Direct energy

Energy input from direct energy resources is calculated by multiplying the consumed amount of the energy resource by its energy equivalent. The following are common direct energy resources in agriculture:

2.6.1.1 Electricity

The energy of electricity in the primary energy-based analysis is the energy embodied in the life cycle of electricity production, which should be used in the calculation of the energy input.

The amount of energy embodied in electricity production in each country depends on the structure and fuel composition of its power plants. An average demand of 12.0 MJ per kWh is reported by Ortiz-Canavate and Hernanz (1999) which is the energy embodied in its produc-tion (8.4 MJ kWh^-1) in addition to its secondary energy value (3.6 MJ kWh^-1). The share of renewable energy is not reported, but it can be assumed that this share is small and there-fore not relevant to the end results. According to CED, only the production energy should be used as the electrical energy equivalent what that is used in this study.

2.6.1.2 Fuels

The energy input from the direct consumption of fuels includes the energy content of fuel in the base of HHV, in addition to the energy embodied in its production, such as the energy

fossil fuel production was assumed by Börjesson (1996) to correspond to 10% of the energy content of the fuels. Furthermore, another 4% of the energy content of diesel corresponds to energy input in the form of lubricants. Therefore, with a HHV of 38.7 MJ l^-1, Börjesson pre-sumed that the energy input from diesel consumption was 44.3 MJ l^-1. Table 3 shows the energy equivalent of various energy resources reported by Ortiz-Canavate & Hernanz (1999).

Table 3 Energy equivalent of fuels in MJ per unit (Ortiz-Canavate & Hernanz, 1999)

Energy resource Unit HHV ^a Consumed energy in production Total energy equivalent

Gasoline l 38.2 8.1 46.3

Diesel l 38.7 9.1 47.8

Fuel oil l 38.7 9.1 47.8

LPG ^b l 26.1 6.2 32.3

Natural Gas m³ 41.4 8.1 49.5

Coal kg 30.2 2.4 32.6

Electricity kWh - 8.4 12.0

a Higher heating value; ^b Liquid petroleum gas;

Fuel consumption of machinery

To calculate the fuel consumption of a machine, several methods are used. Factories, re-searchers and agricultural engineering associations have introduced various theoretical for-mulae to calculate the fuel consumption of tractors and self-propelled agricultural machiner-ies. Another method uses empirical data adapted to different agricultural machinery opera-tions (table 4). These equaopera-tions or tables are based on the specificaopera-tions of the engine, im-plement, and soil and estimate the fuel consumption of a machine per hectare or per hour of operation. However, due to many factors affecting machinery operation, such as weather, soil, depth of work, field shape and size, and particularly managerial factors, both of these methods may not determine the fuel consumption of different machinery in different sites precisely. For example, a fuel consumption rate of 17.5 and 24.2 litre per hectare for mould-board operation was recorded in two different regions (Bowers, 1992) that are very different.

The field measuring techniques, such as fuelling the tank before and after the operation or use of measuring instruments, can estimate the fuel consumption more accurately than use of theoretical data (Fathollahzadeh et al., 2011). Fuelling and refuelling the tank before and after the operation introduces some errors (Fathollahzadeh et al., 2011), but it is the simplest way to measure farm fuel consumption that is practiced by the farmers. Fuel consumption should include all consumption between the entrance and the exit of the machinery from the field, in addition to the transportation of the machinery between farms.

Table 4 Diesel consumption in farm operations estimated by Ortiz-Canavate & Hernanz (1999) Operation Consumption (l ha^-1) Operation Consumption (l ha^-1)

Mouldboard plough 25±7 Centrifugal fertilizer 2±0.5

Disc plough 22±5 Manure spreader 7±2

Chisel (straight arm) 13±2 Mounted sprayer 1.5±0.5

Chisel (curved arm) 10±2 Trailed sprayer 3±0.5

Heavy disc harrow 9±3 Grain drill 5±0.5

Medium disc harrow 7±2 Row planter 5.5±1

Heavy cultivator 10±2 Ridge planter 17±1.5

Light cultivator 8±1 Combine 18±2

Vibro-cultivator 6±1 Cutterbar mower 4±0.5

Rotary hoe 4±1 Rotary mower 5.5±0.5

Roller 4±1 Swather 3±1

Rotary cultivator 20±4 Baler 5±1

Hoeing toolbar 2±0.5 Forage harvester 25±5

Combined equipment for

ploughing - seedbed preparation 24±6 Sugar beet harvester 60±10

2.6.1.3 Human

In several studies, such as Ozkan et al. (2004b), human work was included in the energy analysis as an energy input resource, with an equivalent of 1.96 MJ h^-1. However, according to VDI Guideline 4600 and Pimentel et al. (1983), no energy input from labour is considered in energy analysis.

Energy input from labour could be categorised as secondary direct energy input. However, it is hard to clearly define an exact relationship between the energy embodied in human food and the energy produced in the human body or the energy used for physical work.

Regarding the claimed energy equivalent to human work, the share of the energy input by human work in the total energy input into the farm is insignificant. It is reported by Ozkan et al. (2004b) to be 2.6% of the total energy input for an orange farm, and by Maysami et al.

(2009) to be between 0.5% and 2.1% for wheat cultivation and 4.6% for onion cultivation, where more labour work for weeding is required. These low shares did not include labour energy in the energy analysis, while in most cases, human labour is a high value input due to its availability and cost. Therefore, other indicators could be applied to investigate a system based on its labour requirement. Pimentel et al. (1983) used labour productivity or produced yield per one hour of labour work to assess production systems. This indicator could be

rede-fined as the amount of energy produced per one hour of labour work or labour energy productivity (LEP).