Takuji Sawamoto

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 (1995∼2000), 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.

Life cycle inventory-based analysis of greenhouse gas emissions from arable land farming systems in Hokkaido, northern Japan

Abstract To assess their impacts on net global warming, total greenhouse gas emissions (mainly CO2, N2O and CH4) from agricultural production in arable land cropping systems in the Tokachi region of Hokkaido, Japan, were estimated using life cycle inventory (LCI) analysis. The LCI data included CO2 emissions from on-farm and off-farm fossil fuel consumption, soil CO2 emissions induced by the decomposition of soil organic matter, direct and indirect N2O emissions from arable lands and CH4 uptake by soils, which were then aggregated in CO2-equivalents. Under plow-based conventional tillage (CT) cropping systems for winter wheat, sugar beet, adzuki bean, potato and cabbage, on-farm CO2 emissions from fuel-consuming operations such as tractor-based field operations, truck transportation and mechanical grain drying ranged from 0.424 Mg CO2 ha−1 year−1 for adzuki bean to 0.826 Mg CO2 ha−1 year−1 for winter wheat. Off-farm CO2 emissions resulting from the use of agricultural materials such as chemical fertilizers, biocides (pesticides and herbicides) and agricultural machines were estimated by input–output tables to range from 0.800 Mg CO2 ha−1 year−1 for winter wheat to 1.724 Mg CO2 ha−1 year−1 for sugar beet. Direct N2O emissions previously measured in an Andosol field of this region showed a positive correlation with N fertilizer application rates. These emissions, expressed in CO2-equivalents, ranged from 0.041 Mg CO2 ha−1 year−1 for potato to 0.382 Mg CO2 ha−1 year−1 for cabbage. Indirect N2O emissions resulting from N leaching and surface runoff were estimated to range from 0.069 Mg CO2 ha−1 year−1 for adzuki bean to 0.381 Mg CO2 ha−1 year−1 for cabbage. The rates of CH4 removal from the atmosphere by soil uptake were equivalent to only 0.020–0.042 Mg CO2 ha−1 year−1. From the difference in the total soil C pools (0–20 cm depth) between 1981 and 2001, annual CO2 emissions from the CT and reduced tillage (RT) soils were estimated to be 4.91 and 3.81 Mg CO2 ha−1 year−1, respectively. In total, CO2-equivalent greenhouse gas emissions under CT cropping systems in the Tokachi region of Hokkaido amounted to 6.97, 7.62, 6.44, 6.64 and 7.49 Mg CO2 ha−1 year−1 for winter wheat, sugar beet, adzuki bean, potato and cabbage production, respectively. Overall, soil-derived CO2 emissions accounted for a large proportion (64–76%) of the total greenhouse gas emissions. This illustrates that soil management practices that enhance C sequestration in soil may be an effective means to mitigate large greenhouse gas emissions from arable land cropping systems such as those in the Tokachi region of northern Japan. Under RT cropping systems, plowing after harvesting was omitted, and total greenhouse gas emissions from winter wheat, sugar beet and adzuki bean could be reduced by 18%, 4% and 18%, respectively, mainly as a result of a lower soil organic matter decomposition rate in the RT soil and a saving on the fuels used for plowing.

Soil respiration in Siberian taiga ecosystems with different histories of forest fire.

