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Chapter 6: Agriculture

6.1 Sector overview

The agriculture sector contributed 37,667.6 Gg carbon dioxide equivalent (Gg CO2-e) (48.4 per cent) of total emissions in 2006. Emissions in this sector are now 5,168.8 Gg CO2-e (15.9 per cent) higher than the 1990 level of 32,498.9 Gg CO2-e (Figure 6.1.1). The increase is primarily attributable to a 2,300.2 Gg CO2-e (10.5 per cent) increase in methane (CH4) emissions from “enteric fermentation” and a 2,693.3 Gg CO2-e (26.8 per cent) increase in nitrous oxide (N2O) emissions from the “agricultural soils” category.

Figure 6.1.1 Agricultural sector emissions from 1990 to 2006 (all figures are Gg CO2-e)

Year

Gg CO2-equivalent

1990

32,498.9

1991

32,529.2

1992

31,931.0

1993

32,331.1

1994

33,346.3

1995

33,745.3

1996

34,074.5

1997

34,760.0

1998

34,116.0

1999

34,714.3

2000

35,959.1

2001

36,380.4

2002

36,477.8

2003

37,136.2

2004

37,186.1

2005

37,579.1

2006

37,667.6

In 2006, emissions of CH4 from “enteric fermentation” produce 64.0 per cent of CO2-e emissions in the sector and 31 per cent of New Zealand’s total emissions. Nitrous oxide emissions from “agricultural soils” are the other major component of the sector comprising 33.8 of agricultural CO2-e emissions.

Agriculture is a major component of the New Zealand economy and agricultural products comprise over 50 per cent of total merchandise exports. This is because of the favourable temperate climate, the abundance of agricultural land and the unique farming practices used in New Zealand. These practices include the extensive use of year-round grazing systems and a reliance on nitrogen fixation by legumes rather than nitrogen fertiliser.

Figure 6.1.2 Change in emissions from the agricultural sector from 1990 to 2006 (all figures Gg CO2-e)

Note: The per cent change for rice cultivation is not occurring (NO) within New Zealand.

Category

1990
(Gg CO2-equivalent)

2006
(Gg CO2-equivalent)

Enteric fermentation

21,810.4

24,110.7

Manure management

616.6

808.1

Rice cultivation

Not occurring

Not occurring

Agricultural soils

10,039.8

12,733.2

Prescribed burning of savannahs

3.2

1.0

Field burning of savannahs

28.7

14.6

Since 1984, there have been changes in the proportions of the main livestock species farmed. There has been an increase in dairy and deer production because of high world demand and favourable prices. This has been counterbalanced by land coming out of sheep production and decreasing sheep numbers. Beef numbers have remained relatively static. There have also been productivity increases across all major animal species and classes. The land area used for horticulture has not changed significantly since 1990 although the types of produce grown have changed. There is now less grain grown, but more vegetables, fruit, and grapes (for wine production) than in 1990.

There has been a gradual increase in the implied emission factors for dairy cattle and beef cattle from 1990 to 2006. This is to be expected because the methodology uses animal performance data that reflects the increased levels of productivity achieved by New Zealand farmers since 1990. Increases in animal liveweight and productivity (milk yield and liveweight gain per animal) require increased feed intake by the animal to meet higher energy demands. Increased feed intake results in increased CH4 emissions per animal.

6.1.1 Methodological issues for the Agriculture Sector

New Zealand uses a June year for all animal statistics as this reflects the natural biological cycle for animals in the southern hemisphere. The models developed to estimate emissions work on a monthly timeframe beginning in July of one year and ending in June of the next year. To obtain emissions for single calendar years (January to December) emissions from the last six months of a July to June year are combined with the first six months’ emissions of the next July to June year.

To ensure consistency, a single livestock population characterisation and feed intake estimate is used when estimating CH4 emissions from “enteric fermentation”, CH4 and N2O emissions from “manure management” and N2O emissions from “animal wastes deposited directly onto pasture”.

Information on livestock population census and survey procedures is included in Annex 3.1.

6.2 Enteric fermentation (CRF 4A)

6.2.1 Description

Methane is a by-product of digestion in ruminants, eg, cattle, and some non-ruminant animals such as swine and horses. Ruminants are the largest source of CH4 as they are able to digest cellulose. The amount of CH4 released depends on the type, age and weight of the animal, the quality and quantity of feed and the energy expenditure of the animal.

Methane emissions from “enteric fermentation” have been identified as the largest key category for New Zealand in the level assessment, excluding LULUCF. In accordance with IPCC good practice guidance (IPCC, 2000), the methodology for estimating CH4 emissions from “enteric fermentation” in domestic livestock was revised to a Tier 2 modelling approach for the 2003 inventory submission. All subsequent inventories have used this Tier 2 approach.

In 2006, enteric fermentation was the largest single category of New Zealand’s inventory contributing 24,110.7 Gg CO2-e. This represents 31.0 per cent of New Zealand’s total CO2-e emissions and 64.0 per cent of agricultural emissions. Cattle contributed 14,023.9 Gg CO2-e (58.2 per cent) of emissions from “enteric fermentation” and sheep contributed 9,287.0 Gg CO2-e (38.5 per cent) of emissions. Emissions from “enteric fermentation” in 2006 are 2,300.2 Gg CO2-e (10.5 per cent) above the 1990 level of 21,810.4 Gg CO2-e. Since 1990 there have been changes in the source of emissions within the “enteric fermentation” category. The largest increase has been in emissions from dairy cattle. In 2006, dairy cattle were responsible for 8,615.6 Gg CO2-e, an increase of 3,604.3 Gg CO2-e (71.9 per cent) from the 1990 level of 5,011.4 Gg CO2-e. This increase has been partially offset by decreases in emissions from sheep and minor livestock populations such as goats, horses and swine. In 2006, emissions from sheep were 9,287.0 Gg CO2-e, a decrease of 1,993.0 Gg CO2-e (17.7 per cent) from the 1990 level of 11,280.0 Gg CO2-e.

6.2.2 Methodological issues

Emissions from cattle, sheep and deer

New Zealand’s Tier 2 methodology (Clark et al, 2003) uses a detailed livestock population characterisation and livestock productivity data to calculate feed intake for the four largest categories in the New Zealand ruminant population (dairy cattle, beef cattle, sheep and deer). The amount of CH4 emitted is calculated using CH4 emissions per unit of feed intake (Figure 6.2.1).

