Sonoko D. Kimura

Variation in the emission factor of N2O derived from chemical nitrogen fertilizer and organic matter: A case study of onion fields in Mikasa, Hokkaido, Japan

Abstract Variability in the emission factors of nitrous oxide (N2O) associated with the application of chemical fertilizer (EFF) and organic matter (EFO) were analyzed in two onion fields (GL, Gray Lowland soil [Gleysol; Food and Agriculture Organization/UNESCO]; BL, Brown Lowland soil [Fluvisol; Food and Agriculture Organization/UNESCO]) in Mikasa, Hokkaido, Japan. Nitrous oxide flux was measured using a closed chamber technique in four treatments (FOP, chemical nitrogen fertilization and organic matter application, with plants; F, chemical nitrogen fertilization only, without plants; OP, organic matter application only, with plants; C, control, no fertilization or organic matter application, without plants) for 4 years in GL (2000, 2003–2005) and for 1 year in BL (2005). The application rate of chemical fertilizer nitrogen ranged from 237 to 242 kg N ha−1 year−1 in GL and was 284 kg N ha−1 year−1 in BL; organic matter nitrogen ranged from 81 to 117 kg N ha−1 year−1 in GL and was 181 kg N ha−1 year−1 in BL. The emission factors (EF) were calculated using the equations: EFF (%) = (N2O emission in FOP–N2O emission in OP)/(applied chemical nitrogen fertilizer) × 100 and EFO (%) = (N2O emission in FOP–N2O emission in F)/(applied organic matter nitrogen) × 100. The annual N2O emissions for treatments FOP, F, OP and C were 7.2–17, 5.7–17, 3.2–9.9 and 2.0–12 kg N ha−1 year−1, respectively, in GL and 5.6, 2.8, 1.9 and 1.8 kg N ha−1 year−1, respectively, in BL. The EFF ranged from 1.3% to 5.5% in GL and was 1.3% in BL. The EFF was positively correlated with the mean annual air temperature (P < 0.01), suggesting that N2O emission derived from chemical nitrogen fertilizer increases as air temperature rises. The EFO, however, differed greatly between GL (ranging from −5.2% to 9.1%) and BL (1.5%). The EFO was positively correlated with the mean annual relative humidity, although the correlation was not significant (P = 0.23). This finding suggests that much wetter climatic conditions may increase N2O emissions derived from organic matter nitrogen. The estimated N2O emissions based on these EF values and the rate of nitrogen application coincided well with the measured N2O emissions in the FOP treatment in both soils.

Estimation of global warming potential from upland cropping systems in central Hokkaido, Japan

Abstract Seven upland cropping systems in Central Hokkaido, Japan, were investigated during the growing season in 2003 to evaluate the magnitude of N2O emission, CH4 uptake and soil carbon sequestration, and their net effect on the global warming potential (GWP). N2O and CH4 fluxes were measured from field soils planted with crops and CO2 fluxes were measured from bare soils in attached plots at each site using the closed chamber method. Cumulative N2O emissions ranged from 0.02 g N m−2 to 0.62 g N m−2 for different soil types, which accounted for 0.35–4.44% of the applied fertilizer nitrogen. Cumulative CH4 uptake rates ranged from −0.08 g C m−2 to 0 g C m−2. Soil carbon sequestration, defined as the difference between the net primary production and carbon loss through harvest and soil microbial decomposition, ranged from −410 to −193 g C m−2, indicating that the carbon loss from soils could not be compensated by the carbon input through plant photosynthesis. The net GWP from the investigated cropping systems ranged from 749 to 1790 g CO2 equivalents m−2. CO2 emission contributed to 84–99% of the net GWP and N2O contributed 1–16%.

