Mariko Shimizu

Hydrological process controls on nitrogen export during storm events in an agricultural watershed

Abstract The dynamic characteristics of nitrogen (N) and suspended solids (SS) were investigated in stream water during four storm events in 2003 in the Shibetsu watershed, eastern Hokkaido, Japan. Analysis showed that total nitrogen (TN), nitrate-N (NO- 3-N), dissolved organic nitrogen (DON), particulate nitrogen (PN) and SS concentrations all peaked sharply during the rising limb of the discharge hydrograph, but peaks in PN and SS were more significant than the peak in dissolved N. Particulate N and SS consistently displayed clockwise hysteresis with higher concentrations during rising flows, whereas NO- 3-N and DON showed different patterns among the storms depending on the antecedent soil moisture. An M (V) curve, defined as the nutrient mass distribution versus the volume of discharge, showed that a “first flush” of PN, NO- 3-N, DON and SS was observed; however, the distribution of nutrient loads in the discharge was different. Particulate N and SS had a shorter flushing characteristic time constant (t 1/e, defined as the time interval required for a decline in nutrient concentrations in discharge water to e−1 [37%] of their initial concentrations), but contributed 80% of fluxes during the first 50% of the discharge, whereas the longer flush time (t 1/e) of NO- 3-N and DON with slowly decreased concentrations led to half loads during the recession of the discharge. These data indicate that flush mechanisms might be distinguished between particulate nutrients and dissolved N. Analysis showed that the concentrations of PN and SS derived from soil erosion were related to surface run-off. In contrast, NO- 3-N originated from the near-surface soil layer associated with the rising shallow groundwater table and mainly flushed with subsurface run-off. The different flushing mechanisms implied that different watershed best management practices should be undertaken for effectively mitigating water quality degradation.

Effect of chemical fertilizer and manure application on N2O emission from reed canary grassland in Hokkaido, Japan.

Abstract We evaluated the effect of chemical fertilizer and manure applications on N2O emission from a managed grassland by establishing three treatment plots of chemical N fertilizer (chemical fertilizer), manure combined with chemical N fertilizer (manure) and no N fertilizer (control) at the Shizunai Experimental Livestock Farm in southern Hokkaido, Japan. The N2O fluxes from the soils were measured using a closed-chamber method from May 2005 to April 2008. Soil denitrifying enzyme activity (DEA) in the root-mat layer (0–2.5 cm) and in the mineral soil layer (2.5–5 cm) of each treatment plot was measured using an acetylene inhibition method after treatment with NO3 −-N addition, glucose addition, both NO3 −-N and glucose addition or neither NO3 −-N nor glucose addition. Annual N2O emission ranged from 0.6 to 4.9 kg N2O-N ha−1year−1, with the highest emission observed in the manure plot and the lowest in the control plot. The chemical fertilizer induced emission factor (EF) (range: 0.85–1.32%) was significantly higher than the manure-induced EF (range: 0.35–0.85%). The denitrification potential of the soil horizons was measured with the addition of both NO3 −-N and glucose, and was significantly higher in root-mat soil than in mineral soil. Soil DEA in the root mat with the addition of NO3 −-N with and without the addition of glucose had a significantly positive correlation with soil pH (P < 0.05). Soil pH was significantly influenced by N source, which was significantly lower in the chemical fertilizer plot than in the control and manure plots. For a fixed quantity of available N, the application of manure could result in higher N2O emission compared with chemical fertilizer, owing to higher soil pH values under manure application than under chemical fertilizer application.

Nitrogen budget and relationships with riverine nitrogen exports of a dairy cattle farming catchment in eastern Hokkaido, Japan

Abstract Dairy farming regions are important contributors of nitrogen (N) to surface waters. We evaluated the N budget and relationships to riverine N exports within the Shibetsu River catchment (SRC) of a dairy farming area in eastern Hokkaido, Japan. Five drainage basins with variable land-cover proportions within the SRC were also evaluated individually. We quantified the net N input (NNI) to the catchment from the difference between the input (atmospheric deposition, chemical fertilizers, N fixation by crops and imported food and feed) and the output (exported food and feed, ΔS liv and ΔS hu, which are the differences between input and output in livestock and human biomass, respectively) using statistical and measured data. Volatilized ammonia (NH3) was assumed to be recycled within the catchment. The riverine export of N was quantified. Agricultural N was a dominant source of N to the SRC. Imported feed was the largest input (38.1 kg N ha−1 year−1), accounting for 44% of the total inputs, followed by chemical fertilizers (32.4 kg N ha−1 year−1) and N fixation by crops (13.4 kg N ha−1 year−1). The exported food and feed was 24.7 kg N ha−1 year−1 and the ΔS liv and ΔS hu values were 7.6 and 0.0 kg N ha−1 year−1, respectively. As a result, the NNI amounted to 54.6 kg N ha−1 year−1. The riverine export of total N from the five drainage basins correlated well with the NNI, accounting for 27% of the NNI. The fate of the missing NNI that was not measured as riverine export could possibly have been denitrified and/or retained within the SRC. A change in the estimate of the deposition rate of volatilized NH3 from 100 to 0% redeposited would have decreased the NNI by 37%, although we believe that most NH3 was likely to have been redeposited. The present study demonstrated that our focus should be on controlling agricultural N to reduce the impact of environmental pollution as well as on evaluating denitrification, N stocks in soil and the fate of NH3 volatilization in the SRC.

