Changes In Emissions To The Atmosphere

Finally, the technological development in agricultural production systems induce changes in the emissions of greenhouse gases and ammonia, and nitrate leaching to groundwater. Here we concentrate on the gaseous emissions, which are suitable indicators of climate-change effects of agricultural production.

Table 5.3 Disposal of animal manure on grazing land and application in pastoral and mixed/industrial systems, and N fertilizer use for 1970, _1995 and 2030 (N in Tg/yr)_

Region

Pastoral Mixed/ industrial

Application

Pastoral Mixed/ industrial

Totala

Fertilizer

Developing

1970

20.8

10.9

0.8

7.8

53.0

8.6

1995

23.2

17.5

0.9

13.0

73.5

52.7

2030

28.8

24.7

1.4

15.0

96.5

73.1

Industrialized

1970

2.3

8.2

0.0

7.3

19.5

14.9

1995

3.0

8.9

0.0

7.2

20.9

25.6

2030

3.2

8.6

0.0

7.0

20.6

31.0

Transition

1970

0.0

4.6

0.0

4.4

10.1

7.2

1995

0.0

4.0

0.0

4.3

9.4

4.7

2030

0.0

4.1

0.0

4.5

9.7

5.9

Global

1970

23.1

23.8

0.8

19.5

82.6

30.7

1995

26.2

30.3

1.0

24.5

103.7

82.9

2030

32.0

37.4

1.4

26.6

126.8

110.0

Source: Bouwman et al. (2005b).

a Total manure N includes, apart from grazing and application, NH3 volatilization from stored and collected manure, and animal manure that is not part of the agricultural system, such as manure excreted in urban areas, and stored but unused manure.

We use the approach described by Alcamo et al. (1998) to calculate CH4 emissions from enteric fermentation in the digestive tract of ruminants. In this approach, the emissions depend on the type and quality of the feed consumed by ruminants. Methane emissions from enteric fermentation have increased between 1970 and 1995 mainly as a result of increases in livestock herds in developing countries (Table 5.4). There has been a fast growth in ruminant production (Figure 5.2) which was not balanced by a simultaneous decrease in the feed conversion (Figure 5.5). In contrast, meat and milk production by ruminants grew much less rapidly in industrialized and transitional countries, and with a slow decrease of feed conversion rates the CH4 emissions have not changed considerably. The global annual CH4 emission from enteric fermentation is projected to increase from 94 to 131 Tg between 1995 and 2030 (Table 5.4).

The CH4 emission from wetland rice fields has increased only slightly during the 1970-1995 time period (Table 5.4), and is projected to stabilize in the coming three decades. This development is the result of a strong increase in paddy rice production (from 550 to 770 Tg/yr in the 1995-2030 period), a nearly constant harvested area due to strongly increasing yields, and decreasing organic

Table 5.4 Regional and global CH4 emissions from livestock production (enteric fermentation + animal waste) and wetland rice systems expressed as emission of CH4 in Tg/yr and % of total emission from all sources for 1970, 1995 and 2030

Year

Developing

Industrialized

Transition

World

countries

countries

countries

(Tg/yr) (%)

(Tg/yr)

(%)

(Tg/yr)

(%)

(Tg/yr)

(%)

Livestock

1970

39 36

24

34

10

28

73

16

1995

60 36

25

32

8

20

94

18

2030

98 31

24

28

8

14

131

19

Wetland rice

1970

26 24

1

2

0

0

28

6

1995

31 18

1

1

0

0

32

6

2030

30 9

1

1

0

0

31

4

amendments which are (partly) responsible for CH4 generation (IMAGE-team, 2001).

Global direct emissions of N2O from animal manure calculated according to (IMAGE-team, 2001) strongly increased from 1.2 to 1.4 Tg N2O-N/yr between 1970 and 1995 (Table 5.5). For the coming three decades a further increase to 1.7 Tg is projected. In the period 1970 to 1995 the N2O emission from N fertilizers increased rapidly from 0.4 to 1.0 Tg N2O-N/yr, and a further 30% increase to 1.4 Tg N2O-N/yr 2030 is projected for 2030.

Ammonia emissions are calculated with different approaches for stable and grazing emissions (Bouwman et al., 1997) and manure and fertilizer application (Bouwman et al., 2002). Emissions increased from 21 Tg/yr in 1970 to 38 Tg/yr in 1995, based on calculations of (Bouwman et al., 2005b). For the coming three decades an increase to 48 Tg/yr is projected. This increase is less than that for the period 1970-1995, mainly due to increasing N use efficiencies in livestock production.

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