Livestock population data

The New Zealand ruminant population is separated into four main categories: dairy cattle, beef cattle, sheep and deer. Each livestock category was further subdivided by population models (Clark et al, 2003). The populations within a year are adjusted on a monthly basis to take account of births, deaths and transfers between age groups. This is necessary because the numbers present at one point in time may not accurately reflect the numbers present at other times of the year. For example, the majority of lambs are born and slaughtered between August and May and so do not appear in the June figures.

Animal numbers are provided by Statistics New Zealand from census and survey data conducted in June each year.

Figure 6.2.1 Schematic diagram of New Zealand’s enteric fermentation calculation methodology

Livestock productivity data

For each livestock category, the best available data are used to compile the inventory. These data are from Statistics New Zealand and industry statistics. To ensure consistency, the same data sources are used each year. This ensures that the data provide a time-series that reflects changing farming practices, even if there is uncertainty surrounding the absolute values.

Obtaining data on the productivity of ruminant livestock in New Zealand, and how it has changed over time, is a difficult task. Some of the information collected is complete and collected regularly, for example the slaughter weight of all livestock exported from New Zealand are collected by the Ministry of Agriculture and Forestry from all slaughter plants in New Zealand. This information is used as a surrogate for changes in animal liveweight over time. Other information, for instance liveweight of dairy cattle and liveweight of breeding bulls, is collected at irregular intervals, from small survey populations, or is not available at all.

Livestock productivity and performance data are summarised in the time-series tables in the excel workbooks available for download with this report from the Ministry for the Environment’s website. The data includes average liveweights, milk yields and milk composition of dairy cows, average liveweights of beef cattle (beef cows, heifers, bulls and steers), average liveweights of sheep (ewes and lambs), average liveweights of deer (breeding and growing hinds and stags).

Dairy cattle: Data on milk production are provided by Livestock Improvement Corporation Limited (2006). These data include the amount of milk processed through New Zealand dairy factories plus an allowance for town-milk supply. Annual milk yields per animal are obtained by dividing the total milk produced by the total number of milking dairy cows and heifers. Milk composition data are taken from the Livestock Improvement Corporation national statistics. For all years, lactation length was assumed to be 280 days.

Average liveweight data for dairy cows are obtained by taking into account the proportion of each breed in the national herd and its age structure based on data from the Livestock Improvement Corporation. Dairy cow liveweights are only available from the Livestock Improvement Corporation from 1996 onwards. For earlier years in the time-series, liveweights are estimated using the trend in liveweights from 1996 to 2006 together with data on the breed composition of the national herd. Growing dairy replacements at birth are assumed to be 9 per cent of the weight of the average cow and 90 per cent of the weight of the average adult cow at calving. Growth between birth and calving (at two years of age) is divided into two periods: birth to weaning, and weaning to calving. Higher growth rates apply between birth and weaning when animals receive milk as part of their diet. Within each period the same daily growth rate is applied for the entire length of the period.

No data are available on the liveweights and performance of breeding bulls. An assumption was made that their average weight was 500 kg and that they were growing at 0.5 kg per day. This was based on expert opinion from industry data. For example, dairy bulls range from small Jerseys through to larger-framed European beef breeds. The assumed weight of 500 kg and growth rate of 0.5 kg/day provide an average weight (at the mid-point of the year) of 592 kg. This is almost 25 per cent higher than the average weight of a breeding dairy cow but it is realistic given that some of the bulls will be of a heavier breed/strain (eg, Friesian and some beef breeds). Because these categories of animal make only small contributions to total emissions, eg, breeding dairy bulls contribute 0.089 per cent of emissions from the dairy sector, total emissions are not highly sensitive to the assumed values.

Beef cattle: The principal source of information for estimating productivity for beef cattle was livestock slaughter statistics provided by the Ministry of Agriculture and Forestry. All growing beef animals are assumed to be slaughtered at two years of age and the average weight at slaughter for the three subcategories (heifers, steers and bulls) was estimated from the carcass weight at slaughter. Liveweights at birth are assumed to be 9 per cent of an adult cow weight for heifers and 10 per cent of the adult cow weight for steers and bulls. Growth rates of all growing animals are divided into two periods: birth to weaning, and weaning to slaughter, as higher growth rates apply before weaning when animals receive milk as part of their diet. Within each period the same daily growth rate is applied for the entire length of the period.

The carcass weights obtained from Ministry of Agriculture and Forestry slaughter statistics do not separate carcass weights of adult dairy cows and adult beef cows. Thus a number of assumptions1 are made in order to estimate the liveweights of beef breeding cows. A total milk yield of 800 litres per breeding beef cow was assumed.

Sheep: Livestock slaughter statistics from the Ministry of Agriculture and Forestry are used to estimate the liveweight of adult sheep and lambs, assuming killing-out percentages of 43 per cent for ewes and 45 per cent for lambs. Lamb birth liveweights are assumed to be nine per cent of the adult ewe weight with all lambs assumed to be born on 1 September. Growing breeding and non-breeding ewe hoggets are assumed to reach full adult size at the time of mating when aged 20 months. Adult wethers are assumed to be the same weight as adult breeding females. No within-year pattern of liveweight change was assumed for either adult wethers or adult ewes. All ewes rearing a lamb are assumed to have a total milk yield of 100 litres. Breeding rams are assumed to weigh 40 per cent more than adult ewes. Wool growth (greasy fleece growth) was assumed to be 5 kg/annum in mature sheep (ewes, rams and wethers) and 2.5 kg/annum in growing sheep and lambs.

Deer: Liveweights of growing hinds and stags are estimated from Ministry of Agriculture and Forestry slaughter statistics, assuming a killing-out percentage of 55 per cent. A fawn birth weight of 9 per cent of the adult female weight and a common birth date of mid-December are assumed. Liveweights of breeding stags and hinds are based on published data, changing the liveweights every year by the same percentage change recorded in the slaughter statistics for growing hinds and stags above the 1990 base. No within-year pattern of liveweight change was assumed. The total milk yield of lactating hinds was assumed to be 240 litres (Kay, 1995).

Dry matter intake calculation

Dry matter intake (DMI) for the classes (dairy cattle, beef cattle, sheep and deer) and sub-classes of animals (breeding and growing) was estimated by calculating the energy required to meet the levels of animal performance and dividing this by the energy concentration of the diet consumed. For dairy cattle, beef cattle and sheep, energy requirements are calculated using algorithms developed in Australia (CSIRO, 1990). These algorithms are chosen as they specifically include methods to estimate the energy requirements of grazing animals. The method estimates a maintenance requirement (a function of liveweight and the amount of energy expended on the grazing process) and a production energy requirement – influenced by the level of productivity (eg, milk yield and liveweight gain), physiological state (eg, pregnant or lactating) and the stage of maturity of the animal. All calculations are performed on a monthly basis.

