Work Energy Analysis of the Agriculture, Forestry and Fisheries Sector

Introduction to Work Energy of the Agriculture and Related Sectors

This sector includes a variety of activities which are all related to the exploitation of "natural systems", be they terrestrial or aquatic. Thus, in principle, the sector spans from a more intensive use of land by agriculture via more extensive uses such as permaculture, agroforestry or "mild" management of more natural areas through grazing to managed forests that—to a greater or lesser extent—resemble nature. In this sector, we therefore attempt to include all crop and livestock production, as well as all types of forestry and fisheries.

Agriculture on the island of Samso accounts for 75% of the land use on the island. Together with the approximately 8% of the area used for forestry of varying intensities, these types of activities involve up to 83% of the total island area.

As already mentioned, agriculture involves both the growth of actual crops together with a more traditional raising of livestock. The products of crop farming are either consumed by humans in more or less processed form, or else they enter into livestock production when used for raising animals. In the first case, the work energies are exported from the island, whereas in the second case, they stay on the island until livestock, related products or waste materials are exported.

The livestock on the island in 2011 was overwhelmingly dominated by cows and pigs, but the situation changes continuously. No slaughterhouse exists on the island, so almost all livestock is sooner or later exported from the island. All milk is also taken to dairies on the mainland for processing, with the exception of a minor quantity of "organic" milk which, during the time of the project, was used locally for farm cheese production.

On most of the island, the forestry seems to be of the low-intensity kind. That is, stands may well be artificial, and real plantations do exist, but most forest areas on the island have the character of an ecosystem with a fairly low degree of disturbance; that is they may be considered relatively undisturbed and approaching the levels of a climax plant community.

Commercial fishery is no longer practised on the island, for several reasons. The main reason is that fisheries are not economically feasible at present, as fishermen report the nearby coastal waters to be almost devoid of fish. This condition has been reported constantly during recent years and even seems to be worsening.

All in all, socio-economically speaking, the island is very much a "nature- driven" society; that is, it is driven by activities connected with exploitation of natural areas, with highly intensive production and processing of crops as well as pastures. The crops on the island consist of a diverse variety of about 90 types, most of which are exported to the rest of the country—a transfer of ecosystem services from the countryside to cities.

Work Energy and Crop Production

The following section discusses the calculation of work energy stocks, the work energy (expenditures) invested in crop-growing activities—and the various outputs of work energy from crop production. Usually, discussions focus on the economic aspects of this system, but the estimates produced during this study indicate that many potential measures could be taken within the agricultural sector which would help to mitigate the greenhouse effect, for instance through the development of techniques serving to increase carbon sequestration in the systems.

In general, the main stocks are the crops that are raised during the year, usually consisting of annual crops. Perennial and permanent crops play only a minor role in Danish agriculture today. Stock development starts from almost zero (the sowing input) to the final state of finished materials ready for harvest. It is commonly believed that as a "rule-of-thumb", the aboveground biomass (AGB-biomass) is mirrored by an equivalent amount of below-ground biomass (BGB-biomass). This must be considered a crude estimate. Nevertheless, it has been used for convenience in this study in order to estimate the total dry matter and carbon fixed in the system.

A general overview of the inputs needed to establish an agricultural crop production is as follows:

  • • Seeds for sowing
  • • Fuels for soil preparation and handling, weed and pest protection and harvest
  • • Electricity, or heat—for drying harvested crops
  • • Fertilizers, artificial and natural
  • • Herbicides and pesticides
  • • Machinery, tractors, vehicles and other equipment

In this analysis, the outputs from agricultural crop production represent a far more complex situation than we normally consider. The reason for this is that our general interest and attention are now directed not only to accounting for products which are of direct socio-economic importance; in order to establish a societal system independent of non-renewable resources, we must also pay increased attention to some crop production wastes which may become important and interesting in the future.

Thus, in addition to harvested products, the non-harvested material left in the fields, together with the root parts (unless the root is actually the part harvested, as in beets) may, for example, turn out to contribute towards conserving organic material in the soil (carbon sequestration). For cereal crops in particular, the non-grain part of the above-ground biomass may serve as an input of renewable resources to energy production (straw and biofuels such as biogas and bioethanol) or simply as bedding for livestock production.

