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• 3.1 OVERVIEW OF METHODOLOGY
  • 3.1.1 Farm Unit Definitions
  • 3.1.2 Data Collection by Survey
  • 3.1.3 Data Processing
  • 3.1.4 Farm Outputs
  • 3.1.5 Direct Energy Inputs
  • 3.1.6 Indirect Energy Inputs
• 3.2 FARM OUTPUTS
  • 3.2.1 Milk
  • Table 3.1 Range of Gross Composition of Cow's Milk in New Zealand (after Holmes et al, 1984)
  • Table 3.2 Energy and Carbon Content of Organic Substances (Energy data after Holland et al, 1991)
• 3.3 DIRECT INPUTS
  • 3.3.1 Fuel and Lubricants
  • 3.3.2 Electricity
  • 3.3.3 Fuel Use by Contractors
  • Table 3.3 Average Fuel Consumption Rates (Diesel) for Agricultural Operations (adapted from McChesney (1981) & Bone et al (1996))
• 3.4 INDIRECT INPUTS
  • 3.4.1 Fertilisers
    • 3.4.1.1 Nitrogenous Fertilisers
    • Table 3.4 Energy Requirements to Manufacture Urea (46 percent N)
    • 3.4.1.2 Phosphate Fertilisers
    • 3.4.1.5 Compound Fertilisers
    • Table 3.5 Energy Coefficients and Carbon Dioxide Emission Factors for Fertiliser Elements
  • 3.4.2 Agri-chemicals
    • Table 3.6 Energy Requirements and Carbon Dioxide Emissions from Manufacture, Packaging and Distribution of Agri-chemicals
  • 3.4.3 Seed
  • 3.4.4 Bought-In Animal Feed Supplements
    • 3.4.4.1 Grass Silage
    • Table 3.7 Energy and Carbon Dioxide Emission Costs of Grass Silage Production
    • 3.4.4.2 Maize Silage
    • Table 3.8 Energy and Carbon Dioxide Emission Costs of Maize Silage Production
    • 3.4.4.3 Hay
    • 3.4.4.4 Cereals
  • 3.4.5 Grazing-Off
  • Table 3.9 Live-weight as Percentage of Average Live-weight of Mixed Age Cows (after Church & Pond, 1988; Fleming et al, 1996)
• 3.5 CAPITAL ENERGY INPUTS
  • 3.5.1 Self-propelled Vehicles
    • Table 3.10 Energy Coefficients, Carbon Dioxide Emission Factors and Assumed Working Life of Motor Vehicles and Farm Implements
    • Figure 3.1 Relationship between Rated Power and Mass of Tractors
    • 3.5.1.2 Light Trucks and Utilities
    • 3.5.1.3 Motorbikes
    • 3.5.1.4 Heavy Trucks & Other Self Propelled Machinery
  • 3.5.2 Tractor Powered Implements
    • Table 3.11 Number and Average Mass of Implements found on Surveyed Dairy Farms
  • 3.5.3 Dairy Shed
    • Figure 3.2 Capital Energy of Dairy Shed as a Function of the Number of Sets of Cups
  • 3.5.4 Other Buildings
  • 3.5.5 Farm Tracks and Races
  • 3.5.6 Fences
  • 3.5.7 Stock Water Supply
  • 3.5.8 Irrigation
  • 3.5.8.1 Border Strip
  • 3.5.8.2 Spray Irrigation
  • 3.5.9 Drainage
  • 3.5.10 Effluent Disposal
    • Table 3.12 Holding Pond Requirements for Land Based Dairy Effluent Treatment

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3 - Methodology for Determining Energy Indicators

In order to calculate the indicators listed in Table 2.2 it was necessary to determine total energy inputs and outputs for each farm in the survey. To collect the necessary information from each farm a questionnaire was developed in consultation with consultants from Agriculture New Zealand Ltd. This was a simplified version of that used in the pilot study (Wells, 1998) which in turn was based on one previously developed by McChesney (1979). The questionnaire surveyed production, direct energy inputs, other inputs (e.g. fertilisers) and capital items (e.g. buildings and machinery). From this data the equivalent total primary energy was determined using a set of energy coefficients. A general overview of the technique to determine the energy inputs and outputs is described in section 3.1. Detailed methods for the determination of the energy coefficients and calculation of energy inputs and outputs are presented in sections 3.2 to 3.5.

3.1 OVERVIEW OF METHODOLOGY

3.1.1 Farm Unit Definitions

For this study the basic dairy farm unit consists of a 'milking platform' (paddocks rotationally grazed during the milking season) and any unproductive land making up the 'home farm'. In some cases a 'run-off' block (whether owned or leased), is also included where the run-off is maintained as a permanent part of the dairy farm operation (e.g. fertiliser and irrigation application are the responsibility of the dairy farm owner/sharemilker). Run-off blocks usually accommodate grazing of young replacement stock and over-wintering of the milking herd. The term 'grazing-off' refers to the practice of short-term leasing of pasture from another enterprise (usually a sheep/beef unit) as an alternative to operating a permanent run-off block. In line with industry practice, productivity indicators were calculated on the basis of the area of the milking platform known as the 'effective milking area' rather than the total area of land owned by the dairy enterprise.

3.1.2 Data Collection by Survey

In the first phase (1997/98) survey forms were sent out to all 134 dairy farms used in MAF farm monitoring, of which 96 completed returns were obtained. After initial analysis (Wells, 1999) a further 54 farms were surveyed in the second phase (1998/99).

3.1.3 Data Processing

Survey data was entered into a database programme and checked manually for data entry errors. The database was then linked to a series of spreadsheets for analysis. The spreadsheets contained all the necessary energy coefficients (sections 3.2 to 3.5) and were used to calculate the total energy inputs, outputs and energy indicators, for each farm surveyed, and averages for each district and for the 'national average' dairy farm. Due to the importance of irrigation as a determining factor indicators have also been evaluated for average irrigated and non-irrigated properties.

3.1.4 Farm Outputs

For each farm the milk production in kilograms of milk solids was recorded for a financial year period (either for the 1997/98 year or the 1998/99 year). From this, the energy and nutrient content of the milk was calculated using the energy coefficients detailed in section 3.2. In the pilot survey (Wells, 1998) allowance was also made for meat production from cull animals. However, obtaining accurate stock reconciliations for all farms surveyed proved to be difficult. From those farms that did provide reliable data (73) it was estimated that meat made up 8 percent of the total calorific energy output. However, considering that much of this output would not be for human consumption it was decided not to include meat as a primary dairy farm output. Thus the overall energy ratios (OER), protein energy ratios (PER) and net carbon emissions values reported here only include milk production. The energy coefficients for farm outputs are discussed in section 3.2 below.

