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Rice planting (RP) is significant to methane (CH4) emissions from paddy fields, but its effect on the relative contribution of the acetoclastic methanogenesis to total CH4 production (Fac) and the fraction of CH4 oxidized (Fox) is poorly understood. To quantify the responses of the Fac and Fox to RP, we investigated CH4 fluxes, CH4 production and oxidation potentials, dissolved CH4 concentrations, and their stable carbon isotopes in a flooded paddy soil. The mcrA and pmoA gene copies were also determined by quantitative polymerase chain reaction (qPCR). Compared with the unplanted soil (control, CK), the seasonal CH4 emissions from the planted soil were significantly enhanced, 13.6 times, resulting in large decreases in the CH4 concentrations in the soil solution. This indicated that much more CH4 was released into the atmosphere by the RP than was stored in the soils. Acetoclastic methanogenesis became more important from the tillering stage (TS) to the ripening stage (RS) for the CK, with Fac values increased from 17%–20% to 46%–55%. With RP, the Fac values were enhanced by 10%–20%, and it significantly increased the copy numbers of the mcrA gene at the four rice stages (TS, booting stage (BS), grain-filling stage (GS), and RS). Furthermore, the effect of the RP on the abundance of the mcrA gene was highly concurrent with the effect on the Fac values. At the TS, the Fox values at the soil-water interface were around 50%–75% for the CK, being 15%–20% lower than those of the RP in the rhizosphere. It increased to 65%–100% at the GS, but was reduced by 20%–30% after the RP. These differences might be because the copy numbers of the pmoA gene were significantly raised at the TS while lowered at the GS by the RP. This was further demonstrated by the strong correlations between the effect of the RP on the abundance of the pmoA gene and the effect on the Fox values. These findings suggest that RP markedly impacts on the abundances of the mcrA and pmoA genes, affecting the pathway of CH4 production and the fraction of CH4 oxidization, respectively.

Ratoon rice (RR) is a practice that involves achieving a second crop originating from the stubble left after the previous main rice crop (MR) harvest. There has been little previous study on methane (CH₄) and nitrous oxide (N₂O) emissions from ratoon paddy fields. A 3‐year field experiment was conducted to simultaneously measure CH₄ and N₂O emissions from traditional single rice (SR) and MR + RR fields in Sichuan Province, southwest China. The CH₄ and N₂O flux peaks were earlier for MR than SR. The CH₄ emissions from the RR season accounted for 8–30% of total emissions from MR + RR. Compared with SR, MR + RR increased seasonal CH₄ emissions by 3–15%. Correlation analysis showed that the seasonal variation of CH₄ fluxes for MR + RR was significantly related to soil redox potential (Eh). The proportion of emitted N₂O from RR to MR + RR was 11–42%. The average cumulative N₂O emissions from MR and MR + RR were increased by 49 and 110% relative to those from SR plots across the 3 years, respectively. The global warming potential (GWP) of RR occupied 10–27% of MR + RR. The GWP of MR + RR was 7–62% higher than that of SR, and it was chiefly dependent on the contribution of CH₄ emissions, despite the greater increase in N₂O emissions. Grain yield in RR was 11–18% of that in MR + RR. MR + RR significantly increased rice yield by 19%, but the yield‐scaled GWP was comparable to SR. Our results suggest that MR + RR increases the amount of CH₄ and N₂O emissions from rice paddy fields and rice grain yield. The yield gaps of ratoon rice would be narrowed by optimizing field management practices to realize sustainable rice production under future climate change conditions. The CH₄ and N₂O emission peaks of ratoon rice were earlier than those of single rice. The CH₄ and N₂O emissions from ratoon rice fields were significantly higher than from single rice fields. Ratoon rice significantly increased yield and GWP compared to single rice. No significant difference in yield‐scaled GWP was observed between ratoon rice and single rice. HIGHLIGHTS: The CH₂ and N₂O emission peaks of ratoon rice were earlier than those of single rice. The CH₄ and N₂O emissions from ratoon rice fields were significantly higher than from single rice fields. Ratoon rice significantly increased yield and GWP compared to single rice. No significant difference in yield‐scaled GWP was observed between ratoon rice and single rice.

Agricultural plastic-film residues have been considered as one of the important sources of microplastics in the agroecosystem. However, limited researches were conducted on the accumulation of microplastics in long-term film-mulched paddy soil. This study aims to investigate the distribution and the weathering characteristics of filmy microplastics in a mulched paddy field (non-mulch, four years of mulched, and ten years of continuous mulched soil were investigated) in Southwest China. More than 50 % of the microplastics in the mulched soil were 1-3 mm, whereas the largest percentage of the microplastics in the non-mulched soil was1 mm (55.3 %). Microplastic compositions in this field mainly consist of polyester (PES) and polyethylene (PE) (82.1 %). The abundance of microplastics increases with the film mulching time, which were 76.2 ± 18.4, 118.6 ± 44.8, and 159.6 ± 23.5 items kg