For deer, an approach similar to that used for cattle was adopted using algorithms derived from New Zealand studies on red deer. The algorithms take into account animal liveweight and production requirements based on the rate of liveweight gain, sex, milk yield and physiological state.

Monthly energy concentrations

A single set of monthly energy concentrations of the diets consumed by beef cattle, dairy cattle, sheep and deer was used for all years in the time-series. This is because there are no comprehensive published data available that allow the estimation of a time-series dating back to 1990. The data used are derived from farm surveys on commercial cattle and sheep farms.

Methane emissions per unit of feed intake

There are a number of published algorithms and models2 of ruminant digestion for estimating CH4 emissions per unit of feed intake. The data requirements of the digestion models make them difficult to use in generalised national inventories and none of the methods have high predictive power when compared against experimental data. Additionally, the relationships in the models have been derived from animals fed indoors on diets unlike those consumed by New Zealand’s grazing ruminants.

Since 1996, New Zealand scientists have been measuring CH4 emissions from grazing cattle and sheep using the SF6 tracer technique (Lassey et al, 1997; Ulyatt et al, 1999). New Zealand now has one of the largest data sets in the world of CH4 emissions determined using the SF6 technique on grazing ruminants. To obtain New Zealand-specific values, published and unpublished data on CH4 emissions from New Zealand were collated and average values for CH4 emissions from different categories of livestock were obtained. Sufficient data were available to obtain values for adult dairy cattle, sheep more than one year old and growing sheep (less than one year old). These data are presented in Table 6.2.1 together with IPCC (2000) default values for per cent gross energy used to produce CH4. The New Zealand values fall within the IPCC range and are adopted for use in this inventory calculation. Table 6.2.2 shows a time-series of CH4 implied emission factors for dairy cattle, beef cattle, sheep and deer.

Not all classes of animals are covered in the New Zealand data set and assumptions had to be made for these additional classes. The adult dairy cattle value was assumed to apply to all dairy and beef cattle irrespective of age and the adult ewe value was applied to all sheep greater than one year old. An average of the adult cow and adult ewe value (21.25g CH4/kg DMI) was assumed to apply to all deer. In very young animals receiving a milk diet, no CH4 was assumed to arise from the milk proportion of the diet.

Table 6.2.1 Methane emissions from New Zealand measurements and IPCC defaults

  Adult dairy cattle Adult sheep Adult sheep < 1 year

New Zealand data (g CH4/kg DMI)

21.6

20.9

16.8

New Zealand data (%GE)

6.5

6.3

5.1

IPCC (2000) defaults (%GE)

6 ± 0.5

6 ± 0.5

5 ± 0.5

Table 6.2.2 Time-series of implied emission factors for enteric fermentation (EF) (kg methane per animal per annum)

Year Dairy cattle Beef cattle Sheep Deer

1990

69.4

50.7

9.3

18.8

1991

71.6

51.8

9.4

19.3

1992

72.0

52.4

9.4

20.2

1993

73.9

53.5

9.5

20.4

1994

71.8

54.4

9.6

19.7

1995

71.6

53.1

9.5

20.6

1996

74.1

54.5

9.8

20.9

1997

74.7

55.1

10.2

21.0

1998

73.2

55.1

10.2

21.2

1999

75.9

54.2

10.2

21.3

2000

77.2

56.5

10.7

21.8

2001

77.6

56.9

10.7

21.7

2002

76.8

56.4

10.7

21.6

2003

79.8

55.9

10.7

21.6

2004

78.2

56.8

11.0

21.7

2005

79.3

57.7

11.1

22.2

2006

79.4

58.0

11.0

22.2

Emissions from other farmed species

A Tier 1 approach is adopted for minor species such as goats, horses and swine using either IPCC default emission factors (horses and swine) or New Zealand derived values (goats). These minor species comprised 0.3 per cent of total enteric CH4 emissions in 2006. Adopting a Tier 1 as opposed to a Tier 2 approach for these species has little effect on total estimated enteric methane emissions.

Livestock population data

The populations of goats, horses and pigs are reported using the animal census (or survey) data from Statistics New Zealand.

Livestock emissions data

Horses and swine: Enteric CH4 from these classes of livestock are not a key category and in the absence of data to develop New Zealand emission factors, IPCC default values are used.

Goats: Enteric CH4 from goats is not a key category. There are no published data on which to attempt a detailed categorisation of the performance characteristics as has been done for the major livestock categories. New Zealand uses a country-specific value of 9 kg CH4/head/yr. This was calculated by assuming a default CH4 emission value from goats for all years which is equal to the per head value of the average sheep in 1990 (ie, total sheep emissions/total sheep population). The goat value was not indexed to sheep over time because there are no data to support the kind of productivity increases that have been seen in sheep.

6.2.3 Uncertainties and time-series consistency

Livestock numbers

Many of the calculations in this sector require livestock numbers. Both census and survey data are used. Surveys occur each year between each census. Detailed information from Statistics New Zealand on the census and survey methods is included in Annex 3.1.1.

Methane emissions from enteric fermentation

In the 2003 inventory submission, the CH4 emissions data from domestic livestock in 1990 and 2001 were subjected to Monte Carlo analysis using the software package @RISK to determine the uncertainty of the annual estimate (Clark et al, 2003). For the 2006 data, the uncertainty in the annual estimate was calculated using the 95 per cent confidence interval determined from the Monte Carlo simulation as a percentage of the mean value, ie, in 2001, the uncertainty in annual emissions was ± 53 per cent.

Table 6.2.3 Uncertainty in the annual estimate of enteric fermentation emissions for 1990, 2001 and 2006 estimated using Monte Carlo simulation (1990, 2001) and the 95 per cent confidence interval (2006)

Year Enteric CH4 emissions (Gg/annum) 95% CI min 95% CI max

1990

1,038.6

488.1

1,589.1

2001

1,123.0

527.8

1,718.2

2006

1,148.1

539.6

1,756.6

Note: The methane emissions used in the Monte Carlo analysis exclude those from swine and horses.

Uncertainty in the annual estimate is dominated by variance in the measurements used to determine the “CH4 per unit of intake” factor. For the measurements made of this factor, the standard deviation divided by the mean is equal to 0.26. This uncertainty is predominantly due to natural variation from one animal to the next. Uncertainties in the estimation of energy requirements, herbage quality and population data are much smaller (0.005–0.05), so these variables play a much smaller role.