3.1.5 Direct Energy Inputs

Direct energy inputs were obtained as quantities on an annual basis for the following inputs:

• Diesel (litres)
• Petrol (litres)
• Lubricants (litres)
• Electricity (kWh)

No other energy sources were observed within the survey group. Electricity use was divided between irrigation, dairy shed and other uses. Electricity usage for domestic dwellings was excluded.

In some cases liquid fuel purchases were only available in terms of dollar expenditure. In these cases actual quantities were estimated according to the following:

• Diesel @ 45c
• Petrol @ 90c
• Lubricants @ $5

Fuel use by contractors working on the property was estimated from records of type of machine, hours of operation, areas worked, or amount of material carted or spread. An allowance was made for cartage of fertilisers based on quantity and distance to fertiliser works less any quantities carted using farm vehicles where the fuel would already have been accounted for. Cartage of stock was allowed for in a similar manner. No allowance has been made for indirect or capital energy inputs for contractors such as manufacture and maintenance of equipment.

Energy coefficients for direct energy inputs and contractor operations are discussed fully in section 3.3.

3.1.6 Indirect Energy Inputs

Indirect energy inputs were accounted for by the farm operation in a number of areas. Overall annual usage of indirect inputs was recorded for the following:

• fertiliser use by fertiliser type or nutrient quantity;
• agri-chemicals (acid and alkali cleaners, bloat oil, zinc & magnesium, other animal remedies, herbicides, other chemicals);
• seeds;
• feed that was bought-in from outside or sold (grass & maize silage, balage, hay & straw, grains & meals, milk powder, molasses, etc).
• grazing-off recorded by number of animals and time away from the property; and
• any substantial purchases brought in for farm maintenance such as aggregate for road maintenance.

Energy coefficients for indirect energy inputs are presented in section 3.4.

3.1.7 Capital Inputs

Items of capital plant, equipment and improvements were recorded. The embodied energy (total primary energy to manufacture) was determined using the energy coefficients as discussed in section 3.5. To determine an effective annual energy requirement the total embodied energy of each item was discounted over an assumed life using straight-line depreciation.

Items of capital included in the survey were:

• the dairy shed (type and number of sets of cups);
• other buildings (type and plan area);
• self propelled vehicles (tractors, trucks, utilities, motor bikes);
• machinery (type and number);
• fences and races (type and length);
• stock water supply (area covered);
• irrigation and drainage (type and area covered); and
• effluent disposal system (type).

Energy coefficients for capital energy inputs are presented in section 3.5.

3.2 FARM OUTPUTS

The primary output from dairy farms is milk. In addition, quantities of meat are produced from cull animals. Other secondary outputs may include items such as surplus conserved feed or outputs from co-existing enterprises, e.g. fruit, forestry. None of the farms considered in the survey produced any secondary outputs of consequence apart from some sales of conserved feed which were accounted for as negative purchases under indirect inputs. Meat was included in the pilot study but has been excluded in this study as already discussed in section 3.1.4 above.

3.2.1 Milk

Milk is a colloidal substance consisting of water, lactose, proteins, fat and some minerals. The composition of milk can vary depending on herd breed and composition, time of year and type of feed available. Table 3.1 gives a summary of values for the composition of milk in New Zealand.

Table 3.1 Range of Gross Composition of Cow's Milk in New Zealand (after Holmes et al, 1984)

The heat content of fats, proteins, carbohydrates (lactose) and minerals are assumed to be as shown in Table 3.2.

 

Table 3.2 Energy and Carbon Content of Organic Substances (Energy data after Holland et al, 1991)

Table 3.1 and Table 3.2, the average heat content (calorific value) of New Zealand milk was calculated to be approximately 3.11 MJ per kilogram or 3.01 MJ per litre (assuming an average density of 1.032 kg per litre). By comparison, Holland et al (1991) gave the average heat content of whole milk in Britain as 2.75 MJ/kg and in the Channel Islands as 3.27 MJ/kg. Smith & McChesney (1979) used a figure of 3.09 MJ/kg for New Zealand milk.

In New Zealand, most dairy farms are paid on the basis of the milk solids (MS) content of the milk (fat plus protein) and this is the production figure most often quoted. On this basis, the average calorific value of milk is 38 MJ/kgMS based on a milk solids content of 82 g MS per kg of milk (see Table 3.1).

In order to assess the carbon removal from a dairy farm, it is necessary to predict the carbon content of the outputs. Typical carbon contents of organic substances are given in Table 3.2. From this it can be estimated that New Zealand milk typically contains 68.4 grams of carbon per kg of whole milk or 834 grams of carbon per kilogram of milk solids. Thus each kilogram of milk solids is equivalent to 3.06 kilograms of sequestrated carbon dioxide.

3.3 DIRECT INPUTS

3.3.1 Fuel and Lubricants

The primary fuel inputs into dairy production systems are diesel and petrol for tractors, trucks, utilities and farm bikes.

In the pilot study report the gross calorific value and base carbon emission factors of fuels and lubricants were used to calculate overall energy consumption and carbon dioxide emissions. In this final report where the boundaries have been extended to include total primary energy supply, the effect of fugitive use and emissions has also been included.

The gross energy contents of diesel and petrol were obtained by averaging values from three oil companies and were found to be 38.0 MJ for diesel and 34.5 MJ for petrol. Variations between oil companies were insignificant. The variation between 91 and 96 octane petrol was also found to be insignificant. The gross calorific value of lubricant oil was assumed to be 40 MJ (IPCC, 1996). In a recent study carried out by the NZ Dairy Research Institute, Keedwell (pers. comm.) estimated that each MJ of delivered fuel energy is equivalent to 1.23 MJ of primary energy. The extra 23 percent allowance

accounts for fugitive uses such as extraction, processing, refining and transport of crude oil and final products to and within New Zealand, and an allowance to capital energy inputs. Thus the total energy consumption for diesel, petrol and lubricants were taken to be 46.7, 42.3 and 49.2 MJ.

The base carbon dioxide emissions associated with the consumption of diesel and petrol were taken to be 0.0741 and 0.0693 kg CO₂/MJ respectively, based on the IPCC (1996) carbon emission factors of 20.2 and 18.9 g C/MJ. The base carbon dioxide emission factor for lubricants was assumed to be 0.0367 kg CO2/MJ based on the IPCC methodology, assuming total carbon emissions at 20 g C/MJ (73.3 gCO2/MJ) and 50 percent oxidisation during use. To these base emission factors, an allowance of 0.0067 kg CO₂/MJ for fugitive emissions (Keedwell, pers. comm.) has been added, making the overall emission factors equal to 0.0808, 0.0760, and 0.0434 kg CO₂/MJ.