Substituting nitrogen fertilizer with organic manure is a common fertilization practice in farmland, but its potential effect on heavy metal pollution and greenhouse gas (GHG) emissions remains unclear. A three-year field experiment was conducted in the rice-wheat rotation system, with two different substitution ratios (25% and 50%) of sewage sludge compost (SS) and pig manure compost (PM). With the substitutions of SS and PM, the heavy metals, including Cu, Zn, Cd, and Pb were accumulated in the soil, but the pollution load index was1 (0.39-0.66), indicating that soil was not polluted. Heavy metals Ni and Cu were mainly found in rice chaff, while Zn and Cd were accumulated in rice stalk, and the accumulation of Pb occurred in the leaf. For wheat, Ni, Cu, and Pb were accumulated in chaff, while grain and stalk had the highest concentrations of Zn and Cd, respectively. Moreover, the bioconcentration factor of heavy metals was 0-0.787, and their contents were below the standard limits for foods for rice and wheat in China, implying that the grains were unpolluted. Given the 5-8 fold increase in the sequestration rate of soil organic carbon with SS and PM substitutions, the annual net GHG emissions were reduced by 115-166%. Most importantly, 50% SS substitution exhibited the lowest net GHG emissions and highest rice and wheat yields. Overall, the results suggested that 50% SS substitution would be a feasible fertilization strategy that not only is unlikely to pose a high risk of soil and grain pollution but also significantly mitigates net GHG emissions and maintains high yields.

To reduce the utilization of chemical fertilisers, which cause substantial nitrogen loss and widespread nonpoint source pollution, the application of organic manure has become an increasingly popular alternative in rice agriculture. It plays key roles in improving soil quality and maintaining rice yields, but its integrated impacts on trace gas emissions and heavy metal contents in rice grains remain poorly documented. We conducted a three-year field experiment with two application ratios (25% and 50%) of sewage sludge compost (S) and pig manure compost (P) during the rice season in eastern China. The emissions of methane (CH

Tillage with the incorporation of stubble is a common practice in rice cultivation, but its effect on the net global warming potential (GWP) and greenhouse gas intensity (GHGI) is poorly documented. A three-year field experiment in a double-cropping rice system was conducted to investigate the rate of sequestration of soil organic carbon, CH4 and N2O emissions, the net GWP and the GHGI. Two timings of tillage with three amounts of stubble incorporation were prepared: winter tillage (tillage after the harvest of late rice) and spring tillage (tillage before the transplantation of early rice) with no (0 t ha−1), low (3.5 t ha−1) and high (5.2 t ha−1) amounts of stubble incorporation. The results showed that the rates of sequestration of soil organic carbon with the incorporation of stubble were 0.85–1.06 t C ha−1 yr−1 for winter tillage, 67–429% higher than for spring tillage. Winter tillage significantly increased CH4 and N2O emissions in the winter fallow season relative to spring tillage, whereas it tended to decrease both emissions in the early and late rice seasons, thus playing a small part in the annual emissions. The total CH4 and N2O emissions averaged 106.5–198.2 kg ha−1 yr−1 and 114.4–229.4 g N ha−1 yr−1, respectively. Significant decreases in the net GWP (46–82%) and GHGI (49–84%) were observed when changing the tillage practices with the incorporation of stubble from spring to winter. Compared with high levels of stubble incorporation, winter tillage with low levels of stubble incorporation significantly decreased both the net GWP and the GHGI. The total grain yield was 13.0–13.3 t ha−1 yr−1 for winter tillage, 3–5% higher than for spring tillage. These findings suggest that tillage with the incorporation of stubble in the winter fallow season, particularly with 3.5 t ha−1 stubble, is an effective strategy to mitigate the net GWP and GHGI while maintaining a high grain yield in the double-cropping rice system.

Rice cultivation faces increasing challenges to enhance the net ecosystem economic budget (NEEB), which is the balance between economic benefits and environmental costs. Plastic film mulching cultivation (MC) was evaluated for its ability to decrease the global warming potential (GWP) while increasing economic benefits relative to rainfed (RF) and traditional irrigation (TI). To comprehensively assess the effect on NEEB, the CH4 and N2O emissions and grain yields in a rice-based cropping system were measured from 2010 to 2014. The effects of urease and nitrification inhibitors (UNIs) and controlled release fertilizer (CRF) were also estimated. Shifting the field management from RF to MC had unclear impact on CH4 emissions, but increased N2O emissions by 77%. In contrast, switching TI to MC caused a significant reduction (45–85%) in CH4 emissions, producing a strong decrease in GWP, although N2O emissions substantially increased (206–1153%). The decrease in CH4 emissions was attributed to the reduced dissolved organic carbon and CH4 production, whereas the increase in N2O emissions might have resulted from the higher NH4+ concentrations and more favorable soil water content. Integrated assessment showed that MC significantly enhanced NEEB by 6136–8362 CNY ha−1 y−1 relative to RF as the yields increased and input costs reduced. Although MC reduced the yields, the much lower input and GWP costs led to a substantial increase in NEEB (2607–5593 CNY ha−1 y−1) relative to TI. Under MC conditions, applying UNIs and CRF obviously increased input costs though it always tended to enhance grain yields, thus decreasing NEEB by approximately 490–960 CNY ha−1 y−1, except CP addition, which had a positive effect on NEEB. The results demonstrate that MC, particularly MC + CP, are effective management strategies to reduce the environmental costs and increase the economic benefits of rice fields suffering from a lack of water supply.

