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This is a preliminary exercise to complete

before you collect your own data and

calculate energy flow through a farm.

How much fossil fuel energy can be saved by adopting a sustainable farming system?

Energy Flow Through Agroecosystems (Farms)

Prepared for SSAC byMartha Rosemyer – Ecological Agriculture Program; Evergreen State College

© The Washington Center for Improving the Quality of Undergraduate Education. All rights reserved. 2005

Quantitative concepts and skills•Unit conversions•Unit based comparisons•Ratios •Orders of magnitude•Scientific Notation•Significant figures

SSAC2005.S561.MR1.1

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Conventional agriculture is currently supported by non-renewable energy resources, i.e. fossil fuel. Rising oil prices will continue to affect agricultural management and decision making. Understanding energy use informs us about farm sustainability.

As discussed in Gliessman1 Chapter 18, the cultural energy inputs of a farm are designated as either industrial or biological. Industrial inputs generally are non-renewable energy sources including fossil fuels and machinery involved in planting, cultivating and harvesting, as well as electricity derived from the burning of fossil fuels. Industrial energy values involve both the ‘direct’ energy of burning the fuel and in the ‘indirect’ of energy involved in the refining, transportation and manufacture of the machinery. Industrial inputs are also involved in the production of fertilizers, pesticides and tools, both as the raw material and the the indirect energy of manufacture. Biological inputs include human labor, animal labor and renewable organic inputs such as organic fertilizers. They also involve both “direct” energy, for example the energy released from burning a compost, and “indirect” human energy involved in making the compost. In order to evaluate sustainability, we are interested not only in assessing the values of industrial and biological energy inputs to farms in kcals, but also to identify them as renewable or non-renewable sources as a basis for calculating energy efficiencies and agroecosystem sustainability.

Preview

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• Slide 4 asks you to think about what factors you will need in order to turn easily collected data from a farm into kcal and to determine how you use this information to convert it to kcal. This will be the basis for setting up the formulas necessary for the spreadsheets. Please do this before continuing!

• Slides 5-8 start with a set of biological inputs from Common Ground Farm CSA, Olympia WA, as collected by Ecological Agriculture students in 2003. Calculations will help you practice converting units from acres (ac) to hectares (ha) and lbs to kg on the way to conversion to kcal. Conversion factors in BTU will be given by Fluck2 (1995). Slide 6 treats industrial inputs, converting them from BTU to kcal. Slide 7 asks you to calculate the outputs in kcal. You will need to embed the unit conversions within the cell equations of your spreadsheet.

• Slides 9-16 helps you visualize the respective importance of the various inputs through a pie chart

• Slides 10-12 asks you to calculate total outputs and inputs and convert them to kcals and calculate the ratio of output to input.

• Slide 13 asks you to calculate production efficiencies

• Slides 14-17 provide an assignment for you to complete and hand in to your instructor.

Overview of Module

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Before you continue with the module,

please answer the following:

1. What types of information should I collect on the farm?

2. What information do I need in order to convert data collected in common units to kilocalories (kcal) per hectares (ha)?

3. How do I set up these conversions using pen and paper?

Conceptual thinking

In this exercise we will calculate energy outputs and inputs and compare energy efficiency ratios of two farms, while reviewing unit conversions

and other mathematical concepts useful in assessing agricultural sustainability.

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B C D2 Farm Area 2.0 acres3 0.809389 hectares4 Significant Figures 0.81 has

Common Ground farm has 2.0 acres in vegetable production. 1. How many hectares is this? 2. What is the formula to convert acres to hectares? 3. How many significant figures should you report?

All information was collected by the students from the farmer in lbs (or English tons) per acre.

Recreate this spreadsheet, putting in the correct formula.

= Cell with an equation in it.

= Cell with a number in it.

•An acre (43,560 ft2) is approximately the size of a football field.

•A hectare is 10,000 m2.

•Significant figures are the number of digits that reflect the accuracy of the measurement. •In unit conversions we maintain the significant figures of the original measurement.