3.3.2 Electricity

Electricity is mainly used on dairy farms for milking shed operation and water pumping. The appropriate basic conversion factor for electricity is 3.6 MJ/kWhe, however this does not take into account the efficiency of electricity generation. Keedwell (pers. comm.) estimated the overall conversion factor to be 8.18 MJ/kWhe based on 1997 data, that is 2.27 kWh of primary energy are required to supply 1 kWh of consumer energy.

Using the same data, Keedwell (pers. comm.) has estimated the carbon dioxide emission factor for New Zealand's electricity generation system to be 0.209 kg CO2/kWhe or 0.0581 kg CO2/MJ. This is nearly twice the value used in the previous report of 0.119 kg CO₂/kWhe (Wells, 1998) but reflects a truer picture of the current electricity generating mix and fugitive emissions. In this report no account has been taken of possible differences between carbon dioxide emission factors of North Island and South Island generators.

Based on the above data source the renewable fraction of electricity, based on primary energy, is approximately 57 percent. This is a lower figure than appears in most literature but represents the total primary energy input rather than the consumer energy output (see section 2.5.2).

3.3.3 Fuel Use by Contractors

Fuel use by contractors was calculated from estimates of the amount of work carried out on the farms surveyed. Allowance was made for contracting operations such as: spraying, fertiliser cartage from point of manufacture or port of entry, fertiliser spreading, pasture renewal, silage and hay making and associated cartage, and stock cartage to and from grazing. Cartage of products off the property was excluded, i.e. milk to the factory as this is included in the dairy processing sector analysis. The methodology employed allowed for the separation of operations partially carried out by contractors and by the farmer. For example, some farmers cut and condition their own hay but employ a contractor to bale and cart.

Fuel consumption data for various farm activities was developed from McChesney (1981). In all cases an average value corresponding to medium working conditions on average soil types was assumed. The energy requirement for transport was assumed to be 0.079 (/net-tonne-km or 3 MJ per net-tonne-km assuming diesel as the fuel (Bone et al, 1996). This information is summarised in Table 3.3. For aerial topdressing an average application rate of 400 kg/ha was assumed. For aerial spraying an average application rate of 0.5 kg active ingredient per hectare was assumed.

Activity	Fuel Use	Activity	Fuel Use
Ploughing	18 l /ha	Fertiliser Spreading	3 l /ha
Cultivating	6 l /ha	Aerial Topdressing	7 l /ha
Discing	12 l /ha	Aerial Spraying	0.035 l /ha
Rolling	4 l /ha	Mowing-Conditioning	6 l /ha
Power Harrowing	8 l /ha	Hay Raking or Tedding	2 l /ha
Light Harrowing	4 l /ha	Baling/Wrapping	2 l /tonne
Conventional Drilling	5 l /ha	Hay Pickup	1 l /tonne
Direct Drilling	10 l /ha	Forage Harvesting	2 l /tonne
Spraying	3 l /ha	Road Cartage	0.079 l /tonne-km

Table 3.3 Average Fuel Consumption Rates (Diesel) for Agricultural Operations (adapted from McChesney (1981) & Bone et al (1996))

3.4 INDIRECT INPUTS

3.4.1 Fertilisers

Fertilisers are the most significant indirect energy input to most dairy farms. In particular, nitrogenous fertilisers are important due to their high usage and their high energy cost to manufacture. The technique used in this study to estimate the energy use and carbon dioxide emissions for fertiliser manufacture has been to estimate the requirements and emissions for production of one unit each of N, P, K and S by the most typical route. For nitrogen this is assumed to be the ammonia-urea process using natural gas as a feed stock. For phosphorous this is based on mining rock phosphate. Requirements and emissions for potassium have been based on production of KCl and for sulphur on a combination of the Frasch process and industrial by-product recovery.

3.4.1.1 Nitrogenous Fertilisers

Common sources of nitrogen used in the New Zealand dairy industry are urea, ammonium sulphate and compound fertilisers.

In New Zealand, urea is manufactured by Petrochem at Kapuni. Natural gas is used to synthesise ammonia which is then reacted with carbon dioxide to produce urea. Some urea is also imported from the Middle East. Mudahar & Hignett (1987) gave the primary energy input for urea production at around 35 MJ/kg urea based on synthesis of ammonia at around 45 MJ/kg ammonia (Table 3.4). More recent estimates for urea production, using best available techniques (BAT), give a value of around 25 MJ/kg urea (EFMA, 1995b). There is evidence to suggest that this may be more in line with actual production at the Petrochem urea plant, which produces approximately 200,000 tonnes of urea annually and uses about 6 PJ of natural gas. On the basis of these figures a value of 30 MJ/kg urea or 65 MJ/kg N has been used in this report. This includes some allowance for capital and indirect inputs (e.g. buildings, plant, catalysts) above the BAT values.

Table 3.4 Energy Requirements to Manufacture Urea (46 percent N)

IPCC (1996) recommend using a value of 1.6 kg CO₂/kg ammonia produced to account for carbon dioxide emissions from the natural gas feed stock. This value is supported by data from Stout (1990). To this must be added the CO₂ emissions from process heat and electricity generation requirements to manufacture the ammonia. Assuming that the additional energy required for ammonia production (process heat and electricity generation) is 4 MJ per kg NH3 (EFMA, 1995a) this results in additional emissions of 0.21 kg CO₂/kg NH3 or approximately 1.8 kg CO₂/kg NH3 overall.

Approximately 575 kg of NH₃ is required to manufacture 1 tonne of urea, with consequent emissions of 1.04 tonnes of CO₂. Although some carbon is incorporated into the urea (200 kg of carbon per tonne of urea) this oxidises rapidly on application so is not assumed to be sequestrated. In addition to the emissions associated with the production of the ammonia feed stock, on average an additional 3 GJ of natural gas is required per tonne of urea for process heating (EFMA, 1995b). This results in an additional 158 kg CO₂ per tonne of urea (based on 0.0527 kg CO₂/MJ for natural gas). Thus, the total CO₂ emission is 1.2 kg CO₂/kg urea or 2.6 kg CO2/kg N using BAT. In this report a value of 3.0 kg CO₂/kg N has been used, which includes a similar allowance for capital and indirect inputs over BAT, as used for the energy requirement.

3.4.1.2 Phosphate Fertilisers

In New Zealand phosphate has traditionally been applied as single superphosphate or more recently as reactive rock phosphate (RPR). The dairy farms surveyed also used various grades of potash super (particularly in the North Island), sulphur super, diammonium phosphate and a variety of proprietary NPKS mixtures.