An extended set of information is required to account for all the points mentioned before. A key item for determining inputs is the thousand grain weight (see Section 7.2.23) for calculation of the necessary input of sowing seed. Fuel is needed for soil handling; this quantity is taken from Dalgaard et al. (2002). The production outcomes (harvest) are taken as much as possible from the average figures for crops, gathered from a wide range of sources. If such data have not been available from the authorities, other sources have been used, such as the expected outcomes given by companies, or reports on specific crops by for instance the farmers' organizations. A harvest index has been used to estimate the total Above Ground Biomass (AGB), which also permits calculation of the Below Ground Biomass (BGB), as well as the potential biomass available for other purposes such as fodder, biogas and heating, among others.

Work Energy of Stocks in Crop Production

The major stocks in agricultural crop production are likely to consist of the buildings and machinery necessary for crop production. The proportion of energy crops in which the harvested materials are used more or less directly as input in the energy sector could also be grouped in this section. Likewise, the geochemical fraction of the soils could be understood as an important contributor to the natural resource input.

Renewable Energy-Bound Work Energy of Stocks in Crop Production (REBES_CROP)

Stocks of energy of this kind are probably non-existent.

Non-Renewable Energy-Bound Work Energy of Stocks in Crop Production (NEBES_CROP)

The storage of fuels on the farms is assumed to be kept at a minimum, and if so, this pool should be considered close to zero and hence negligible.

Renewable Matter-Bound Work Energy of Stocks in Crop Production (RMBES_CROP)

This part of the work energy stock consists mainly of not only buildings— but also the equipment and materials used on the farms.

The major permanent work energy stock of crop production is composed of the farm buildings (residential housing excluded, since this is considered under private households in Chapter 5) and the equipment used for soil handling: tractors, tilling equipment and other gear. The work energy of buildings on Samso belonging to this sector is estimated to be 1,568 TJ.

The work energy stock of the crop varies over the year, probably peaking around harvest time, which, for major stocks such as cereals, rape/canola and beets is autumn. So this is a highly variable indicator which over the year may span from close to zero (e.g. bare fields in winter or spring) to a peak in biomass just before harvest (usually autumn). A conservative (average) estimate such as the amount of above-ground biomass harvested gives a figure of 3,288 TJ.

The above-ground crop stock represents an eco-exergy value of 677,622 TJ (as a live crop), assuming a general beta value for crop plants of 200.

Non-Renewable Energy-Bound Work Energy of Stocks in Crop Production (NMBES_CROP)

These stocks will mainly consist of the equipment used on the farms. No data have been identified estimating the work energy of the various types of machinery. A feasible method is needed for obtaining such an estimate.

Work Energy Inputs to Crop Production

The work energies of inputs are partly taken after conversion of the data from PlanEnergi, using values calculated from a number of sources in the literature. As mentioned earlier, the inputs are assumed to consist of the sowing seed and the fuels needed for soil handling, among others.

Renewable Energy-Bound Work Energy of Inputs to Crop Production (REBEI_CROP)

Initially, we here consider only the renewable inputs stemming from electricity consumption. The value is taken from PlanEnergi's energy budget, according to which the agricultural sector, together with greenhouse production, consumes 19 TJ. Correcting for greenhouse production and dividing the remainder equally between the crop production and livestock sectors, we obtain a consumption of work energy for agricultural crop production of 10 TJ. The role of this is likely to increase in future as several farms have started to erect their own wind turbines the energy of which can be used for drying harvested crops.

Meanwhile, as we shall see, this leaves the system in a rather odd situation with respect to efficiency. At some point, we need to consider that a considerable amount of solar radiation input is also consumed before we can properly assess the productivity of this sector (ecosystem services).

Non-Renewable Energy-Bound Work Energy of Inputs to Crop Production (NEBEI_CROP)

This category comprises mainly the work energy stemming from fossil fuels, predominantly diesel consumption in the various soil-handling activities mentioned earlier. Recommendations for soil handling can be found in the cultivation directions issued by various authorities giving guidance to farmers on such issues. It has been assumed that farmers tend to follow these instructions, and the calculations have been based on this.

For some crops, recommendations about soil handling are very detailed. Where such detailed recommendations could not be found, it has been assumed that types of crops which resemble each other will receive similar treatment in terms of soil preparation so that the associated energy costs will also be similar.

The fuel consumption per hectare for the various types of soil-handling activities has been taken from Dalgaard et al. (2002). Assuming (as stated earlier) that farmers follow the advice given in the instructions for cultivation, an estimated diesel consumption of 30.7 TJ can be calculated for soilhandling activities.