Conversions

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B C D E F G2 22.2 English tons/ha3 10.09090909 Metric tons/ha4 10090.90909 kg/ha5 10100 kg/ha taking into account significant figures6 1.01E+04 kg/ha in scientific notation7 1800 kcal/kg (Conversion Factor from Gliessman, Table 18.2)8 18163636.36 kcal/ha9 1.82E+07 kcal/ha in scientific notation form (with significant figures)

The farm applied 22.2 T/ha of manure.What is the weight of applied manure in kg per hectare? In kcal?

1. Determine the formula to change English short tons (= 2000 lbs which is what we generally use in the US) to MT and MT to kg and eliminate non-significant figures

2. Put in formula for conversion to kcal using the given conversion factor and show the answer in scientific notation.

Recreate this spreadsheet filling in the correct formulas and using the given conversion factor.

Biological Inputs

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Other Biological Inputs: Human labor, seeds and tools (wooden handle with metal head)

Recreate this spreadsheet putting in formula for conversion to kcal and show in scientific notation.

Not all factors have available indirect values.

B C D E F G H

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Direct Value

Indirect Value

Total Conversion

Factor3 Labor Hours 4600 hr/yr 400 13200 13600 kcal/yr4 62560000 kcal5 6.26E+07 kcal in scientific notation67 Seeds 37.76 kg 3.66E+03 kcal/kg8 138202 kcal9 1.38E+05 kcal in scientific notation1011 Hand Tools 2 tools 8300 kcal/tool12 16600 kcal13 1.66E+04 kcal in scientific notation14

15 TOTAL 6.27E+07 kcal

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Industrial cultural inputs: what is their value in kcal?

•Recreate the spreadsheet with the formulas. •Use the conversion factors in the handout from Fluck (1995).

•You will need the BTU to kcal conversion value as well.

Direct values refer to the energy released upon burning, indirect refer to the energies involved in mining, manufacturing and transportation.

B C D E F G H

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Direct Value

Indirect Value

Total Conversion

Factor3 Electricity 97 kwh 3412 9878 13290 BTU/kwh4 1291788 BTU5 3.26E+05 kcal in scientific notation67 Unleaded Gas 170 gal 126000 27178 153178 BTU/gal8 26040260 BTU9 6.56E+06 kcal in scientific notation1011 Diesel Gas 8.00 gal 139700 30133 169833 BTU/gal12 1358664 BTU13 3.42E+05 kcal in scientific notation14

15 TOTAL 7.23E+06 kcal

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Using a pie chart to visualize the orders of magnitude of different energy inputs

•Make a spreadsheet summarizing the inputs. •Use the help function if you are unsure how to make the pie chart. •Include the total amount of energy in the title so that the total value can be kept in mind when comparing percentages.

Which inputs differ from others by one or more orders of magnitude?

B C2 Input kcal/ha3 Manure 1.82E+074 Electricity 3.26E+055 Unleaded Gas 6.56E+066 Diesel Gas 3.42E+057 Labor 6.26E+078 Seeds 1.38E+059 Tools 1.66E+0410 Total 8.81E+07

Common Ground CSA Inputs in kcal/haTotal Input = 8.81E+07 kcal/ha

20.6%

0.4%

7.4%

0.4%

71.0%

0.2% 0.0%

Manure

Electricity

Unleaded Gas

Diesel Gas

Labor

Seeds

Tools

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Outputs: How many kcals are leaving the farm in the form of harvested vegetables?

The conversion factors for determining the energy (kcal) contained in vegetables from the mass of that vegetable can be found in Food Values of Portions

Commonly Used3 or a calorie counter, such as in Rombauer and Becker’s, Joy of Cooking4. Note that the calories we are counting are really kcal! You may have to

weigh a unit measurement such as a “medium” potato to find its mass in kgs.

Recreate this spreadsheet filling in the correct formulas

B C D E

2 Mass (kg)Conversion

Factor (kcal/kg)

Total kcal

3 Yellow fin Potatoes 5638 760 42848804 Broccoli 2882 320 9222405 Beans 808 320 2585606 Basil 528 440 2323207 Squash 1177 190 2236308 Snow Peas 175 840 1470009 Snap Peas 323 840 271320

10 Zucchini 1866 190 35454011 Other 10056 488 490732812 Total 1160181813 Total in Scientific Notation 1.16E+07

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What is the ratio of outputs to inputs? Recreate the spreadsheet below to determine this ratio.

