Long-Term Ecological Assessment of Farming Systems (LEAFS)
at Green Mountain College
Kenneth Mulder1 and Benjamin Dube
Green Mountain College, 1 Brennan Circle, Poultney VT, 05764
Introduction
While many sectors of the US and global economies are heavily reliant on fossil fuels,
agricultural is an essential component not only of our economy but also our life-support systems
for which there is no clear path to sustainability once our fossil subsidies come to an end.
Indeed, the reliance upon fossil fuels at all levels of the food chain has led some commentators to
remark that we are eating oil2. A reduction in fossil fuel utilization will require an increase in
other agricultural inputs. In particular, both land and labor can be used to substitute for energy
inputs. Land can be used to produce biofuels or to support draft animals. Fossil-fuel-derived
nutrient sources can be reduced, but either at a loss in yields or an increase in fallow lands and
cover crops. Much of the increase in agricultural energy has been to reduce labor inputs, and the
process can run in the other direction should energy become scarce.
The Long-Term Ecological Assessment of Farming
Systems (LEAFS) project at Green Mountain College in
Poultney, VT aims to assess the trade-offs associated with animaland human-powered vegetable production as well as the energy
efficiency of these systems. We hypothesize that through the use
of appropriate technologies, it is feasible to efficiently produce
vegetables with human and animal power, but that there will be a
significant cost in terms of labor and land inputs.
Oxen harvesting their own
energy.
Methods
To test this hypothesis, three different vegetable production
treatments have been established, one human powered, one oxen powered, and the third powered
by a BCS walking tractor. The human- and tractor-powered treatments are comprised of four
232m2 plots while the oxen treatment consists of one 1858 m2 plot. Each treatment is producing
approximately the same proportion of 18 different crops. Treatments not only differ in their
power sources but also in their nutrient management systems, reflecting their different strengths.
The only external inputs to the human system are seeds, potting soil and waste leaves for
mulching. 20% of the growing area is in leguminous cover crops. Permanent beds and minimal
tillage should maximize the development of nutrient cycling. The oxen treatment utilizes the
manure byproducts from forage production areas for nutrient management and every third year
the system will be in fallow cover for nutrient development and weed control. The tractor
system uses imported compost for nutrients as well as other purchased organic amendments as
needed reflecting a “conventional organic” production approach.
For each treatment, all labor, land, and fossil fuel inputs are tracked as well as the
embodied energy in potting soil and significant seed inputs. Labor for oxen feed and
maintenance as well as oxen work outputs are recorded as well. With these data, we estimated
1
Principal Investigator, [email protected], 802-287-2941.
Manning, R. 2004. “The oil we eat: Following the food chain back to Iraq.” Harpers Magazine, Feb. 2004, pp.3745.
2
the energy, land and labor efficiency of each system. Two different systems were used for the
oxen calculations as to be comparable with other energy studies (Figure 1). The oxen direct
system (Oxen-D) considers oxen metabolic energy as an external input. The oxen combined
system (Oxen-CS) considers the oxen-forage system as internal to the system, thereby increasing
land and labor inputs. 2011 was the first season of research.
Energy Boundary—Combined System
Energy Flow
Results
Oxen Hay and
Labor Flow
Pasture Area
Table 1 presents our estimates for labor, land, and energy
efficiency for the three treatments for 2011. As anticipated,
Human
Labor
the tractor area was the most labor efficient while the human
area was the most land and energy efficient. All three
Oxen
systems appear to be labor efficient based on earnings per
Oxen
Vegetable
Production
hour assuming organic wholesale prices. The oxen treatment
Area
was significantly lower with regard to land efficiency (51.4%
to 81.9% worse than the human treatment) for only a small
Figure 1
gain in labor productivity (4.0% to 10.6%) over the human
treatment. We anticipate the labor productivity of all three systems to improve as they develop.
Energy Boundary —
Vegetable System Only
Table 1--Labor, land and energy effiency of three systems
Labor Efficiency
Land Efficiency
Kg/hr
$/hr
kg/ha
$/ha
6.60
$22.94
16,253
$56,497
Human
8.84
$30.79
15,365
$53,503
Tractor
6.63
$23.86
3,098
$11,144
Oxen-CS
7.05
$25.38
7,907
$28,445
Oxen-D
EROI = Energy Return on Energy Invested
Energy Efficiency
kg/MJ
EROI
4.30
5.1
1.61
2.3
3.49
7.0
3.23
6.5
kJ/kg
Significant differences were seen with energy efficiency, although all three systems were
significantly more efficient than US conventional vegetable production where energy return
(EROI) values range from 0.26 to 1.6.3 Energy inputs per unit of production are shown in Figure
2. The embodied energy in cover crop and potato
Energy Inputs by Type
seeds was a significant addition to the energy budget of
Oxen Metabolic
each treatment. The largest energy input was the fuel
300
Oxen Maintenance
Gasoline
for the BCS tractor. The oxen direct system had
250
Seeds
Potting Soil
slightly higher energy inputs reflecting the energy
200
Human Metabolic
efficiency of the oxen forage system: more oxen work
150
energy is produced than is required in human labor to
100
50
manage the oxen-forage system, although at a cost of
0
higher labor and land inputs.
Human
Tractor
Oxen-CS
Treatment
Oxen-D
Conclusion
Figure 2
The data from our first season suggest that
human power can increase energy efficiency over 150% while animal power can increase it over
100%. The former requires 34% more labor to achieve this while the latter requires a severalfold increase in land because of forage and space requirements. All three systems were very
energy efficient in comparison to industrial agriculture.
3
Pimentel and Pimentel, 2008. Food, Energy and Society. CRC Press, New York, 2008.