Mitigating effects of ex situ application of rice straw on CH4 and N2O emissions from paddy-upland coexisting system

Abstract

The in situ application of rice straw enhances CH4 emissions by a large margin. The ex situ application of rice straw in uplands, however, may mitigate total global warming potential (GWP) of CH4 and N2O emissions from paddy-upland coexisting systems. To evaluate the efficiency of this practice, two field trials were conducted in rice-rice-fallow and maize-rape cropping systems, respectively. Year-round measurements of CH4 and N2O emissions were conducted to evaluate the system-scaled GWP. The results showed that CH4 accounted for more than 98% of GWP in paddy. Straw removal from paddy decreased 44.7% (302.1 kg ha−1 yr−1) of CH4 emissions and 51.2% (0.31 kg ha−1 yr−1) of N2O emissions, thus decreased 44.8% (7693 kg CO2-eqv ha−1 yr−1) of annual GWP. N2O accounted for almost 100% of GWP in upland. Straw application in upland had insignificant effects on CH4 and N2O emissions, which increased GWP only by 91 kg CO2-eqv ha−1 yr−1. So, the transfer of straw from paddy to upland could decrease GWP by 7602 kg CO2-eqv ha−1 yr−1. Moreover, straw retention during late rice season contributed to 88.2% of annual GWP increment. It is recommended to transfer early rice straw to upland considering GWP mitigation, nutrient recycling and labor cost.

Investigation into the Effects of Straw Retention and Nitrogen Reduction on CH4 and N2O Emissions from Paddy Fields in the Lower Yangtze River Region, China

“…In double-rice-cropping systems, straw retention also significantly increased CH 4 and reduced N 2 O emission [34]. However, Wang et al [35] and Wu et al [36] showed that rice straw incorporation increased the field's N 2 O emissions. GHG emissions in paddy fields were sensitive to the straw retention mode, for instance, emissions of CH 4 and N 2 O in paddy fields with straw mulching were lower than those with straw incorporation into the soil [37].…”

“…Theoretically, straw retention affects CH 4 and N 2 O emissions by changing the soil's physical and chemical properties. Straw incorporation can decrease the soil's oxygen content during the rice season and provide organic substrates for microbial methanogens, thereby increasing the paddy field's CH 4 emissions [1,11,34,35,38]. The effect of straw incorporation on N 2 O emission is still controversial [1].…”

“…The effect of straw incorporation on N 2 O emission is still controversial [1]. Some researchers believe that returning straw to the field reduces N 2 O emissions [1,33,34,39], whereas others believe the exact opposite [35,36]. This controversy stems from the fact that paddy fields rich in N easily produce N 2 O via the nitrification process, while N 2 O emissions are reduced in a strong reducing environment because N 2 O can be transformed into N 2 during the denitrification process [40].…”

Rice straw as a feedstock for biofuels: Availability, recalcitrance, and chemical properties

“…This generates approximately 1140 million tons of rice straw considering the fact that approximately 1.5 tons of rice straw is generated per ton of rice. About 50% of rice straw is burnt in the field while the remaining is utilized as fodder or used in the wood‐composite industry, or left, as such, to decompose in landfills . Inefficient burning of rice straw releases large amounts of harmful gases including carbon monoxide, polycyclic aromatic hydrocarbons, volatile organic compounds, and nitrous oxides, along with suspended particulate matter .…”

“…[4][5][6] Ineffi cient burning of rice straw releases large amounts of harmful gases including carbon monoxide, polycyclic aromatic hydrocarbons, volatile organic compounds, and nitrous oxides, along with suspended particulate matter. 6 Th is leads to alarming levels of environmental pollution and represents a tremendous waste of lignocellulosic biomass resource. Hence, there is an urgent need to develop high-volume, value-added conversion technologies to harness the energy potential of surplus rice straw.…”