Modeling impacts of farming management alternatives on CO₂, CH₄, and N₂O emissions: A case study for water management of rice agriculture of China

Abstract

[1] Since the early 1980s, water management of rice paddies in China has changed substantially, with midseason drainage gradually replacing continuous flooding. This has provided an opportunity to estimate how a management alternative impacts greenhouse gas emissions at a large regional scale. We integrated a process-based model, DNDC, with a GIS database of paddy area, soil properties, and management factors. We simulated soil carbon sequestration (or net CO 2 emission) and CH 4 and N 2 O emissions from China's rice paddies (30 million ha), based on 1990 climate and management conditions, with two water management scenarios: continuous flooding and midseason drainage. The results indicated that this change in water management has reduced aggregate CH 4 emissions about 40%, or 5 Tg CH 4 yr À1 , roughly 5-10% of total global methane emissions from rice paddies. The mitigating effect of midseason drainage on CH 4 flux was highly uneven across the country; the highest flux reductions (>200 kg CH 4 -C ha À1 yr À1 ) were in Hainan, Sichuan, Hubei, and Guangdong provinces, with warmer weather and multiple-cropping rice systems. The smallest flux reductions (<25 kg CH 4 -C ha À1 yr À1 ) occurred in Tianjin, Hebei, Ningxia, Liaoning, and Gansu Provinces, with relatively cool weather and single cropping systems. Shifting water management from continuous flooding to midseason drainage increased N 2 O emissions from Chinese rice paddies by 0.15 Tg N yr À1 ($50% increase). This offset a large fraction of the greenhouse gas radiative forcing benefit gained by the decrease in CH 4 emissions. Midseason drainage-induced N 2 O fluxes were high (>8.0 kg N/ha) in Jilin, Liaoning, Heilongjiang, and Xinjiang provinces, where the paddy soils contained relatively high organic matter. Shifting water management from continuous flooding to midseason drainage reduced total net CO 2 emissions by 0.65 Tg CO 2 -C yr À1 , which made a relatively small contribution to the net climate impact due to the low radiative potential of CO 2 . The change in water management had very different effects on net greenhouse gas mitigation when implemented across climatic zones, soil types, or cropping systems. Maximum CH 4 reductions and minimum N 2 O increases were obtained when the mid-season draining was applied to rice paddies with warm weather, high soil clay content, and low soil organic matter content, for example, Sichuan, Hubei, Hunan, Guangdong, Guangxi, Anhui, and Jiangsu provinces, which have 60% of China's rice paddies and produce 65% of China's rice harvest.

Validation of the DNDC-Rice model by using CH4and N2O flux data from rice cultivated in pots under alternate wetting and drying irrigation management

“…Li et al (2005) ) were well correlated (n ¼ 9, r 2 ¼ 0.93, p < 0.01), but the estimation errors ranged from À220% to þ28.6%. Fumoto et al (2010) tested the DNDC-Rice model by using data from a paddy field in Japan; they found simulated seasonal N 2 O emissions of 0.08 to 0.65 kg N ha…”

“…Simulation of N 2 O fluxes by using the DNDC model or the DNDC-Rice model has been reported by Li et al (2005), Babu et al (2006), and Fumoto et al (2010). Li et al (2005) reported that the DNDC model was capable of estimating the seasonal magnitudes of N 2 O fluxes from paddy sites, although discrepancies existed for about 20% of their tested cases.…”

“…Li et al (2005) reported that the DNDC model was capable of estimating the seasonal magnitudes of N 2 O fluxes from paddy sites, although discrepancies existed for about 20% of their tested cases. Babu et al (2006) also validated the model, by using data from Delhi and Ludhiana, India, and reported that the total observed and simulated seasonal N 2 O emissions were strongly correlated, although the daily fluxes revealed discrepancies and the simulated seasonal N 2 O emissions were 248% lower to 28.6% higher than the observed values.…”

The global methane budget 2000–2012

“…The geographical distribution of the emissions is assessed by global (USEPA, 2006(USEPA, , 2012EDGARv4.2FT2010, 2013 and regional Chen et al, 2013;Chen and Prinn, 2006;Yan et al, 2009;Castelán-Ortega et al, 2014; inventories or by land surface models (Spahni et al, 2011;Zhang and Chen, 2014;Ren et al, 2011;Tian et al, 2010Tian et al, , 2011Li et al, 2005;Pathak et al, 2005). The emissions show a seasonal cycle, peaking in the summer months in the extratropics associated with the monsoon and land management.…”

Agricultural Sustainability

“…This Tier 1 estimate of CH4 emissions was then compared to a Tier 3 estimate generated using the DeNitrification-DeComposition (DNDC) model, which was modified for paddy-rice through the addition of anaerobic soil biogeochemical processes (Li et al 2004(Li et al , 2005. Due to the passage of the Rice Straw Burning Act of 1991, the burning of rice residue in California has been gradually phased out (Hill et al 2006).…”