Stubble return, drainage, and tillage are common practices in rice agriculture, but their integrated effects in the winter season on greenhouse gas (GHG) emissions and soil organic carbon (SOC) and total nitrogen (STN) sequestration remain poorly known. A six-year experiment was carried out in a double-rice field to measure CH4 and N2O fluxes and SOC and STN contents, and then the net global warming potential (GWP) and yield-scaled GWP were estimated. Shifting the fields from no management in tradition to tillage in the winter season tended to reduce total CH4 emissions of double-rice seasons by 14.7%, and it significantly decreased the emissions by 28.3% under drainage conditions. An additional reduction of 27.3% was further found without returning stubble. Therefore, winter tillage and drainage substantially reduced total GWP by 28.0%, in particular, a larger decrease (47.2%) was observed by no stubble return though N2O emissions were strongly stimulated by 82.1%. Moreover, winter tillage significantly reduced SOC sequestration rate while played little role in STN sequestration rate. However, winter tillage with stubble return (2.5–4.1 t ha−1) under drainage conditions showed the largest SOC (1.58 t C ha−1 yr−1) and STN (0.15 t N ha−1 yr−1) sequestration rates. Therefore, the net GWP and yield-scaled GWP were significantly decreased by 227% and 30.5%, respectively. Overall, our results suggest that winter drainage and tillage with stubble incorporation would be an effective management strategy to promote soil C and N sequestration and mitigate GHG emissions from the double-rice fields.

Ratoon rice involves the production of a second crop after the previous main crop harvest, originating from the remaining stubble. Plastic film mulching (PM) cultivation is considered a promising technique for improving economic benefits and reducing greenhouse gas intensity (GHGI). However, the effects of the different cultivation practices differences on the GHGI and the net ecosystem economic budget (NEEB) remain unclear. A three-year experiment was performed to measure CH4 and N2O emissions and grain yields, and then comprehensively assess the GHGI and NEEB. Four rice cropping treatments were established in a traditional single rice field: continuously flooded (CF), rainfed (RF), PM, and PM with ratoon rice cultivation (PM + RR). Compared with CF, RF increased N2O emissions by 108% and reduced CH4 emissions and grain yield by 75% and 22%, respectively, resulting in a reduction of NEEB by 1396 CNY ha−1 y−1. Switching from CF to PM, however, decreased annual CH4 emissions by 56% and increased N2O emissions by 358%, resulting in a 51% reduction in GHGI and an 883% increase in NEEB. Under PM, RR further reduced GHGI by 12% and increased NEEB by 18%. Compared with CF, PM + RR not only significantly increased crop yield by 1.32 t ha−1 and NEEB by 4410 CNY ha−1 y−1, but also dramatically decreased GHGI by 57%. These findings indicate that planting ratoon rice under PM can improve NEEB and reduce GHGI, potentially leading to a win-win situation for the environment and growers in water-stressed regions.

Winter flooded paddy fields emit considerable amounts of CH4 and N2O that add to global warming potential (GWP). However, mitigating the GWP and water use without compromising crop yield in the fields is poorly documented. A 3 year-round field experiment was conducted with the use of PM (plastic film mulching cultivation with water-saving irrigation in rice season while drainage in winter season) in comparison of two traditional paddies that were flooded in the winter season but either rain-fed (TC1) or continuously flooded (TC2) in the rice season. Shifting TC1 into PM significantly promoted rice tiller and increased grain yields by 23 %, showing a significant increase in effective number of panicles per m2 (40 %), total filled grains per m2 (55 %) and filled grains percentage (4.2 %). Changing TC2 into PM, however, had little effect on these variables. Compared with TC1 and TC2, the PM reduced annual water use by 20–69 %. Meanwhile, it decreased annual cumulative CH4 emissions by 23–64 % and increased N2O emissions by 56–4.2 %. This change was probably related to the significant decreases in both dissolved organic carbon content (DOC) and CH4 production potential (MPP) for CH4, and much higher NH4+-N concentration at the beginning of the rice season and a more favorable soil water content (SWC) for N2O. Because mean CH4 emission was positively correlated with mean DOC and MPP, and mean N2O emission was negatively related to mean SWC, respectively. Overall, the PM reduced annual GWP by 18–60 % and yield-scaled GWP by 34–60 % relative to TC1 and TC2. The findings suggest that the application of PM in the winter flooded paddy fields substantially mitigates GWP and has a great potential to reduce water use while maintaining high yields.