs. Yet, the degree of this effect is complex and thus difficult
to form conclusions on management recommendations. N 2 O emissions from the
application of organic and inorganic fertilizers are, however, an important topic as
they represent 5% of global anthropogenic emissions (IPCC 2007). Although N 2 O
is considered negligible during most rice production, which is flooded or kept saturated, trends towards more aerobic rice systems due to water limitations and increasing upland crop rotation make N 2 O a concern. A meta-analysis on 112 assessments
showed that straw incorporation can reduce N 2 O emissions from fertilizer by 27%
in rice, although straw incorporation alone generally increased N 2 O due to the
inherent N content of straw (Shan and Yan 2013). There is also evidence that CH 4
emissions from straw incorporation are affected by fertilizer. A meta-analysis of
155 data pairs showed that N fertilizer stimulated CH 4 emissions in 64% of cases
and the stimulatory effect of N fertilizer on CH 4 was two to threefold greater with
urea than with ammonium sulphate (Banger et al. 2012).
J. Allen et al.