Katsuyuki Minami

Effect of organic matter application on methane emission from some Japanese paddy fields

Abstract Emission rates of CH4 from four Japanese paddy fields were measured throughout the cultivation period in 1988 by using the closed chamber method. Large seasonal variations of the CH4 flux were observed. The emission was closely related to the decrease of the redox potential (Eh) in paddy soils. Drainage and supplementary application of mineral fertilizer substantially reduced the CH4 emission. Emission rates of CH4 differed markedly with the soil types. The highest rate was observed in a paddy field consisting of Peat soil (44.8 g-CH4/m2 during a cultivation period), followed by Gley soil (8.0-27.0). The emission rates in the Andosols were significantly lower (0.6-12.6). Application of rice straw at a rate of 6-9 t/ha to the paddy fields increased the CH4 emission rates 1.8- to 3.5-fold. Application of compost slightly increased the CH4 emission. Annual emission rates of CH4 from individual plots were positively correlated with the contents of readily mineralizable carbon (RMC) in paddy soils col...

Methane and nitrous oxide emissions from rice paddy fields as affected by nitrogen fertilisers and water management

Methane and N2O emissions affected by nitrogen fertilisers were measured simultaneously in rice paddy fields under intermittent irrigation in 1994. Ammonium sulphate and urea were applied at rates of 0 (control), 100 and 300 kg N ha-1. The results showed that CH4 emission, on the average, decreased by 42 and 60% in the ammonium sulphate treatments and 7 and 14% in the urea treatments at rates of 100 and 300 kg N ha-1, respectively, compared to the control. N2O emission increased significantly with the increase in the nitrogen application rate. N2O emission was higher from ammonium sulphate treatments than from the urea treatments at the same application rate. A trade-off effect between CH4 and N2O emission was clearly observed. The N2O flux was very small when the rice paddy plots were flooded, but peaked at the beginning of the disappearance of floodwater. In contrast, the CH4 flux peaked during flooding and was significantly depressed by mid-season aeration (MSA). The results suggest that it is important to evaluate the integrative effects of water management and fertiliser application for mitigating greenhouse gas emissions in order to attenuate the greenhouse effect contributed by rice paddy fields.

Effect of water management on methane emission from a Japanese rice paddy field: Automated methane monitoring

The effect of differing water management schemes on the emission of methane (CH4) from rice paddies to the atmosphere was studied in a Japanese paddy field. Using an automated sampling and analyzing system, the test site was divided into two plots: a continuously flooded plot which was maintained flooded by constant irrigation from May to August, and an intermittently drained plot in which short-term draining practices were performed several times during the flooding period . The draining practice had a strong effect on CH4 emission. A large flush of CH4 emission was observed in the intermittently drained plot immediately after each drainage. It was followed by a rapid decrease in CH4 flux in most of the cases. A large flush of CH4 was observed after the final drainage at the end of August in the continuously flooded plot, accounting for about 7% of the total CH4 emitted in the plot. Total emission rates of CH4 during the cultivation period were 14.8 and 8.63 g m−2 for 1991 and 9.49 and 5.18 g m−2 for 1993 in the continuously flooded and intermittently drained plots, respectively. Companion N2O flux measurements showed that almost no N2O was emitted from either plot until the final drainage. These results indicate that short-term draining practices strongly reduce CH4 emission from rice paddy fields, and that improvement in water management can be one of the most important mitigation strategies for CH4 emission from rice paddy fields.

Possible options for mitigating methane emission from rice cultivation

Studies focused on mitigating CH4 emission from rice paddy fields are summarized and the possibilities and limits that the options might be applied to worlds rice cultivation are discussed. The mitigation options are water management, soil amendments, organic matter management, different tillage, rotation, and cultivar selection. Altering water management, in particular promoting midseason aeration by short-term drainage, is one of the most promising strategies, although these practices may be limited to the rice paddy fields where the irrigation system is well prepared. Improving organic matter management by promoting aerobic degradation through composting or incorporating into soil during off-season drained period is another most promising candidate. There are several formidable obstacles to adopt the mitigation options into local rice farming, including limited applicability to different types of rice fields, increasing cost and labor, negative effects on rice yield and soil fertility, and time requirement for practical application. Further studies to verify the mitigation options should focus on the feasibility for local farmers.

Measurements of CH4 and N20 emissions from rice paddies in Fengqiu, China

Abstract Methane emissions were measured by a closed chamber method in rice plots with sandy, loamy, and clayey soil, respectively, under a water regime consisting of a flooding and draining cycle in Fengqiu, Henan Province, China in 1993 and 1994. Nitrous oxide emissions were measured for every two measurements of CH4 flux in 1994. The results showed that CH4 emissions were low compared with those recorded in previous reports and the means of CH4 fluxes ranged from 0.16 to 1.86 mg CH4 m-2 h-1 in the growing season (108 d). The lowest mean flux of CH4 was observed in the clayey plot in both years. Statistically, soil temperature and soil Eh at 5 em depth significantly affected the fluctuations of the CH4 flux measured in the morning and afternoon, but they were not the main factors controlling the seasonal variation of the CH. flux. Flooding and draining cycle, as well as high rate of water percolation and low organic matter content of the soils resulted in low emissions of CH4. In contrast, the studied p...

