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Denmark's Greenhouse Gas Projections until 2012, an update including a preliminary projection until 2017

5 Agriculture

The emission calculations in this section was done together with a working group with participants from, the Ministry of Food, Agriculture and Fisheries, Danish Institute of Agriculture and Fisheries Economics, Danish Institute of Agricultural Sciences and the National Environmental Research Institute, as reported in [47,48].

5.1 CH₄ from Enteric Fermentation & Manure Management

Methane is produced as a by-product during the digestive processes in animals. All domestic animals emit CH₄, but the largest contribution comes from ruminants, due to their ability to breakdown cellulose. The number of domestic livestock in Denmark is shown in Table 17 and Figure 7. The data sources are the Danish ten-year statistical review [21] for all the types of domestic animals except for dairy cows, and turkey-ducks-geese, which are taken from a series of Danish annual statistics [22]. In the Second Communication to the UNFCCC [1] cows kept for suckling were included in "dairy cows". They are now included in "other cattle", since they have an emission factor similar to that category. Fur animals are not included since no emissions factors exist for this category. The number of cows is assumed to decrease 1.8% per year [46]. The amount of pigs slaughtered annually is assumed to increase 1.5% p.a. from 2000 until 2012; this number is then driving the future amount of sows [46]. As shown below, the total emissions in 2000 of CH₄ from agriculture was 170.3 kt, consisting of 134.2 kt from enteric fermentation and 36.1 kt from manure management.

Table 17.
Domestic livestock in Denmark

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Figure 7.
Development of the main livestock categories

5.1.1 CH₄ emissions from enteric fermentation

IPCC gives two alternative ways to estimate CH₄ emissions. Tier 1, which just uses the IPCC default emission factors for the region, and Tier 2, in which emission factors are calculated based on local conditions. The CH₄ emission per animal is here calculated based on weight, weight gain, frequency of pregnancy, fat % of the milk, and the energy efficiency of the animal. In the Second Danish Communication [1], Tier 1 was used for all animal categories. However, due to new information [23], Tier 2 is now used for cattle, which by far is the largest CH₄ emitter from enteric fermentation.

Table 18 shows that the emission factor for dairy cows in Tier 2 is expected to increase from the present 101 kg CH₄/yr/head to 119 kg CH₄/yr/head in 2012 [23], due to the expected higher productivity per head..

Table 18.
CH₄ emission factors for enteric fermentation

Figure 8 shows that the CH₄ emission has been decreasing from about 200 kt in the seventies to 134 kt in 2000 due to the decreasing number of cattle. Since the enteric emission factor for pigs are much lower, the increasing number of pigs only result in a small increase in the emissions. Emissions for chickens, fowls and fur animals are not included since no emission factors are available. The emissions in 2000 from horses (0.7 kt) and sheep (1.2 kt) are too small to be seen on Figure 8. The above-mentioned decrease in the number of cattle outweighs the increase in the emission factor for cattle and the increase in the number of pigs.

Figure 8.
CH₄ emissions from enteric fermentation in domestic livestock

5.1.2 CH₄ emissions from manure management

Two changes have been made in the present emission calculations for CH₄ from manure management compare to the one presented in the Second Danish Communication [1], where Tier 1 was used for all animal categories. Based on the information in [23], Tier 2 is now used for all animal categories. The second change is that the emission factors for a cool climate, having an average temperature below 15 degrees, are now used (see definition in the IPCC Revised Guidelines [36], footnote to table 4-6). In the Second Danish Communication [1] the Tier 1 emission factors for temperate climate, with average annual temperatures in the range 15-25 degrees were used.

The resulting total CH₄ emissions from manure management are very sensitive to which set of emission factors that are use for Denmark. Figure 9 shows that the total CH₄ emission decreases from 38,6 kt CH₄ in 2000 to 36.5 kt. CH₄ in 2012.

Table 19.
CH₄ emission factors for manure management.

The Tier 2 CH₄ emission factors for "other cattle", "other pigs", "other fowls", and "Turkeys-ducks-geese" are weighted averages of emission factors calculated in [23].

Figure 9.
CH₄ emissions from manure management (excl. biogas plants).

Figure 9 shows that the CH₄ emission has been decreasing from about 42 kt in the seventies to 38,6 kt in 2000. The increase in the emission from the manure from the increasing number of pigs has almost balanced the drop due to the decreasing number of dairy cattle. The total CH₄ emission from horses, sheep and fowls is so small (0.8 kt) that it is almost impossible to see it on Figure 9. The CH₄ emission projection for manure management is based on the animal projection in Table 17 and the emission factors in Table 19.