Estimates of energy costs of rock phosphate fertiliser vary from about 0.5 MJ/kg to 2.1 MJ/kg fertiliser or 2.1 to 7.1 MJ/kg of P2O5 (Mudahar & Hignett, 1987). Leach (1976) estimated the energy cost of phosphate fertiliser to be 0.33 kg oil equivalent/kg P including mining, concentration, processing, packaging, transport and distribution. This is equivalent to 13.8 MJ/kg P or 5.7 MJ/kg P2O5. In this study a value of 15 MJ/kg P has been assumed.

For the purposes of estimating the carbon dioxide emissions from the production of phosphate fertilisers, it was assumed that energy is primarily supplied from fossil fuels with an average emission coefficient of 0.06 kg CO2 per MJ. There are no fugitive emissions of CO2 associated with the chemical reactions for the production of phosphate fertilisers. On an elemental basis, the average carbon dioxide emission coefficient was assumed to be 0.9 kg CO2/kg P.

3.4.1.3 Potassium

Mudahar & Hignett (1987) estimated that the world average energy use for potash production is 3.8 MJ/kg or 6.4 MJ/kg of K2O. Dawson (1977, 1978) obtained values of 5.1 MJ/kg of KCl and 9.7 MJ/kg of K. In this study, values of 5 MJ/kg of KCl or 10 MJ/kg of elemental K were used. Correspondingly CO2 emissions are 0.3 kg CO2 per kg of KCl, or 0.6 kg CO2/kg elemental K.

3.4.1.4 Sulphur

Dawson (1977, 1978) obtained an energy value of 5.3 MJ/kg sulphur. Mudahar & Hignett (1987) calculated values ranging between 7.4 MJ/kg, for sulphur from the Frasch process and no energy change, where the sulphur is recovered from other industrial processes. In this study, a value of 5 MJ/kg of S is used with corresponding CO2 emissions of 0.3 kg CO₂/kg S.

3.4.1.5 Compound Fertilisers

A wide range of proprietary brand fertilisers is available in New Zealand. Many of these are produced by blending, although a few such as ammonium sulphate, diammonium phosphate and superphosphate are produced chemically. In this study energy requirements and carbon dioxide emissions for the production of fertilisers have been determined by multiplying the basic energy and emission factors for N P K and S described above (Table 3.5), by the percentage of these elements in the final fertiliser. This simple technique produced results slightly greater than those reported in the literature but include allowances for capital and indirect energy inputs.

The energy requirement for manufacturing ammonium sulphate was reported by Mudahar & Hignett (1987) as 12.2 MJ/kg fertiliser. Using the energy coefficients yields a value of 14.9 MJ/kg fertiliser, 22 percent greater than reported but in line with the 20 percent extra allowance over BAT for capital and indirect energy inputs included in the urea coefficient.

Mudahar & Hignett (1987) report the energy requirement for the manufacture of single superphosphate (9 percent P) are around 1.7 MJ/kg fertiliser. Dawson (1977, 1978) obtained a value of 1.8 MJ/kg. Using the energy coefficients gives a value of 2.0 MJ/kg fertiliser (12 percent greater). Similarly the value calculated for triple superphosphate (21 percent P) is 3.8 MJ/kg fertiliser compared to values of 1.2 to 4 MJ/kg reported by Mudahar & Hignet (1987) depending on the source of phosphoric acid.

Element	Energy Coefficient (MJ/kg element)	CO2 Emission Factor (kg CO2/kg element)
Nitrogen (N)	65	3.0
Phosphorous (P)	15	0.9
Potassium (K)	10	0.6
Sulphur (S)	5	0.3

Table 3.5 Energy Coefficients and Carbon Dioxide Emission Factors for Fertiliser Elements

Energy requirements for the production of diammonium phosphate (DAP) vary depending on the process used to make the phosphoric acid intermediary. For

DAP, Mudahar & Hignett (1987) calculated values of 13.2 MJ/kg fertiliser (dihydrate, dry rock feed) and 9.7 MJ/kg fertiliser (hemihydrate, wet rock feed). DAP fertilisers available in New Zealand (Burtt, 1997) have a typical analysis of 18 percent N, 20 percent P and 2 percent S. Thus the energy coefficient used in this study, calculated from the energy coefficients in Table 3.5, is 14.8 MJ/kg DAP. This is 12 percent and 52 percent greater than the reported values for dihydrate and hemihydrate DAP respectively. However, the extra allowance is justifiable in terms of capital and indirect inputs and international transport.

3.4.1.6 Lime and Dolomite

Dawson (1977, 1978) estimated the energy cost of agricultural lime in New Zealand to be 2.1 MJ/kg product. Mudahar & Hignett (1987) estimated 0.53 MJ/kg of product for ground limestone world-wide. Quantities of burned or hydrated lime used in agriculture were assumed to be negligible. For the purposes of this study a value of 0.6 MJ/kg was assumed.

The carbon dioxide emission associated with mining and crushing is 0.036 kg CO₂/kg limestone, based on 0.06 kg CO₂/MJ of fossil fuel used. On reaction with the soil, or during the burning/hydration process, carbon dioxide is evolved at a rate of 0.44 kg CO₂/kg of CaCO3 (IPCC, 1996). Therefore, assuming limestone of 90 percent purity, the total carbon dioxide emission is assumed to be 0.43 kg CO2/kg lime applied.

Mudahar & Hignett (1987) also estimated an energy cost of 0.53 MJ/kg of dolomite. For the purposes of this study a value of 0.6 MJ/kg was assumed. Using the IPCC (1996) methodology the total carbon dioxide evolution will be 0.47 kg CO₂/kg dolomite. This is made up of 0.036 kg CO₂/kg from fossil fuels in mining and processing and 0.429 kg CO₂/kg fugitive emissions from soil reactions (0.477 kg CO₂/kg dolomite ( 90 percent purity). On the basis of 90 percent purity approximately 12 percent of the dolomite is magnesium. Therefore, the energy requirement is approximately 5 MJ/kg Mg and the carbon dioxide emission is 3.9 kg CO2/kg Mg.

3.4.2 Agri-chemicals

A number of different classes of agri-chemicals are commonly used on dairy farms, including acid and alkalis for cleaning, herbicides, animal supplements such as magnesium and zinc, and animal health remedies.

Stout (1990) presented data on the energy requirement for manufacturing herbicides from a number of sources. Green (1978) supplied similar data. From this an average requirement of about 270 MJ/kg of active ingredient can be derived including allowances for production, packaging and transport. A random survey of product available on the New Zealand market gave an average concentration of around 50 percent, that is 500 g active ingredient per litre or kilogram of product. Thus in this study herbicides are assumed to require 135 MJ/kg of product used.