Work Energy Input in Renewable Matter in Crop Production (RMBEI_CROP)

The material inputs necessary to grow crops (besides the farmland that is used) are the input of sowing seeds and the chemically bound energies of fertilizers and pesticides. Here the first part—the seeds—is considered to belong to the renewable matter part, whereas the other two are considered to be non-renewable as they both depend to a large extent on energy from fossil fuels for their production, or they are derived directly from finite and non-renewable natural resources (e.g. phosphate rock).

The general equation given in the literature is used to calculate the amount of seeds needed—the seeding rate can be found in Section 3.6.4.3. The amount of seed needed has been calculated for all crops with the exception of one vegetable (Jerusalem artichoke) for which no values could be found at the time. In some cases, values from organic farming guides were used as the information was only available from such sources. Again, a large variety of sources have been used, spanning from official growing instructions to the catalogues of seed companies.

A total seed quantity corresponding to approximately 1,594-ton DW of biomass has been invested to grow the crops on Samso. This corresponds to 29.8 TJ of work energy. Since these are living seeds, the value in terms of eco-exergy will correspond to 5,960 TJ.

Work Energy Input in Non-Renewable Matter in Crop Production (NMBEI_CROP)

The non-renewable matter-bound work energies originate from the treatment of crops with artificial fertilizers, pesticides and growth enhancers. Treatment of seeds is also included.

The amounts of chemicals such as fertilizers may also be seen as representing chemical work energy. Data for the main fertilizers are reported in an inconsistent manner; that is it is not always clearly indicated how a given work energy value is derived. Also, in several cases the relevant literature states cumulative values, that is values of work energy which also include the work energy used during the production process.

Assumptions made:

Although in the cultivation instructions several other nutrients are stated to be necessary for some particular crops, here only the values for nitrogen (N), phosphorus (P) and potassium (K) have been included. Again, it is assumed that farmers follow the cultivation instructions, and the recommended amounts and respective areas of crops are used in calculations.

For the calculation of the total inputs of N, P, and К for the growth of crops on Samso, the values of Hovelius (1997) were used. The work energy inputs in the form of fertilizers or of pesticides are 58.1 and 5.1 TJ, respectively, or

63.2 TJ in total.

To summarize, the crop sub-sector receives an input of renewable work energy of 10 TJ, non-renewable work energy of 30.7 TJ, renewable matter- bound work energy of 29.8 TJ and non-renewable matter-bound energy of

63.2 TJ (see Figure 7.1).

Work Energy Outputs in Matter from Crop Production

Work Energy Output in Renewable Energy from Crop Production (REBEO_CROP)

No such sources have been identified and this output was probably not relevant in 2011. A minor and very local production of biodiesel is known to exist, but it remains and is used on the island.

FIGURE 7.1

The work energy distribution of the various inputs to the crop production system of Samso in 2011, which shoe the dominance of fertilizers, fuels and seeds to the production budget. These costs make up 88% of the necessary inputs of work energy.

Work Energy Output in Non-Renewable Energy from Crop Production (NEBEO_CROP)

As no energy production has been identified in the sector, no output (loss) is believed to occur, except for crop respiration, which has not been estimated. In this project, the major concern is to identify the net fluxes in the system, and respiration is implicitly accounted for in the net crop production.

Work Energy Output in Renewable Matter from Crop Production (RMBEO_CROP)

The outputs of work energies of this type are dominated by the biomasses. However, their relative importance depends greatly on what type of work energy is considered—whether it is the chemical work energy or the eco-exergy.

In addition, all energy inputs used in the sector have been lost by dissipation.

The major part of the crops produced on the island is exported either directly after being packed or indirectly after being processed at Trolleborg (see Chapter 8). Eventually, all harvested material may be considered as leaving the island; only a minor part is sold on the island to local residents or tourists. The amount of organic material produced on the island is estimated to represent a value of 817.1 TJ.

If we assume that a major part of the fodder consumed by livestock is produced on the island (or at least could potentially have been supplied by the island), we may estimate this to 375.5 TJ. Much of this may be represented as hay. If grains from cereals are used to feed cattle or pigs, careful attention should be paid to avoid double accounting, as materials used for fodder cannot also be exported.

