2 Introduction

2.1 BACKGROUND

In general, New Zealand farmers practise a form of 'industrialised' agriculture that relies on relatively high inputs of fossil fuels, not only to power machinery directly but also for the manufacture of artificial fertilisers and agri-chemicals. While modern agricultural practises have overcome the limitations of 'pre-industrial' agriculture and enabled the feeding of an increasingly urban population, they have also contributed to the degradation of the environment through nutrient run-off, soil salination, greenhouse gas emissions and loss of bio-diversity.

The price of increased agricultural productivity has been increased energy dependency, particularly dependency on fossil fuels. For example, traditional rice culture in the Philippines has an annual energy requirement of around 173 MJ/ha for a yield of 1,250 kg/ha or 0.14 MJ/kg of rice (Stout, 1990). By comparison, modern rice culture in the United States requires an annual energy input of 64,885 MJ/ha for a yield of 5,800 kg/ha or 11.19 MJ/kg. Thus, although the modern system is 4.6 times more productive per hectare it requires 79 times the energy use per kilogram of product. Similar comparisons for maize production reveal a five-fold increase in productivity but a 33-fold increase in energy use per unit of production.

Added to this is the higher energy cost of food products derived from animals compared to plants. People in developed countries not only have higher calorie intakes than their least developed counterparts; they also derive more of these calories from animal sources. Pimentel (1997) estimated that in the United States the average energy cost of protein is 28 MJ of fossil energy per 1 MJ of animal protein compared to 3.3 MJ of fossil energy per 1 MJ of plant protein. Thus 'industrialised' agriculture is more likely to be susceptible to shortages or increasing prices for fossil energy in the future.

New Zealand is heavily dependent on exports of food and fibre products to earn overseas exchange. Despite changes in the nature of the New Zealand economy in the last thirty years, agriculture remains the most important industry with food and fibre exports accounting for nearly 50 percent of our exports by value (Figure 2.1). Traditional exports of wool, dairy and meat products continue to dominate, making up over a third of total export value, with dairy products being the dominant export commodity.

Figure 2.1 New Zealand Exports for the Year Ended 31 December 1999 (Provisional = NZ$22.5 billion fob) (Statistics NZ, 2000)

Figure 2.1 New Zealand Exports for the Year Ended 31 December 1999 (Provisional = NZ$22.5 billion fob) (Statistics NZ, 2000)

 

2.1.1 Environmental Issues

Against this background New Zealand farmers must now operate within a climate of increasing environmental awareness, both nationally and globally. This can be view as either a threat or an opportunity. Arguably the most significant development has been the Resource Management Act (RMA), enacted in 1991, to promote the sustainable management of natural and physical resources in New Zealand.

Within the RMA natural and physical resources are defined to be:

"...land, water, air, soil, minerals and energy, all forms of plants and animals (whether native to New Zealand or introduced) and all structures."

The Ministry for the Environment (MfE) must monitor the effect and implementation of the RMA. To achieve this a core set of environmental indicators is being developed as a measure of the environmental 'health' of our ecosystems (MfE, 1995, 1996). This reflects a world-wide trend in the development of environmental indicators, including indicators for energy use. The proposed indicators for the environmental effect of energy in New Zealand (MfE, 2000) are general in nature, with only 10 pressure indicators to summarise the national energy system. Thus there is no disaggregation of individual industries. This report focuses on developing detailed indicators at an industry level.

2.1.2 Trends in the New Zealand Dairy Industry

There have been a number of significant trends in the New Zealand dairy industry over the last two decades, such as the increase in average herd size from 126 cows per herd in 1980/81 to 229 in 1998/99. Over the same period the number of herds declined from 16,089 to 14,362 but the total number of dairy cows increased from 2.0 million to 3.3 million (Figure 2.2), a steady increase of about 66,000 cows per annum.

Figure 2.2 Trends in New Zealand Dairy Herd Size and Number

Figure 2.2 Trends in New Zealand Dairy Herd Size and Number

Accompanying the increase in average herd size there has been only a small increase in the average dairy farm size (including run-offs) from 69 ha in 1972/73 to 80 ha in 1994/95 (Taylor, 1996). The net result has been an increase in stocking density from about 1.8 cows/ha to 2.4 cows/ha, over the same period. The overall area occupied by dairy farming decreased from 1.34 million ha to 1.07 million hectares by 1992, reflecting a considerable loss of dairy land (20 percent) to horticulture and other agricultural enterprises, particularly during the 1980s when dairy farmers received lower subsidies than other agricultural sectors and lower milk payouts.

