Rice straw biochar mitigates N2O emissions under alternate wetting and drying conditions in paddy soil

Assessment of greenhouse gas mitigation from rice cultivation using alternate wetting and drying and rice straw biochar in Thailand

We analyzed the effects of rice straw biochar (RSBC) and swine manure biochar (SMBC) on N2O emission from paddy soil. The biochars were added to soil at the rates of 1% and 5% (w/w), and N2O emission, soil properties and soil enzyme activities were determined at the elongation, heading and maturation stages of rice growth. The N2O flux started within 2 h of adding the biochar, and decreased significantly thereafter during the three growth stages. The cumulative N2O emission was suppressed by 45.14–73.96% following biochar application, and 5% SMBC resulted in the lowest cumulative emission. In addition, biochar application significantly increased soil pH, soil organic carbon (SOC), NO3− levels and urease activity, and decreased soil NH4+ and nitrate reductase activity. Regression analysis indicated that cumulative N2O emission was correlated positively to NH4+, and negatively to soil pH, SOC and NO3−. SEM further revealed that biochar application weakened the denitrification process, and the NH4+ level had the most significant impact on N2O emission. Taken together, RSBC and SMBC regulated the nitrogen cycle in paddy soil and mitigated N2O emission by increasing soil pH, decreasing nitrate reductase activity and NH4+ content.

We studied the effects of water regimes and nutrient amendments on CH4 and N2O emissions in a 2 9 3 factorial, completely randomised growth chamber experiment. Treatments included continuously flooded (CF) and alternate wetting and drying (AWD), and three organic amendments: no amendment-control, rice straw (RS) and biochar (BC). Compound fertiliser was applied to all treatments. Rice was grown in columns packed with a paddy soil from Cambodia. Results revealed faster miner- alisation of organic carbon (RS and BC) when applied in water-saturated conditions lasting for 2 weeks instead of flooding. This resulted in lower total CH4 emissions in treatments under AWD than those under the CF water regime, namely 44 % in RS treatments and 29 % in BC treatments. Nitrous oxide fluxes were generally non- detectable during the experimental period except after fertilisation events, and the total N2O-N emissions accounted for on average 1.7 % of the total applied mineral fertiliser N. Overall, the global warming potentials (GWPs) were lower in treatments under AWD than those under the CF water regime except for the control treatment with only mineral fertiliser application. Grain yields were slightly higher in treatments under AWD than the CF water regime. Hence, the yield-scaled GWP was also lower in the treat- ments under the AWD water regime, namely 51 % in RS, 59 % in BC and 17 % in control treatments. Control treatments had the lowest GWP, but provided the highest yield. The yield-scaled GWP under these treatments was therefore lower than under the other treatments.

Soil organic carbon content affects the stability of biochar in paddy soil

The DNDC (DeNitrification-DeComposition)-Rice model, one of the most advanced process-based models for the estimation of greenhouse gas emissions from paddy fields, has been discussed mostly in terms of the reproducibility of observed methane (CH4) emissions from Japanese rice paddies, but the model has not yet been validated for tropical rice paddies under alternate wetting and drying (AWD) irrigation management, a water-saving technique. We validated the model by using CH4 and nitrous oxide (N2O) flux data from rice in pots cultivated under AWD irrigation management in a screen-house at the International Rice Research Institute (Los Baños, the Philippines). After minor modification and adjustment of the model to the experimental irrigation conditions, we calculated grain yield and straw production. The observed mean daily CH4 fluxes from the continuous flooding (CF) and AWD pots were 4.49 and 1.22 kg C ha−1 day−1, respectively, and the observed mean daily N2O fluxes from the pots were 0.105 and 34.1 g N ha−1 day−1, respectively. The root-mean-square errors, indicators of simulation error, of daily CH4 fluxes from CF and AWD pots were calculated as 1.76 and 1.86 kg C ha−1 day−1, respectively, and those of daily N2O fluxes were 2.23 and 124 g N ha−1 day−1, respectively. The simulated gross CH4 emissions for CF and AWD from the puddling stage (2 days before transplanting) to harvest (97 days after transplanting) were 417 and 126 kg C ha−1, respectively; these values were 9.8% lower and 0.76% higher, respectively, than the observed values. The simulated gross N2O emissions during the same period were 0.0279 and 1.45 kg N ha−1 for CF and AWD, respectively; these values were respectively 87% and 29% lower than the observed values. The observed total global warming potential (GWP) of AWD resulting from the CH4 and N2O emissions was approximately one-third of that in the CF treatment. The simulated GWPs of both CF and AWD were close to the observed values despite the discrepancy in N2O emissions, because N2O emissions contributed much less than CH4 emissions to the total GWP. These results suggest that the DNDC-Rice model can be used to estimate CH4 emission and total GWP from tropical paddy fields under both CF and AWD conditions.

