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Our previous pot experiments showed that using Azolla either or both as dual and green manure with rice increases its yield or significantly reduces either or both methane (CH4) and nitrous oxide (N2O) emissions. To confirm these findings in an actual field, Azolla was either grown as a dual crop (herein Cover) or incorporated as green manure plus dual cropping (herein AGM + Cover) at the beginning of the experiment along with rice. Compared with the control (chemical fertilizer; herein NPK), NPK + Cover and AGM + Cover treatments did not influence cumulative CH4 emissions throughout the rice growth period. However, AGM + Cover treatment affected significant CH4 emissions at early, middle, and later rice growth stages by 140.6%, 24.6%, and 33.1%, respectively, compared with NPK + Cover treatment. These emissions were attributed to the readily available carbon substrate for methanogens following the incorporation of Azolla as green manure. Compared with NPK, NPK + Cover and AGM + Cover significantly increased N2O emissions by 645.9% and 816.2%, respectively, during the middle rice growth stage. No significant N2O emission differences were observed in the three treatments in the early or later rice growth stages. The higher N2O emissions from the middle rice growth stage were ascribed to high substrate availability from the dead Azolla by higher summer air temperature in the 2019 season. AGM + Cover significantly decreased rice yield by 37.5% (NPK) and 35.3% (NPK + Cover), with no significant differences between NPK and NPK + Cover. This reduction was attributed to nitrogen immobilization from the incorporated Azolla during the early stage. Therefore, to ascertain the potential of Azolla in paddy fields to address environmental safety while sustaining yield, emphasis on the interaction of different application methods with various management practices is necessary. [ABSTRACT FROM AUTHOR]

Composts are an attractive organic-farming alternative to chemical fertilizers and are used for carbon sequestration to increase soil carbon storage. In Japan, a new type of mixed compost fertilizer called compost-compound fertilizer mixture (CCFM) has been registered. It exhibits several merits for organic farming; that is, it is odorless, easy to handle, and has a controllable nutrient content. CCFM consists of compost mixed with chemical fertilizer, such that nutrient content can be effectively adjusted. Although it has been pointed out that pellet composts generate more greenhouse gas emissions (GHGEs), such as carbon dioxide (CO₂) and nitrous oxide (N₂O), the mechanism involved is not clearly understood. To investigate the effect of CCFM on GHGEs, soil microbial properties and plant growth, incubation and pot experiments were conducted in a Hungarian Chernozem and a Japanese Andosol. Both soils were incubated with 1) CCFM prepared using pig manure mixed with chemical fertilizer, 2) chemical fertilizer only, or 3) no fertilizer. A pot experiment was conducted using Komatsuna (Brassica rapa). In the Chernozem, the maximum N₂O production rate was observed after chemical fertilizer treatment. The emission factors of chemical fertilizer and CCFM were 0.25% and 0.19%, respectively. In contrast, N₂O production was not detected in the Andosol. Meanwhile, CO₂ production was higher (P < 0.05) in the Chernozem than in the Andosol; furthermore, it was higher under CCFM than under chemical fertilizer treatment, with 7.5% of amended carbon changing to CO₂, thus suggesting that dominant carbon remained in the soil. Microbial biomass increased faster in the Andosol than in the Chernozem and the change was faster under the CCFM than under the chemical fertilizer or control treatments. In the pot experiment, CCFM tended to enhance plant growth in both soils. These experiments showed that CCFM has a soil-carbon storage effect with less resultant GHGEs, especially in Andosols, thereby leading to a more sustainable agriculture. Nonetheless, further studies are required for long-term experiments with other crops. [ABSTRACT FROM AUTHOR]

To investigate the influence of Azolla (A. filiculoides Lam.) incorporated as a green manure and its subsequent growth as a dual crop with rice on simultaneous methane (CH4) and nitrous oxide (N2O) emissions from a flooded alluvial soil planted with rice, a pot experiment with three treatments, chemical fertilizers (NPK) as the control, incorporation of Azolla as green manure (AGM), and AGM plus basal chemical fertilizers (NPK+AGM) was conducted in Tsuruoka, Yamagata, Japan in 2017. AGM and NPK+AGM treatments significantly increased CH4 emissions at early rice growth stages before 63 days after transplanting (DAT) by 123.0% and 176.7% compared to NPK, respectively. At late rice growth stages (after 63 DAT), only the NPK+AGM treatment significantly increased CH4 emission by 22.1% compared to NPK. However, percentage of CH4 emitted after 63 DAT relative to the seasonal CH4 emission followed the order of NPK (86.2%) > AGM (76.5%) > NPK+AGM (73.3%). Higher CH4 emissions from AGM and NPK+AGM before 63 DAT were attributed to the incorporated Azolla, while the higher emissions after 63 DAT in all treatment groups were ascribed to rice photosynthesis. AGM and NPK+AGM treatments significantly decreased N2O emissions by 71.6% and 81.1% compared to NPK, respectively, at early rice growth stages. Azolla incorporation may have restricted N2O emission from initial soil nitrate before 63 DAT and not have contributed to N2O emissions after 63 DAT. Significantly higher grain yields were observed under the AGM (32.5%) and NPK+AGM (36.3%) compared to NPK. Together, AGM and NPK+AGM treatments significantly increased seasonal CH4 emissions by 31.5% and 43.5%, and decreased seasonal N2O emissions 3.4- and 4.6- fold compared to NPK, respectively. There were no significant differences in the CH4 emissions per grain yield among the treatments; however compared to NPK, AGM and NPK+AGM treatments significantly reduced N2O emissions per grain yield by 78.7% and 84.1%, respectively. [ABSTRACT FROM AUTHOR]