The increase in average farm size has been attributed to a combination of farm amalgamations and exiting of smaller operations from the industry. The last decade has seen an increase in the total land area occupied by dairy farms, 1.2 million ha by 1994/95, as a result of conversions both on the fringes of established dairying areas and into areas such as Canterbury and Southland where dairying was not previously common. In the last three years there has been a decrease in the total number of suppliers (Figure 2.2). Possible reasons for this include continued amalgamation, slowing down in the rate of new conversions, and continued exiting of smaller and less economic units.

Figure 2.3 Historical Distribution of Dairy Cattle by Region

Figure 2.3 Historical Distribution of Dairy Cattle by Region

Figure 2.3 shows the trend in dairy cattle numbers for various regions over the last decade. The most noticeable trend is that dairy cattle numbers have remained relatively static or even declined in the traditionally important dairy regions (Northland, Auckland, Waikato, Taranaki) while numbers in other regions have increased. Numbers in Canterbury have more than doubled in a decade, while numbers in Otago, Southland and the rest of the South Island have quadrupled.

Accompanying the changing distribution of dairy cattle numbers is a changing regional distribution of milk production. This is particularly marked between the North and South Islands. In 1994/95 the South Island produced only 14 percent of the total New Zealand milk production (103 million kilograms of MS). By 1998/99 this had risen to 21 percent of the national total (179 million kilograms of MS) a 73 percent increase (NZDB, 2000). During the same period production in the North Island only rose by about 6 percent. Thus most of the increased production is coming from the South Island and from Canterbury and Southland in particular. The move to Canterbury and Southland is largely explained in terms of availability and the relatively low cost of land. In 1996 real prices for dairy land in Canterbury were about 55 percent of those in the Waikato (Taylor, 1996).

Figure 2.4 shows the trends in total milk solids production since 1981. This indicates an average increase in production of about 20 million kilograms of milk solids per year over the last two decades as a result of rising cow numbers. Average milk solids production per cow has varied between about 250 and 300 kgMS/cow, most likely as a result of seasonal effects (weather and grass growth), but the average has not changed significantly over the period.

Figure 2.4 Trends in Annual Milk Solids Production

Figure 2.4 Trends in Annual Milk Solids Production

In summary the major trends in the New Zealand dairy production industry over the last twenty to thirty years have been:

  • a steady increase in the total number of dairy cows and total production (which peaked in 1997/98);
  • a steady decrease in the total number of suppliers and the total land area occupied;
  • a steady increase in the average herd size, stocking density and therefore production per hectare; and
  • the majority of new production has come from the South Island (particularly from conversions in non-traditional dairy areas such as Canterbury and Southland).

2.2 PREVIOUS RESEARCH

In the decade between 1974 and 1984 a number of research projects where carried out on energy use in the agricultural production and food processing sectors, funded by the New Zealand Energy Research and Development Committee (NZERDC). The first 'oil shock' in 1973 and an awareness of agriculture's dependence on fossil fuels stimulated this research.

2.2.1 Energy Use in Agricultural Production

Hendtlass (1987) reviewed much of the research on energy use in agriculture, carried out by the Joint Centre for Environmental Sciences (JCES). Sims et al (1983) also carried out a detailed study of energy use in New Zealand agriculture with particular emphasis on identifying opportunities for energy conservation.

Stanhill (1984) compared the intensity of energy outputs, fossil fuel energy and labour inputs from a number of national agricultural systems during the 1970s. New Zealand

emerged as a relatively low food output-low fossil fuel energy input system on a par with the United States. No further investigations into energy in agriculture appear to have been carried out until the mid 1990s when energy efficiency in agriculture was reviewed as part of a wider study of opportunities for the adoption of energy efficient technologies across the whole economy (Sims et al, 1996).

A summary of these previous studies reveals a number of key points and apparent paradoxes.

  • Total energy inputs are made up of about one-third direct inputs and two-thirds indirect and capital inputs.
  • Direct inputs are mainly oil-based fuels for transport and field operations.
  • Indirect inputs are dominated by fertiliser use.
  • Other significant indirect inputs are repairs and maintenance, farm services and capital goods.
  • Agriculture is highly dependent on oil both as fuel and in the production of indirect inputs.
  • There is a high level of complacency among farmers about energy saving measures, probably because of the relatively low costs of direct energy within total farm budgets.
  • Total agricultural energy input intensities ([energy/unit area] or [energy/unit production]) and food energy production intensities ([production/unit area] or [food output energy/unit area]) are on a par with those of the United States and are generally lower than European countries.