N2O and CH4 fluxes from a volcanic grassland soil in Nasu, Japan: Comparison between manure plus fertilizer plot and fertilizer-only plot

Abstract We examined the effects of manure + fertilizer application and fertilizer-only application on nitrous oxide (N2O) and methane (CH4) fluxes from a volcanic grassland soil in Nasu, Japan. In the manure + fertilizer applied plot (manure plot), the sum of N mineralized from the manure and N applied as ammonium sulfate was adjusted to 210 kg N ha−1 year−1. In the fertilizer-only applied plot (fertilizer plot), 210 kg N ha−1 year−1 was applied as ammonium sulfate. The manure was applied to the manure plot in November and the fertilizer was applied to both plots in March, May, July and September. From November 2004 to November 2006, we regularly measured N2O and CH4 fluxes using closed chambers. Annual N2O emissions from the manure and fertilizer plots ranged from 7.0 to 11.0 and from 4.7 to 9.1 kg N ha−1, respectively. Annual N2O emissions were greater from the manure plot than from the fertilizer plot (P < 0.05). This difference could be attributed to N2O emissions following manure application. N2O fluxes were correlated with soil temperature (R = 0.70, P < 0.001), NH+ 4 concentration in the soil (R = 0.67, P < 0.001), soil pH (R = –0.46, P < 0.001) and NO− 3 concentration in the soil (R = 0.40, P < 0.001). When included in the multiple regression model (R = 0.72, P < 0.001), however, the following variables were significant: NH+ 4 concentration in the soil (β = 0.52, P < 0.001), soil temperature (β = 0.36, P < 0.001) and soil moisture content (β = 0.26, P < 0.001). Annual CH4 emissions from the manure and fertilizer plots ranged from –0.74 to –0.16 and from –0.84 to –0.52 kg C ha−1, respectively. No significant difference was observed in annual CH4 emissions between the plots. During the third grass-growing period from July to September, however, cumulative CH4 emissions were greater from the manure plot than from the fertilizer plot (P < 0.05). CH4 fluxes were correlated with NH+ 4 concentration in the soil (R = 0.21, P < 0.05) and soil moisture content (R = 0.20, P < 0.05). When included in the multiple regression model (R = 0.29, P < 0.05), both NH+ 4 concentration in the soil (β = 0.20, P < 0.05) and soil moisture content (β = 0.20, P < 0.05) were significant.

The effect of fertilizer and manure application on CH4 and N2O emissions from managed grasslands in Japan

The objectives of this study were to clarify the effect of chemical fertilizer and manure application on methane (CH4) and nitrous oxide (N2O) emissions from intensively managed grassland on Andosols in Japan and to determine the controlling factors of the CH4 and N2O emissions. The emission factors (EF) for both fertilizer- and manure-induced N2O emissions were calculated. Three experimental plots were set up in five grasslands across four climatic regions in Japan: one plot for treatment with chemical fertilizer (fertilizer plot); another plot for treatment with cattle manure and chemical fertilizer (manure plot), and the final plot was not treated with chemical fertilizer or manure (control plot). The type of chemical fertilizer was ammonium-based fertilizer or a combination fertilizer of ammonium and urea. CH4 and N2O emissions were measured at the study sites for six years. For the manure plot, a supplement of chemical fertilizer was added to equalize the supply rate of mineral nitrogen (N) relative to that of the fertilizer plots. There were no significant differences in CH4 emissions among the treatment plots, and the effect of fertilizer or manure application was not evident. CH4 emissions tended to be larger at sites with higher soil moisture content. The application of chemical fertilizer or manure increased N2O emissions at all the sites, and there were significant differences among the sites and across different years. Background N2O emissions (N2O emissions at the control plot) had strong positive correlations with air temperature and precipitation, along with weak positive correlations with soil carbon and N content. Therefore, an empirical model (Background N2O emission = 0.298 × air temperature + 0.512 × soil N content −3.77) was established. Fertilizer-induced N2O emission factor (EF) had a positive correlation (R2 = 0.50, p < 0.01) with precipitation (Fertilizer-induced EF = 0.0022 × precipitation −1.3), and increasing precipitation enhanced N2O production through the denitrification process due to applied fertilizer N. There were no significant differences in manure-induced EFs among the sites, and the average was 0.36% except for an outlier.