Abstract Soil respiration includes soil microbial respiration, soil fauna respiration, and plant root respiration, therefore it reflects the biological activity of the soil ecosystems. The Siberian Taiga often experiences serious damage from forest fire, due to the very low precipitation in spring. We measured the soil respiration in five forest soil ecosystems with different histories of forest fire in Yakutsk in August 1997. The dominant tree species was Larix cajanderi, and the soils were Spodosols with a sandy and loamy texture. We also measured the soil respiration in a grassland. At severely burned sites, almost all the trees had fallen, litter and vegetation on the forest floor had burned, other forms of vegetation, including bryophytes or herbs, had invaded. At less severely burned forest sites, the trees were still standing but litter and vegetation on the forest floor had disappeared. Soil temperature, moisture, pH, and EC all increased after severe forest fires, the A-horizon showed a higher organic carbon content and a lower CN ratio. Soil respiration rate ranged from 18 to 397 (10-6 g CO2 m-2 s-1) in the same order reported so far. Soil respiration in severely burned forests was significantly lower than in intact forests, and was similar to that of grassland. Furthermore, mildly burned forests showed soil respiration values intermediate between those of severely burned and intact forests. These findings suggest that tree root respiration is considerably higher than root respiration of other plants or microbial and fauna respiration in soil. Soil microbial respiration was determined by the incubation method under the same temperature and soil moisture conditions as those in situ. Multiple regression analysis for mineral soils showed that the soil microbial respiration increased with the increase of the soil temperature and organic carbon content, that the soil microbial respiration decreased with the increase of pH. Whole soil microbial respiration within 1 m depth was higher in severely burned forests than in intact forests. These findings show that forest fire increased the soil microbial respiration and confirm that the loss of tree root respiration was the main reason for the decrease in soil respiration after severe forest fire. The contribution of tree root respiration to soil respiration was estimated to exceed 50%. Severe forest fire kills trees, and consequently results in a decrease of soil respiration.

Three years of nitrous oxide and nitric oxide emissions from silandic andosols cultivated with maize in Hokkaido, Japan

Abstract We measured nitrous oxide (N2O) and nitric oxide (NO) emissions during the snow-free season (April–November) over a 3-year period (1998–2000) from a Silandic Andosols cultivated with maize (Zea mays L.) in central Hokkaido, Japan. In May, before furrowing, composted cattle manure was broadcast onto the field at a rate of 3.0 g N m−2. After furrowing, chemical fertilizer (NH4)2SO4-N + (NH4)3PO4-N : urea-N at a ratio of 10:3 was applied to the row at a rate of 13 g N m−2. An impermeable layer lay 1.3 m below ground level. As a result, after heavy rains and during the snow-melting period, the groundwater table rose to near the ground surface. The N2O and NO emission rates ranged from 0.0 to 6.4 and from 0.00 to 0.94 mg N m−2 h−1, respectively. The highest N2O emission was observed after heavy rain in summer and autumn. The magnitude and seasonal pattern of N2O emissions from the inter row were similar to those from the row itself, although chemical fertilizer had not been applied to the inter row. In contrast, an increase in NO emissions was observed only from the row. Seasonal fluctuations in soil NH− 4 and NH− 3 concentrations and the emission ratio N2O-N/NO-N suggested that N2O and NO emitted after fertilizer application (May to early July) were produced mainly by nitrification, whereas N2O emitted after heavy rains (after mid-July) was produced mainly by denitrification. Total N2O and NO emissions during the snow-free season ranged from 0.7 to 2.8 and from 0.0 to 0.7 g N m-2, respectively, over a 3-year period. The N2O and NO emissions from our field were relatively high compared with those reported worldwide. In contrast, reported N2O emission rates from agricultural Andosols in Japan are typically lower than those from other agricultural soils in Japan and around the world. Therefore, the results of the present study suggest that high N2O emissions may occur from Japanese agricultural Andosols that are poorly drained.

Soil respiration and net ecosystem production in an onion field in Central Hokkaido, Japan

Abstract In order to evaluate the effect of cultivation and fertilization on the carbon balance in an onion field, soil respiration rate was measured by the closed chamber method during the growth season for 2 years. Measurements were performed under the following conditions: Ti, fertilized onion-growing treatment; T2, fertilized bare field treatment; T3, unfertilized onion-growing treatment; and T4, unfertilized bare field treatment. Soil respiration rates and the cumulative soil respiration ranged from 11 to 307 mg C m-2 h-1 and from 188 to 496 g C m−2 year−1, respectively. These values were higher in the onion-growing treatments than in the bare field treatments. The Q10 values ranged from 1.6 to 3.1 and were significantly higher in the onion-growing treatments than in the bare field treatments. This difference was mainly due to root respiration. Fertilization did not exert any significant effect on soil respiration. Net primary production (NPP) ranged from 152 to 217 g C m−2 year−1 for the onion-growing treatments, and was higher in the fertilized treatments. Estimated net ecosystem production (NEP) ranged from −222 to +27 g C m2 year−1, which was higher in the fertilized onion-growing treatment owing to the higher NPP. The difference between NEP and the amount of carbon in harvested onion (about 80% of NPP) corresponded to the amount of carbon sequestration in soil. The values ranged from −222 to −145 g C m−2 year−1. These negative values indicate that carbon loss by organic matter decomposition in soil was not compensated by the amount of organic matter input into soil.