In 1998 agriculture's share of total consumer energy was just under 5 percent (20.1 PJ out of 428.3 PJ) (MoC, 2000). Delivered energy to agriculture is primarily 50 percent diesel, 30 percent petrol, and 15 percent electricity (EECA, 1996).

Indirect energy associated with the manufacture of farm inputs is also significant. Energy inputs for fertiliser can be estimated from official statistics (Statistics NZ, 2000). Annual use of superphosphate is around 1.5 million tonnes per year or about 3 PJ (assuming an average energy content of 2 GJ/tonne). Other fertilisers account for another 0.5 million tonnes. Assuming that these are primarily nitrogenous, with a high proportion of urea3, then the indirect energy input associated with these is at least 10 PJ (average primary energy input of 20 GJ/tonne manufactured). With lime included, it is assumed that fertiliser manufacture uses about 15 PJ/annum in total.

2.2.2 Energy Use in Food Processing

Paralleling research in the agricultural production sector, similar studies funded by the NZERDC were carried out in the food-processing sector. These were reviewed by Patterson (1984) (also Patterson & Earle, 1985) and updated by Earle (1996). The dairy and meat processing industries accounted for 45 percent and 21 percent of direct energy consumed by the sector and dominate energy use. The third largest direct energy consumer was fruit and vegetables (7 percent). Energy sources are dominated by fossil fuels. In the 1994/95 year, 33 percent of the delivered energy was from coal, 34 percent from gas (natural & LPG) and 10 percent from diesel and petrol. Electricity made up 21 percent of delivered energy.

 

Product

Range of Specific Heat Energy (GJ/t)

Range of Specific Electrical Energy (GJ/t)
Butter

1.7 to 7.9

0.2 to 2.0
Cheese

1.5 to 8.1

0.6 to 3.2
Spray Milk Powders

12.3 to 37.8

1.0 to 2.6
Casein

12.7 to 31.4

1.1 to 4.4
Anhydrous Milk Fat

1.0 to 5.9

0.3 to 2.0
Caseinates

34.5 to 56.0

4.2 to 4.6
Whey Powders

12.6 to 123.1

2.6 to 45.7

Table 2.1 Range of Specific Energy Requirements for Manufacturing Milk Products (after Lovell-Smith & Baldwin, 1988)

Although the energy base of the food-processing sector is more broadly based than the agricultural production sector, it is still reliant on fossil fuels. Specific fuel consumption for production of milk products varies widely among milk processors (Table 2.1), reflecting differences in plant age, size, technology, load and economic factors (Lovell-Smith & Baldwin, 1988). Similarly, in the meat industry, specific fuel consumption varies widely for similar reasons to those listed for dairy processing but also depends on the degree of processing of by-products on site (Earle, 1996)

Increasing energy efficiency in the food processing sector is largely being driven by economic considerations as the industry becomes more competitive, rather than by concerns for preserving energy supplies or mitigating environmental effects (Earle, 1996)

2.2.3 Energy Indicators

Wadsworth (1995) developed a set of indicators of energy sustainability for the New Zealand economy and applied those indicators within the constraints of available data. He concluded that New Zealand was on an unsustainable energy pathway. Patterson (1996) reviewed a range of energy efficiency indicators and methodological problems associated with their operationalisation.

2.3 PURPOSE OF STUDY

The aim of this project was to further develop and test indicators of agricultural sustainability based on total energy inputs. In particular, the study has developed baseline values of energy indicators for the dairy production sector. Concurrent with this project the New Zealand Dairy Research Institute is conducting a similar bench-marking exercise for the dairy-processing sector.

The project supports the Ministry of Agriculture and Forestry's (MAF) goal in the following area:

Work Area 3, Programme 3.4: Maintain and monitor an information base on key indicators of sustainable agriculture and forestry.

This report covers research undertaken as an extension of a pilot study undertaken for MAF Policy (Wells, 1998). In the pilot study a set of indicators (Table 2.2) was developed for the 'on-farm' dairy sector after consulting with a group of industry experts.