Nitrous oxide emissions and nitrogen cycling in managed grassland in Southern Hokkaido, Japan

Abstract Nitrous oxide (N2O) emissions were measured and nitrogen (N) budgets were estimated for 2 years in the fertilizer, manure, control and bare plots established in a reed canary grass (Phalaris arundinacea L.) grassland in Southern Hokkaido, Japan. In the manure plot, beef cattle manure with bark was applied at a rate of 43–44 Mg fresh matter (236–310 kg N) ha−1 year−1, and a supplement of chemical fertilizer was also added to equalize the application rate of mineral N to that in the fertilizer plots (164–184 kg N ha−1 year−1). Grass was harvested twice per year. The total mineral N supply was estimated as the sum of the N deposition, chemical fertilizer application and gross mineralization of manure (GMm), soil (GMs), and root-litter (GMl). GMm, GMs and GMl were estimated by dividing the carbon dioxide production derived from the decomposition of soil organic matter, root-litter and manure by each C : N ratio (11.1 for soil, 15.5 for root-litter and 23.5 for manure). The N uptake in aboveground biomass for each growing season was equivalent to or greater than the external mineral N supply, which is composed of N deposition, chemical fertilizer application and GMm. However, there was a positive correlation between the N uptake in aboveground biomass and the total mineral N supply. It was assumed that 58% of the total mineral N supply was taken up by the grass. The N supply rates from soil and root-litter were estimated to be 331–384 kg N ha−1 year−1 and 94–165 kg N ha−1 year−1, respectively. These results indicated that the GMs and GMl also were significant inputs in the grassland N budget. The cumulative N2O flux for each season showed a significant positive correlation with mineral N surplus, which was calculated as the difference between the total mineral N supply and N uptake in aboveground biomass. The emission factor of N2O to mineral N surplus was estimated to be 1.2%. Furthermore, multiple regression analysis suggested that the N2O emission factor increased with an increase in precipitation. Consequently, soil and root-litter as well as chemical fertilizer and manure were found to be major sources of mineral N supply in the grassland, and an optimum balance between mineral N supply and N uptake is required for reducing N2O emission.

The Impact of Sunlight Conditions on the Consistency of Vegetation Indices in Croplands—Effective Usage of Vegetation Indices from Continuous Ground-Based Spectral Measurements

A ground-based network of spectral observations is useful for ecosystem monitoring and validation of satellite data. However, these observations contain inherent uncertainties due to the change of sunlight conditions. This study investigated the impact of changing solar zenith angles and diffuse/direct light conditions on the consistency of vegetation indices (normalized difference vegetation index (NDVI) and green-red vegetation index (GRVI)) derived from ground-based spectral measurements in three different types of cropland (paddy field, upland field, cultivated grassland) in Japan. In general, the vegetation indices decreased with decreasing solar zenith angle. This response was affected significantly by the growth stage and diffuse/direct light conditions. The decreasing response of the NDVI to the decreasing solar zenith angle was high during the middle growth stage (0.4 < NDVI < 0.8). On the other hand, a similar response of the GRVI was evident except in the early growth stage (GRVI < 0). The response of vegetation indices to the solar zenith angle was evident under clear sky conditions but almost negligible under cloudy sky conditions. At large solar zenith angles, neither the NDVI nor the GRVI were affected by diffuse/direct light conditions in any growth stage. These experimental results were supported well by the results of simulations based on a physically-based canopy reflectance model (PROSAIL). Systematic selection of the data from continuous diurnal spectral measurements in consideration of the solar light conditions would be effective for accurate and consistent assessment of the canopy structure and functioning.

