In Japan, the focus of sustainable agriculture is on crop production practices, such as low input of chemical fertilizer for carrot to conserve groundwater quality (Kagamihara City Groundwater Study, 1989). Japanese laws on the agroenvironment and sustainability refer to livestock husbandry only in terms of manure application for soil fertility and soil health and livestock excreta management. The primary aim of these regulations is to preserve water quality in the environment and to reduce the direct effects on people (e.g., preventing excreta odors). However, the contribution of agricultural practices to global warming is a significant aspect in the evaluation of sustainable farming. Livestock husbandry had a greater influence on N2O emissions than crop production over the study period. Direct and indirect N2O emissions from livestock husbandry during livestock excreta management, which are the main sources of N2O emissions, are not addressed by any existing laws. Deodorization during composting by trapping NH3 or excreta handling to prevent NH3 effluence and changing the conventional method of composting to reduce the high levels of N2O emissions would be possible mitigation options. Over the study period, a reduction in crop production reduced total N2O emissions and emissions per unit area cultivated. Therefore, efforts to reduce N2O emissions from livestock husbandry should be the primary aim in future.
The decline in N2O emissions resulted mainly from a reduction of N input from 126 kg N ha"1 in 1985 to 92 kg N ha"1 in 2005. Although the decline in the area planted in crops caused other problems, such as a reduction in crop production and rate of self-sufficiency of Japanese food production, reducing N input might have environmental benefits. However, trends in N input per area differ among crop types (e.g., Mishima et al., 2006). The successful reduction in N inputs to vegetables and tea is a recent need.
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