1 Total energy input

Mass (or volume) of production

 Baseline comparison of total energy requirement
2 Total energy input

Area of productive land

 Historical baseline indicator of energy intensity
3

a, b, c

 Percentage of direct, indirect and capital energy inputs Possible indicator of sustainability. Relative energy outlay on farm running versus manufacture of inputs and capital items.
4 Percentage renewable energy input Simple measure of sustainability
5 Overall Energy Ratio (OER) =

Total energy input

Total food energy output

 Measure of energy conversion efficiency to food
6 Protein Energy Ratio (PER) =

Total energy input

Protein energy output

 Measure of energy conversion efficiency to protein
7 & 8 Gross & Net CO2 output

Mass (or volume) of production

 Simple measure of environmental effect
9 & 10 Gross & Net CO2 output

Area of productive land

 Simple measure of environmental effect

Table 2.2 Total Energy Indicators for the 'On-farm' level

The indicators were evaluated using a pilot survey of 12 dairy farms (six in Canterbury and six in South Auckland) for the 1996/97 season. The indicators included measures of total energy use per unit of effective milking area (energy intensity) and per unit of milk production. For international comparison measures of energy conversion efficiency in terms of the overall energy ratio (energy input per unit food energy output) and the protein energy ratio (energy input per unit of protein energy output) were included. Other indicators considered the proportion of renewable energy inputs, the mix of direct, indirect and capital energy inputs, and the gross and net carbon dioxide emissions from energy use.

Several potential uses of the indicators are envisaged:

  • as tools for farmers and policy advisers to assess the overall sustainability of agricultural activities;
  • to ensure the continued competitiveness of food and fibre products in international markets; and
  • to provide policy-makers with measures with which to assess the best use of land in the future.

2.4 INDICATORS TO BE USED IN THE PRESENT STUDY

This section summarises the process by which the indicators presented in Table 2.2 were developed. Further discussion of energy indicators can be found in Patterson (1996) and Wells (1998).

In February 1997, a workshop was held with 10 participants from the agricultural and energy sectors to discuss the most appropriate indicators to use in this project. Several people who could not attend the workshop added additional comments. The group decided that this project should primarily focus on defining appropriate indicators for 'on-farm' situations. However, it would be useful to compare the energy associated with various stages of the food and fibre processing chain in broad terms. A diagram to explain this relationship was developed (Figure 2.5).

The boxes on the left represent a number of farm types, while successive boxes to the right represent transport of raw materials to the processing plant, processing, and transport to markets for each product type.

Figure 2.5 Framework for the Development of Energy Indicators for Comparison Between Different Sectors of the Food and Fibre Industries

Figure 2.5 Framework for the Development of Energy Indicators for Comparison Between Different Sectors of the Food and Fibre Industries

For each farm type, it is possible to compare enterprises within the same region (Dimension A) or between different regions (Dimension B). In a similar manner, it may be possible and desirable to compare different farm types (Dimension C).

By aggregating energy indicators along the production-processing pathway for a particular product (Dimension D), it may be possible to compare different sectors on an overall basis (Dimension E). More importantly, it may be possible to compare sectors internationally (Dimension F - not shown). This could be at an on-farm level (essentially an extended Dimension B) or for a particular product (extended Dimension E). Furthermore, any of these comparisons could be made on a temporal basis (Dimension T) as indicators of change (hopefully, an improvement in performance).

This analysis led to a number of points being raised about the desirability and practicality of particular comparisons. More usefully, it also allowed a sensible choice of indicator types to be identified for each dimension.

2.4.1 Dimensions A (Farms in Same Region) and B (Farms in Different Regions)

These dimensions allow the comparison between individual farms, of the same type, on a local, regional or national basis.

The indicators considered to be most appropriate are as given in Table 2.2. Indicators 5 and 6, based on food energy content, were added to the original list to allow comparisons with indicators from international studies. Note that the numerator and denominator in these indicators are reversed compared to the 'traditional' concept of efficiency as output per unit input since it is desired to compare energy use per unit of production. In addition the original carbon dioxide emission indicator has been expanded to include gross and net emissions per unit of productive area (7 and 8) and per unit of production (9 and 10).

It was considered necessary to define all terms precisely and in line with overseas developments where appropriate. The question of comparison with indicators from other countries was also debated. It was decided that this is best handled by clearly defining all underlying data used to calculate indicators, thus allowing recalculation of indicators where necessary to conform with any changes in overseas indicator developments.