Acids and alkali rinses, used to clean dairy milking equipment, were assumed to have an energy requirement of 10 MJ/kg based on the requirements of producing industrial phosphoric acid (Mudahar & Hignett, 1987) and nitric acid (Stout, 1990). As with herbicides, average commercial product concentrations are around 50 percent active ingredient per unit of product, making the energy requirement 5 MJ/kg product.

An energy cost of 5 MJ/kg was assumed for animal supplements such as magnesium and zinc, based on the price of these minerals relative to agricultural fertilisers and chemicals with known energy contents. This is also consistent with data on the cost of magnesium in the form of dolomite (see section 3.4.1.6).

Animal health remedies and any other chemicals used were assumed to have an average energy requirement of 220 MJ/kg active ingredient (Wells, 1998) and 50 percent concentration.

For all agri-chemicals the carbon dioxide emission factor was taken to be 0.06 kgCO2/MJ assuming that all energy used in production, packaging and distribution is derived from fossil fuels. Energy coefficients and carbon dioxide emission factors for agri-chemicals used in this study are summarised in Table 3.6.

Agri-chemicals	Energy Coefficient (MJ/kg active ingredient)	CO2 Emission Factor (kg CO2/kg active ingredient)
Generic Herbicide	270	16.2
Acids and alkalis	10	0.6
Animal supplements (e.g. magnesium, zinc)	5	0.3
Animal remedies (e.g. drench, bloat aids)	220	13.0
Other chemicals	220	13.0

Table 3.6 Energy Requirements and Carbon Dioxide Emissions from Manufacture, Packaging and Distribution of Agri-chemicals

3.4.3 Seed

In New Zealand dairy farm systems, seed inputs are required for pasture renewal. Species used are primarily grasses and clovers. Occasionally brassica species, such as turnips or kale, are used as an intermediate crop in the pasture renewal process. Green feed maize is also planted in some areas.

In determining the energy coefficient of seed it is necessary to distinguish between the metabolizable energy content of the seed (the output) and the energy required to grow the seed (the input). For this study, where seed is being considered as an input to the dairy system, the latter is the appropriate measure, i.e. the amount of energy required to grow the seed excluding solar energy inputs.

A recent study in Canterbury (Muscroft-Taylor, pers. com.) determined energy requirements of 8 to 15 MJ/kg seed for pasture species. Dawson (1977, 1978) found the energy cost of seed dressing to be 0.15 or 0.6 MJ/kg seed for plain and coated seed respectively.

On this basis an average energy coefficient for seeds of 10 MJ/kg was used. The corresponding carbon dioxide emission coefficient is 0.6 kg CO2/kg seed assuming that the predominant inputs are liquid fuels and fertilisers having an average emission coefficient of 0.06 kg CO2/MJ.

3.4.4 Bought-In Animal Feed Supplements

The energy requirement of bought-in supplementary feeds was determined based on the marginal cost of producing the feed. In the case of silage and hay this was calculated by considering the energy cost of replacing the fertiliser nutrients removed with the silage, the direct energy cost to harvest the crop and, in the case of maize, to establish it, plus an allowance for agri-chemicals. The same methods were used to determine the energy content of any surplus feed that was sold off the farm.

3.4.4.1 Grass Silage

Fertiliser recommendations for grass silage (McLaren & Cameron, 1996) are 5 kg of P, 20 kg of K and 3 kg of S per tonne of dry matter. This corresponds closely to the amount of nutrient removal in the silage, based on a typical leaf analysis (McLaren & Cameron, 1996). Removal of nitrogen will be around 50 kg per tonne of dry matter, however a proportion of this will come from fixation by clover. It was assumed that only 25 percent of the nitrogen removed is replaced by fertilisers. Harvest costs of grass were calculated assuming 3 t DM/ha or 10 wet tonnes/ha (Fleming & Lucas, 1996).

Energy requirements for grass silage production, excluding transport are summarised in Table 3.7. From this it was estimated that the energy cost of bought-in grass silage is 1,500 MJ/tonne of dry matter. The associated carbon dioxide emission is 87 kg CO2/tDM or 0.058 kgCO2/MJ. Energy requirements for balage were calculated assuming one-third tonne dry matter per bale or 500 MJ/bale.

Input	Input or Use	Energy Coefficient	Energy per tonne of Dry Matter (MJ/t DM)	Carbon Dioxide Coefficient	Carbon Dioxide Emission (kg CO2/t DM)
Fertiliser
Nitrogen	12.5 kg N/t DM	65 MJ/kg	813	3.0 kg CO2/kg N	37.5
Phosphorous	5 kg P/t DM	15 MJ/kg	75	0.9 kg CO2/kg P	4.5
Potassium	20 kg K/t DM	10 MJ/kg	200	0.6 kg CO2/kg K	12.0
Sulphur	3 kg S/t DM	5 MJ/kg	15	0.3 kg CO2/kg S	0.9
Other operations
Mowing-Conditioning	3 t DM/ha	280 MJ/ha	93	0.0808 kg CO2/MJ	7.5
Forage Harvester	0.3 t DM/t	93 MJ/t	310	0.0808 kg CO2/MJ	25.0
Total			1,506		87.4

Table 3.7 Energy and Carbon Dioxide Emission Costs of Grass Silage Production

3.4.4.2 Maize Silage

The energy cost of maize silage production was calculated in a similar manner, with the addition of ground preparation and seeding costs. Recommendations for base nitrogen application are 10 kg N per tonne of dry matter (Pioneer Genetics Tech Ltd, pers. com.). For this study it was assumed that 50 percent more nitrogen will be applied above base levels. Other nutrients were assumed to be applied in similar quantities to that for grass silage. Cultivation and seeding requirements were assumed to include plough, cultivation, power harrow (2 passes), roller, and drill. Maize yield was assumed to be 20 t DM/ha or 60 wet tonnes/ha.

Table 3.8 shows that the energy cost of maize silage is only marginally higher than grass silage. A value of 1,650 MJ/t DM was assumed for the study. Note that the associated carbon dioxide emission is 0.057 kg CO2/MJ compared to 0.058 calculated for grass silage or 0.06 recommended by the IPCC (1996) for fossil fuels. As a result a value of 0.058 kg CO2/MJ has been assumed for all supplementary feeds.

Table 3.8 Energy and Carbon Dioxide Emission Costs of Maize Silage Production

3.4.4.3 Hay

The energy requirement for hay was determined from the energy cost of grass silage by assuming a similar energy cost per tonne of dry matter. This assumes that additional operation costs such as tedding are counteracted by the lower transport cost due to lower water content. Thus, the energy cost of a conventional 'small' bale will be 30 MJ assuming 20 kg of dry matter per bale. Round bales were assumed to be equivalent to 12 conventional bales (240 kg dry matter and large rectangular bales equivalent to 15 conventional bales (300 kg DM).