Alternate wetting and drying (AWD) frequently triggers nitrous oxide (N2O) emissions from paddy fields, while the inhibitory effect of 3,4-dimethylpyrazole phosphate (DMPP) on N2O under various water managements remains uncertain. Here, we evaluated the effects of DMPP on N2O emissions and associated biological indicators under three water managements: continuous flooding (CF), mild AWD (Mi-AWD), and moderate AWD (Mo-AWD). The Mi-AWD and Mo-AWD practices increased N2O emissions by 2- and 0.9-fold compared to the CF treatment, respectively, due to enhanced oxygen availability, facilitating coupled nitrification-denitrification. DMPP application notably reduced N2O emissions in the AWD treatments, attributed to the reductions in nitrifier abundances, nitrification rates, and nitrate accumulation. Nevertheless, DMPP failed to suppress nitrification and, thereby, N2O emissions in the CF treatment. Overall, DMPP effectively mitigates N2O emissions under oxygen-rich AWD rather than anaerobic CF conditions, highlighting that the trade-offs between water-saving irrigation and N2O mitigation can be overcome via nitrification inhibitors application.

Urea deep placement (UDP) and the alternate wetting and drying (AWD) irrigation method are two promising rice production technologies. However, studies on the impact of UDP under AWD irrigation on nitrous oxide (N2O) and nitric oxide (NO) emissions are limited. In this study, the effects of UDP with AWD irrigation on these emissions, nitrogen use efficiency (NUE), and rice yields are investigated, compared to conventional broadcast application. N2O and NO emissions from three fertilizer treatments – no nitrogen, UDP, and broadcast application of prilled urea (PU) – were measured. Measurements were taken using an automated gas sampling and analysis system continuously for two consecutive Boro (dry) rice seasons. N2O emission peaks were observed after broadcast application of PU but not after UDP. In contrast, large spikes in N2O emission were observed after UDP, compared to broadcast application, during dry periods. Despite differences in emission peaks, seasonal cumulative N2O emissions from UDP and broadcast treatments were similar. However, NO emissions were minimal and unaffected by UDP or AWD. UDP increased rice yields by 28% and N recovery efficiency by 167%, compared to broadcast urea. This study demonstrates that UDP with AWD irrigation can increase yields and NUE without increasing N2O and NO emissions.

Alternate wetting and drying (AWD) water management is being promoted to replace continuous flooding (CF) water regime in rice cultivation for agricultural countries, including Thailand, to achieve the net zero greenhouse gas (GHG) emissions and cope with drought. However, its adoption in different areas yielding variable results that requires the careful approaches to prevent negative impacts on rice yield, particularly the aroma of fragrant rice, along with mitigating GHG emissions, mainly methane (CH4) and nitrous oxide (N2O). This study aims to assess the impacts of AWD on CH4 and N2O emissions, productivity, water use, and soil characteristics of fragrant rice cultivation in Thailand. Khao Dawk Mali (KDML) 105 cultivar was cultivated in the wet season and Pathum Thani (PTT) 1 cultivar was planted in the dry season under CF and AWD at different dry levels of 10 cm (AWD10), 15 cm (AWD15), and 20 cm (AWD20) below the soil surface. The emissions of GHG and water use were measured throughout the study period using closed-chamber technique and water meter equipment, respectively. Rice yields and soil properties were analyzed after crop harvesting. The results showed that rice cultivation under AWD in both wet and dry seasons reduced CH4 emissions (18.4%–27.6%) but stimulated N2O emissions (11.8%–15.0%). However, its global warming potential (GWP) was lower than CF, lowered by an average of 17.7%, 26.8%, and 25.5% under the AWD10, AWD15, and AWD20, respectively. Relative to CF, unsuccessful AWD in the wet season did not change rice yield quantity and aroma (2-acetyl-1-pyrroline: 2AP) of KDML 105. Conversely, successful AWD10 and AWD15 in the dry season promoted rice grain yield and 2AP (0.27–0.33 ppm) of PTT1, while AWD20 did not alter rice yield amount but increased rice aroma (0.47 ppm). AWD can save irrigation water in the range of 12.8%–23.0% and 15.5%–18.7% in the wet and dry seasons, respectively. AWD water regime did not importantly change the soil characteristics after crop harvest. This study concludes that AWD, especially AWD15 and AWD20, has the potential to reduce GHG emissions without affecting the quantity and quality of rice yield, along with saving water.