Optimizing Nitrogen Fertilizer Application for Rice Production in the Taihu Lake Region, China

Abstract To determine the optimal amount of nitrogen (N) fertilizer for achieving a sustainable rice production at the Taihu Lake region of China, two-year on-farm field experiments were performed at four sites using various N application rates. The results showed that 22%–30% of the applied N was recovered in crop and 7%–31% in soils at the rates of 100–350 kg N ha−1. Nitrogen losses increased with N application rates, from 44% of the applied fertilizer N at the rate of 100 kg N ha−1 to 69% of the N applied at 350 kg N ha−1. Ammonia volatilization and apparent denitrification were the main pathways of N losses. The N application rate of 300 kg N ha−1, which is commonly used by local farmers in the study region, was found to lead to a significant reduction in economic and environmental efficiency. Considering the cost for mitigating environmental pollution and the maximum net economic income, an application rate of 100–150 kg N ha−1 would be recommended. This recommended N application rate could greatly reduce N loss from 199 kg N ha−1 occurring at the N application rate of 300 kg N ha−1 to 80–110 kg N ha−1, with the rice grain yield still reaching 7 300–8 300 kg DW ha−1 in the meantime.

Nitrous oxide fluxes from upland soils in central Hokkaido, Japan.

Nitrous oxide (N2O) fluxes from soils were measured using the closed chamber method during the snow-free seasons (middle April to early November), for three years, in a total of 11 upland crop fields in central Hokkaido, Japan. The annual mean N2O fluxes ranged from 2.95 to 164.17 microgN/(m2 x h), with the lowest observed in a grassland and the highest in an onion field. The instantaneous N2O fluxes showed a large temporal variation with peak emissions generally occurring following fertilization and heavy rainfall events around harvesting in autumn. No clear common factor regulating instantaneous N2O fluxes was found at any of the study sites. Instead, instantaneous N2O fluxes at different sites were affected by different soil variables. The cumulative N2O emissions during the study period within each year varied from 0.15 to 7.05 kgN/hm2 for different sites, which accounted for 0.33% to 5.09% of the applied fertilizer N. No obvious relationship was observed between cumulative N2O emission and applied fertilizer N rate (P > 0.4). However, the cumulative N2O emission was significantly correlated with gross mineralized N as estimated by CO2 emissions from bare soils divided by C/N ratios of each soil, and with soil mineral N pool (i.e., the sum of gross mineralized N and fertilizer N) (P < 0.001).

Evaluation of the soil carbon budget under different upland cropping systems in central Hokkaido, Japan

Abstract To evaluate the carbon budget in soils under different cropping systems, the carbon dioxide (CO2) flux from soils was measured in a total of 11 upland crop fields within a small watershed in central Hokkaido over the no snow cover months for 3 years. The CO2 flux was measured using a closed chamber method at bare plots established in each field to estimate soil organic matter decomposition. Temporal variation in instantaneous soil CO2 fluxes within the sites was mainly controlled by soil temperature and moisture. Annual mean CO2 fluxes and cumulative CO2 emissions had no significant relationship with soil temperature and moisture (P > 0.2). However, there was a significant quadratic relationship between annual mean CO2 flux or cumulative CO2 emission and soil clay plus silt content (%) (R2 = 0.72∼0.74, P < 0.0003). According to this relationship, the optimum condition for soil CO2 emission is at a clay plus silt content of 63%. The cumulative CO2 emission during the no snow cover season within each year varied from 1,159 to 7,349 kg C ha−1 at the different sites. The amount of crop residue carbon retained in the soils following a cropping season was not enough to offset the CO2 emission from soil organic matter decomposition at all sites. As a consequence, the calculation of the soil carbon budget (i.e. the difference between the carbon added as crop residues and compost and the carbon lost as CO2 from organic matter decomposition) ranged from –7,349 to –785 kg C ha−1, except for a wheat site where a positive value of 4,901 kg C ha−1 was observed because of a large input of organic carbon with compost. The negative values of the soil carbon budget indicate that these cropping systems were net sources of atmospheric CO2.