However, the emissions shown on Figure 9 are not the actual emissions of CH₄ from manure management. The reductions caused by the biogas plants have to be subtracted. The production of biogas at sewage gas plants, industrial biogas plants and landfill biogas plants is subtracted from the total production of biogas according to the Danish Energy Agency. The rest is then the production at agricultural biogas plants as shown in Figure 10. The main part of the production is on joint biogas plants the rest on smaller plants on single farms. Of the total production in 2000 of 2.92 PJ, 0.58 came from landfill gas plants, 0.86 PJ from sewage gas plants, 0,07 from industrial biogas plants. From agricultural biogas plants the production was therefore 1.42 PJ. The data before 1995 is from [29] combined with information from landfill biogas production. The production from agricultural biogas plants is expected to increase 46% from the 1.4 PJ in 2000 to around 2 PJ in 2004. The production values are from [28], which however is lower than the former projection in the Danish Energy Plan "Energi21". There is thus not included any new biogas plants after 2004 in the projection.

Figure 10.
Total biogas production

Assuming a calorific value for biogas of 24 MJ/m³ biogas, a content of 60% CH₄ in biogas [29], a CH₄ density of 0.72 kg/ m³, the 2000 production e.g. equals 25.5 kt CH₄. However, the emissions of 38.6 kt CH₄ from manure management in 2000 shown on Figure 9 are not reduced by this value but only with 9.7% of 22.5 or 2.5 kt CH₄. This is because the manure produces much more CH₄ in a biogas plant than under normal storage conditions. The 9.7 % were calculated based on the new information in [63], where the reduction in CH₄ emission from biogas plants has been calculated. If 1 kg average volatile solid (VS) containing 30% cattle manure, 26% pig manure and 44% industrial organic waste is processed in a biogas plant it will produce 0.314 m³ CH₄. Combining this with the information in the report [63] that the emission reduction by the treatment of 1 kg VS is 0.0218 kg CH₄ = 0.030 m³ CH₄ the result is a reduction of 9.7%. With the projected biogas production in Figure 10, the emission of 36.5 kt CH₄ in 2012 on Figure 9 will be reduced by 3.5 kt CH₄ to 33.0 kt CH_4.

5.2 N₂O from agriculture

Production of N₂O in soils is a result of nitrification (an aerobic microbial oxidation of ammonium to nitrate) and denitrification (an anaerobic microbial reduction of nitrate to nitrogen gas). Nitrous oxide (N₂O) is a gaseous intermediate in the reaction sequence of both processes. Formation of N₂O is enhanced by an increase of available nitrogen. Only anthropogenic emissions are included, defined as emissions from cultivated land. Emissions from unfertilised fields are considered as background emission.

The total N₂O emission in 2000 from Danish agriculture was 27.3 kt N₂O expected to decrease to 24.3 kt N₂O in 2010 (see Table 21, part 2). The N₂O emissions were calculated for the sources listed in Table 20 by multiplying the emission factors with the respective activity data for the N-inputs after subtraction of the NH₃ evaporation (except for manure management, where the emission factor is use before subtraction of evaporation). The emission factors are the IPCC default values [36].

Table 20.
N₂O emission factors for agriculture

Table 20 shows that the largest N₂O emissions originates from Nitrogen leaching & runoff (7.2) and from crop residues (6.2 kt). The third largest source is the synthetic fertilisers (4.7 kt). As a new thing a line has been introduced to account for the reduction of N₂O due to the treatment of manure at biogas plants, the emission reduction increases from 0.01 kt N₂O in 1990 to 0.05 kt N₂O in 2010. This reduction is based on the projection for biogas production in section 5.1.2., using the information in [63] that if 1 kg of the average volatile solid (VS) is treated in a biogas plants it will produce 0.314 m³ CH₄ and will reduce emission by 0.325 kg N₂O from the manure. Combining this with the information in section 5.1.2 of the total biogas production gives the N₂O emission reduction mentioned.

Table 20 do not include the emission of 0.11 kt N₂O from the use of 5.8 kt N in synthetic fertilisers used on parks and lawns.

Table 21 (part 1 and part 2) shows how these N₂O emissions from the above-mentioned sources were calculated for the period 1985-2010. The source of the synthetic fertiliser user is [53]. Here the 1997/98 value is used for 1998 and the 5.8 kt N in synthetic fertilisers used on parks and lawns subtracted. According to table 4.12 in the midterm evaluation of "Vandmiljøplan II" a reduction in synthetic fertiliser use of 19.7 kt N had been reached in 1999 of goals in the plan and 59.8 kt plus 13.5 (Agenda 2000) is expected to be reached in 2003. The 2003 value for fertiliser used in the projection is therefore the 1999 value of 256.9 kt minus the extra 53.5 to be reached in the period 1999-2003 plus the impact of the extra initiatives in the Danish government’s plans for "Vandmiljøplan II" [51] and NH₃ emission reductions [52]. These initiatives are expected to reduce the use of synthetic fertiliser with 24.3 kt before 2003. The value for 2003 is therefore 179.1 kt N. Before the N₂O emission is calculated by multiplying with the emission factor of 1.25% from Table 20, the N content of NH₃ emission in Table 21, part 3 from the fertiliser use (close to 2%) is subtracted.