2.4.2 Dimension C (Different Farm Types)

There was considerable debate about the necessity to compare different enterprise types at this level and the practicality of doing so. The primary reason would be to test the sustainability of different land use types (e.g. dairying versus forestry). In this case, energy indicators, as part of a suite of environmental, social and economic indicators, could be used to assess the desirability of changing land use patterns in an area. In order to be of much use, the indicators would have to be of the general intensity type (total energy input [or output]/ha, for example Indicator 2, Table 2.2, or of the thermodynamic-economic type (total energy input/$ of output). It would also be useful to compare the percentage of renewable energy inputs and the net CO2 emissions per $ of output.

2.4.3 Dimension D (Comparison Between Parts of Food Chain)

The desirability of indicators of energy usage between different parts of the harvesting and processing chain would be to quantify where energy is being added within the production and processing pathway. For this reason, an overall assessment of total energy input per unit of final product would be useful for each step in the chain. Also, the percentage of renewable energy and net CO2 emissions per unit of product would help define the sustainability of each step. As stated previously, useful information would also be obtained by looking at the temporal rate of change of these indicators.

2.4.4 Dimension E (Comparison Between Outputs)

Indicators in this dimension between different sectors are an extension of Dimension C and provide a means of comparing the sustainability of total energy inputs into a range of products arriving at market. As with Dimension C, the value of an energy indicator at this level would be in assessing the sustainability of a sector when combined with appropriate social, environmental and economic indicators. Suitable energy indicators would be of the thermodynamic-economic type (total energy input/$ of output). Comparing the percentage renewable energy in products and net CO2 emissions per dollar of product may also have some value.

2.4.5 Dimension F (International Comparisons)

The workshop group spent considerable time debating the merits and practicality of comparing indicators from specific sectors at an international level. One example of extending Dimension E would be to estimate the total energy inputs, percentage of renewable energy and net CO2 emissions to produce and land a New Zealand product on a foreign market compared to the local product (e.g. butter to Europe). There are many difficulties with this approach including:

  • accounting for energy required for final processing in foreign countries;
  • determining standards for comparison; and
  • obtaining information from foreign competitors.

International comparisons, at an on-farm level, provide useful information about the energy inputs and sustainability of different farming systems producing the same product. For example, this study shows that on average extensive 'all- grass' dairying systems used in New Zealand require less energy to produce milk at the farm gate than partial or zero-grazing systems used in Europe and North America. However this energetic advantage could be outweighed by higher energy inputs further up the processing and transport chain. Thus international comparisons of the energetics and sustainability of agricultural production systems need to take a life cycle costing approach that includes all costs of production, processing and transportation.

2.5 DEFINITIONS

2.5.1 Boundaries

At the workshop it was originally decided that the boundary for the study for 'on-farm' production should be defined as closely as possible to the physical boundary of the farm. However, in the strictest sense this would mean only including energy supplied directly to the property (e.g. fuel & electricity) and then converted to another form (e.g. work, heat or light) within the farm boundary. However, since the goal of the project was to consider total energy inputs as an indicator of sustainability it was necessary to relax this definition. As a consequence the energy requirements to manufacture and transport consumable items such as fertiliser and supplementary bought-in feeds were included as indirect energy inputs. Similarly the energy inputs associated with the manufacture of capital items such as vehicles, machinery and other farm improvements were included by determining the primary energy requirement and then discounting over the expected life of the item.

2.5.2 Primary Energy versus Consumer Energy

Consumer energy (delivered energy) is defined as the energy delivered to the consumer, for example the kilowatt hours as measured by a consumer's electrical power meter or the higher calorific value of delivered diesel fuel. Primary energy is defined to be the consumer energy plus all other energy inputs required to deliver that energy to the consumer. Thus the primary energy includes not only the 'useable' energy but also the energy expended or lost during processes such as extraction, refining, generation, conversion, transportation and distribution.

In the pilot study (Wells, 1998) direct energy inputs (fuel & electricity) were only accounted for as consumer energy, whereas energy for the production and manufacture of consumable inputs (indirect energy) and capital items (e.g. buildings, machinery) were largely given in terms of primary energy requirements. This inconsistency has been rectified in this final report to obtain compatibility with the concurrent study being performed by the NZ Dairy Research Institute on the dairy processing sector. This methodology also conforms to the IPCC guidelines (IPCC, 1996) for determining greenhouse gas emissions from energy conversions and adopts a life-cycle costing approach. Thus all indicators developed in this report represent the total primary energy requirement to produce milk to the point where it leaves the farm in a milk tanker.