6.2.4 Source-specific QA/QC and verification

Methane from enteric fermentation was identified as a key category (level and trend assessment). In preparation for this inventory, the data for this category underwent Tier 1 quality checks.

Methane emission rates measured for 20 dairy cows scaled up to a herd have been corroborated using micrometeorological techniques. Laubach and Kelliher (2004) used the integrated horizontal flux technique and the flux gradient technique to measure CH4 flux above a dairy herd. Both techniques are comparable, within estimated errors, to scaled-up animal emissions. The emissions from the cows measured by integrated horizontal flux and averaged over three campaigns are 329 (± 153) g CH4/day/cow compared to 365 (± 61) g CH4/day/cow for the scaled-up measurements reported by Waghorn et al, (2002; 2003). Methane emissions from lactating dairy cows have also been measured using the New Zealand SF6 tracer method and open-circuit respiration chamber techniques (Grainger et al, 2007). Total CH4 emissions were similar, 322 and 331 g CH4/day, when measured using chambers or the SF6 tracer technique respectively.

6.2.5 Source-specific recalculations

For the 2008 inventory submission all agricultural activity data is reported using single year values rather than 3-year average values. This change was introduced in the agriculture and LULUCF sectors to allow data to be compiled in a timely manner and to allow more time for overall inventory quality checking. The resulting annual values show greater variation than the 3-year average values over the 1990-2006 time series.

6.2.6 Source-specific planned improvements

A national inter-institutional ruminant CH4 expert group was formed to identify the key strategic directions for research into the CH4 inventory and mitigation, and to develop a collaborative approach to improve the certainty of CH4 emissions. This expert group is funded through the Ministry of Agriculture and Forestry. The Pastoral Greenhouse Gas Research Consortium has been established to carry out research, primarily into mitigation technologies and management practices but also improving on-farm inventories. The consortium is funded by both the public and private sectors. The implementation of the Tier 2 approach for CH4 emissions from enteric fermentation and manure management is a consequence of the research identified and conducted by the expert group.

6.3 Manure management (CRF 4B)

6.3.1 Description

Emissions from the “manure management” category comprised 808.1 Gg CO2-e (2.1 per cent) of emissions from the agriculture sector in 2006. Emissions from manure management have increased by 191.5 Gg CO2-e (31.1 per cent) from the 1990 level of 616.6 Gg CO2-e.

Livestock manure is composed principally of organic material. When the manure decomposes in the absence of oxygen, methanogenic bacteria produce CH4. The emissions of CH4 are related to the amount of manure produced and the amount that decomposes anaerobically. Methane from “manure management” has been identified as a key category (level assessment).

This category also includes emissions of N2O related to manure handling before the manure is added to the soil. The amount of N2O released depends on the system of waste management and the duration of storage. With New Zealand’s extensive use of all-year-round grazing systems, this category is relatively small at 65.0 Gg CO2-e in 2006. In comparison, agricultural soil emissions of N2O totalled 12,733.2 Gg CO2-e.

In New Zealand, only dairy cows have a fraction (5 per cent) of the excreta stored in anaerobic lagoon waste systems. The remaining 95 per cent of excreta from dairy cattle is deposited directly on pasture. These fractions relate to the proportion of time dairy cattle spend on pasture compared to the time they spend in the milking shed. All other ruminant species (sheep, beef cattle, deer and goats) graze outdoors all year round and deposit all of their faecal material directly onto pastures. This distribution is consistent with the revised 1996 IPCC guidelines (IPCC, 1996) for the Oceania region. New Zealand scientists and Ministry of Agriculture and Forestry officials considered the defaults were applicable to New Zealand farming practices. Table 6.3.1 shows the distribution of livestock in animal waste management systems in New Zealand.

Table 6.3.1 Distribution of livestock across animal waste management systems in New Zealand

  Percentage of animals in each animal waste management system
Livestock Anaerobic Lagoon Pasture, range and paddock Solid Storage and drylot Other

Non-dairy cattle

_

100

_

_

Dairy cattle

5

95

_

_

Poultry

_

_

3

97

Sheep

_

100

_

_

Swine

55

_

17

28

Goats

_

100

_

_

Deer

_

100

_

_

Horses

_

100

_

_

6.3.2 Methodological issues

Methane from manure management

Methane emissions from ruminant animal wastes in New Zealand have used the IPCC Tier 2 approach since the 2006 inventory submission. The methodology adopted is based on the methods recommended by Saggar et al, (2003) in a review commissioned by the Ministry of Agriculture and Forestry.

The approach relies on (1) an estimation of the total quantity of faecal material produced; (2) the partitioning of this faecal material between that deposited directly onto pastures and that stored in anaerobic lagoons; and (3) the development of specific New Zealand emission factors for the quantity of methane produced per unit of faecal dry matter deposited directly onto pastures and that stored in anaerobic lagoons. Table 6.3.2 summarises the key variables in the calculation of methane from manure management.

Table 6.3.2 Derivation of methane emissions from manure management

Animal species Proportion of faecal material deposited on pasture CH4 from animal waste on pastures (g CH4 /kg faecal dry matter) Proportion of faecal material stored in anaerobic lagoons Water dilution rate (litres water/kg faecal dry matter) Average depth of a lagoon (metres) CH4from anaerobic lagoon (g CH4/m2/year)

Dairy cattle

0.95

0.98

0.05

90

4.6

3.27

Beef cattle

1.0

0.98

0.0

Sheep

1.0

0.69

0.0

Deer

1.0

0.92

0.0

New Zealand-specific emissions factors are not available for CH4 emissions from manure management for swine, horses and poultry. These are minor livestock categories in New Zealand and emissions estimates for these species use IPCC default emission factors.

Dairy cattle

Faecal material deposited directly onto pastures: The quantity of faecal dry matter produced is obtained by multiplying the quantity of feed eaten by the dry matter digestibility of the feed, minus the feed retained in product. These feed intake and dry matter digestibility estimates are those used in the enteric methane and nitrous oxide inventories. Consistent with the nitrous oxide inventory, 95 per cent of faecal material arising from dairy cows is assumed to be deposited directly onto pastures (Ledgard and Brier, 2004). The quantity of methane produced per unit of faecal dry matter is 0.98 g CH4/kg. This value is obtained from New Zealand studies on dairy cows (Saggar et al, 2003; Sherlock et al, 2003).