• For example, for every 1 kcal of output how many kcals of inputs are needed? ___ kcal output : __ kcal input

• Recreate spreadsheet, total inputs and outputs and format the formula as a ratio.

• Do we harvest more energy than we put in?

Output : Input Ratio

The ratio of outputs to inputs is called the energy efficiency. The energy efficiency allows

you to compare farming systems with each other.

B C D E2 Input kcal/ha Output kcal/ha3 Manure 1.82E+07 Vegetables 1.16E+074 Electricity 3.26E+055 Unleaded Gas 6.56E+066 Diesel Gas 3.42E+057 Labor 6.26E+078 Seeds 1.38E+059 Tools 1.66E+04

10 Total 8.81E+07 Total 1.16E+071415 Output: Input 0.1316 Output: Input Ratio 0.13 : 1

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1. Which of these inputs in your previous slide are non-renewable? 2. What is the ratio of output to non-renewable input?

(This is another type of energy efficiency ratio.)

You can use your previous spreadsheet to create a subset of values and

calculate the ratio. Put in your own words what this ratio means.

In a sustainable farming system our goal is to use as few non-

renewable inputs as possible, as well to make the most efficient use

that we can of whatever non-renewable inputs we have to use. Which ratio is larger of the two

energy efficiency ratios you have calculated and why?

Ratio of Output to Non-renewable Input

B C D E2 Input kcal/ha Output kcal/ha3 Electricity 3.26E+05 Vegetables 1.16E+074 Unleaded Gas 6.56E+065 Diesel Gas 3.42E+056 Total 7.23E+06 Total 1.16E+0778 Output: Input 1.60E+009 Output: Input Ratio 1.60 : 1

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When comparing crops that are not grown for energy sources (lettuce), you can calculate their output in productivity (weight in

g) with each kcal of input (either nonrenewable or total kcal)These ratios can be called productivity efficiencies.

•Recreate the spreadsheet and fill in the formulas. •What do these productivity efficiency ratios mean and why might they be important?

Productivity Efficiencies

B C D

2 Output Mass (kg) Mass (g)

3 Yellow fin Potatoes 5638 56380004 Broccoli 2882 28820005 Beans 808 8080006 Basil 528 5280007 Squash 1177 11770008 Snow Peas 175 1750009 Snap Peas 323 32300010 Zucchini 1866 186600011 Other 10056 1005600012 Total 234530001314 Total Kcal input (from Slide 11) 8.81E+0715 Total Kcal non-renewable input (Slide 12) 7.23E+0616 Productivity Ratio (g output: kcal input) 2.66E-0117 Non-renewable Productivity Ratio 3.24E+0018 Productivity Ratio Written in Ratio Notation 0.266 : 119 Non-renewable Productivity Ratio in Ratio Notation 3.24 : 1

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End of Module AssignmentsAssignment Question #1:

In this simulation of a conventional farm, we will include fertilizers and pesticides, while eliminating 90% of the manure and 50% of the

labor.

1. Recalculate the energy efficiency values if the farm used 600 kg/ha of ammonium nitrate (note the %N and conversion factor for N), 10 lbs of an active ingredient of herbicide and 4 lbs of active ingredient of fungicide per ha per year. Assume no change in mechanization or yield.

2. What are the tradeoffs?: a) With the change in the total amount of non-renewable energy

in this way, what has happened to the total amount of energy? b) Has the total amount of renewable energy changed with the

use of these inputs? c) Is this more or less energy efficient than Common Ground CSA

farm?

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Recreate this spreadsheet with the correct formulas.