2.6 CURRENT STUDY

2.6.1 Extent of Survey

This report presents the findings of a survey of 150 dairy farms throughout New Zealand with the intention of developing reliable benchmark levels for each indicator. The survey was carried out in two phases:

  1. conducted in conjunction with the 1998 round of MAF Farm Monitoring and incorporating data from 95 dairy farms covering the 1997/98 season (Wells, 1999);
  2. data collected in 1999 from a further 55 dairy farms making a total survey of approximately 1 percent of all dairy farms nationally.

The extra farms were selected to cover regions that were under represented in the first phase and also included some larger farms and more farms using irrigation, one of the most important determinants of overall energy use.

2.6.2 Relationships Between Input Factors, Coefficients and Indicators

Careful consideration of the list of indicators (Table 2.2) shows that there are close and even direct relationships between a number of the indicators. In addition to the energy indicators a number of production indicators are also relevant to the analysis. These are given in Table 2.3.

1 Annual Milk Solids Production (kgMS)

Number of Cows in Milk (1st Dec)

 Indicator of average productivity of animals
2 Number of Cows in Milk (1st Dec)

Effective Milking Area (ha)

 Indicator of intensity of utilisation of land area
3 Annual Milk Solids Production (kgMS)

Effective Milking Area (ha)

 Indicator of productivity of land area

Table 2.3 Production Indicators for the 'On-farm' level

For completeness, results for all the indicators have been presented in this report. However the discussion will focus around five key indicators, that is:

  • the milk solids production per effective milking hectare, referred to as the production intensity;
  • the total primary energy requirement per effective milking hectare, referred to as the energy intensity;
  • the total carbon dioxide emissions per effective milking hectare, referred to as the gross emission intensity;
  • the overall energy ratio, the ratio of total primary energy requirement to calorific energy output; and
  • the proportion of renewable energy within the total primary energy requirement.

The total primary energy input (E) is determined from the sum of the level of a number of independent input factors (Fi) multiplied by appropriate energy coefficients for that factor (Bi).

E = S(Bi Fi)

Similarly the gross carbon dioxide emission (G) is found by multiplying the individual components of the primary energy input by the appropriate carbon dioxide emission factor (Ci) and summing.

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Other factors required to calculate the indicators are: the annual milk solids production (M), the effective production (milking) area (A), and the number of cows in milk (N) determined at the 1st of December each year. The average production per cow (mC) and the stocking density (n) can be determined from these factors.

mC = M/N

The production intensity (m), energy intensity (e) and gross emission intensity (g) are effectively intermediate variables or indicators that are determined by the total milk solids production, total primary energy input, gross carbon dioxide emissions and effective milking area. That is:

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The gross emission intensity is a strong function of the energy intensity since the carbon dioxide emission factors do not vary greatly between different energy sources and the majority of primary energy used on dairy farms is liquid fossil fuels. For example carbon dioxide emission factors for fuels used in this study varied for 0.058 kg CO2 per MJ of primary energy for electricity to 0.081 for diesel, including fugitive emissions associated with production and distribution.

The gross carbon dioxide emission per kilogram of milk solids (gp) is found by dividing the gross emission intensity by the production intensity and therefore has the same relative relationship to the emission intensity as the total energy per unit milk solids does to the energy intensity.

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The net carbon dioxide emission per kilogram of milk solids production (fp) can be found directly from the gross emission per kilogram of milk solids, since the difference is the equivalent carbon dioxide sequestrated in a kilogram of milk solids. This is assumed to be constant (3.057 kg CO2/kgMS). The net emission intensity (f) is then found by multiplying by the production intensity.

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If the production intensity is multiplied by the calorific energy coefficient of milk (Bm) then the energy output intensity (eo) can be derived.

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The ratio of the energy intensity to the production intensity gives the primary energy requirement per unit of milk solids production (ep).

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Similarly the ratio of the energy intensity to the output energy intensity yields the overall energy ratio (OER).

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The protein energy ratio (PER) can be found directly from the overall energy ratio since the protein fraction (P) is assumed to be constant.

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It can be seen that there are strong linear relationships between most of the indicators and therefore a degree of redundancy. Since different international studies use different indicators all the results will be presented here to aid comparison, however only the limited set, described above is required to fully specify the energy performance of a dairy farm.


3 Petrochem produces approximately 0.2 million tonnes of urea using 6 PJ of natural gas per annum.

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