Effect of reduced nitrogen application using swine manure compost on the environmental impacts from greenhouse gas emission and nitrate leaching in a Japanese pear field

Abstract

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.