A lower value of 1000 MJ/t DM was assumed for cereal straw given the lower nitrogen removal rate compared to grass or maize.

3.4.4.4 Cereals

Nguyen & Haynes (1995) measured the energy requirement to grow large seeds (wheat, barley, and peas) in Canterbury. Their measurements included direct and some indirect inputs but did not include capital energy. Input energy requirements were found to range between about 1.5 and 1.0 MJ/kg of seed output. Muscroft-Taylor (pers. com.) determined the energy input cost of wheat grown in Canterbury to be around 2.5 MJ/kg of grain. For this study a value of 2500 MJ/tonne of ground meal was assumed. Note that this equates to 2900 MJ/t DM assuming 14 percent moisture content and is thus roughly twice that of grass silage.

3.4.5 Grazing-Off

A number of farms in the survey grazed some or the entire herd off the property (that is on land other than the milking platform or run-off) for some period of the year. The energy requirement of maintaining these animals off the property was accounted for in the following way.

The daily dry matter requirement of the livestock was assumed to be 0.015 kg DM per day per kg of live-weight (Fleming et al, 1996). From this the total dry matter requirement was calculated for each class of stock from the number of animals and their average live-weight. The live-weight of young stock was calculated as a percentage of the average live-weight of the mixed age cows in the herd using the data in Table 3.9. It was further assumed that the pasture growth rate for hill country and dry-land over the whole of New Zealand averaged out at 15 kg DM/ha/day (Fleming & Lucas, 1996). From this the area of pasture required for each class of livestock could be calculated. This was then reduced according to the length of time that the animals were off-farm. The total primary energy requirement for this type of pasture was assumed to be 2 GJ per hectare per annum (McChesney et al, 1982).

This process is best illustrated by an example. Assume 100 rising two-year-old heifers are grazed-off for 26 weeks. If the average live-weight of the mixed age herd is 400 kg per cow then the rising two-year-old stock will have an estimated live-weight of 300 kg (Table 3.9). Therefore, the feed requirement of all the 100 animals will be 450 kg DM/day. This corresponds to an area of 30 hectares, on the assumption of average pasture growth of 15 kg DM/ha/day during the grazing period. Since the animals only occupy this area for 26 weeks the occupancy is 15 ha per annum, and the energy requirement will be 30 GJ.

 

Age Class	Live-weight compared to Mixed Age Cows (%)
Mixed Age Cows (MAC)	100
Rising 2 year old Heifers (R2y)	75
Rising 1 year old Heifers (R1y)	35
Calves	5
Bulls	120

Table 3.9 Live-weight as Percentage of Average Live-weight of Mixed Age Cows (after Church & Pond, 1988; Fleming et al, 1996)

It is acknowledged that there are a number of limitations with this methodology including variability of pasture growth rates between districts and season, and whether stock are on maintenance or weight gain diets. However, it was felt that this simple methodology would at least give a first estimate of the energy requirements for grazing-off. Note that transport of stock between the farm property and the grazing-off site is accounted for separately.

3.4.6 Aggregate

On some farms, aggregate was purchased annually for race maintenance. Where this occurred it was included as an annual indirect energy cost. All forms of aggregate were assumed to have a bulk density of 1500 kg/m3, an energy coefficient of 0.1 MJ/kg (Baird et al, 1997), and a carbon dioxide coefficient equal to that of diesel (0.0808 kg CO2/MJ).

3.5 CAPITAL ENERGY INPUTS

For all capital items the same general methodology was followed. This involved estimating the total mass of each component of each item of capital and multiplying by an appropriate energy coefficient that represents the sum of embodied⁴, manufacturing and maintenance energy costs. The annual capital energy charge to the property is then calculated by dividing by the expected working life of the item by assuming straight-line depreciation.

Carbon dioxide emissions are determined in a similar manner by assuming that the carbon is emitted over time, rather than all in one go at the time of manufacture, or purchase. This was considered to be the fairest way of accounting for the carbon emissions of the enterprise over time. If all emissions were attributed to the enterprise at the time of purchase, this would mean that the indicators could vary widely from year to year depending on the level of capital purchases occurring. This would be particularly marked during the start-up phase of a dairy conversion.

It should be noted that figures obtained for carbon emissions in this report should not be used as part of national greenhouse gas emission calculations as this would result in double counting since they are already accounted for in consumer energy supply. The carbon emission indicators have only been designed to allow comparison between individuals or groups of enterprises.

3.5.1 Self-propelled Vehicles

Self-propelled vehicles on dairy farms fall into four main categories: tractors, trucks, utilities and motor bikes. Dawson (1977, 1978) found values of 165 MJ/kg and 162.5 MJ/kg for tractors and combine harvesters respectively in New Zealand although other estimates are usually lower than this. For example, Doering (1980) gave a value of around 70 MJ/kg for American farm vehicles and Stout (1990) gave 85 MJ/kg as an international average. McChesney et al (1978) used a value of 90 MJ/kg but added 60 percent for repairs and maintenance over the life of the vehicle to arrive at a total of 144 MJ/kg. This is closer to the figure of 159 MJ/kg used by Roller et al (1975). For all vehicle types in New Zealand the capital energy cost was assumed to be 160 MJ/kg tare weight. This includes the embodied energy of the raw materials, the fabrication energy, an allowance for repairs and maintenance, and international freight.

To calculate the carbon dioxide emissions it was assumed that on average the manufacture of all components requires inputs of fossil fuel energy with an average emission factor of 0.07 kg CO2/MJ. In addition the IPCC (1996) guidelines recommend allowing additional emissions of 1.6 kg CO2/kg of steel and iron products due primarily to the oxidisation of coke during the smelting process. As the majority of the mass of motor vehicles is steel, the carbon emission coefficient for vehicles was calculated by multiplying the energy coefficient (160 MJ/kg) by 0.07 kg CO2/MJ and adding 1.6 kg CO2/kg. This results in an overall emission factor of 12.8 kg CO2/kg vehicle weight or 0.08 kg CO2/MJ.

The assumed useful working lives of the four classes of farm motor vehicles are given in Table 3.10. These values are consistent with McChesney et al (1978).

