Nitrous oxide emissions from three rice paddy fields in China

Nitrous oxide (N₂O) fluxes from rice paddy fields were measured in Nanjing, Yingtan and Fengqiu, using closed chamber method in 1994. The results showed that N₂O fluxes varied temporally, spatially and geographic regionally, with the total amounts of N₂O emissions during the period of rice growth ranged from 13.66 to 98.11mg/m² in Nanjing, 1.73 to 3.65mg/m² in Yingtan and 178.04 to 472.26mg/m² in Fengqiu, respectively. Soil water regime and soil texture had significant effects on N₂O production and emission from rice paddy fields. The mean N₂O fluxes from sandy, loamy and clayey rice paddy fields were 182.2,82.8 and 68.7 μg N₂O-N/m²/h, respectively. High N₂O fluxes occurred when rice paddy fields were imposed by alternation of irrigation and drainage and almost no N₂O emitted when the fields were submerged continuously. The rice paddy field applied with ammonium sulphate emitted more N₂O than with urea and N₂O-N losses of applied ammonium sulphate and urea ranged from 0.038 to 0.28% and 0.033 to 0.16%, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

Methane emission from rice paddy fields in all of Japanese prefecture

Field measurements of CH₄ emission from rice paddy field during cultivation periods were performed at all of 47 Japanese prefectures under the project of ‘Research for evaluation of CH₄ and N₂O emissions from agricultural land, and improvement methods of soil, water and fertilizer management’ conducted by Agricultural Production Bureau, the Ministry of Agriculture, Forestry and Fisheries. Although this project was carried out at 159 fields, the data of 132 fields were used for this report because other 27 fields had not enough data to be suitable for the statistics analyses. The measurements at rice paddy fields in various locations in Japan showed that there were large temporal variations of CH₄ flux and that the fluxes differed markedly with climate, characteristics of soil and paddy, application of organic matter and mineral fertilizer, and agricultural management practices. These data mainly indicated that CH₄ emission from Gley soils was greater than those from other soil types such as Andosols, Upland soils, fine-textured Lowland soils, medium and coarse-textured Lowlands soils and gravelly Lowland soils, and that water and organic matter managements influenced CH₄ emission. It is suggested that midsummer drainage treatment suppressed while the application of fresh organic matter such as rice straw and wheat straw enhanced CH₄ emission, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

Nitrous oxide emissions from fertilized upland fields in Thailand

Nitrous oxide (N₂O) emission from fertilized maize fields was measured using a closed chamber at four experimental sites in Thailand. The average measured N₂O flux from unfertilized plots through crop season was 4.16 ± 1.52, 5.05 ± 1.65, 5.25 ± 1.68 and 6.74 ± 2.95 g N₂O-N m^-2 h^-1, at Nakhon Sawan, Phra Phutthabat, Khon Kaen and Chiang Mai, respectively. Increased N₂O emissions by the application of nitrogen fertilizer were 0.22–0.44, 0.19–0.38%, 0.12–0.24 and 0.08–0.15% of the applied N, respectively. Compared to other data, N₂O emission rate to applied nitrogen was not significantly different between the data of Thailand and the Temperate Zone.     

The effect of agricultural practices on methane and nitrous oxide emissions from rice field and pot experiments

The authors of this paper measured the methane and nitrous oxide fluxes emissions from rice field with different rice varieties and the two fluxes from pot experiments with different soil water regime and fertilizer treatment. The experiment results showed that: (1) The CH₄ emission rates were different among different varieties; (2) There was a trade-off between CH₄ and N₂O emissions from rice field with some agricultural practices; (3) We must consider the mitigation options comprehensively to mitigate CH₄ and N₂O emissions from rice fields. This revised version was published online in August 2006 with corrections to the Cover Date.     

Atmospheric methane and nitrous oxide: sources, sinks and strategies for reducing agricultural emissions

I discuss production, emission and oxidation of CH₄ in rice paddy fields and N₂O in fertilized soils. The quantity of CH₄ emitted from rice paddy fields depends upon several important factors including soil factors, nutrient management, water regimes, cultivation practices and others. Important factors for N₂O emitted from fertilized soils are soil water content, temperature, nitrate or ammonium concentration, available organic carbon for denitrification and pH. I provide an estimate of mitigation potential in agricultural systems based on this estimate and the management technology. This revised version was published online in August 2006 with corrections to the Cover Date.     

