Effect of biochar on CH4 and N2O emission from soils vegetated with paddy

Biochar is believed to have positive impact on soil properties and plant yield. Due to the presence of C, it can also enhance CH₄ emission in paddy soils. On the other hand, ammonium sulphate can decrease CH₄ emission due to negative impacts on methanogenesis. Keeping these points in view, a pot experiment was conducted to determine the effect of biochar along with ammonium sulphate on CH₄ and N₂O emission from paddy soil. Analysis revealed that biochar treated soils released more CH₄ compared to untreated. Ammonium sulphate treated soil emitted the highest N₂O whereas biochar addition decreased its emission significantly. Further, total emission was found to be higher for CH₄ (16.9–34.7 g/m²) in comparison to N₂O (?0.05 to 0.02 g/m²) for all treatments. Biochar application has positive impact on plant variables such as panicle number and weight of panicles. This study suggests that biochar application significantly decrease N₂O emission and increase CH₄ emission possibly due to affecting the availability of organic C in the soil to microbial activity for methanogenesis. Another possibility for enhancing CH₄ emission by following biochar could be attributed to the increase in plant biomass.     

中国中南部双季稻栽培CH_4和N_2O排放特征及其环境成本评估

CH4和N2O是水稻生产过程中产生的2种重要温室气体。本文评估了中国中部和南部双季稻生产CH4和N2O排放及潜在温室效应环境成本。通过评估1992~2011年华中、华南10省(区)CH4和N2O排放量和环境成本发现:(1)20 a间,华中、华南CH4和N2O年均排放总量变化趋势一致,呈V字走势,2003年为转折点。(2)1992~1996、1997~2001、2002~2006、2007~2011年华中、华南CH4和N2O年均排放量表现逐渐下降,近几年排放量有增加态势;单位面积排放量逐渐增加;CH4和N2O排放量对应环境成本变化与其一致。(3)华中CH4、N2O年均排放总量分别为200.13、0.66万t,单位面积排放量分别为234.89、0.89 kg/hm2。华南CH4、N2O年均排放总量分别为125.42、0.48万t,单位面积排放量分别为216.78、1.17 kg/hm2。(4)华中CH4、N2O年均排放量环境成本分别为7.05、0.41亿美元,单位面积成本分别为98.65、5.54美元/hm2;华南CH4、N2O年均排放量环境成本分别为4.60、0.40亿美元,单位面积成本为91.05、7.25美元/hm2。(5)华中的湖南和江西CH4、N2O分别占华中排放总量的68.02%、61.07%,华南的广东和广西CH4、N2O分别占华南排放总量的80.49%、75.51%,需重点考虑减少这些地区的CH4、N2O排放,降低生产环境成本。由此可见,中国中南部双季水稻种植CH4、N2O排放量和环境成本较高,需要采取符合实际情况的减排措施,适度降低温室气体排放量和环境成本。     

耕作方式对双季稻田土壤剖面CH4和N2O分布特征的影响

目的 探明双季稻稻田土壤剖面CH₄和N₂O的时空分布特征,有利于揭示农艺措施对稻田土壤温室气体产生和排放过程的作用机制。方法通过小区试验,研究了旋耕（RT）和免耕（NT）在不同培肥措施[不施肥（CK）、仅施化肥（F）、化肥+秸秆还田（FS）]下对双季稻主要生育期田面水和土壤剖面CH₄和N₂O分布特征的影响。结果 早晚稻季田面水CH₄浓度显著低于土壤剖面CH₄浓度;而田面水N₂O浓度高于土壤剖面N₂O浓度。土壤剖面CH₄浓度随深度增加而下降;而N₂O浓度在土壤剖面中无显著变化。耕作方式对土壤剖面CH₄和N₂O浓度存在显著效应。与NT相比,RT显著增加了土壤剖面CH₄浓度,尤其是0-5 cm和5-10 cm土层;而在部分生育期显著降低土壤剖面N₂O浓度。早晚稻季CH₄净排放通量与上层土壤CH₄浓度相关性高于下层土壤和田面水。表层土壤是影响早稻季N₂O排放的主要因素,而中下层土壤是影响晚稻季N₂O排放的主要因素。结论 双季稻田土壤剖面CH₄和N₂O具有明显的时空变化特征,而耕作方式对其浓度具有显著影响。     