Seasonal variations in methane flux andδl3CH4 values for rice paddies in Japan and their implications

We have made measurements of the methane (CH4) flux and δ13C value in CH4 from rice paddies in Ryugasaki, Japan. This study is the first we are aware of in which a significant change in the δ13C signature of emitted CH4 has been documented over the rice growing season. Nutrient treatments studied were of two kinds: compound mineral fertilizer either with or without rice straw from the previous growing season incorporated into the inorganic fertilizer. The calculated annual emission rates during the 1990 growing season were 43.1 g/m2 (straw) and 40.6 g/m2 (no straw) for the two treatments. In both treatments, CH4 started out relatively enriched in 13C, became lighter in 13C, and then became more enriched again during the latter part of rice growth. The 1991 growing season showed a lower integrated flux in both nutrient treatments than for 1990 but plots of the fluxes versus time had the same general shape as the flux curves in 1990 and a similar although less pronounced trend in δ13CH4 signal. Seasonal changes in δ13C are probably related to changes in CH4 production and oxidation and plant-mediated transport. The likelihood of each process occurring and its effect on δ13C values is discussed. The range of δ13CH4 values from seasonal effects was ∼12‰ in 1991 for both nutrient treatments. The δ13CH4 range for 1991 was ∼10‰ (straw) and ∼5‰ (no straw). Our data indicate that when using flux-weighted isotopic signatures to put constraints on the tropospheric CH4 budget, attention should be paid to seasonal changes in isotopic signatures from rice paddy CH4 in a manner similar to that previously suggested from measurements in natural wetlands.

Methods for measuring N2O flux from water surface and N2O dissolved in water from agricultural land

A new chamber method and a stripping method were developed for field measurements of the rate of N2O emission from the water surface and for determinations of dissolved N2O in water from agricultural land. These methods were used for the measurement of drainage canal water and flooded water of rice fields during the period of June 1982 to January 1983. The results demonstrate that aquatic systems of agricultural land may provide both source and sink for atmospheric N2O.

Emission of dimethyl sulfide, carbonyl sulfide, and carbon bisulfide from paddy fields

Abstract Emission rates of dimethyl sulficle (DMS), carbonyl sulfide (COS), and carbon disulfide (CS2) to the atmosphere from paddy fields at Ryugasaki, Ibaraki Prefecture, Japan were measured by using the closed chamber method. DMS was emitted mainly through the rice plant and its emission rate was much higher than those of COS and CS2. During a cropping period COS was slightly absorbed by the rice plant. Significant diurnal and seasonal variations of DMS iuxes were observed. The highest DMS iux was observed immediately after the heading day of rice plant. The annual DMS emission rate was in the order of mineral plot > straw plot > no-N plot, ranging from 4.5 to 6.9 mg S m-2 yr-1. The annual COS emission rate was in the order of straw plot > no-N plot > mineral plot, ranging from -0.2 to 1.8 mg S m-2 yr-1. The annual CS2 emission rate was slightly higher in the straw plot, ranging from 0.9 to 2.0 mg S m-2 yr-1.

Effects of the depth of NO and N2O productions in soil on their emission rates to the atmosphere: analysis by a simulation model

Many factors are concerned in the changing forms of nitrogen compounds in soil, so it is not easy to make precise models to simulate the concentration profiles of soil nitric oxide (NO) and nitrous oxide (N2O) and their emission rates under various soil conditions. We prepared a simple mathematical simulation model based on soil concentration profiles of NO and N2O. The profiles were measured at lysimeters filled with Andosol soil and fertilized with ammonium sulfate at rate of 200 kgNha-1, incorporating to plow layer (Hirose & Tsuruta, 1996). In this model, diffusion of gases in soil followed Ficks law and the diffusion coefficient was adopted from Sallam et al. (1984). The gas production rate was set up at constant value in the site of gas production, and the gaseous consumption followed Michaelis-Menten kinetics. By changing only the depth of NO and N2O production in soil in this model, we obtained the following results.(1) When the depth of gas production was set at near the soil surface (NO: 0–10 cm, N2O: 0-8 cm), the emission rates of both gases corresponded with the results of the lysimeter-measurement.(2) When the depth of gas production was shifted down 10 cm deeper (NO: 10–20 cm, N2O: 10-18 cm), the gas emission rate of NO decreased to 1.3% of (1), while that of N2O was almost the same as (1).(3) In the case that the total intensity of produced gases was not changed from (1) or (2), but that the extent of gas productions expanded 3 times wider (NO: 0–30 cm, N2O: 0–24 cm) than (1) or (2), the emission rates of NO and N2O became 26% and 95% of (1), respectively.The above results suggest the possibility of mitigating NO emission by setting the site of gaseous production in deeper soil, e.g. by means of deep application of fertilizer.

Methane emission from rice paddy fields in the central plain of Thailand

Abstract Emission rates of CH4 from rice paddy fields were measured in the central plain of Thailand. The measurements taken monthly during the cultivation periods showed a significant difference in CH4 emission rates among three sites. One paddy field, in Suphan Buri, showed a relatively high emission of CH4, with average fluxes of 19.5–32.2 mg m−2 h−1. The average fluxes from the other two paddy fields, in Khlong Luang and Chai Nat, were 3.8 and 1.6 mg m−2 h−1, respectively, being one order of magnitude lower than those from Suphan Buri. The low emission of CH4 at the two sites was attributed to the high concentration of sulfate in soil or the high soil Eh due to the lower abundance of the reducing capacity in relation to the oxidizing capacity of soil. The results suggest that it is essential to provide a data base of soil characteristics, such as soil type and chemical composition of soil affecting the oxidation-reduction process, as well as conduct extensive field measurements in various rice growing...