Concerning animal manure, the historical data is from [25] (1998/99 values are used for 1999 etc.) and the future data for 2003 and 2010 are from [26], this historical report [25] contain information for the years 1984, 1989, 1995, 1996, 1997, 1998 and 1999. Linear interpolation is used for the years in-between. For the years in-between values are interpolated linearly. In the column in Table 21, part 1 showing N-input from animal grazing, the NH₃ emission shown in Table 21, part 3 is subtracted. The values in Table 21, part 1 for N-input from animal fertiliser on soils is also after subtraction of NH₃ evaporation. However the N content in manure management in Table 21, part 3 is according to the IPCC rules before any NH₃ evaporation has taken place. The fractions of the total amount of manure, which are solid (21.5%) and liquid (71.5%) [24] are kept constant in the time series.

The N-input from nitrogen fixation in Table 21, part 2 is lower than in former inventories, because now only the symbiotic N-fixation is included (about 90% of the total N-fixation). The data is from Appendix A in [26], where 1998/99 data is used for 1999 and also for all future years.

The activity data for the historic N-inputs from industrial waste and sewage sludge used as fertilisers are from the field-N-balance appendix 3.1 in [27]. The future N-input from industrial waste has been put equal to the 1999 value. According to [23] the N-input from sewage sludge is expected to decrease in the period 1999-2003.

The combined action of "Vandmiljøplan I" (called The Action Plan on the Aquatic Environment), the Danish Action Plan for Sustainable Agriculture and the "Vandmiljøplan II" was expected to result in a decrease in the N-input from leaching & runoff (="udvaskning") from 230 mill. kg to 130 mill. kg in 2003. With the new initiatives in the Governments plan after the midterm evaluation of "Vandmiljøplan II"[51] the 100 mill. kg N reduction in the leaching & runoff is expected to be reached in 2003. However, one of the initiatives in this plan is to speed up the increase in the wetland area in such a way that it will absorb 3.6 kt N in 2003. This is the reason for the expected 2003 value in Table 21, part 2 for leaching & runoff to be 133.6 kt N instead of 130.0 kt N. No change is expected after 2003.

The IPCC method [36] for the calculation of N₂O emissions from crop residues was used in the calculations. Here it is assumed that the amount of Nitrogen in the crop residues is equal to the N-content in the crops. The values in the "N- in crops" column in Table 21, part 2 is from the appendices in [25], except that the historical amounts of cereal straw and rape/pea straw has been subtracted and shown in two separate columns. The amount of rape/pea straw is from [54] and has an N-content of 1%, the double of the N-content in cereal straw. The values for cereal straw are from [25]. The future projection for the N-content in cereal straw is expected to be proportional to the increase in the amount of straw used in the energy sector. According to the midterm evaluation of "Vandmiljøplan II" the N-content in catch crops will increase to 3 kt N in 2003.

The total area in Denmark covered with histosols, defined as colour-code 7/JB 11 in the Danish soil classification, is 237,700 ha. Histosols are cultivated organic soils originating from old N-rich organic matter. However, only 184,400 ha are used for agricultural purposes. Of this area again 90% is used for grassland, which is in a stable situation, without N₂O emissions. This means that only 10%, or 18,400 ha of histosols area [23] is included in Table 21, with an annual emission of 0.14 kt N₂O using the emission factor of 5 kg N₂O-N/ha shown in Table 20. When these soils are cultivated, their surface gradually sinks. However, emission of CO₂ from this process in histosols has not been included.

The only source of N₂O in Table 21 not yet mentioned is the N₂O release after deposition of NH_3. According to Table 20 an emission factor of 1% should be used for the NH₃ deposited in Denmark. However, IPCC recommend that the deposition = evaporation of NH₃ - N from Denmark (import/export are not taken into account). Time series for all the sources of NH₃ emission are shown in Table 21, part 3. These data for NH₃ from synthetic fertiliser, animal manure, straw leaching and evaporation from sludge is from the new projection of NH₃ emissions to be published in [64]. Here the emission of NH₃ has increased primary due to a change in the estimation of the way the manure is being spread on the fields. There exist no statistics on the practice used by the farmers and an estimate has to be used. The total evaporation from agriculture in e.g. 2010 has with this change increased from 61.2 kt NH₃-N to 75.6 kt NH₃-N and thereby increasing the N₂O emission by 0.2 kt N₂O.

The NH₃ emission from straw leaching is expected to drop to zero in 2003 according to the expected ban on this activity [52].

Table 21.
N-input and N₂O emissions from agriculture

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