 

Capital Item	Energy Coefficient	Carbon Dioxide Emission Factor	Working Life (years)
Tractors	160 MJ/kg	12.8 kg CO2/kg	15
Heavy Trucks	160 MJ/kg	12.8 kg CO2/kg	15
Light Trucks/Utilities	160 MJ/kg	12.8 kg CO2/kg	15
Motor Bikes	160 MJ/kg	12.8 kg CO2/kg	10
Farm Implements	80 MJ/kg	7.2 kg CO2/kg	20

Table 3.10 Energy Coefficients, Carbon Dioxide Emission Factors and Assumed Working Life of Motor Vehicles and Farm Implements

Rather than compile a list of all tractors encountered in the survey and their mass an alternative method was developed to estimate the mass of the vehicle based on the rated power output. Most farmers know the rated power of their machines or these can be obtained from dealer information if required. Rated power was expressed in horsepower (hp) rather than kilowatts (kW) as most farmers and dealers are still more familiar with this unit of measuring power.

To develop the methodology, specifications of power and mass for 149 tractor models available in New Zealand were obtained from dealers. This included 49 two wheel drive (2WD) models and 100 four wheel drive (4WD) models. This data is plotted in Figure 3.1. A linear regression was fitted through all the data with an R2 of 94 percent.

Mass = 40.8 Power + 190

(All tractors)

where mass is in kilograms and power is rated engine output in horsepower.

Figure 3.1 Relationship between Rated Power and Mass of Tractors

Since individual regressions of 2WD and 4WD tractors did not improve the fit it was decided to use the above equation for all tractor types. This equation

underestimates the mass of 4WD tractors by about 40 kg and overestimates the mass of 2WD tractors by about 50 kg. However, this is not significant except for small tractors under about 25 hp of which there are only a limited number in use.

3.5.1.2 Light Trucks and Utilities

Using information published periodically by the Automobile Association on the price and specification of new vehicles is was found that the mass of most modern farm utilities (single and double cabs of between 2 and 3 litres engine capacity) ranges between 1300 and 1500 kg. In this study an average mass of 1400 kg has been used for each utility.

3.5.1.3 Motorbikes

All but four of the farms surveyed owned at least one two-wheel motorbike or four-wheel quad bike. A survey of 13 popular makes of quad bike, popular with farmers, showed that the average mass (tare weight) was 190 kg. It was further assumed that the average two wheel motor bike would have a mass of 90 kg.

3.5.1.4 Heavy Trucks & Other Self Propelled Machinery

Obtaining the tare weight (mass) of heavy trucks was straightforward as, by law, it is written on the side of the vehicle. Only 15 of the farms surveyed owned a heavy truck and five owned other self propelled vehicles such as a grader or forage harvester. The mass of these was recorded on an individual basis.

3.5.2 Tractor Powered Implements

Dawson (1977, 1978) derived energy coefficients for New Zealand farm machinery of 75 MJ/kg. In the USA, Doering (1980) gave an example equivalent to 80 MJ/kg. In this study a value of 80 MJ/kg was used. The corresponding carbon dioxide emission coefficient is 7.2 kg CO₂/kg or 0.09 kg CO₂/MJ based on the same formula used for motor vehicles. The assumed working life for implements was 20 years.

Implement	Number in Survey	Average Mass (kg)	Implement	Number in Survey	Average Mass (kg)
Mower-Conditioner	129	500	Plough	27	1500
Forage Harvester	24	400	Discs	42	1500
Silage Feed Wagon	99	1600	Cultivator	51	1000
Bale Feeder	13	500	Harrows	74	200
Front-end Loader	148	500	Roller	80	1500
Fertiliser Spreader	126	200	Drill	34	2000
Sprayer	110	100	Trailer	30	1000
Hay Rake	102	500	Post Rammer	8	500
Hay Baler	30	2000	Grader Blade	6	500

Table 3.11 Number and Average Mass of Implements found on Surveyed Dairy Farms

The most common implements owned included: a mower, a silage feed-out wagon, a fertiliser spreader, a front-end loader and sometimes a roller. Few farms owned their own cultivation and seeding equipment (plough, discs, cultivators, and drill) preferring to use contractors for pasture renewal.

Using data from Wells (1998) and the Phase 1 survey average masses for each type of implement were determined to the nearest 100 kg. These are shown in Table 3.11 along with the number of each type of implement actually encountered in the survey.

3.5.3 Dairy Shed

Wells (1998) carried out a detailed analysis of the capital energy required for the construction of a dairy shed including: yards, yard railings, backing gates, roof, walls, floor of the milking area and the milk room, tanker pad, vat stand, water tanks and milking plant. From the 13 milking sheds involved in the pilot survey it was found that the total capital energy was strongly correlated to the number of sets of milking cups (Figure 3.2). This relationship is:

Capital Energy (GJ) = 24.2 Sets of Cups + 293

From the same data it was found that the carbon dioxide emission coefficient was 0.1 kg CO₂/MJ. This is higher than the average carbon dioxide emission factors for fossil fuels due to the fugitive emissions associated with the production of cement and smelting of iron. Dairy sheds were assumed to have a working life of 20 years.

 

Figure 3.2 Capital Energy of Dairy Shed as a Function of the Number of Sets of Cups

3.5.4 Other Buildings

The energy and carbon dioxide emission costs of other farm buildings were determined based on the cost of dairy shed roofing systems. Most other buildings encountered on the survey farms were hay barns and implement sheds built using the portal frame construction method. Often one or two sides are enclosed with a corrugated steel wall. On average an allowance of 0.5 square metres of wall for every square metre of floor was made. This makes the energy requirement of a typical farm building 590 MJ/m2 of floor. The carbon dioxide emission factor will be 59 kg CO₂/m2 of floor (0.1 kg CO2/MJ).

3.5.5 Farm Tracks and Races

The construction of new farm races was assumed to involve the use of 750 kg of aggregate per metre of race, based on a bulk density of 1,500 kg/m3 for aggregate, an average race width of 5 metres, and aggregate depth of 0.1 metres. The energy value of aggregate was taken to be 0.1 MJ/kg (Baird et al, 1997) with a corresponding carbon dioxide emission coefficient equal to that for the use of diesel fuel. Therefore the capital energy coefficient for farm races is 75 MJ/m. Races were assumed to have a working life of 30 years.

Analysis of data from the pilot survey revealed that the length of races could be estimated based on the average paddock size (degree of subdivision) and farm area using the following formula:

where	R = length of races (km)
	A = farm area (ha)
	N = number of paddocks

For example a 100 ha property divided into 25 paddocks of 4 ha each would have approximately 2.2 kilometres of races.

On most properties race maintenance was also carried out on an annual basis. In many cases this involved use of farm vehicles and aggregate from on-farm sources. In these cases energy use would be accounted for in farm fuel use. Where contractors carried out race maintenance or it involved purchase of aggregate from off-farm sources this was accounted for under indirect costs (Section 3.4.6).