Nitrous oxide emissions for 6 years from a gray lowland soil cultivated with onions in Hokkaido, Japan

We studied nitrous oxide (N₂O) emissions every growing season (April to October) for 6 years (19952000), in a Gray Lowland soil cultivated with onions in central Hokkaido, Japan. Emission of N₂O from the onion field ranged from 0.00 to 1.86 mgN m^–2 h^–1. The seasonal pattern of N₂O emission was the same for 6 years. The largest N₂O emissions appeared near harvesting in August to October, and not, as might be expected, just after fertilization in May. The seasonal patterns of soil nitrate (NO₃ ^–) and, ammonium (NH₄ ⁺) levels and the ratio of N₂O to NO emission indicated that the main process of N₂O production after fertilization was nitrification, and the main process of N₂O production around harvest time was denitrification. N₂O emission was strongly influenced by the drying–wetting process of the soil, as well as by the high soil water content. The annual N₂O emission during the growing season ranged from 3.5 to 15.6 kgN ha^–1. The annual nitrogen loss by N₂O emission as a percentage of fertilizer-N ranged from 1.1 to 6.4%. About 70% of the annual N₂O emission occurred near harvesting in August to October, and less than 20% occurred just after fertilization in May to July. High N₂O fluxes around the harvesting stage and a high proportion of N₂O emission to total fertilizer-N appeared to be probably a characteristic of the study area located in central Hokkaido, Japan.     

Effect of nitrapyrin on nitrous oxide emission from fallow soils fertilized with anhydrous ammonia

Nitrous oxide emission from three soils was measured using a chamber technique. Treatments sampled were unfertilized soil, and soil fertilized with 60 or 80 kg N ha^–1 of band-applied anhydrous ammonia ± nitrapyrin. The flux of nitrous oxide from unfertilized soil was very low (1.1 to 1.6 g N ha^–1 day^–1).Application of anhydrous ammonia caused a significant increase in the cumulative emission of nitrous oxide in two soils over 27 or 29 days compared with unfertilized soil. Fertilizer-induced loss of nitrous oxide was highest in a calcareous clay soil which had the highest nitrification rate and accumulated the highest concentration of nitrite within the fertilizer bands. Fertilizer-induced losses of nitrous oxide were < 0.05% of the applied fertilizer.Addition of nitrapyrin inhibited nitrification in all soils and reduced nitrite accumulation in the fertilizer bands. Nitrapyrin addition significantly reduced fertilizer-induced loss of nitrous oxide only in the calcareous clay soil. In the other soil, nitrapyrin had a lower bioactivity (relative inhibition of nitrification) which may have been due to its higher organic matter content.

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Resumo Este trabalho constitui de uma avaliação da quantidade de óxido nitroso emitido por três solos. A emissão de óxido nitroso foi determinada em solos não fertilizados e onde a amônia-anidra (60 e 80 kg de N ha^–1) foi aplicada, em bandas, com e sem nitrapyrin. O fluxo diário de óxido nitroso nos solos onde não se aplicou o fertilizante variou entre 1.1 e 1.6 g N ha^–1. A aplicação da amônia-anidra causou um significativo aumento na emissão de óxido nitroso em dois solos. A emissão de óxido nitroso induzida pela aplicação do fertilizante foi mais alta em um solo calcáreo-argiloso. Foi neste solo onde a nitrificação ocorreu mais intensamente e um maior acúmulo de nitrito foi observado. As perdas de óxido nitroso induzidas pela aplicação da amônia-anidra foram menores do que 0.05% do fertilizante aplicado. A aplicação conjunta de nitrapyrin com o fertilizante inibiu parcialmente a nitrificação nos três solos e reduziu o acúmulo de nitrito nas bandas do fertilizante. A adição de nitrapyrin reduziu significativamente a emissão de óxido nitroso somente no solo calcáreo-argiloso. No outro solo, a inibição relativa da nitrificação (bio-atividade) foi a mais baixa observada. A baixa bio-atividade do nitrapyrin sugere um efeito causado pelo mais alto teor de matéria orgânica verificado neste solo.

     