Faecal material stored in anaerobic lagoons: Five per cent of faecal (dung and urine) material arising from dairy cows is assumed to be stored in anaerobic lagoons. The method adopted here is to assume that all faeces deposited in lagoons are diluted with 90 litres of water per kilogram of dung dry matter (Heatley, 2001). This gives a total volume of effluent stored. Annual CH4 emissions are estimated using the data of McGrath and Mason (2002). McGrath and Mason (2002) calculated specific emissions values of 0.33–6.21 kg CH4/m2/year from anaerobic lagoons in New Zealand. The mean value of 3.27 CH4/m2/year of this range is assumed in the New Zealand Tier 2 calculations.

Beef cattle

The quantity of faecal dry matter produced is obtained by multiplying the quantity of feed eaten by the dry matter digestibility of the feed, minus the feed retained in product. These feed intake and dry matter digestibility estimates are those used in the enteric methane and nitrous oxide inventories. Beef cattle are not housed in New Zealand and all faecal material is deposited directly onto pastures. No specific studies have been conducted in New Zealand on CH4 emissions from beef cattle faeces and values obtained from dairy cattle studies (0.98 g CH4/kg) are used (Saggar et al, 2003; Sherlock et al, 2003).

Sheep

The quantity of faecal dry matter produced is obtained by multiplying the quantity of feed eaten by the dry matter digestibility of the feed, minus the feed retained in product. These feed intake and dry matter digestibility estimates are those used in the enteric methane and nitrous oxide inventories. Sheep are not housed in New Zealand and all faecal material is deposited directly onto pastures. The quantity of methane produced per unit of faecal dry matter is 0.69g CH4/kg. This value is obtained from New Zealand studies on sheep (Carran et al, 2003).

Deer

The quantity of faecal dry matter produced is obtained by multiplying the quantity of feed eaten by the dry matter digestibility of the feed, minus the feed retained in product. These feed intake and dry matter digestibility estimates are those used in the enteric methane and nitrous oxide inventories. Deer are not housed in New Zealand and all faecal material is deposited directly onto pastures. There are no New Zealand studies on methane emissions from deer manure and values obtained from sheep and cattle are used. The quantity of methane produced per unit of faecal dry matter is assumed to be 0.92 g CH4/kg. This value is the average value obtained from all New Zealand studies on sheep (Carran et al, 2003) and dairy cattle (Saggar et al, 2003; Sherlock et al, 2003).

Nitrous oxide from manure management

This subcategory reports nitrous oxide emissions from the anaerobic lagoon, solid storage and drylot, and other animal waste management systems. Emissions from the “pasture, range and paddock” animal waste management system are reported in the “agricultural soils” category.

The calculations for the quantity of nitrogen in each animal waste management system are based on the nitrogen excreted (Nex) per head per year multiplied by the livestock population, the allocation of animals to animal waste management systems (Table 6.3.1) and a nitrous oxide emission factor for each animal waste management system (Annex 3.1).

The Nex values are calculated from the nitrogen intake less the nitrogen in animal products. Nitrogen intake is determined from feed intake and the nitrogen content of the feed. Feed intake and animal productivity values are the same as used in the Tier 2 model for determining methane emissions (Clark et al, 2003). The nitrogen content of feed is estimated from a review of over 6,000 pasture samples of dairy and sheep and beef systems (Ledgard et al, 2003).

The nitrogen contents of products are derived from industry data. For lactating cattle the nitrogen content of milk is derived from the protein content of milk (nitrogen = protein/6.25) published annually by the Livestock Improvement Corporation. The nitrogen content of sheep meat, beef and wool and the nitrogen retained in deer velvet are taken from New Zealand based research.

Table 6.3.3 shows Nex values increasing over time reflecting the increases in animal production in New Zealand since 1990.

Table 6.3.3 Nex values for main livestock classes over time

  Sheep N
(kg/head/yr)
Non-dairy
Cattle N
(kg/head/yr)
Dairy
Cattle N
(kg/head/yr)
Deer N
(kg/head/yr)

1990

12.61

65.39

103.87

24.88

1991

12.83

66.93

107.02

25.64

1992

12.80

67.67

107.49

26.83

1993

12.93

69.25

109.80

27.06

1994

12.97

70.34

106.85

26.20

1995

12.84

68.79

106.50

27.42

1996

13.34

70.70

109.81

27.76

1997

13.85

71.51

110.46

27.84

1998

13.95

71.41

108.50

28.06

1999

14.00

70.17

111.96

28.24

2000

14.63

73.17

113.41

28.91

2001

14.69

73.67

113.95

28.85

2002

14.68

72.88

113.12

28.74

2003

14.68

72.18

117.40

28.67

2004

15.09

73.36

115.27

28.88

2005

15.21

74.59

116.72

29.47

2006

15.12

74.98

116.59

29.48

6.3.3 Uncertainties and time-series consistency

Emission factors from manure and manure management systems, the livestock population, nitrogen excretion rates and the usage of the various manure management systems are the main factors causing uncertainty in N2O emissions from manure management (IPCC, 2000).

New Zealand uses the IPCC default values for EF3 (direct emissions from waste) for all AWMS except for EF3(PR&P) (manure deposited on pasture, range and paddock). The IPCC default values have uncertainties of –50 per cent to +100 per cent (IPCC, 2000). The value of EF3(PR&P), which is a country-specific factor, is 0.01 kg N2O–N/kg N (further details in section 6.5.2).

The overall inventory uncertainty analysis shown in Annex 7 (Table A.7.1) demonstrates that the effect of uncertainty in annual emissions from manure management is relatively minor compared to the effect of CH4 emissions from enteric fermentation and N2O from agricultural soils.

6.3.4 Source-specific QA/QC and verification

Methane from manure management was identified as a key category (level assessment). In preparation for this inventory submission, the data for this category underwent Tier 1 quality checks.

6.3.5 Source-specific recalculations

For the 2008 inventory submission all agricultural activity data is reported using single year values rather than 3-year averaged values. This change was introduced in the agriculture and LULUCF sectors to allow data to be compiled in a timely manner and to allow more time for overall inventory quality checking.

6.3.6 Source-specific planned improvements

The National Institute of Water and Atmospheric Research have recently completed continuous measurement of anaerobic lagoons emissions over a full year. New Zealand will assess whether this research can be used to update the manure management estimates in the future.

6.4 Rice cultivation (CRF 4C)

6.4.1 Description

There is no rice cultivation in New Zealand. The “NO” notation is reported in the CRF.