Emissions of CH4 and CO2 from paddy fields as affected by tillage practices and crop residues in central China

A field experiment was conducted to investigate effects of tillage practices [no-tillage (NT) and conventional intensive tillage (CT)] and oilseed rape residue returning levels (0, 3000, 6000, 9000 kg dry matter ha^?1) on methane (CH₄) and carbon dioxide (CO₂) emissions and grain yield from paddy fields during the 2011 rice growing season after 2 years oilseed rape-rice rotation in central China. The experiment was established following a split-plot design of a randomized complete block with tillage practices as the main plots and residue returning levels as the sub-plots. NT significantly decreased CO₂ and CH₄ emissions by 38.8 and 27.3 % compared with CT, respectively. Residue returning treatments released significantly more CO₂ and CH₄ by 855.5–10410 and 51.5–210.5 kg ha^?1 than no residue treatments, respectively. The treatments of 3,000 and 6,000 kg ha^?1 residue returning significantly increased rice grain yield by 37.9 and 32.0 % compared with the treatment of no residue returning, respectively. Compared with NT, CT increased yield-scaled emissions of CH₄ and CO₂ by 16.0 %. The treatments of 6,000 and 9,000 kg ha^?1 residue returning significantly increased yield-scaled emissions of CH₄ and CO₂ by 18.1 and 61.5 %, respectively, compared with the treatment of no residue returning. Moreover, the treatment of NT in combination with 3,000 kg ha^?1 residues had the lowest yield-scaled emissions of CH₄ and CO₂ across tillage and residue treatments. In this way, this study revealed that the combination of NT with 3,000 kg ha^?1 residues was a suitable strategy for optimizing carbon emissions and rice grain yield.     

Improvement of liquid absorption properties of nonwoven polypropylene substrates by low pressure plasma treatment with CH4-O2 mixture gas

The use of nonwoven textile substrates for filtration and absorption purposes is generalized due to the high surface area they can provide. Many of these applications require good wetting properties to increase efficiency. In this work, low pressure plasma treatment with a CH₄-O₂ mixture gas has been used to increase surface wettability and subsequent absorption properties on nonwoven polypropylene substrates. CH₄ plasma treatment leads to a plasma polymerization process which results in hydrophobic surface finishing, but in combination with O₂, it is possible to form a functionalized plasmapolymerized layer thus improving wetting properties. Changes in wetting properties have been studied by contact angle measurements showing that optimum wetting properties are obtained with exposure times to plasma treatment of about 10 min, and no significant changes are obtained for longer exposure times. Absorption efficiency has been followed by determining three different parameters by the guidelines of the UNE-EN-ISO 9073-6 standard: wetting time, liquid absorption capacity (LAC) and liquid propagation rate or absorption speed. All these properties are remarkably improved as the exposure time to CH₄-O₂ plasma increases; this improvement is remarkably high for relatively short exposure times (5?C10 min) and no significant changes are obtained for long exposure times so that, it is possible to conclude that previous plasma treatment with exposure times in the 5?C10 min range is an efficient method to improve overall absorption properties of nonwoven polypropylene substrates.     

Mitigating N2O and NO Emissions from Direct-Seeded Rice with Nitrification Inhibitor and Urea Deep Placement

Soil-emitted nitrous oxide (N₂O) and nitric oxide (NO) in crop production are harmful nitrogen (N) emissions that may contribute both directly and indirectly to global warming. Application of nitrification inhibitors, such as dicyandiamide (DCD), and urea deep placement (UDP), are considered effective approaches to reduce these emissions. This study investigated the effects of DCD and UDP, compared to urea and potassium nitrate, on emissions, nitrogen use efficiency and grain yields under direct-seeded rice. High-frequency measurements of N₂O and NO emissions were conducted using the automated closed chamber method throughout the crop-growing season and during the ratoon crop. Both UDP and DCD were effective in reducing N₂O emissions by 95% and 73%, respectively. The highest emission factor (1.53% of applied N) was observed in urea, while the lowest was in UDP (0.08%). Emission peaks were mainly associated with fertilization events and appeared within one to two weeks of fertilization. Those emission peaks contributed to 65%–98% of the total seasonal emissions. Residual effects of fertilizer treatments on the N₂O emissions from the ratoon crop were not significant; however, the urea treatment contributed 2%, whereas UDP contributed to 44% of the total annual emissions. On the other hand, cumulative NO emissions were not significant in either the rice or ratoon crops. UDP and DCD increased grain yields by 16%–19% and N recovery efficiency by 30%–40% over urea. The results suggested that the use of DCD and UDP could mitigate N₂O emissions and increase grain yields and nitrogen use efficiency under direct-seeded rice condition.     