Biochar applied to soil can reduce nitrous oxide (N2O) emissions produced by freeze–thaw processes. Nonetheless, how biochar modification affects N2O emissions during freeze–thaw cycles is not completely clear. In our research, during freeze–thaw cycles, microcosm experiments were conducted to investigate the effects of maize straw biochar (MB) or rice straw biochar (RB) addition on soil N2O emissions under different water conditions. The N2O emissions peaked at the initial stage of thawing in all the soils, and the total N2O emissions were considerably greater in the flooded soils than in the nonflooded soils. Compared with the soils without biochar addition, RB and MB amendments inhibited N2O emissions by 69 and 67%, respectively. Moreover, after biochar addition, the abundance of AOB amoA genes decreased by 9–13%. Biochar addition significantly decreased the content of microbial biomass nitrogen (MBN) in flooded soil during thawing, which was significantly correlated with N2O emissions and nitrification and denitrification communities. The PLS-PM further revealed that biochar can inhibit the production and emission of soil N2O by reducing soil MBN during soil thawing. In addition, soil moisture directly significantly affects N2O emissions and indirectly affects N2O emissions through its influence on soil physicochemical properties. Our results revealed the important function of biochar in decreasing the emission of N2O in flooded soil during freeze–thaw cycles.

Alternate wetting and drying maintains rice yield and reduces global warming potential: A global meta-analysis

Effects of water management on greenhouse gas emissions from farmers' rice fields in Bangladesh

Alternate Wetting and Drying of Rice Reduced CH4 Emissions but Triggered N2O Peaks in a Clayey Soil of Central Italy

Climate change and water scarcity threaten the sustainability of rice production systems. Alternate wetting and drying (AWD) is a promising option to reduce methane (CH4) emission from irrigated paddy fields. However, its effect on rice yield remains to be clarified. Organic amendment can increase rice yield but may also increase CH4 emission. We therefore hypothesized that the combination of AWD with organic amendment could both increase rice yield and decrease CH4 emission. We carried out field experiments in six consecutive rice seasons during 2019 − 2022 in Central Java, Indonesia. We examined the effect of water management (continuous flooding [CF] and AWD) with (+M) and without (−M) the amendment of cattle manure as a locally available organic matter on rice growth and yield and the emissions of CH4 and nitrous oxide (N2O). AWD significantly (p < 0.05) decreased CH4 emission by 29% but marginally (p < 0.1) increased N2O emission by 10% relative to CF. There was no significant effect of AWD alone on rice yield. AWD significantly increased water productivity (the ratio of rice yield to irrigated water volume) by 50%. Cattle manure amendment significantly increased CH4 emission by 12% and rice yield by 5% but did not affect N2O emission. The combination effect of AWD+M relative to CF−M (control) was additive and resulted in a 7% increase in rice yield, a 19% decrease in the global warming potential (GWP) of CH4 + N2O emissions during both growing and fallow periods, and a 24% decrease in yield-scaled GWP. Our results indicated that the combination of AWD with cattle manure amendment would be a promising means to increase rice yield while reducing total soil greenhouse gas emission from irrigated rice paddies.