Characteristics and issues related to regional-scale modeling of nitrogen flows

Abstract This paper summarizes the characteristics of regional-scale nitrogen (N) flow models. The regional scale is generally considered to be an area that ranges from more than 10 km2 to the size of a continent. Parameterization is the key process in creating a regional-scale model. During parameterization, transfer functions that reflect the controlling factors must be created at the target scale because the influence of different factors will change with the size of the scale. Watersheds are the most useful unit for evaluating overall N discharge; however, regional activity data is most often available for municipal units. Thus, municipal units must be reaggregated into watershed units. A longer time period is desirable to normalize seasonal and annual variations at regional scales. Parameters that influence N flow must match the investigated spatial and temporal scales. Given the need to use a range of parameters that vary in terms of the quality of the data, models exhibit inevitable uncertainties. Quantification of the uncertainties and verification of the estimated results are required. Error propagation, the Monte Carlo simulation method and maximum and minimum values have been used to obtain different threshold values of uncertainty. To verify regional-scale N flow models, the following five approaches have been used or proposed: (1) calibration of the model by detailed monitoring at multiple sites, (2) verification of the most important process of the extrapolation mechanisms, (3) verification of the N budget, paying particular attention to water quality, (4) comparison with the results quantified by different models, (5) comparison with aerial or satellite image analysis. As regional-scale modeling of N flow will become more important in the future, it is important to develop models than can accurately estimate N dynamics at this scale.

Effects of environmental factors on temporal variation in annual carbon dioxide and nitrous oxide emissions from an unfertilized bare field on Gray Lowland soil in Mikasa, Hokkaido, Japan

Abstract Soil is an important source of atmospheric carbon dioxide (CO2) and nitrous oxide (N2O). Studies of CO2 and N2O emissions from bare soil may explain annual changes in carbon (C) in soil organic matter (SOM) and help analyze N2O production from SOM. Therefore, CO2 and N2O emissions associated with the decomposition of SOM from bare soil are important factors for assessing the C budget and N2O emission in agricultural fields. We conducted a study over 7 years to assess the controlling factors of CO2 and N2O emissions from unplanted and unfertilized soil in Mikasa, Hokkaido, Japan. The CO2 flux increased in summer and there were significant positive correlations between the CO2 flux and soil temperature in the first 4 years. However, apparent relationships between CO2 flux and water-filled pore space, soil NH4 and NO3 concentrations were not observed. The slope of monthly CO2 emission against mean monthly temperature was positively correlated with monthly precipitation. These results suggest that the response of CO2 production to increases in soil temperature became more sensitive in wet soils. The average CO2 emission during the study period was 2.53 Mg C ha−1 year−1, and uncertainty in the annual CO2 emission was 24%. Annual precipitation explained the yearly variation (CO2 emission [Mg C ha−1 year−1] = 0.0021 × annual precipitation [mm year−1] −0.0499, R = 0.976, P < 0.001). Nitrous oxide flux increased from July to October and was positively correlated with CO2 flux. Based on the ratio of N2O-N : NO-N of fluxes, N2O appeared to be the main product of denitrification. The average N2O emission over the study period was 4.88 kg N ha−1 year−1, and uncertainty in the annual N2O emission was 58.5%. Strong relationships between the monthly emissions of CO2 and N2O suggest that N2O production by denitrification is strongly affected by SOM decomposition. Unlike CO2 emission, a relationship between N2O emission and precipitation was not observed because of the multiple pathways of nitrification and denitrification for N2O production induced by SOM decomposition.

Influence of long-term changes in nitrogen flows on the environment: a case study of a city in Hokkaido, Japan