End of Module AssignmentsAssignment Question #1, cont…

B C D E F G H2 Non-renewable inputs: Pesticides and Fertilizers3 Fertilizers BTU/lb active ingredient kcal/lb kcal/kg conv. Farm4 Nitrogen as N 32720 8245 37485 Phosphorus as P2O5 7502 1891 859

6 Potassium as K2O 5890 1484 67578 Pesticides kcal/kg9 Herbicides 122377 30839 14018 308390 10 lb10 Insecticides 99481 25069 1139511 Fungicides 78211 19709 8959 98546 5 lb12 Other pesticides 100023 25206 114571314 %N lb N kg N kcal/kg N 600 lb15 Anhydrous ammonia 82 492 224 83817316 Urea 46 276 125 47019517 Ammonium sulfate 21 126 57 21465418 Ammonium nitrate 34 204 93 3475351920 Additional non-renewable inputs 7.54E+05 kcal21 Previous inputs from slide (10% manure, 50% labor) 3.31E+07 kcal22 Total inputs 3.39E+0723 Total Outputs 11601818 1.16E+0724 O:I 3.42E-01 0.34 : 1 ratio25 I (non-renewable) 7.23E+06 4.11E+0726 O:I non-renewable 2.82E-01 0.28 :1 ratio

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1. Use the following values that are an order of magnitude lower, as many authors do, to recalculate the Output to Input Ratios, as seen in the spreadsheet on the right.

2. How does using these two lower values affect your results?

End of Module AssignmentsAssignment Question #2:

Placing an appropriate value on human labor has been an oft disputed topic. The value depends on whether the kcals involved in the entire human life cycle are included.

3. Make two pie charts of inputs using the values. 4. Compare them to each other and the previous pie chart in Slide 9. 5. How do these conversion factors affect the input pie chart?

B C D E2 input total (kcal)3 manure 1.82E+07 1.82E+07 1.82E+074 electricity 8.60E+05 8.60E+05 8.60E+055 gas-unleaded 6.56E+06 6.56E+06 6.56E+066 gas-diesel 3.42E+05 3.42E+05 3.42E+057 labor 6.26E+07 5.52E+06 5.75E+058 seeds 1.38E+05 1.38E+05 1.38E+059 tools 1.66E+04 1.66E+04 1.66E+04

10 TOTAL 8.87E+07 3.16E+07 2.67E+0711 output (kcal)12 vegetables 1.16E+0713 TOTAL 1.16E+071415 Output:Input 1.31E-01 3.67E-01 4.35E-0116 Out:Input format 0.13 : 1 0.367 : 1 0.435 : 1

B C D E F2 Human Labor Values3 BTU/hr kcal/hr O:I source4 54133 13642 0.131 net energy analysis5 1200 0.367 food energy-working6 125 0.435 muscular energy

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1. Relate your results to the discussion of agricultural sustainability.

2. How many kcals of fossil fuel can be saved by using sustainable farming methods (only renewable inputs with the exception of hand tools with a metal head)? Assume all electricity is produced by the coal-powered power plant in Chehalis WA.

3. How many 356 kcal 2” pieces of chocolate cake does this saving represent?

All assignment questions due ____

Turn in a hard copy of the spreadsheets or pie charts in all slides that require your work with the formulas visible along with all the answers to the questions. Hint: Work through this methodically slide by slide. Title your printouts including the slide number.

End of Module AssignmentsAssignment Question #3:

Kcal non-renewable fuel saved 586258 Using value from Slide 14Number of 2" pieces of chocolate cake this represents 1647

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Endnotes and References

•A 1 kg mass weighs 2.205 lb in the earth’s gravitational field, so we often use “weight”, as we will in this exercise, where “mass” is actually the correct term.

•Metric Tons is abbreviated MT.

•Scientific notation is a way of writing exponents (E) to the 10 th power. For example 300 = 3 x 102 = 3E+02. •A T in England is ”long” = 2240 lbs. A long T*x=MT?Return to Slide 6

1 Fluck, R. 1995. Energy: The Hidden Input, Southern Regional Workshop Evaluating Sustainability, University of Florida, Gainesville, SARE/ACE.

2 Gliessman, S. 1998. Agricultural Ecology: Ecological Processes in Sustainable Agriculture. Ann Arbor Press

3Pennington, J.1998. Bowes and Church’s Food Values of Portions Commonly Used, 17th Ed., Lippincott,Williams and Wilkins Pub.

4Rombauer, IS, Becker, MR, and Becker, E. 2006. Joy of Cooking: 75th Anniversary Edition, Scribner.