Comparison of N2O and CO2 concentrations and fluxes in the soil profile between a Gray Lowland soil and an Andosol

Abstract We measured nitrous oxide (N2O) and carbon dioxide (CO2) fluxes from the soil surface and in the soil through to a depth of 0.3 m, and their concentration profiles through to a depth of 0.6 m in both a Gray Lowland soil with macropores and cracks and an Andosol with undeveloped soil structure in central Hokkaido, Japan. The objective of the present study was to elucidate any differences in N2O production and flux in the soil profile between these two soil types. In the Gray Lowland soil, the N2O concentration above 0.4 m increased with an increase in soil depth. In the Andosol, there were no distinctive N2O concentration gradients in the topsoil when the N2O flux did not increase. However, the N2O concentration at a depth of 0.1 m significantly increased and this concentration was higher than the concentration below 0.2 m when the N2O flux greatly increased. Thus, the N2O concentration profiles were different between these two soils. The contribution ratios of the N2O produced in the top soil (0–0.3 m depth) to the total N2O emitted from the soil to the atmosphere in the Gray Lowland soil and the Andosol were 0.86 and 1.00, respectively, indicating that the N2O emitted from the soil to the atmosphere was mainly produced in the top soil. However, the contribution ratio of the subsoil to the N2O emitted from the Gray Lowland soil was higher than that of the Andosol. There was a significant positive correlation between the N2O flux through to a 0.3 m depth and the flux from the soil to the atmosphere in the Gray Lowland soil only. These results suggest that N2O production in the subsoil of the Gray Lowland soil could have been activated by NO3 − leaching through macropores and cracks, and subsequently the N2O produced in the subsoil could have been rapidly emitted to the atmosphere through the macropores and cracks.

Comparison of the closed-chamber and gas concentration gradient methods for measurement of CO2 and N2O fluxes in two upland field soils

Abstract We measured nitrous oxide (N2O) and carbon dioxide (CO2) fluxes from Gray Lowland soil (onion field) and Andosol soil (maize field) using the closed-chamber method and the concentration-gradient method based on Ficks law (gradient method). Measurements of gas concentration (at a depth of 0.05 m) and relative gas diffusion coefficients (D/D 0) (0–0.05 m depth) in the soil were carried out every week during the snow-free season (May–October) each year for 6 years in the Gray Lowland soil (1995–2000) and for 3 years in the Andosol soil (1998–2000). The seasonal pattern of N2O and CO2 fluxes using the chamber method was similar to those using the gradient method, and there were significant positive correlations between the fluxes using the chamber and gradient methods when extremely high N2O flux values were excluded (Smirnov–Grubbs’ outlier test, P < 0.01). There were no significant differences in N2O fluxes between the two methods, but CO2 flux using the chamber method was higher than that using the gradient method. As the gradient method could not measure the production, consumption and gas diffusion in the surface soil above the soil-air sampling tube (upper 0.05 m), differences in extremely high N2O and CO2 fluxes between the two methods resulted when the production and consumption of these gases were active in the soil above the installed location of the soil-air sampling tube. Measurements of gas concentration and D/D0 in the soil were required at every measurement during the investigation period because these values showed large seasonal variation. The measurement of CO2 flux was more influenced by plants than the N2O measurements. Therefore, it is necessary to consider the distance between the instruments (chambers and soil-air sampling tubes) and nearby plants. Our results suggest that the gradient method could lead to under or over estimation of CO2 flux and to extremely high N2O flux measurements. In contrast, the gradient method could be used for N2O flux measurement, excluding extremely high fluxes, and to understand seasonal patterns in CO2 flux. The gradient method is useful because it can estimate gas fluxes both in the soil and from soil to the atmosphere at the same time.