Effects of soil aggregate size, moisture content and fertilizer management on nitrous oxide production in a volcanic ash soil

A laboratory incubation study was conducted to determine the effects of soil aggregate size, soil moisture content and manure application on nitrous oxide (N2O) production through nitrification and denitrification. In Southern Hokkaido, soil samples were taken from a mineral soil layer (2.5–10 cm) of a grassland to which chemical fertilizer and manure had been applied. The soil aggregates were air-dried and sieved with 4.5 mm and 2 mm sieves, and the soil moisture was adjusted to 60% and 80% of field water capacity (FWC). Immediately after moistening, incubation was initiated and lasted for 9 days at 20°C. Following the start of incubation, a flush of N2O, carbon dioxide (CO2) and nitric oxide (NO) was observed. Production of all gases was higher in larger aggregates from the manure-applied soil. Productions of CO2 and NO were not significantly influenced by soil moisture content, but N2O production was considerably higher in 80% FWC as compared with 60% FWC. Based on the results of the N2O–nitrogen (N)/NO–N ratio, the process of N2O production was mainly due to nitrification in 60% FWC and denitrification in 80% FWC. Soil chemical properties, especially ammonium–N –N), nitrate–N (NO3–N) and water extractable organic C (WEOC) and microbial biomass C (MBC) also changed immediately after moistening. These changes were higher in larger aggregates from the manure-applied soil. Potential denitrification enzyme activity (DEA) was significantly higher in larger aggregates from manure-applied soil with higher moisture content. The N2O production in both 60% and 80% FWC correlated significantly with MBC and DEA. Regardless of soil moisture conditions, MBC correlated significantly with DEA, WEOC consumption and apparent N mineralization. These facts suggest that larger soil aggregates could have quickly developed suitable internal conditions for microbial activity inside the aggregates and consequently stimulated N2O production through nitrification and denitrification.

Nitrous and nitric oxide emissions from a cornfield and managed grassland: 11 years of continuous measurement with manure and fertilizer applications, and land-use change

ABSTRACT Changes in weather and management practices such as manure and fertilizer applications have a major effect on nitrous oxide (N2O) and nitric oxide (NO) emissions from soils. N2O and NO emissions exhibit high intra- and inter-annual fluctuations, which are also highly influenced by land-use change. In this study we investigated how land-use change between grassland and cornfield affects soil N2O and NO emissions using long-term field measurements in a mollic andosol soil in Southern Hokkaido, Japan. Soil N2O and NO emissions were monitored for 5 years in a 30-year old grassland (OG), which was then plowed and converted to a cornfield for 3 years and then converted back to grassland (new grassland, NG) for another 3 years. We established four treatment plots: control, without any nitrogen (N) input (CT plot); chemical fertilizer only (F plot); chemical fertilizer and manure (MF plot); and manure only (M plot). Changing land use from OG to cornfield increased annual N2O emissions by 6–7 times, while the change from cornfield to NG resulted in a 0.3–0.6 times reduction in annual N2O emissions. N2O emissions in the newly established grassland were 2–5 times higher than those in the 30-year old grassland. Soil mineral N (NO3− and NH4+) was higher in cornfield, followed by NG and lowest in OG, while water extractable organic carbon (WEOC) did not significantly change with changing land use but tended to be higher in OG and NG than in cornfield. The ratio of WEOC to soil NO3− was the most important explanatory variable for differences in N2O emissions as land use changed. High N input, surplus soil N, and precipitation and low soil pH led to increased N2O emissions. N2O emissions in fertilizer- and/or manure-amended plots were 3–4, 2–5 and 1.4–2 times higher than those in the control treatment in OG, cornfield and NG, respectively. NO emissions were largely influenced by soil mineral N and N addition, and showed less response to changing land use. There were high inter-annual variations in both NO and N2O emissions in all plots, including the control treatment, highlighting the need for long-term measurements when determining local emission rates.

Nitrous oxide fluxes from soil under different crops and fertilizer management.

The effect of mineral fertilizer (F) and mineral combined with organic fertilizer (MF) on N2O flux in grassland and cornfield was investigated for one year in Southern Hokkaido, Japan. Annual N2O flux was higher in grassland than in cornfield, and it was higher in MF plot (14.9 kg N/ha/period) than in F plot (11.1 kg N/ha/period) in grassland. However, in cornfield, the annual N2O flux was equal between both plots (5.6 kg N/ha/period). These results clarified that high nitrogen application was not always responsible for the high soil N2O flux. N2O flux was significantly correlated with air, soil temperature and water-filled pore space. More than 80% of the annual N2O flux occurred before freezing and less than 4% during melting period. Denitrification was the main process of N2O flux during study, it was evidenced by the distribution of N2O and NO ratio which is from 1 to 1000. The denitrification activity (DEA) potentially increased in grassland soil in the beginning and the end of winter season when NO3-N was abundant; on the other hand the abundance of carbon potentially increased DEA in cornfield soil.