A laboratory study was conducted to study the effects of liming and different biochar amendments on N2O and CO2 emissions from acidic tea field soil. The first experiment was done with three different rates of N treatment; N 300 (300 kg N ha-1), N 600 (600 kg N ha-1) and N 900 (900 kg N ha-1) and four different rates of bamboo biochar amendment; 0%, 0.5%, 1% and 2% biochar. The second experiment was done with three different biochars at a rate of 2% (rice husk, sawdust, and bamboo) and a control and lime treatment (dolomite) and control at two moisture levels (50% and 90% water filled pore space (WFPS)). The results showed that dolomite and biochar amendment significantly increased soil pH. However, only biochar amendment showed a significant increase in total carbon (C), C/N (the ratio of total carbon and total nitrogen), and C/IN ratio (the ratio of total carbon and inorganic nitrogen) at the end of incubation. Reduction in soil NO3--N concentration was observed under different biochar amendments. Bamboo biochar with the rates of 0.5, 1 and 2% reduced cumulative N2O emission by 38%, 48% and 61%, respectively, compare to the control soil in experiment 1. Dolomite and biochar, either alone or combined significantly reduced cumulative N2O emission by 4.6% to 32.7% in experiment 2. Reduction in N2O production under biochar amendment was due to increases in soil pH and decreases in the magnitude of mineral-N in soil. Although, both dolomite and biochar increased cumulative CO2 emission, only biochar amendment had a significant effect. The present study suggests that application of dolomite and biochar to acidic tea field soil can mitigate N2O emissions. [ABSTRACT FROM AUTHOR]

Agricultural soil is a major source of nitrous oxide (NO), and the application of nitrogen and soil drainage are important factors affecting NO emissions. This study tested the use of polymer-coated urea (PCU) and polymer-coated urea with the nitrification inhibitor dicyandiamide (PCUD) as potential mitigation options for NO emissions in an imperfectly drained, upland converted paddy field. Fluxes of NO and methane (CH), ammonia oxidation potential, and ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) abundances were monitored after the application of PCU, PCUD, and urea to upland soil. The results showed that urea application increased the ammonia oxidation potential and AOB and AOA abundances; however, the increase rate of AOB (4.6 times) was much greater than that of AOA (1.8 times). These results suggested that both AOB and AOA contributed to ammonia oxidation after fertilizer application, but the response of AOB was greater than AOA. Although PCU and PCUD had lower ammonia oxidation potential compared to urea treatment, they were not effective in reducing NO emissions. Large episodic NO emissions (up to 1.59 kg N ha day) were observed following heavy rainfall 2 months after basal fertilizer application. The episodic NO emissions accounted for 55-80 % of total NO emissions over the entire monitoring period. The episodic NO emissions following heavy rainfall would be a major source of NO in poorly drained agricultural fields. Cumulative CH emissions ranged from −0.017 to −0.07 kg CH ha, and fertilizer and nitrification inhibitor application did not affect CH oxidation. [ABSTRACT FROM AUTHOR]

Abstract: Animal manures from intensive livestock operations can be pelleted to improve handlings and recyclings of embodied nutrients. The aim of this study was to evaluate the influence of pelleted poultry manure on N2O and NO fluxes from an Andisol field. In autumn 2006 and summer 2007, poultry manure (PM), pelleted poultry manure (PP), and chemical fertilizer (CF) were applied at a rate of 120kgNha−1 in each cultivation period to Komatsuna (Brassica rapa var. peruviridis). Nitrous oxide and NO fluxes were measured using an automated monitoring system. A soil incubation experiment was also conducted to determine the influence of intact and ground pelleted manure on N2O, NO, and CO2 production with a water-filled pore space (WFPS) of 30 or 50%. In the field measurements, N2O emission rates from the organic fertilizer treatments were larger than that from the CF treatment, possibly because organic C stimulated denitrification. The highest N2O flux was observed from the PP treatment after a rainfall following fertilization, and the cumulative emission rate (2.72±0.22kgNha−1 y−1) was 3.9 and 7.1 times that from the PM and CF treatments, respectively. In contrast, NO emission rates were highest from the CF treatment. The NO/N2O flux ratio indicated that nitrification was the dominant process for NO and N2O production from the CF treatment. Cumulative N2O emission rates from all treatments were generally higher during the wetter cultivation period (autumn 2006) than during the drier cultivation period (summer 2007). In contrast, NO emission rates were higher in the drier than in the wetter cultivation period. The incubation experiment results showed a synergistic effect of soil moisture and the pelleted manure form on N2O emission rates. The intact pelleted manure with the 50% WFPS treatment produced the highest N2O and CO2 fluxes and resulted in the lowest soil NO3 − content after the incubation. These results indicate that anaerobic conditions inside the pellets, caused by rainfall and heterotrophic microbial activities, led to denitrification, resulting in high N2O fluxes. Controlling the timing of N application by avoiding wet conditions might be one mitigation option to reduce N2O emission rates from the PP treatment in this study field. [Copyright &y& Elsevier]