Direct and indirect emissions from agriculture

Direct and indirect N2O emissions from livestock husbandry and crop production are shown in Fig. 40.2 (bar graph). Total N2O emissions peaked in 1990 (46,672 Mg) as a result of an increase in livestock husbandry, then declined until 2005 (37,620 Mg). The decline in N2O emissions resulted mainly from a decline in crop production from 17,644 Mg in 1985 to 12,088 Mg in 2005. Livestock husbandry also declined between 29,381 Mg in 1990 and 25,532 Mg in 2005, however less than crop production. Mishima (2006) indicated that crop production and non-utilized N by agricultural production peaked in 1985, then declined until 2002. The main cause of this decline was a reduction in the use of chemical N fertilizer in crop production. Livestock excreta N production, which reflects livestock production, peaked in 1990 then declined more slowly than the rate of reduction in chemical N fertilizer application. Livestock husbandry comprised a higher proportion of total agricultural N2O emissions than crop production. Direct N2O emissions exceeded indirect, and originated mainly from livestock excreta handling. We used the N volatilization rates of Mishima et al. (2008) (72% for cattle, 50% for pig, and 80% for poultry), which are higher than those of GIO (10% for cattle, 20% for pig, and 30% for poultry). Therefore, our estimates of indirect emissions by N deposition would be greater than those of GIO (2007), although, because

GIO did not report indirect emissions, we could not compare the amounts. Crop production was responsible for less N2O emissions than livestock husbandry. Crop production direct emission was larger than indirect emission. The emission factor indicated by Akiyama et al. (2006), which has been proposed as a Japanese emission factor, is smaller than the IPCC default value. Therefore, the proportion of direct emissions might be still smaller in Japan than in other countries. Because there are insufficient data for estimation of the indirect emission factor, we used the IPCC default value in our estimation. Indirect emissions have been little discussed (e.g., van der Gon and Bleeker, 2005), and more studies on indirect emissions are needed for precise estimation of N2O indirect emissions.

50 n

50 n

This study GIO(2007)

Livestock Indirect Emission ■ Livestock Direct Emission Q Crop Indirect Emission ^ Crop Direct Emission

1985 1990 1995 2000 2005 Year

Fig. 40.2 Direct and indirect N2O emission from crop production and livestock husbandry.

This study GIO(2007)

Livestock Indirect Emission ■ Livestock Direct Emission Q Crop Indirect Emission ^ Crop Direct Emission

1985 1990 1995 2000 2005 Year

Fig. 40.2 Direct and indirect N2O emission from crop production and livestock husbandry.

N2O emissions per unit of cultivated area peaked in 1990 (8.489 kg ha"1) then declined in 2005 (8.015 kg ha"1) as a result of a fall in crop production from 3.275 kg ha"1 in 1985 to 2.575 kg ha"1 in 2005 (Fig. 40.3). N2O from livestock husbandry peaked in 1990, then slightly decreased. N2O from crop production declined as a result of a reduction in chemical N fertilizer and manure input per cultivated area (Mishima et al., 2009). Crop production in Japan, as measured by cultivated area and quantity of N fertilizer applied, has been declining (Mishima et al., 2009). This trend is reflected in N2O emissions. However, livestock husbandry has declined more slowly than crop production and its relative importance to agriculture has therefore increased. This trend may have significant environmental implications.

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