Part of the harvested but not digestible material such as straw makes a considerable contribution to the heating systems on the island. The quantity is taken from PlanEnergi and represents an amount of 87 TJ, which may be converted (using a value of work energy density of 0.5) to represent a work energy content of 43.5 TJ.

Work Energy Output in Non-Renewable Matter from Crop Production (NMBEO_CROP)

This output includes the amount of fertilizers and pesticides exported from the sector either as run-off to streams, by breakdown, by binding to soils and/or as infiltration to ground-water.

Figure 7.2 shows the output work energies of the crop sub-sector of agriculture. The figure demonstrates a clear dominance of the work energies of exported goods.

The distribution of the remaining non-harvested biomass and the partitioning between use for fodder or heat must be considered as being quite arbitrary. First of all, the amount dedicated to fodder is the amount available,

FIGURE 7.2

The work energy outputs of the crop sub-sector of Sam so 2011 showing the dominance of direct or indirect exports of food items from the island, as well as the large potentials for straw for heating and use as fodder.

not necessarily what is used. Second, the two possible uses are exclusive in the sense that what is used for fodder cannot be used for heat and vice versa.

The latter point serves to illustrate issues that need further consideration if the plans for a biogas plant on the island are implemented.

Work Energy Budget of Crop Production

The complete budget of work energies involved in the agricultural crop system may be summarized and illustrated as in Figure 7.2.

What immediately strikes the eye is that the dominant part of the biomass produced is represented by the work energy accumulated in the crop stocks. At the same time, when neglecting the input from primary production originating in solar radiation, the exports from the system exceed the inputs by a factor of 10. In principle, this could be interpreted as a highly efficient system where much arises from nothing.

This is explained by the fact that in this calculation, we have ignored the inputs from solar radiation. When viewed conservatively, this input must at least correspond to the amount of above-ground harvested biomass. This leads to an output of 1,279.6 TJ from a minimum input of 3,358 TJ—or a maximum efficiency of the system of about 38%. A recalculation including the below-ground biomass would reduce the efficiency to about half this (19%). When considering that we have dealt with net fluxes only, this is considered to be the absolute maximum efficiency of the system.

If we estimate the efficiency based on the associated destruction of eco- exergy occurring in the system, the efficiency will become much lower than this—about 0.2%.

Sustainability Indicators of Crop Production

The indicators established in Section 3.8 may now be estimated for the part of the agricultural sector involved in the production of crops on the island of Samso in 2011 (see Figure 7.3).

Stock Indicator of Crop Production

The stock of work energy in this sector peaks around harvest time and is estimated from the amount of infrastructure in buildings (1,568 TJ) and the total biomass, above and below ground (3,388.1 TJ) which sums up to 4,956.1 TJ. This stock is maintained by a total input of 3,494.4 TJ y1.

Thus, the work energy stock efficiency for this sector is

indicating a sector with a relatively high cost. However, it is considered more appropriate not to take the ecosystem services from the sun into account.

FIGURE 7.3

The work energy flows involved in the production of crops on the island of Samso in 2011. In a similar manner as earlier chapters, a slash is separating the energy and estimated work energy values. For the major living biomass components—seeds used and amount of crop produced— a value of the natural work energy including information (NWEI = eco-exergy) is given. This illustrates the bias introduced to the evaluation if this indicator is used.

This would lead to a stock value of 4,956.1 for a reduced cost of 136.4, giving a WESE figure of 36.3.

Renewability Indicators of Crop Production

If we consider the fossil-fuel-based energy as a non-renewable input of work energy and the inputs from wind and solar systems together with biomass as the renewable input, we get a renewable to non-renewable index (RNNI) for the sector of

or a renewable efficiency RIEF for the sector of

The latter value shows that the input energies are dominated by the renew- able/sustainable work energy part—a point that really stresses the importance of the ecosystem service delivered by solar radiation.

O/I Indicator of Crop Production

The output-input efficiency based on work energy for this sub-sector— WEOIEF—is calculated from the export of materials used for district heating and the potential amount of fodder used on the island. The calculated O/l efficiency would be

meaning that 35% of the input work energy is exported by the system. This may be seen as a relatively low value, but considering that the crop system includes potential outputs which may be used elsewhere and preserves organic material in the soil, it is probably a value that may be taken to be positive. In the case, where all work energies leave the island this would correspond to exhaustion of the soils.

 
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