Energy Use and Efficiency
Environmental and economic sustainability are key issues in evaluating the potential of using hog manure as a fertilizer for forage crops in beef cattle production. Energy use and energy efficiency are important aspects of the sustainability studies in the La Broquerie Research Project.
Energy use and efficiency were studied by constructing energy budgets for the systems being evaluated in this project. An energy budget is very similar to a financial budget, but uses megajoules (MJ) as its currency instead of dollars.
What is a megajoule?
The megajoule is an SI unit of energy. One MJ is equivalent to:
- 0.278 kilowatt hours
- 239 kcal (commonly called Calories), or about one serving of rice (150 g) or of wheat bread (200 g) (wikipedia)
- the energy contained in 28.7 ml (about 1 ounce) of gasoline
- the energy required to produce and deliver 29 g (about 1 ounce) of urea fertilizer to the farm.
Energy budgets were created for grazing systems with and without liquid hog manure application and for hay production systems with and without liquid hog manure application. In this part of the study, only the full spring application of manure was considered. Information used in energy budgets was a mixture of actual measurements from the La Broquerie Research Project and estimates based on typical farming operations in southern Manitoba.
- Amounts of nutrients applied (110 lb N/ac)
- Hay yields
- Nutrient quality of forage
- Live weight gain of cattle
- “Typical” hog operation producing the manure: 10,000 head feeder operation (25,000 hogs/year); 6.5 million imperial gallons of manure produced per year
- “Typical” manure application systems: 7257 imperial gallons per acre; slurry wagon application for grazing systems; drag hose application for hayed systems
- “Typical” grazing system: includes fencing and watering systems
- “Typical” haying equipment: includes hay cutting, baling and hauling
Energy required for each system was itemized by activity (e.g. manure application, hay cutting, hay baling, etc.). Energy budgets for each activity included not only fuel use, but also embedded energy in all machines and materials used for each operation. As an example, the energy for manure spreading included all energy used to produce all the tractors and equipment required. This embedded energy was then divided by the lifespan of the equipment (hours), and then multiplied by the number of hours the equipment was used for this job. The energy inputs for the grazing system and the hay system are presented in Tables 1 and 2 below.
|Activity||Energy Input (MJ/ac)|
|Manure Spreading (slurry wagon)||884.2||0.0|
|Activity||Energy Input (MJ/ac)|
|Manure Spreading (drag hose)||882.2||0.0|
The majority of energy spent in both the hay and grazing systems with manure was the manure application itself. Hay harvesting activities also added significantly to the energy inputs, especially in the “manure” system, where hay yields were much higher than in the “no manure” system. Other energy inputs in the grazed system (for fencing and watering systems) were quite small compared to energy required for manure application.
Approximately 90% of the energy spent in the systems with manure application was in fuel use. The other 10% of the energy was embedded in the machinery and equipment used.
In order to compare the same units between the grazing and the hay systems all hay production was converted to units of live weight gain per acre, while the live weight gain per acre of the cattle in the grazing system was measured directly. The energy produced in both systems is presented in Table 3.
|System||Live Weight Gain (lb/ac)|
Live weight gain was higher in the manure systems due to higher forage productivity and better forage quality. In the grazing system, productivity was more than doubled when manure was applied. In the hay system, productivity was almost tripled when manure was applied.
Manure application substantially increased the productivity and energy output of both the grazing and the hay systems.
Energy efficiency for each system was calculated by dividing the live weight gain/ac by the energy inputs/ac, resulting in lb LWG / MJ input. Energy efficiency for both systems is presented in Table 4.
|System||Energy Efficiency (lb LWG / MJ of energy input)|
The most energy efficient system in this study was the grazing system without manure. This system was 5 times more energy efficient than the hay system without manure. It was 10 times more energy efficient than the grazing system with manure.
The hay system was 2.5 times more energy efficient without manure than with manure.
When manure was applied, the grazing system was slightly more energy efficient than the hay system.
Energy efficiency of both the grazing and the hay systems was considerably reduced when manure was applied.
Energy Cost of Nitrogen
Another way to view the energy input into this beef production system is to calculate the energy cost per unit of N applied. By dividing the energy cost of manure application by the amount of N applied we arrive at a value for energy cost per unit of available N. For example, our N application rate was 110 lb available N/ac and the energy cost to apply manure in the hay system to achieve this available N rate was 882.2 MJ/ac, giving us an energy cost of 8.02 MJ/lb of N. Table 5 below shows the energy costs for both the grazing system and the hay system, and includes comparisons with estimates of the energy cost of N if 110 lb N/ac were to be derived from banded anhydrous ammonia (AA) or broadcast urea instead of manure.
|System||Energy Cost of N ( MJ/lb available N)|
|Manure||Banded AAz||Broadcast Urea|
|z Anhydrous ammonia
y The energy costs of anhydrous ammonia and urea are calculated from the fertilizer energy coefficients from the publication entitled Energy Coefficients for Agricultural Inputs in Western Canada by Cecil Nagy, published May 31, 1999 through the Canadian Agricultural End-Use Data Analysis Centre (CAEEDAC). Values shown in the table include the total energy required to produce, transport and apply the fertilizer.
The energy cost of spreading liquid hog manure on forage land in this study was much lower than the energy cost of either anhydrous ammonia or urea fertilizer. Manure application used only about one-third of the energy associated with AA, and less than one-quarter of the energy associated with urea fertilizer.
It is important to note that these calculations DO include the energy required to produce the synthetic fertilizers (and transport and apply it) but DO NOT include the energy required to produce the hog manure. In this study, hog manure was considered to be purely a waste product from the hog production process. However, it is also important to remember that the origin of the N in liquid hog manure is N in the soil that came mostly from synthetic fertilizers that nourished the crops that nourished the pigs. As long as the majority of our feed grains are fertilized with synthetic N fertilizer we will remain heavily dependent on fossil fuels as a source of nutrients for our crops whether we use manure or not.
P-Based Manure Management
Switching to a phosphorus-based manure management system would have implications for the energy use and efficiency of livestock production systems. Applying manure to P-removal rates requires lower manure application rates, which in turn requires a larger land base for application and longer hauling distances. However, even at P-removal rates, applying manure as a fertilizer source is more energy efficient than applying commercial fertilizers.
- liquid hog manure application was the largest user of energy in this study, mainly due to fuel consumption
- the most energy efficient system in this study was the grazing system with no manure applied
- grazing systems were more energy efficient than hayed systems
- beef production on unmanured land was more energy efficient than on manured land
- however, beef production on manured land is still more efficient than beef production on land where synthetic fertilizers are applied, even if manure is applied only to P-removal rates
This page posted August 2007.