A category for estimate of CH4 emission from rice paddy fields in China

Based on key factors influencing CH₄ fluxes from rice paddy fields in China, a category for estimation of total CH₄ emission was suggested and the constraints for the estimation were discussed in the paper. Recently, CH₄ fluxes measured in situ have been built up dramatically with the efforts of both Chinese scientists and those from abroad. After reviewing published data on CH₄ fluxes from rice paddy fields, we found that although there are many other influencing factors, water regime and organic manure application are two key factors controlling CH₄ emission; thus, rice paddy fields in China were classified by these two factors to estimate CH₄ emission. In the suggested category, the water regime of rice paddy fields was classified into mid-season aeration at least once during the period of rice growth (MSA), continuous flooding during the period of rice growth but well-drained after rice harvest (CFD), and permanent flooding (PF) even in winter, and fertilization was classified into mineral fertilizers only (MIN), amendment with organic manures at the rate of less than or equal to 15 t ha^-1 (MU < 15) and at the rate of higher than 15 t ha^-1 (MU > 15), and with rice straw or other fresh plant materials (RS). Combining both water regime and fertilization together, we classified rice paddy fields in China into 12 types. The seasonal mean CH₄ flux of each type of rice paddy field was calculated by the data available and showed that the lowest CH₄ flux was found in the type MSA-MIN, and the highest in PF-MU > 15. The total emission estimated by this category was 8.05 Tg CH₄ yr^-1 with a standard deviation of 3.69 Tg CH₄ yr^-1. This revised version was published online in August 2006 with corrections to the Cover Date.     

The effect of nitrogen fertilizer use and other practices on methane emission from flooded rice

Methane (CH₄) flux measurements from rice paddy fields in the world and its controlling factors, especially fertilizer effects are summarized. The measurements at rice paddy fields in various locations of the world showed that there were large temporal variations of CH₄ flux and that the flux differed markedly with climate, characteristics of soil and paddy, application of organic matter and mineral fertilizer, and agricultural practices. From the data, it appears that identifying and controlling CH₄ flux factors have a potential to reduce CH₄ emission from rice cultivation. Potential mitigation options include: the form and amount of nitrogen and other chemical fertilizers, the method of fertilizer applications, the application of other chemical amendments, water management and cultivation practices.     

Nitrous oxide emissions from paddy soil in three rice-based cropping systems in China

Rice-flooding fallow, rice-wheat, and double rice-wheat systems were adopted in pot experiment in an annual rotation to investigate the effects of cropping system on N₂O emission from rice-based cropping systems. The annual N₂O emission from the rice-wheat and the double rice-wheat cropping systems were 4.3 kg N ha^–1 and 3.9 kg N ha^–1, respectively, higher than that from rice-flooding fallow cropping system, 1.4 kg N ha^–1. The average N₂O flux was 115 and 118 g N m^–2 h^–1 for rice season in rice-wheat system and early rice season in double rice-wheat system, respectively, 68.6 and 35.3 g N m^–2 h^–1 for the late rice season in double rice-wheat system and rice season in rice-flooding fallow, respectively, and only 3.1–5.3 g N m^–2 h^–1 for winter wheat or flooding fallow season. Temporal variations of N₂O emission during rice growing seasons differed and high N₂O emission occurred when soil conditions changed from upland crop to flooded rice.     

Nitrous oxide production in riparian zones and groundwater

This paper addresses the question of whether riparian zones and groundwater are hotspots of nitrous oxide (N₂O) flux in the landscape. First, we describe how riparian zones and groundwater function as transformers of N, with a particular emphasis on mechanisms of N₂O production in these ecosystems. We then present specific data on N₂O flux in these ecosystems and attempt to reconcile these data with existing regional scale estimates of N flux for Norway and with estimates of N₂O flux for Norway produced using the OECD/IPCC/IEA Phase II methodology for calculation of regional and global N₂O budgets. While the OECD/IPCC/IEA approach produces estimates of riparian and groundwater N₂O flux that are reasonable, given what we know about regional scale N balances and actual data on N₂O flux, it does not allow us to determine if riparian zones and groundwater are hotspots of N₂O production in the landscape. The approach fails to answer this question because it is unable to account for spatially explicit phenomena such as riparian and groundwater processing of excess agricultural N. Research needs that would allow us to address this question are discussed.     

Effect of rice cultivars and fertilizer management on methane emission in a rice paddy in Beijing

Experiments were conducted during April-Oct. 1994 in a Beijing rice field. Four types of rice varieties have been tested. Large cultivar differences in methane emission flux have been found. Variety 93812 emitted about fivefold more CH₄ than did the Qiuguang variety. An organic amendment plus (NH₄)₂SO₄as the base fertilizer and (NH₄)₂SO₄as the topdressing applied in different amounts and growth stages, compared with no topdressing, reduced methane emission about 58% and increased rice yield about 31.7%. Emission peaks of CH₄ in the tillering stage and reproductive stage were suppressed. A comprehensive strategy could meet both the goal for sustainable rice productivity and methane reduction. Such a strategy includes: 1. Selection of cultivars which have reduced root exudate and litter but increased root mass most of which growing in the oxidized soil layer, cultivars also need an effective number of tillers for optimum yield but with less CH₄transportation ability; 2. Application of organic manure combined with chemical fertilizers, that reduce CH₄ emissions. Fertilizers such as SO₄ ² -or other inhibitors can be maintained for a long period in soil; 3. Adoption of scientific irrigation mode such as flooding-drainage- intermittent irrigation ,that can both increase the rice yield and decrease the CH₄ emission, etc.. This revised version was published online in August 2006 with corrections to the Cover Date.     