There is an urgent need to establish sustainable nutrient cycling. Changes in amounts of N flow and separation of production and consumption sectors are becoming a serious environmental problem. In this study, the yearly N in- and outflow of a city in northern Japan from 1912 to 2002 was investigated based on the statistics and inventory data. Based on the characteristics of the N flow, the period was divided into manure-based period (MBP, 1912–1950), transition period from manure- to chemical fertilizer-based period (TP, 1950–1970), and chemical fertilizer-based period (CBP, 1970–2002). The highest amount of N inflow (up to 350 Mg N y–1) was observed at the end of the MBP, and the second peak (about 300 Mg N y–1) at the beginning of the CBP. The N application rate on farmland increased from 68 kg N ha–1 in 1912 to above 250 kg N ha–1 in the 1950s, then decreased to 168 kg N ha–1 in 2002. The farmland productivity increased from 30 kg N ha–1 at the end of the 1950s to 90 kg N ha–1 in 2002, due to improvement in crop varieties and management methods. In MBP surplus N in farmland and NH3 volatilization accounted for 90% of the N outflow from the city, then in CBP, disposal N and surplus N in farmland became the main N outflow. All these outputs are considered to increase the N concentration in rivers and/or underground water. In the case of surplus N in farmland, it exceeded the amount of optimum N management (<50 kg N ha–1; , Agricult. Ecosyst. Environ. 72: 35–52) during 1935–1970 and 1981–1997. In order to prevent degradation of the environment through artificially altered nutrient flow, we need to be aware of the environmental impact of the N flow and establish proper N management practices.

Estimation of the amounts of livestock manure, rice straw, and rice straw compost applied to crops in Japan: a bottom-up analysis based on national survey data and comparison with the results from a top-down approach

We estimated the application of cattle, swine, and poultry manure and of rice straw and rice straw compost for seven crop groups (paddy rice, upland crops, vegetables, orchards, tea, forage, and fodder) from a bottom-up analysis of government questionnaire data. Vegetable crops consumed the most manure and received the largest amount of swine and poultry manure and of rice straw compost, and the second-highest amount of cattle manure. Paddy rice received the least manure, and depended mainly on organic matter from non-composted rice straw. Fodder (timothy (Phleum pratense. L.), etc.) and forage (dent corn (Zea mays L.), etc.) crops used for cattle husbandry consumed the most cattle manure; however, fodder crops received only one-quarter of the cattle manure received by forage crops. We hypothesized phosphorus (P) is not lost during composting, then estimated the amount of raw materials for livestock manure inversely from applied livestock manure P and carbon (C):nitrogen (N):potassium (K):P ratio of kinds of livestock excreta. More than half of livestock excreta (6224 Gg C, 589 Gg N, 90 Gg P, and 278 Gg K) was utilized for manure. However, manure applied (2300 Gg C, 158 Gg N, 90 Gg P, 154 Gg K) was lower than in a previous study based on a top-down analysis (161 Gg N, 92 Gg P), possibly because mainly poultry excreta (520 Gg C, 75 Gg N, 11 Gg P, 13 Gg K) and a considerable amount of livestock excreta (3654 Gg C, 353 Gg N, 53 Gg P, 174 Gg K, not including loss during storage) were not utilized. A newer survey to grasp the present state of fertilization done by the government could update our assessment of the use of livestock excreta for crop production based purely on top-down approaches.

Denitrification characteristics of pond sediments in a Chinese agricultural watershed.

Abstract Ponds are widely distributed in rice-based agricultural watersheds, particularly in southern China, and may play an important role in nitrate (NO- 3) removal. However, the denitrification rate of pond sediment, measured using the acetylene (C2H2) inhibition technique, indicated that the amount of nitrogen removed by denitrification accounted for <1% of the total nitrogen applied. The present study was undertaken to determine the effects of sediment depth and temperature on denitrification of pond sediment using the C2H2 inhibition technique. The highest denitrification potential was found in the upper 5 cm of sediment, but this only accounted for approximately 34% of the total denitrification of the upper 0–30 cm of sediment, suggesting that sediment denitrification potential would be underestimated if only the upper 5 cm of sediment was measured. The denitrification potential was low and showed a weak response over a temperature range of 6–18°C, whereas denitrification increased significantly from 18 to 30°C, indicating that denitrification may play an important role in the removal of NO- 3 in warm seasons. A comparison of the NO- 3 disappearance and C2H2 inhibition methods showed that they were significantly (P < 0.01) and positively correlated. However, the C2H2 inhibition method gave only approximately 25% of the values determined by the NO- 3 disappearance method.