Manure and standard chemical fertilizers are typically used during the cultivation of Japanese pear (Pyrus pyrifolia Nakai) in Ibaraki Prefecture. Because the nitrogen content in manure is not considered, the total amount of nitrogen tends to exceed the permissible limit. We monitored greenhouse gas (GHG) emissions and nitrate leaching from a Japanese pear field using three application methods: the reduced (RD) method of application, in which 50％ of the fertilizer was replaced with manure; the standard (ST) method of application of chemical fertilizer; and the conventional (CV) method of application, in which a combination of manure and standard chemical fertilizer was used. Direct nitrous oxide (N₂O) emissions and nitrate leaching (indirect N₂O emissions) were higher in the CV method than in the RD and ST methods. No changes in soil carbon level were observed in the CV method, whereas the annual change in soil carbon content was approximately −400 kg C ha⁻¹ and on the decline in the RD and ST methods. The GHG emissions in the RD, ST, and CV methods were 2,159–3,297, 2,264–3,126, and 2,072–4,395 kg CO₂⁻eq ha⁻¹, respectively. The GHG emissions were higher in the CV method than in the RD and ST methods. We estimated the environmental impacts of each fertilization method on both the hydrosphere and atmosphere. The accumulated GHG emissions and NO₃-N leaching over a period of 4 years was higher in the CV method than in the RD and ST methods. These findings suggest that the cultivation of Japanese pear using the RD or ST methods results in lower GHG emissions and NO₃-N leaching compared to the CV method.

We evaluated the effects of shallow tillage (ST) and conventional tillage (CT) conducted during fall and winter on the decomposition of residual rice straw and levels of methane emission in a paddy field during the irrigation season over a period of 3 years. The ST and CT plots were prepared by plowing to depths of 8 cm and 15 cm, respectively. Methane emissions from the ST plot during the irrigation season were equivalent to or 1.3-fold higher than those from the CT plot. In the ST plot, residual rice straw on the soil surface was abundant after fall plowing and was exclusively distributed down to a depth of 10 cm. There was less residual rice straw on the soil surface in the CT plot, and it was distributed down to a plowing depth of 15 cm. Using a mesh-bag burying method, no significant difference was observed in the evaluation of rice straw decomposition between the 5 and 10 cm depths. In contrast, the rice straw on the soil surface had minimal contact with the soil and was exposed to low temperatures, resulting in significantly lower decomposition quantities during the non-irrigation season. The mesh-bag that had been buried or placed on the soil surface was relocated to a depth of 8 cm in April, simulating spring plowing. After transfer, the rice straw on the soil surface decomposed rapidly, and its residual carbon content was equivalent to that of the initially buried rice straw. In the ST plot, the rice straw-derived carbon content was 1.47 Mg ha⁻¹ after spring plowing and 0.96 Mg ha⁻¹ before surface drainage. The decrease in carbon content during the irrigation season in the ST plot was 0.51 Mg ha⁻¹, which was 1.18-fold greater than that in the CT plot. This was likely the cause of increased methane emissions observed during the irrigation season.