Sodium fertilizer application to pasture. 10. A comparison of the responses of dairy cows with high and low milk yield potential

Current recommendations for the intake of sodium of lactating dairy cows are related to milk yield. A study was conducted to compare the responses of cows of high and low milk production potential to the application of sodium fertilizer to grazed perennial ryegrass pasture. The application of sodium fertilizer increased the intake of herbage dry matter (DM), the time that cows spent grazing and the biting rate. It also increased the concentration of sodium, magnesium and calcium in herbage and decreased the concentration of potassium. Applying sodium fertilizer increased milk yield and milk fat concentration and decreased somatic cell count in the milk of cows of low-production potential only, whereas it increased persistency of milk production in the cows of high-production potential. The concentration of lactose in milk increased in both groups after the application of sodium fertilizer. It is concluded that the optimum dietary sodium concentration for grazing cows does not increase with milk yield, and that most immediate advantage will be gained from increasing the sodium concentration in herbage for low-yielding cows.     

秸秆还田下大气CO2浓度升高对水稻生长和CH4排放的影响

【目的】明确秸秆还田下大气CO₂浓度升高对水稻生长和稻田CH₄排放的影响,为气候变化下温室气体排放评估和丰产低碳的稻作技术创新提供理论参考和科学依据。【方法】利用开顶式气室(Open top chamber, OTC)进行田间试验,设置两个CO₂浓度处理,分别为正常大气CO₂浓度处理(简称aCO₂,CO₂浓度约为0.04%)和大气CO₂浓度升高处理(简称eCO₂,CO₂浓度约为0.055%),每个处理的田块混入等量的前茬小麦秸秆,探明秸秆还田下大气CO₂浓度升高对水稻产量等生长特性、稻田CH₄排放及微生物丰度的影响,揭示秸秆还田下大气CO₂浓度升高对CH₄排放的影响机制。【结果】大气CO₂浓度升高显著促进水稻的生长,使剑叶叶面积增加25.0%,地上生物量增加22.0%,产量提高29.0%。大气CO₂浓度升高显著增加了穗数、结实率和千粒重,但对穗粒数影响不显著。秸秆还田下,大气CO₂浓度升高有降低稻田CH₄排放的趋势,使单位产量CH₄排放量降低了39.4%。大气CO₂浓度升高使土壤甲烷氧化关键基因pmoA的拷贝数增加了20.0%,但对甲烷产生关键基因mcrA的拷贝数影响较小。【结论】秸秆还田条件下,未来大气CO₂浓度升高不仅提高了水稻产量,而且有利于减少稻田温室气体CH₄的排放。     

The effect of floating vegetation on CH<Subscript>4</Subscript> and N<Subscript>2</Subscript>O emissions from subtropical paddy fields in China

Duckweed (Lemna minor), a floating macrophyte belonging to the Lemnaceae family, is commonly found in subtropical paddy fields. This plant rapidly takes up nutrients from water and forms dense floating mats over the water surface that may impact the biogeochemical processes and greenhouse gas production in paddy fields. In this study, we measured CH₄ and N₂O emissions from duckweed and non-duckweed plots in a subtropical paddy field in China during the period of rice growth using static chamber and gas chromatography methods. Our results showed that CH₄ emission rate ranged from 0.19 to 26.50 mg m^?2 h^?1 in the duckweed plots, and from 1.02 to 28.02 mg m^?2 h^?1 in the non-duckweed plots. The CH₄ emission peak occurred about 1 week earlier in the duckweed plots compared to the non-duckweed counterparts. The mean CH₄ emission rate in the duckweed plots (9.28 mg m^?2 h^?1) was significantly lower than that in non-duckweed plots (11.66 mg m^?2 h^?1) (p < 0.05), which might be attributed to the higher water and soil Eh in the former. N₂O emission rates varied between ?50.11 and 201.82 µg m^?2 h^?1, and between ?28.93 and 54.42 µg m^?2 h^?1 in the duckweed and non-duckweed plots, respectively. The average N₂O emission rate was significantly higher in the duckweed plots than in the non-duckweed plots (40.29 vs. 11.93 µg m^?2 h^?1) (p < 0.05). Our results suggest that the presence of duckweed will reduce CH₄ emission, but increase N₂O flux simultaneously. Taking into account the combined global warming potentials of CH₄ and N₂O, we found that growing duckweed could reduce the overall greenhouse effect of subtropical paddy fields by about 17 %.     