The study is focused on impact of manure application, rice varieties and water management on greenhouse gas (GHG) emissions from paddy rice soil in pot experiment. The objectives of this study were a) to assess the effect of different types of manure amendments and rice varieties on greenhouse gas emissions and b) to determine the optimum manure application rate to increase rice yield while mitigating GHG emissions under alternate wetting and drying irrigation in paddy rice production. The first pot experiment was conducted at the Department of Agronomy, Yezin Agricultural University, Myanmar, in the wet season from June to October 2016. Two different organic manures (compost and cow dung) and control (no manure), and two rice varieties; Manawthukha (135 days) and IR-50 (115 days), were tested. The results showed that cumulative CH4 emission from Manawthukha (1.084 g CH4 kg-1 soil) was significantly higher than that from IR-50 (0.683 g CH4 kg-1 soil) (P<0.0046) with yield increase (P<0.0164) because of the longer growth duration of the former. In contrast, higher cumulative nitrous oxide emissions were found for IR-50 (2.644 mg N2O kg-1 soil) than for Manawthukha (2.585 mg N2O kg-1 soil). However, IR-50 showed less global warming potential (GWP) than Manawthukha (P<0.0050). Although not significant, the numerically lowest CH4 and N2O emissions were observed in the cow dung manure treatment (0.808 g CH4 kg-1 soil, 2.135 mg N2O kg-1 soil) compared to those of the control and compost. To determine the effect of water management and organic manures on greenhouse gas emissions, second pot experiments were conducted in Madaya township during the dry and wet seasons from February to October 2017. Two water management practices {continuous flooding (CF) and alternate wetting and drying (AWD)} and four cow dung manure rates {(1) 0 (2) 2.5 t ha-1 (3) 5 t ha-1 (4) 7.5 t ha-1} were tested. The different cow dung manure rates did not significantly affect grain yield or greenhouse gas emissions in this experiment. Across the manure treatments, AWD irrigation significantly reduced CH4 emissions by 70% during the dry season and 66% during the wet season. Although a relative increase in N2O emissions under AWD was observed in both rice seasons, the global warming potential was significantly reduced in AWD compared to CF in both seasons (P<0.0002, P<0.0000) according to reduced emission in CH4. Therefore, AWD is the effective mitigation practice for reducing GWP without compromising rice yield while manure amendment had no significant effect on GHG emission from paddy rice field. Besides, AWD saved water about 10% in dry season and 19% in wet season.

The study is focused on impact of manure application, rice varieties and water management on greenhouse gas (GHG) emissions from paddy rice soil in pot experiment. The objectives of this study were a) to assess the effect of different types of manure amendments and rice varieties on greenhouse gas emissions and b) to determine the optimum manure application rate to increase rice yield while mitigating GHG emissions under alternate wetting and drying irrigation in paddy rice production. The first pot experiment was conducted at the Department of Agronomy, Yezin Agricultural University, Myanmar, in the wet season from June to October 2016. Two different organic manures (compost and cow dung) and control (no manure), and two rice varieties; Manawthukha (135 days) and IR-50 (115 days), were tested. The results showed that cumulative CH4 emission from Manawthukha (1.084 g CH4 kg-1 soil) was significantly higher than that from IR-50 (0.683 g CH4 kg-1 soil) (P<0.0046) with yield increase (P<0.0164) because of the longer growth duration of the former. In contrast, higher cumulative nitrous oxide emissions were found for IR-50 (2.644 mg N2O kg-1 soil) than for Manawthukha (2.585 mg N2O kg-1 soil). However, IR-50 showed less global warming potential (GWP) than Manawthukha (P<0.0050). Although not significant, the numerically lowest CH4 and N2O emissions were observed in the cow dung manure treatment (0.808 g CH4 kg-1 soil, 2.135 mg N2O kg-1 soil) compared to those of the control and compost. To determine the effect of water management and organic manures on greenhouse gas emissions, second pot experiments were conducted in Madaya township during the dry and wet seasons from February to October 2017. Two water management practices {continuous flooding (CF) and alternate wetting and drying (AWD)} and four cow dung manure rates {(1) 0 (2) 2.5 t ha-1 (3) 5 t ha-1 (4) 7.5 t ha-1} were tested. The different cow dung manure rates did not significantly affect grain yield or greenhouse gas emissions in this experiment. Across the manure treatments, AWD irrigation significantly reduced CH4 emissions by 70% during the dry season and 66% during the wet season. Although a relative increase in N2O emissions under AWD was observed in both rice seasons, the global warming potential was significantly reduced in AWD compared to CF in both seasons (P<0.0002, P<0.0000) according to reduced emission in CH4. Therefore, AWD is the effective mitigation practice for reducing GWP without compromising rice yield while manure amendment had no significant effect on GHG emission from paddy rice field. Besides, AWD saved water about 10% in dry season and 19% in wet season.