6.5 Agricultural soils (CRF 4D)

6.5.1 Description

In 2006, the “agricultural soils” category produces the majority of N2O emissions in New Zealand comprising 12,733.2 Gg CO2-e. Emissions are 2,693.3 Gg CO2-e (26.8 per cent) above the 1990 level of 10,039.8 Gg CO2-e. The category comprises three subcategories. Each of these subcategories has been identified as a key category.

  • Direct N2O emissions from agricultural soils as a result of adding nitrogen in the form of synthetic fertilisers, animal waste, biological fixation in crops, inputs from crop residues and sewage sludge. Direct soil emissions from animal production contributed 1,736.8 Gg CO2-e (13.6 per cent) of agricultural soil emissions. This is an increase of 1,249.6 Gg CO2-e (256.5 per cent) from the 1990 level of 487.2 Gg CO2-e.

  • Indirect N2O from nitrogen lost from the field as NO3, NH3 or NOx . Indirect N2O from nitrogen used in agriculture contributed 3,387.2 Gg CO2-e (26.6 per cent) of soil agricultural emissions. This is an increase of 685.1 Gg CO2-e (25.4 per cent) from the 1990 level 2,702.2 Gg CO2-e.

  • Direct N2O emissions from animal production (the pasture, range and paddock animal waste management system). Emissions from animal production contributed 7,609.1 Gg CO2-e (59.8 per cent) of agricultural soil emissions. This is an increase of 758.7 Gg CO2-e (11.1 per cent) from the 1990 level of 6,850.5 Gg CO2-e.

Carbon dioxide emissions from limed soils are reported in the LULUCF sector.

6.5.2 Methodological issues

Nitrous oxide emissions are determined using the revised 1996 IPCC guidelines (IPCC, 1996). Emission factors and the fraction of nitrogen deposited on the soils are used to calculate N2O emissions. The two main inputs of nitrogen to the soil are excreta deposited during animal grazing and the application of nitrogen fertilisers.

Three New Zealand-specific factors/parameters are used in the inventory: EF1, EF3(PR&P) and FracLEACH. EF1 (direct emissions from nitrogen input to soil) was reviewed during 2006 and the recommendation by Kelliher and de Klein (2006) to use a country-specific factor of 1 per cent was adopted for agriculture inventory calculations in the 2006 inventory submission. The EF3(PR&P) emission factor of 1 per cent and FracLEACH (0.07) were extensively reviewed and first included in the 2001 inventory submission.

The emission factors and other parameters used in this category are documented in Annex 3.1. The calculations are included in the excel workbooks available for download with this report from the Ministry for the Environment’s website.

Animal production (N2O)

Direct soil emissions from animal production refers to the N2O produced from the pasture, range and paddock animal waste management system. This system is the predominant regime for animal waste in New Zealand as 95 per cent of dairy cattle excreta and 100 per cent of sheep, deer and non-dairy cattle excreta are allocated to it (Table 6.3.1).

The emissions calculation is based on the livestock population multiplied by nitrogen excretion (Nex) values and the percentage of the population on the pasture, range and paddock animal waste management system. The Nex and allocation to AWMS are discussed in section 6.3. The Nex values have been calculated based on the same animal intake and animal productivity values used for calculating CH4 emissions for the different animal classes and species. This ensures that the same base values are used for both CH4 and N2O emission calculations.

New Zealand uses a country-specific emission factor for EF3(PR&P) of 0.01 (Carran et al, 1995; Muller et al, 1995; de Klein et al, 2003; Kelliher et al, 2003). Considerable research effort has gone into establishing a country-specific value for EF3(PR&P). Field studies have been performed as part of a collaborative research effort called NzOnet. The parameter EF3(PR&P) has been measured by NzOnet researchers in the Waikato (Hamilton), Canterbury (Lincoln) and Otago (Invermay) regions for pastoral soils of different drainage classes (de Klein et al, 2003). These regional data are comparable because the same measurement methods were used at the three locations. The percentage of applied nitrogen (as urine or dung) emitted as N2O, and environmental variables, were measured in four separate trials that began in autumn 2000, summer 2002, spring 2002 and winter 2003. Measurements were carried out for up to 250 days or until urine-treated pasture measurements dropped back to background emission levels.

Kelliher et al (2003, 2005), assessed all available EF3(PR&P) data and its distribution to pastoral soil drainage class, to determine an appropriate national annual mean value. The complete EF3(PR&P) data set of NzOnet was synthesised using the national assessment of pastoral soils drainage classes. These studies recognise that:

  • Environmental (climate) data are not used to estimate N2O emissions using the IPCC (1996) methodology.

  • The N2O emission rate can be strongly governed by soil water content.

  • Soil water content depends on drainage that can moderate the effects of rainfall and drought.

  • Drainage classes of pastoral soils, as a surrogate for soil water content, can be assessed nationally using a geographic information system.

In New Zealand, earlier analysis showed the distribution of drainage classes for pasture land is highly skewed with 74 per cent well-drained, 17 per cent imperfectly drained and 9 per cent poorly drained (Sherlock et al, 2001).

The research and analysis to date indicates that if excreta is separated into urine and dung components, EF3 for urine and dung could be set to 0.007 and 0.003, respectively. However, it is recognised that the dung EF3 data are limited. Combining urine and dung EF3 values, the dairy cattle total excreta EF3 is 0.006. Conservatively rounding the total excreta EF3 of 0.006 provides a country-specific value of 0.01 for EF3(PR&P). The IPCC default value of EF3(PR&P) is 0.02 (IPCC, 1996).

Indirect N2O from nitrogen used in agriculture

Nitrous oxide is emitted indirectly from nitrogen lost from agricultural soils through leaching and run-off. This nitrogen enters water systems and eventually the sea, with quantities of N2O being emitted along the way. The amount of nitrogen that leaches is a fraction (FracLEACH) of that deposited or spread on land.

Research studies and a literature review in New Zealand have shown lower rates of nitrogen leaching than are suggested in the revised 1996 IPCC guidelines (IPCC, 1996). A New Zealand parameter for FracLEACH of 0.15 was used in inventory submissions reported before 2003. However, using a FracLEACH of 0.15, IPCC-based estimates for different farm systems were found on average to be 50 per cent higher than those estimated using the OVERSEER® nutrient budgeting model (Wheeler et al, 2003). The model provides average estimates of the fate of nitrogen for a range of pastoral, arable and horticultural systems. In pastoral systems, nitrogen leaching is determined by the amount of nitrogen in fertiliser, dairy farm effluent and that excreted in urine and dung by grazing animals. The latter is calculated from the difference between nitrogen intake by grazing animals and nitrogen output in animal products, based on user inputs of stocking rate or production and an internal database with information on the nitrogen content of pasture and animal products.