Effect of organic,inorganic and slow-release urea fertilisers on CH<Subscript>4</Subscript> and N<Subscript>2</Subscript>O emissions from rice paddy fields

Vietnam is one of the world’s top two rice exporting countries. However, rice cultivation is the primary source of agriculture’s greenhouse gas (GHG) emissions in Vietnam. In particular, strategies are required to reduce GHG emissions associated with the application of organic and inorganic fertilisers. The objective of this study was to assess the effects of various combinations of biochar (BIOC), compost (COMP) and slow-release urea (SRU) on methane (CH₄) and nitrous oxide (N₂O) emissions. In total, 1170 gas samples were collected from closed gas chambers in rice paddies at Thinh Long commune and Rang Dong farm in northern Vietnam between June and October 2014. The gas samples were analysed for CH₄-C and N₂O-N fluxes using gas chromatography. The application of BIOC alone resulted in the lowest CH₄ emissions (4.8–59 mg C m^?2 h^?1) and lowest N₂O emissions (0.15–0.26 µg N m^?2 h^?1). The combined application of nitrogen–phosphorus–potassium (NPK) + COMP emitted the highest CH₄ (14–72 mg C m^?2 h^?1), while ½NPK + BIOC emitted the highest N₂O (1.03 µg N m^?2 h^?1 in the TL commune), but it was the second lowest (0.495 µg N m^?2 h^?1) in the RD farm. Green urea and orange urea reduced N₂O emissions significantly (p < 0.05) compared to white urea, but no significant differences were observed with respect to CH₄ emissions. SRU fertilisers and BIOC alone measured the lowest greenhouse gas intensity, i.e. <2.5 and 3 kg CO₂ eq. kg^?1 rice grain, respectively. Based on these results, application of fertilisers in the form of BIOC and/or orange or green urea could be a viable option to reduce both CH₄ and N₂O emissions from rice paddy soils.     

Mechanism of High Photosynthetic Capacity in BC2F4 LinesDerived from a Cross between Oryza sativa and Wild Relatives O. rufipogon

Abstract

We found that several BC₂F₄ lines had high leaf photosynthetic rates under light-saturated and ambient CO₂ conditions. These lines are progenies of BC₂F₁ plants with high photosynthetic capacities which were generated by backcrossing between Oryza rufipogon (W630) and O. sativa cv. Nipponbare, as a recurrent parent. Some photosynthetic characteristics of the BC₂F₄ lines were investigated to identify the factors increasing photosynthetic rates. Photosynthetic rates of these lines under light-saturated conditions at 50 to 700 ppm CO₂ concentrations were higher than those in Nipponbare. The estimated-maximum photosynthetic rates under light-saturated and CO₂-saturated conditions in BC₂F₄ lines were also higher than that in Nipponbare. The photosynthetic rate under light-saturated and ambient CO₂ conditions was positively correlated with the carboxylation efficiency as an indicator of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity in vivo rather than stomatal conductance. Initial and total Rubisco activities in vitro tended to be higher in the BC₂F₄ lines than in Nipponbare. The content of active Rubisco calculated from the activation state of Rubisco was also higher in the BC₂F₄ lines than in Nipponbare. These results suggest that high photosynthetic capacities of BC₂F₁ plants can be maintained high in their progenies and high photosynthetic rates under light-saturated and ambient CO₂ conditions in the BC₂F₄ lines are achieved mainly by the high activity of Rubisco due to the high active Rubisco content.     

Effects of rice straw,biochar and mineral fertiliser on methane (CH<Subscript>4</Subscript>) and nitrous oxide (N<Subscript>2</Subscript>O) emissions from rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) grown in a rain-fed lowland rice soil of Cambodia: a pot experiment

We studied the effects of water regimes and nutrient amendments on CH₄ and N₂O emissions in a 2 × 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 mineralisation 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 treatments 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.