Properties of Microbial Biomass in Acid Soils and Their Turnover

The soil microbial biomass is important such as pool of plant nutrients and is also driving force of the cycling of C, N, P and S in soil. However, the microbial biomass in acid soil has not been fully investigated due to the limitation of methods, i.e. chloroform-fumigation incubation or substrate-induced respiration because of decreased basal mineralization in chloroform-fumigated soil under acid conditions. This paper reviews improvement and application of these methods and vertical distribution of microbial biomass in two kinds of acid soils; namely, Andisols as dominant upland soils in Japan and tropical peat soils as potentially important lowland soils for agriculture, and also discuss on C and N turnover of microbial biomass in Andisols. Microbial succession in acid soil has also not been investigated so much, but, some studies in another important acid soil, i.e. acid sulfate soil, were also reviewed briefly.

Upward diffusion of nitrous oxide produced by denitrification near shallow groundwater table in the summer: a lysimeter experiment

Movement of nitrous oxide (N2O) produced in subsoil and shallow groundwater is important in determining the direct and indirect N2O emissions from agricultural soils. From the results of our previous study in a lysimeter-contained Gray lowland soil in the summer, we hypothesized that if a large amount of N2O is produced near shallow groundwater table in the summer, it will diffuse upward to the atmosphere. To examine this hypothesis, we conducted a one-year experiment in the same lysimeters for the cultivation of soybean–wheat double cropping (SW) or upland rice (UR). Dissolved N2O concentration in the drainage water in the UR plots exceeded 0.4 mg N L−1 in the summer, whereas that in the SW plots remained <0.1 mg N L−1. Analyses of the concentrations of nitrate and dissolved N2O in the drainage water and their nitrogen and oxygen isotopic compositions (δ15N and δ18O) during the summer revealed that denitrification was the main process for the N2O production near the groundwater table. There was a significant positive correlation between the dissolved N2O concentration and soil-surface N2O flux in the summer. Calculated upward diffusive N2O fluxes at three soil depths by Ficks law also supported our hypothesis. The δ15N values of N2O in the soil-surface flux were similar to those in the shallow groundwater in the UR plots during the summer. Such similarity was not found in the SW plots. We conclude that our hypothesis was confirmed by the above results. Comparison of the monitored data with other seasons indicates that low soil water content was a driving force for the upward N2O diffusion as well as the high dissolved N2O concentration.

Nitrous oxide and nitric oxide fluxes from cornfield, grassland, pasture and forest in a watershed in Southern Hokkaido, Japan

Abstract To develop an advanced method for estimating nitrous oxide (N2O) emission from an agricultural watershed, we used a closed-chamber technique to measure seasonal N2O and nitric oxide (NO) fluxes in cornfields, grassland, pastures and forests at the Shizunai Experimental Livestock Farm (467 ha) in southern Hokkaido, Japan. From 2000 to 2004, N2O and NO fluxes ranged from –137 to 8,920 µg N m−2 h−1 and from –12.1 to 185 µg N m−2 h−1, respectively. Most N2O/NO ratios calculated on the basis of these N2O and NO fluxes ranged between 1 and 100, and the log-normal N2O/NO ratio was positively correlated with the log-normal N2O fluxes (r 2 = 0.346, P < 0.01). These high N2O fluxes, therefore, resulted from increased denitrification activity. Annual N2O emission rates ranged from –1.0 to 81 kg N ha−1 year−1 (average = 6.6 kg N ha−1). As these emission values varied greatly and included extremely high values, we divided them into two groups: normal values (i.e. values lower than the overall average) and high values (i.e. values higher than average). The normal data were significantly positively correlated with N input (r 2 = 0.61, P < 0.01) and the “higher” data from ungrazed fields were significantly positively correlated with N surplus (r 2 = 0.96, P < 0.05). The calculated probability that a high N2O flux would occur was weakly and positively correlated with precipitation from May to August. This probability can be used to represent annual variation in N2O emission rates and to reduce the uncertainty in N2O estimation.