Methanogens in paddy rice soil

The population, methanogenic activities and dominant species of methanogenic bacteria in paddy rice soils under different conditions were studied. Application of fertilizer, especially organic manure and submergence with deep water increased the population and methanogenic activities of methanogenic bacteria in rice soils. No large differences was observed among the population of methanogen in rice soils from different depths of 0-5, 5-13 and 13-18 cm. Soils, which developed from different parent material and had various use history, had notably different cell numbers and activities of methanogenic bacteria. Methanogenic activities in soils developed from fluvo-aquic soil were obviously higher than those in soils developed from quaternary red soil and coastal saline soil, and those in upland soil were pronounced lower than those in rice soil. The methanogenic bacteria that survived in air-dried rice soil could form methane after addition of water and incubation. The dominant species of methanogens were Methanobacterium formicicum, Methanobrevibacter sp., Methanosarcina mazeii and Methanosarcina barkeri. This revised version was published online in August 2006 with corrections to the Cover Date.     

Nitrous oxide (N2O) emissions from soils in warm climates

N₂O emission rates seem to be higher from soils in warm climates than from soils in temperate climates. Warm and moist conditions promote microbial processes that generate N₂O. Clearance of tropical forests enhances N₂O formation, but emission measurements from other agricultural operations in the tropics are few. Limiting fertilizer application to recommended rates applied at appropriate times and avoiding fallow land wherever practical serves to limit N₂O emissions. More specific advice for agriculture in warm climates requires further studies.     

Urease and nitrification inhibitors to reduce emissions of CH4 and N2O in rice production

Strategies used to reduce emissions of N₂O and CH₄ in rice production normally include irrigation management and fertilization. To date, little information has been published on the measures that can simultaneously reduce both emissions. Effects of application of a urease inhibitor, hydroquinone (HQ), and a nitrification inhibitor, dicyandiamide (DCD) together with urea (U) on N₂O and CH₄ emission from rice growing were studied in pot experiments. These fertilization treatments were carried out in the presence and absence of wheat straw, applied to the soil surface. Without wheat straw addition, in all treatments with inhibitor(s) the emission of N₂O and CH₄ was significantly reduced, as compared with the treatment whereby only urea was applied (control). Especially for the U+HQ+DCD treatment, the total emission of N₂O and CH₄ was about 1/3 and 1/2 of that in the control, respectively. In the presence of wheat straw, the total N₂O emission from the U+HQ+DCD treatment was about 1/2 of that from the control. The total CH₄ emission was less influenced. Wheat straw addition, however, induced a substantial increase in emissions of N₂O and CH₄. Hence, simultaneous application of organic materials with a high C/N ratio and N-fertilizer (e.g. urea) is not a suitable method to reduce the N₂O and CH₄ emission. Application of HQ+DCD together with urea seemed to improve the rice growth and to reduce both emissions. The NO₃ ^–-N content of the rice plants and denitrification of (NO₃ ^–+NO₂ ^–)-N might contribute to the N₂O emission from flooded rice fields.     

Nitrogen in percolation water in paddy fields with a rice/wheat rotation

Nitrogen in percolation water was observed in paddy field soil under rice/wheat rotation. Different N-application rates were designed. Porous pipes were installed in triplicate at depths of 30, 60 and 90 cm to collect the water in the period of wheat growth. Suction cups were installed in triplicate at the same depths to collect the water during the period of rice growth. NH₄ ⁺, NO₃ ^- and total N in the water were analysed with a continuous-flow nitrogen analyzer. Results showed that nitrate was the predominant form of nitrogen in percolation water during the period of wheat growth. Nitrate leaching was high in early spring after the `tillering fertilisation'. More than 50 mg l^-1 of nitrate concentration in percolation water was observed for 30 and 60 cm in depth and more than 15 mg l^-1 were observed for 90 cm. The concentration decreased quickly and was very low, less than 2 mg l^-1 usually, in the earring stage of wheat. Nitrate in water was low, less than 1.5 mg l^-1 usually, when the field was flooded during the period of rice growth. Some soluble organic N existed in the water. Nitrate in percolation water increased when the field was drained. The leaching loss of nitrogen during winter wheat growth period was estimated to be about 3.4% of the N-fertiliser applied at the normal application rate of farmers; for the rice growth period it was around 1.8%. Although a reduced N-application decreased N leaching, it caused a marked decrease in crop yield.     

