Changes in weather and management practices such as manure and fertilizer applications have a major effect on nitrous oxide (N 2 O) and nitric oxide (NO) emissions from soils. N 2 O 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 N 2 O and NO emissions using long-term field measurements in a mollic andosol soil in Southern Hokkaido, Japan. Soil N 2 O 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 N 2 O emissions by 6-7 times, while the change from cornfield to NG resulted in a 0.3-0.6 times reduction in annual N 2 O emissions. N 2 O emissions in the newly established grassland were 2-5 times higher than those in the 30-year old grassland. Soil mineral N (NO 3 − and NH 4 + ) 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 NO 3 − was the most important explanatory variable for differences in N 2 O emissions as land use changed. High N input, surplus soil N, and precipitation and low soil pH led to increased N 2 O emissions. N 2 O 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 N 2 O emissions in all plots, including the control treatment, highlighting the need for long-term measurements when determining local emission rates.

Reduction of chemical fertilizers and effective use of livestock excrement are required for the realization of sustainable agriculture and reduction of greenhouse gas (GHG) emissions. The purpose of this study was to estimate the reduction rate of GHG emissions represented by comparing global warming potential (GWP) using organic fertilizers instead of chemical fertilizers. The study was conducted in a managed grassland on Andosol in southern Hokkaido for 3 years from May 2017 to April 2020. There were five treatment plots: no fertilizer, chemical fertilizer, manure, slurry, and digestive fluid. Organic fertilizers were applied such that the amount of NPK did not exceed the recommended application rate, and the shortage was supplemented with chemical fertilizers. Fluxes in CO2 caused by heterotrophic respiration (RH), CH4, and N2O were measured using the closed chamber method. Net ecosystem carbon balance (NECB) was obtained as net primary production + organic fertilizer application—RH—harvest. The GWP was estimated by CO2 equivalent NECB and CH4 and N2O emissions in each treatment. Chemical fertilizer nitrogen application rates in the organic fertilizer treatments were reduced by 10% for manure, 19.7% for slurry and 29.7% for digestive fluid compared to chemical fertilizer only, but the grass yields were not significantly different among the fertilizer treatments. The 3-year NECB showed significantly smallest carbon loss in manure treatment, and smaller carbon loss in the organic fertilizer treatments than in the chemical fertilizer only. The reduction rate in the GWP with use of organic fertilizers relative to that of chemical fertilizer was 16.5% for slurry, 27.0% for digestive fluid, and 36.2% for manure. The NECB accounted for more than 90% of the GWP in all treatments. CH4 emissions were < 0.1% of the GWP. On the other hand, N2O emissions accounted for more than 5% of the GWP, and was larger in the order of slurry > chemical fertilizer only > digestive fluid > manure. As a conclusion, these organic fertilizers can be used without no reduction of crop yield instead of chemical fertilizer, however, manure is the best way to increase soil carbon and to decrease GWP, followed by digestive fluid.

Managed grassland is occasionally renovated to maintain plant productivity by killing old vegetation, ploughing, and reseeding. This study aimed to investigate the combined effect of grassland renovation and long-term manure application on the temporal dynamics of nitrous oxide (N2O) emission and nitrate nitrogen (NO3−–N) leaching. The study was conducted from September 2013 to September 2016 in a managed grassland renovated in September 2013. In this grassland, two treatments were managed—chemical fertilizer application (F treatment) and the combined application of chemical fertilizer and beef cattle manure (MF treatment)—for eight years before the renovation. The control treatment without fertilization (CT) was newly established in the F treatment. The soil N2O flux was measured using a closed chamber method. A leachate sample was collected using a tension-free lysimeter that was installed at the bottom of the Ap horizon (25 cm deep), and total NO3−–N leaching was calculated from leachate NO3−–N concentration and drainage volume was estimated by the water balance method. In the first year after renovation, the absence of plant nitrogen uptake triggered NO3−–N leaching following rainfall during renovation and increased drainage water after thawing. NO3−–N movement from topsoil to deeper soil enhanced N2O production and emission from the soil. N2O emission in MF treatment was 1.6–2.0 times larger than those of CT and F treatments, and NO3−–N leaching in MF treatment was 2.3–2.6 times larger than those of CT and F treatments in the first year. Mineral nitrogen release derived from long-term manure application increased NO3−–N leaching and N2O emission. In the second year, N2O emission and NO3−–N leaching significantly decreased from the first year because of increased plant N uptake and decreased mineral nitrogen surplus, and no significant differences in N2O emission and NO3−–N leaching were observed among the treatments. In the second and third years, NO3−–N leaching was regulated by plant nitrogen uptake. There were no significant differences in NO3−–N leaching among the treatments, but N2O emission in MF treatment was significantly smaller than in the F treatment. Long-term manure application could be a possible option to mitigate N2O emission in permanent grassland; however, the risk of increased NO3−–N leaching and N2O emission in the renovation year induced by manure nitrogen release should be noted.

In order to understand the relationships between understory bamboo and soil properties, we compared microbial community structures in the soil of a Betula ermanii boreal forest with Sasa kurilensis present and removed using high-throughput DNA sequencing. The presence of understory S. kurilensis strongly affected soil properties, including total carbon, total nitrogen, nitrate, and the C:N ratio as well as relative soil moisture. Marked differences were also noted in fungal and bacterial communities between plots. The relative abundance of the fungal phylum Ascomycota was 13.9% in the Sasa-intact plot and only 0.54% in the Sasa-removed plot. Among the Ascomycota fungi identified, the most prevalent were members of the family Pezizaceae. We found that the abundance of Pezizaceae, known to act as mycorrhizal fungi, was related to the amount of total carbon in the Sasa-intact plot. The relative abundance of Proteobacteria was significantly higher, whereas those of Planctomycetes and Actinobacteria were lower in the Sasa-intact plot than in the Sasa-removed plot. Furthermore, the results obtained suggest that some species of the phylum Planctomycetes are more likely to occur in the presence of S. kurilensis. Collectively, these results indicate that the presence of S. kurilensis affects microbial communities and soil properties in a B. ermanii boreal forest.