The IPCC estimates were closer for farms using high rates of nitrogen fertiliser, indicating that the IPCC-based estimates for nitrogen leaching associated with animal excreta were too high. When the IPCC methodology was applied to field sites where nitrogen leaching was measured (four large-scale, multi-year animal grazing trials) it resulted in values that were double the measured values. This indicated that a value of 0.07 for FracLEACH more closely followed actual field leaching (Thomas et al, 2005). The 0.07 value was adopted and is used for all years as it best reflects New Zealand’s national circumstances.

New Zealand uses the IPCC default EF4 emission factor for indirect emissions from volatilisation of nitrogen in the form of ammonia (NH3) and nitrogen oxides (NOx).

Direct N2O emissions from agricultural soils

The N2O emissions from “direct N2O emissions from agricultural soils” category arise from synthetic fertiliser use, spreading animal waste as fertiliser, nitrogen fixing in soils by crops and decomposition of crop residues left on fields. All of the nitrogen inputs are summed together and a country-specific emission factor of 0.01 kg N2O-N/kg N (Kelliher and de Klein, 2006) applied to calculate total direct emissions from non-organic soils.

Nitrogen fertiliser use is provided by the Zealand Fertiliser Manufacturers’ Research Association (FertResearch) from sales records for 1990 to 2006. There has been a six-fold increase in elemental nitrogen applied through nitrogen-based fertiliser over the 1990–2006 time-series from 51,633 tonnes in 1990 to 329,700 tonnes in 2006. The calculation of N2O that is emitted indirectly through synthetic fertiliser and animal waste being spread on agricultural soils is shown in the excel workbooks available with this report from the Ministry for the Environment’s website. Some of the nitrogen contained in these compounds is emitted into the atmosphere as NH3 and nitrogen oxides NOx through volatilisation, which returns to the ground during rainfall and is then re-emitted as N2O. This is calculated as an indirect emission of N2O.

The calculation for animal waste includes all manure that is spread on agricultural soils irrespective of which animal waste management system it was initially stored in. This includes all agricultural waste in New Zealand except for emissions from the pasture range and paddock animal waste management system. New Zealand uses a country-specific value for EF1 of 0.01 kg N2O–N/kg N (Kelliher and de Klein, 2006).

Direct N2O emissions from organic soils are calculated by multiplying the area of cultivated organic soils by an emission factor. Analysis identified 202,181 hectares of organic soils. Kelliher et al (2002) estimated 5 per cent (ie, 10,109 ha) of organic soils are cultivated on an annual basis. New Zealand uses the IPCC default emissions factor (EF2 equal to 8 kg N2O–N/kg N) for all years of the time-series.

6.5.3 Uncertainties and time-series consistency

Uncertainties in N2O emissions from agricultural soils were assessed for the 1990 and 2002 inventory using a Monte Carlo simulation of 5,000 scenarios with the @RISK software (Kelliher et al, 2003) (Table 6.5.1). The emissions distributions are strongly skewed, reflecting pastoral soil drainage whereby 74 per cent of soils are classified as well-drained and 9 per cent are classified as poorly drained. For the 2006 data, the uncertainty in the annual estimate was calculated using the 95 per cent confidence interval determined from the Monte Carlo simulation as a percentage of the mean value, ie, in 2002, the uncertainty in annual emissions was +74 per cent and – 42 per cent.

Table 6.5.1 Uncertainties in N2O emissions from agricultural soils for 1990, 2002 and 2006 estimated using Monte Carlo simulation (1990, 2002) and the 95 per cent confidence interval (2006)

Year N2O emissions from agricultural soils (Gg/annum) 95% CI min 95% CI max

1990

32.4

18.8

56.4

2002

39.6

23.0

68.9

2006

41.1

23.8

71.5

The overall inventory uncertainty analysis shown in Annex 7 demonstrates that the uncertainty in annual emissions from agricultural soils is a major contributor to uncertainty in the total estimate and trend from 1990. The uncertainty between years is assumed to be correlated, therefore the uncertainty is mostly in the emission factors and the uncertainty in the trend is much lower than uncertainty for an annual estimate.

The Monte Carlo numerical assessment was also used to determine the effects of variability in the nine most influential parameters on uncertainty of the calculated N2O emissions in 1990 and 2002. These parameters are shown in Table 6.5.2 together with their percentage contributions to the uncertainty. There was no recalculation of the influence of parameters for the 2006 data. The Monte Carlo analysis confirmed that uncertainty in parameter EF3(PR&P) has the most influence on total uncertainty, accounting for 91 per cent of the uncertainty in total N2O emissions in 1990. This broad uncertainty reflects natural variance in EF3 determined largely by the vagaries of the weather and soil type.

Table 6.5.2 Percentage contribution of the nine most influential parameters on the uncertainty of total N2O emissions inventories for 1990 and 2002

Parameter 1990 2002
  % contribution to uncertainty % contribution to uncertainty

EF3(PR&P)

90.8

88.0

EF4

2.9

3.3

Sheep Nex

2.5

1.8

EF5

2.2

2.8

Dairy Nex

0.5

0.7

FracGASM

0.5

0.5

EF1

0.3

2.4

Beef Nex

0.2

0.3

FracLEACH

0.1

0.2

6.5.4 Source-specific QA/QC and verification

Nitrous oxide emissions from “direct soil emissions” and “pasture, range and paddock manure” are key categories (level and trend assessment). Nitrous oxide from “indirect emissions” is a key category (level assessment). In preparation for this inventory, the data for these categories underwent Tier 1 quality checks.

The nitrogen fertiliser data obtained from FertResearch are corroborated by the Ministry of Agriculture and Forestry using nitrogen imports and exports, urea production figures and industrial applications (including resin manufacture for timber processing) data.

6.5.5 Source-specific recalculations

For the 2008 inventory submission all agricultural activity data is reported using single year values rather than 3-year averaged values. This change was introduced in the agriculture and LULUCF sectors to allow data to be compiled in a timely manner and to allow more time for overall inventory quality checking.

6.5.6 Source-specific planned improvements

Research is continuing by New Zealand scientists to better quantify N2O emission factors for New Zealand’s pastoral soils. This includes development of country specific emission factors for sheep and cattle dung and emission factors for New Zealand hill country pastures.