Nitrous oxide emission from soils amended with crop residues

Crop residues incorporated in soil are a potentially important source of nitrous oxide (N₂O), though poorly quantified. Here, we report on the N₂O emission from 10 crop residues added to a sandy and a clay soil, both with and without additional nitrate (NO₃). In the sandy soil, total N₂O emission from wheat, maize, and barley residues was not significantly different from the control. The total N₂O emission from white cabbage, Brussels sprouts, mustard, sugar beet residues and broccoli ranged from 0.13 to 14.6 % of the amount of N added as residue and were higher with additional NO₃ than without additional NO₃. In the clay soil, similar effects of crop residues were found, but the magnitude of the N₂O emission was much smaller than that in the sandy soil: less than 1 % of the residue N evolved as N₂O. The C-to-N ratio of the residue accounted for only 22–34% and the mineralizable N content of the residue for 18–74% of the variance in N₂O emission. We suggest that the current IPCC methodology for estimating N₂O emission from crop residues may be considerably improved by defining crop specific emission factors instead of one emission factor for all crop residues. This revised version was published online in November 2006 with corrections to the Cover Date.     

Direct emission of nitrous oxide from agricultural soils

This analysis is based on published measurements of nitrous oxide (N₂O) emission from fertilized and unfertilized fields. Data was selected in order to evaluate the importance of factors that regulate N₂O production, including soil conditions, type of crop, nitrogen (N) fertilizer type and soil and crop management. Reported N₂O losses from anhydrous ammonia and organic N fertilizers or combinations of organic and synthetic N fertilizers are higher than those for other types of N fertilizer. However, the range of management and environmental conditions represented by the data set is inadequate for use in estimating emission factors for each fertilizer type. The data are appropriate for estimating the order of magnitude of emissions. The longer the period over which measurements are made, the higher the fertilizer-induced emission. Therefore, a simple equation to relate the total annual direct N₂O–N emission (E) from fertilized fields to the N fertilizer applied (F), was based on the measurements covering periods of one year: E=1+1.25×F, with E and F in kg N ha^-1 yr^-1. This relationship is independent of the type of fertilizer. Although the above regression equation includes considerable uncertainty, it may be appropriate for global estimates.     

Nitrous oxide and nitric oxide fluxes from an upland field in Japan: effect of urea type, placement, and crop residues

Fertilizer type and application mode may influence nitrous oxide(N₂O) and nitric oxide (NO) emissions as well as crop yield. Using astatic chamber method, fluxes of both gases from a Chinese cabbage field inJapan were measured in situ following the application of easily decomposableurea by broadcasting (U-BC) and banding (U-B) and coated urea by banding(CU-B),respectively, at an application rate of 250 kg Nha^–1. The measurements were made throughout the growingseason and continued 3 more months after harvest to determine the effect ofcropresidues on the emissions. Large N₂O fluxes from U-BC occurredwithinabout 2 weeks after the application of the N fertilizer, while that from bothU-B and CU-B was prolonged by about 2 weeks, and significant emissions lasted alonger time but with a smaller emission size. Substantial N₂O fluxesderived from crop residues were observed in the late growing season (especiallyfollowing rainfall) as well as after harvest, at all treatments including thecontrol plots (CK). Large NO fluxes occurred only at U-BC within the first 2weeks through the measurements. Total emissions were estimated to be 38.1,78.3,77.8, and 100.4 mg N₂O-N m^–2 and 0.7,194.9, 8.5, and 11.4 mg NO-N m^–2 at CK, U-BC,U-B,and CU-B, respectively. Statistical analyses indicate that neither the bandmodenor the coated urea was able to significantly reduce the total N₂Oemission through the season, but the band mode substantially reduced the NOemission. However, the application of urea by the band mode presented a 22.8%increase in crop yield as compared with urea applied by broadcasting.Therefore,by improving fertilizer use efficiency to decrease the amount of N needed tobetter meet the crop growing demand, the band mode may be a good agriculturalpractice to also reduce N₂O emission. In addition, the experimentdemonstrated that crop residue is a large source of N₂O emission.     

Re-engineering the paddy rice drying system in the Philippines for climate change adaptation

Abstract

The Philippines is experiencing extreme weather events (typhoons and floods) which often result to significant rice postharvest losses, among other things. In this study, a new and mechanized postharvest system that integrates field handling and drying of the paddy grains is proposed to speed up the operation and help ensure a good quality harvest even when affected by typhoons or floods. The system makes use of eight 500?kg capacity specially-designed bags that function both as grain containers during transport and as drying bins. The drying operation is accomplished using these bags while mounted on the floor inside a typhoon-resistant shelter.