3.5.6 Fences

Wells (1998) presented a detailed analysis of the capital energy costs of fencing. For this study it has been simplified as follows. All boundary fences were assumed to be seven wire post and batten with a capital energy coefficient of 20 MJ/m length. Internal fences were assumed to be three wire electric with an energy coefficient of 4.5 MJ/m length. The carbon dioxide emission factor is 0.09 kg CO2/MJ and working life were assumed to be 25 years for boundary fences and 15 years for internal fences.

The length of boundary fencing was estimated for each property using data from the pilot study from which the following formula was derived:

where the boundary fence length B is in kilometres and farm area A is in hectares

The length of the internal fences was estimated using the relationship developed by Wells (1998):

where	I = length of internal fences (km)
	A = total farm area (ha)
	N = number of paddocks
	R = length of internal races (km)

3.5.7 Stock Water Supply

Analysis of the pilot study data (Wells, 1998) revealed that the average capital energy coefficient for stock water systems was 2.1 GJ/ha with an associated carbon dioxide emission factor of 150 kg CO2/ha or 0.07 kg CO2/MJ. Allowance was made for pipe, trenching, troughs and fittings, water storage tanks, well drilling and pumps. The useful working life of the stock water supply was assumed to be 30 years.

3.5.8 Irrigation

Two basic types of irrigation system were considered, border strip and spray irrigation systems.

3.5.8.1 Border Strip

The energy cost of border strip irrigation schemes was estimated by Dawson (1977, 1978) to be 25 GJ/ha including all headworks and supply races. This value

was used in this study. A carbon dioxide emission factor of 0.08 kg CO2/MJ was assumed as most of the construction of community irrigation systems involves earthworks by diesel driven machinery. Hence the overall carbon dioxide emission was assumed to be 2,000 kg CO₂/ha. The working life of border strip irrigation was assumed to be 30 years.

3.5.8.2 Spray Irrigation

The energy requirements and carbon dioxide emissions associated with spray irrigation systems were calculated by Wells (1998) and included well drilling, pumps, mainline pipes and trenching, and irrigators. The average energy requirement for travelling irrigator systems was found to be 13.5 GJ/ha and for centre pivot systems 12.5 GJ/ha. Other systems such as big guns, and long line lateral were assumed to be the same as a centre pivot. The average carbon dioxide emission factor for spray irrigation systems was found to be 0.06 kg CO₂/MJ. All spray irrigation systems were assumed to have a working life of 30 years.

3.5.9 Drainage

Energy and carbon dioxide emissions were determined for three common types of drainage system on a per hectare basis by Wells (1998). The energy requirement of open drains was estimated to be 50 MJ/m or 5 GJ/ha assuming 100 m of drain per hectare on average. The average working life of open drains was assumed to be 50 years.

Pipe drainage systems, using either clay tiles or plastic drain coil, were estimated to have an energy requirement of 40 GJ/ha and a working life of 30 years. The energy cost of mole drainage systems was determined to be 16 GJ/ha for the collector drains, with a 30-year life, plus 1.7 GJ/ha for the moles, with an average life of 5 years.

Hump and hollow drainage was assumed to require 25 GJ/ha given that a similar amount of earth moving is required per hectare for the development of hump and hollow drainage as for the grading of borders in a border strip irrigation system. Hump and hollow drainage was assumed to have a useful working life of 50 years.

The average carbon dioxide emission factor for all drainage systems was assumed to be 0.08 kg CO₂/MJ given the high proportion of earth moving that would be required using diesel power vehicles.

3.5.10 Effluent Disposal

Two basic types of effluent disposal system are commonly found on New Zealand dairy farms, land application and a combination of anaerobic and aerobic ponds or ditches.

Anaerobic and aerobic ponds are sized by herd size and region (Heatley, 1995). Recommendations for anaerobic ponds range from about 4.5 m3 per cow in the north of New Zealand to 6.5 m3 per cow in the south. An average value of 5 m3 per cow was assumed for this study. It is further assumed that for each cubic metre of pond volume only half a cubic metre of material must be moved as the excavated material can be used to build the batters of the pond. It was also assumed that each cubic metre of material moved is equivalent to two tonnes at an energy cost of 0.1 MJ/kg including compaction of the batters. Thus the energy requirement is 100 MJ/m3 of pond or 500 MJ/cow.

For aerobic ponds, a surface area of 4.8 m2 per cow is recommended in all regions of New Zealand with a depth of 1.2 metre and free board of 500 mm. It is assumed that each square metre of pond will require the removal of one cubic metre of soil, the remaining depth being made up by building the batters above ground level. Thus two tonnes of material must be moved at an energy cost of 200 MJ/m2 of pond or 960 MJ/cow.

Recommendations for sizing barrier ditch systems are similar to those for anaerobic ponds, approximately 4.5 m3 per cow plus an allowance for rainfall (Heatley, 1995). Therefore the energy requirements have been taken to be the same as for anaerobic ponds, that is 500 MJ/cow.

For land based effluent disposal systems a holding pond is required. The size will depend on the number of cows and the region (Heatley, 1995). Holding pond requirements are given in Table 3.12.. Energy requirements for holding ponds were assumed to be the same as for anaerobic ponds, that is 100 MJ/m3, or 160 to 690 MJ/cow depending on region.

Region	Storage Period (months)	Volume Requirement (m3/cow)
Canterbury, North Otago	1	1.6
Northland, Auckland, Nelson, Marlborough	2	3.4
Waikato, Taranaki, Gisborne, Hawke’s Bay, Wellington, Tasman, Southland, South Otago	3	5.0
Bay of Plenty, Manawatu, Wanganui, West Coast	4	6.9

Table 3.12 Holding Pond Requirements for Land Based Dairy Effluent Treatment

The energy requirements of the other components of land based effluent systems were calculated as for big gun irrigation systems (see section 3.5.8) less the allowance for well drilling. This worked out to be 10 GJ/ha with an allowance of 0.04 ha per cow (Heatley, 1995) or 400 MJ/cow.

All components of effluent treatment systems were assumed to have a 30 year working life and an average carbon dioxide emission coefficient of 0.08 kg CO₂/MJ given that a significant proportion of the capital energy requirement would be from earth works using diesel powered machinery. Pond maintenance (removal of sludge) was not include but is not considered to be a significant energy contribution over the life of a pond.

⁴ Embodied energy is defined as the energy to mine and process raw materials to a state ready for use in manufacturing, eg steel billots, plastic resins.

5 In the 1997/98 year only 57 percent of the total primary energy used to generate electricity in New Zealand came from renewable resources (hydro, geothermal, wind etc).

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