149
9.2.2.2 Cropping System
As with irrigation management, the type of cropping system is an important factor
in controlling soil conditions and emissions from rice straw. Because fallow conditions and upland crops mostly eliminate anaerobic conditions for CH 4 production,
the emissions from aerobic decomposition (N 2 O, CO 2 ) and loss in SOC can be significant. For example, SOC levels in a long-term rice–maize rotation at IRRI were
14% lower than that of continuous rice (Witt et al. 2000). For this reason, intensive
rice–upland cropping systems may require complete straw return to the upland crop
to prevent SOC depletion.
9.2.2.3 Tillage
Tillage type and timing can greatly affect emissions from straw returned to the field.
When straw is chopped and incorporated into the soil at least 30 days before flooding, rice CH 4 emissions have been shown to be reduced by up to 80% (Launio et al.
2013; Kajiura et al. 2018). Reduction CH 4 emissions can be attributed to the
increased aerobic decomposition of straw to stabilized SOM before flooding. Due
to the additional benefits of early incorporation to planting and soil quality, it is
considered a CSA priority for flooded rice. In fact, studies show early incorporation
is one the most cost-effective, climate-smart rice straw management options (Launio
et al. 2016).
When residue is removed, tillage has shown to increase emissions and reduce
SOC in rice. A meta-analysis on 48 studies on continuous rice in China showed that
no-till reduced the GWP from CO 2 and CH 4 by 20.4% when straw was removed, but
had no significant effect when straw was returned (Feng et al. 2018; Huang
et al. 2018).
In upland crops after rice, no-tillage with full straw returned is an established
CSA strategy for many rice–upland environments (Grace et al. 2012). A study on
marginal abatement costs suggest that no-till accounted for 70% of the cost- effective
GHG mitigation potential in 2010 across non-rice crops (EPA 2013). The effects of
no-till and straw mulching on yield, GHG emissions, and soil quality are most pronounced in rainfed, light textured soils. In fact, no-till for the rice–wheat rotation is
credited as one of the greatest resource-saving technologies for the Indo-Gangetic
Plains (Erenstein 2009; Zandstra 1982). Tillage is shown to stimulate mineralization and oxidation of SOM in aerobic soils, causing a reduction in SOC and increase
in N 2 O emissions. These effects have been established in many meta-analyses (Zhao
et al. 2015; Feng et al. 2018; Lu 2015; Liu et al. 2014). Therefore, the optimal tillage
management for CSA in rice–upland systems is often complete straw returned as
mulch with no-till in the upland crop followed by early residue incorporation or
removal before flooded rice.
9 Rice Straw Management Effects on Greenhouse Gas Emissions and Mitigation…
9.2.2.2 Cropping System
As with irrigation management, the type of cropping system is an important factor
in controlling soil conditions and emissions from rice straw. Because fallow conditions and upland crops mostly eliminate anaerobic conditions for CH 4 production,
the emissions from aerobic decomposition (N 2 O, CO 2 ) and loss in SOC can be significant. For example, SOC levels in a long-term rice–maize rotation at IRRI were
14% lower than that of continuous rice (Witt et al. 2000). For this reason, intensive
rice–upland cropping systems may require complete straw return to the upland crop
to prevent SOC depletion.
9.2.2.3 Tillage
Tillage type and timing can greatly affect emissions from straw returned to the field.
When straw is chopped and incorporated into the soil at least 30 days before flooding, rice CH 4 emissions have been shown to be reduced by up to 80% (Launio et al.
2013; Kajiura et al. 2018). Reduction CH 4 emissions can be attributed to the
increased aerobic decomposition of straw to stabilized SOM before flooding. Due
to the additional benefits of early incorporation to planting and soil quality, it is
considered a CSA priority for flooded rice. In fact, studies show early incorporation
is one the most cost-effective, climate-smart rice straw management options (Launio
et al. 2016).
When residue is removed, tillage has shown to increase emissions and reduce
SOC in rice. A meta-analysis on 48 studies on continuous rice in China showed that
no-till reduced the GWP from CO 2 and CH 4 by 20.4% when straw was removed, but
had no significant effect when straw was returned (Feng et al. 2018; Huang
et al. 2018).
In upland crops after rice, no-tillage with full straw returned is an established
CSA strategy for many rice–upland environments (Grace et al. 2012). A study on
marginal abatement costs suggest that no-till accounted for 70% of the cost- effective
GHG mitigation potential in 2010 across non-rice crops (EPA 2013). The effects of
no-till and straw mulching on yield, GHG emissions, and soil quality are most pronounced in rainfed, light textured soils. In fact, no-till for the rice–wheat rotation is
credited as one of the greatest resource-saving technologies for the Indo-Gangetic
Plains (Erenstein 2009; Zandstra 1982). Tillage is shown to stimulate mineralization and oxidation of SOM in aerobic soils, causing a reduction in SOC and increase
in N 2 O emissions. These effects have been established in many meta-analyses (Zhao
et al. 2015; Feng et al. 2018; Lu 2015; Liu et al. 2014). Therefore, the optimal tillage
management for CSA in rice–upland systems is often complete straw returned as
mulch with no-till in the upland crop followed by early residue incorporation or
removal before flooded rice.
9 Rice Straw Management Effects on Greenhouse Gas Emissions and Mitigation…