New Zealand is also exploring methods to incorporate mitigation technology such as the application of dicyandiamide nitrification inhibitor on pasture into future inventory submissions. An extensive body of scientific literature has been published on the unique application methods and circumstances for New Zealand pastoral agriculture. Methodologies for incorporating dicyandiamide mitigation technology into the inventory are being assessed in relation to the requirements of IPCC good practice.

6.6 Prescribed burning of savanna (CRF 4E)

6.6.1 Description

Prescribed burning of savanna is not a key category for New Zealand. The New Zealand inventory includes burning of tussock (Chionochloa) grassland in the South Island for pasture renewal and weed control. The amount of burning has been steadily decreasing over the past 50 years as a result of changes in lease tenure and a reduction in grazing pressure. In 2006, total emissions accounted for 1.0 Gg CO2-e, a 2.2 Gg CO2-e (68.0 per cent) reduction from the 3.2 Gg CO2-e reported in 1990.

The revised 1996 IPCC guidelines (IPCC, 1996) state that in agricultural burning, the CO2 released is not considered to be a net emission as the biomass burned is generally replaced by regrowth over the subsequent year. Therefore the long-term net emissions of CO2 are considered to be zero. However the by-products of incomplete combustion, CH4, CO, N2O and NOx, are net transfers from the biosphere to the atmosphere.

6.6.2 Methodological issues

New Zealand has adopted a modified version of the IPCC methodology (IPCC, 1996). The same five equations are used to calculate emissions. Instead of using total grassland and a fraction burnt, New Zealand uses statistics of the total amount of tussock grassland that has been granted a consent (a legal right) under New Zealand’s Resource Management Act (1991) for burning. Only those areas with a consent are legally allowed to be burned. Expert opinion obtained from land managers in local government is that approximately 20 per cent of the area allowed to be burnt is actually burnt in a given year.

Current practice in New Zealand is to burn in damp spring conditions which reduces the amount of biomass consumed in the fire. The composition and burning ratios used in calculations are from New Zealand-specific research (Payton and Pearce, 2001) and the revised 1996 IPCC guidelines (IPCC, 1996).

6.6.3 Uncertainties and time-series consistency

The same sources of data and emission factors are used for all years. This gives confidence in comparing emissions through the time-series from 1990 and 2006. The major sources of uncertainty are the percentage of consented area actually burnt in that season, extrapolation of biomass data from two study sites for all areas of tussock, and that many of the other parameters (ie, the carbon content of the live and dead components, the fraction of the live and dead material that oxidise and the nitrogen to carbon ratio for the tussocks) are the IPCC default values. Uncertainty in the New Zealand biomass data has been quantified at ± 6 per cent (Payton and Pearce, 2001), however many IPCC parameters vary by ± 50 per cent and some parameters lack uncertainty estimates.

6.6.4 Source-specific QA/QC and verification

There was no source-specific QA/QC for this category.

6.6.5 Source-specific recalculations

For the 2008 inventory submission all agricultural activity data is reported using single year values rather than 3-year averaged values. This change was introduced in the agriculture and LULUCF sectors to allow data to be compiled in a timely manner and to allow more time for overall inventory quality checking.

6.7 Field burning of agricultural residues (CRF 4F)

6.7.1 Description

Burning of agricultural residues produced 14.6 Gg CO2-e in 2006. Emissions are currently 14.1 Gg CO2-e lower (-49.2 per cent) than the level of 28.7 Gg CO2-e in 1990. Burning of agricultural residues is not identified as a key category for New Zealand.

New Zealand reports emissions from burning barley, wheat and oats residue in this category. Maize residue is not burnt in New Zealand.

Burning of crop residues is not considered to be a net source of CO2 because the CO2 released into the atmosphere is reabsorbed during the next growing season. However, the burning is a source of emissions of CH4, CO, N2O and NOx (IPCC, 1996). Burning of residues varies between years due to climatic conditions and is a declining source.

6.7.2 Methodological issues

The emissions from burning of agricultural residues are estimated in accordance with the revised 1996 IPCC guidelines (IPCC, 1996). The calculation uses crop production statistics, the ratio of residue to crop product, the dry matter content of the residue, the fraction of residue actually burned, the fraction of carbon oxidised and the carbon fraction of the residue. These figures are multiplied to calculate the carbon released. The emissions of CH4, CO, N2O and NOx are calculated using the carbon released and an emissions ratio. Nitrous oxide and NOx emissions calculations also use the nitrogen to carbon ratio.

IPCC good practice guidance suggests that an estimate of 10 per cent of residue burnt may be appropriate for developed countries but also notes that the IPCC defaults “are very speculative and should be used with caution. The actual percentage burned varies substantially by country and crop type. This is an area where locally developed, country-specific data are highly desirable” (IPCC, 2000). For the years 1990 to 2003 it is estimated that 50 per cent of stubble was burnt. For the years 2004 to 2006, experts assessed this to have decreased to 30 per cent. These values were developed from opinions of the MAF officials working with the arable production sector. The 2007 agricultural census (results due mid 2008) will provide updated data.

6.7.3 Uncertainties and time-series consistency

No numerical estimates for uncertainty are available for these emissions. The fraction of agricultural residue burned in the field is considered to make the largest contribution to uncertainty in the estimated emissions.

6.7.4 Source-specific QA/QC and verification

There was no source-specific QA/QC for this category.

6.7.5 Source-specific recalculations

For the 2008 inventory submission all agricultural activity data is reported using single year values rather than 3-year averaged values. This change was introduced in the agriculture and LULUCF sectors to allow data to be compiled in a timely manner and to allow more time for overall inventory quality checking.

1  Number of beef breeding cows assumed to be 25 per cent of the total beef breeding cow herd; other adult cows slaughtered are assumed to be dairy cows. The carcass weight of dairy cattle slaughtered was estimated using the adult dairy cow liveweights and a killing-out percentage of 40 per cent. The total weight of dairy cattle slaughtered was calculated (carcass weight x number slaughtered) and then deducted from the national total carcass weight of slaughtered adult cows. This figure was then divided by the number of beef cows slaughtered to obtain an estimate of the carcass weight of adult beef cows. Liveweights are then obtained assuming a killing-out percentage of 50 per cent.

2  For example, Blaxter and Clapperton, 1995; Moe and Tyrrel, 1975; Baldwin et al, 1988; Djikstra et al, 1992; and Benchaar et al, 2001 – all cited in Clarke et al, 2003.