Agriculture Reference

In-Depth Information

0.30

35

0.25

30

0.20

25

0.15

20

0.10

1990

1995

2000

Year

2005

2010

N content diet

N efficiency

9000

18

8000

17

7000

16

15

6000

14

5000
1990

1995

2000

Year

2005

2010

Milk production

Methane prodiction

Fig. 2.5.
Dietary nitrogen (N) content (g kg
−1
DM) and N efficiency (g milk N g
−1
feed N) (top) and milk

production (kg fat and protein corrected milk (FPCM) per cow per year) and methane (CH
4
) production

(g CH
4
kg
−1
FPCM) (bottom) for the average dairy cow in the Netherlands from 1990 until 2009. Data and

CH
4
calculations from 1990 until 2008 as described in Bannink
et al
. (2011) with 2009 results added

according to the various sources and calculation procedures mentioned by Bannink
et al
. (2011).

linear equation though, further reductions in

GHG emissions per kg FPCM are possible with an

asymptotic value of 0.86 kg CO
2
-e year
−1
. In this

analysis of dairy production systems with one

average value per country in the database,

increased milk production reduced emissions of

CH
4
and N
2
O per kg milk, but increased CO
2
emis-

sion per kg milk which according to Gerber
et al
.

(2011) reflects the increased use of inputs whose

production requires fossil fuel, notably high-value

feed. In deriving the linear and non-linear equa-

tions, Gerber
et al
. (2011) used different responses

(CO
2
-e per cow per year, or per kg FPCM). It is dif-

ficult to discriminate on statistical grounds

between the two equations. Problems with model

assumptions on normality and homoscedasticity

may occur with both equations. Capper
et al
.

(2009) reported a decline in GHG emission of 3.6 kg

CO
2
-e kg
−1
FPCM (1944; 2061 kg FPCM per cow

per year) to 1.35 kg CO
2
-e kg
−1
FPCM (2007;

8715 kg FPCM per cow per year). According to

the non-linear equation of Gerber
et al
. (2011),

the GHG emission would be 2.51 and 1.38 kg

CO
2
-e kg
−1
FPCM, respectively. The linear equation