We estimated the release of nitrogen from coated urea in rice cultivation, using soil temperature estimated from AMeDAS (Automated Meteorological Data Acquisition System) 1-km-grid data (temperature and sunshine duration). The RMSE of soil temperature estimated at 9 points in Okayama prefecture was 0.89 ℃. Soil temperatures were easily estimated by multiple regression of data observed at 3 points to interpolate data at target sites. The estimated release of nitrogen fit measured values well, with an average difference of approximately 5% and an estimated error of the date of initial release of about 2 days. These results indicate that the release of nitrogen from coated urea can be estimated simply from AMeDAS 1-km-grid data.

In cold regions of Japan, rice straw residues cut and scattered in late autumn are often incorporated into paddy soils the next spring. Generally, emissions of methane (CH₄) from such paddy fields are very high owing to rapid anaerobic decomposition of the straw under flooding. We investigated the effects of incorporating straw by shallow tillage in autumn to decompose under aerobic conditions for reducing emissions of the greenhouse gases CH₄ and nitrous oxide (N₂O). Three plots were prepared: shallow tillage in autumn by plowing at 5–8 cm depth (STA), conventional tillage in autumn by plowing at 18–20 cm depth (CTA), and conventional tillage in the next spring by plowing at 18–20 cm depth (CTS). The study was conducted from 2010 to 2013. In the STA and CTA plots, the straw was incorporated in October, and the plots were plowed the next April. In the CTS plot, the straw was incorporated at plowing in April. All plots were irrigated and rice seedlings were transplanted in late May. CH4 and N2O fluxes were measured by the closed chamber method throughout the cropping period. Tiller number, grain yield, and brown rice quality were also measured. The cumulative CH4 emissions increased in the order of STA (19.9–85.6 g CH₄ m^-2) < CTA (24.8–107.6 g CH₄ m^-2) < CTS (45.6–134.1 g CH₄ m^-2). N₂O emissions in all plots were negligible. Tiller number was higher in the STA plot than in the other plots. There were no significant differences in grain yield or brown rice quality. From the time of snowmelt in March to plowing in April, the soil moisture and the concentration of ferrous iron (Fe²⁺) in soil were lower in the STA plot than in the CTA plot. Consequently, shallow tillage in autumn by plowing at 5–8 cm was the most effective technique for reducing emissions of greenhouse gases from paddy fields with incorporated rice straw in a cold region of Japan.

We examined the suitability of waste fluid from a methane fermentation plant, the Yagi Bio–Ecology Center in Nantan city, Kyoto prefecture, as a nitrogen fertilizer for paddy rice (Oryza sativa L. ‘Kinuhikari’). The plant processes 55 m³ of dairy and pig excreta per day to produce methane for electricity generation. Waste fluid contains about 3.6 g kg^-1 of nitrogen, of which 2.2 g is ammonium–N and 1.4 g is organic–N. A 5–year trial in a 1–m² container revealed that the waste fluid could support rice growth as well as ammonium sulfate with the same ammonium–N content. The ammonium–N in the waste fluid was prone to volatilization, but a quarter of the initial amount of organic–N was mineralized, so the waste fluid might have similar potential as ammonium sulfate when applied at the same rate of ammonium–N as inorganic fertilizer. However, the rice plants took up more N than plants that received ammonium sulfate during successive applications over 5 years. This suggests that successive applications of the waste fluid would build up soil organic–N in paddy fields.