posted October 09, 2005 12:31 PM
Source: BioScience, July 2005 v55 i7 p573(10).
Title: Environmental, energetic, and economic comparisons of organic and
conventional farming systems.
Author: David Pimentel, Paul Hepperly, James Hanson, David Douds and Rita
SIC code: 0100
Organizations: National Research Council
Electronic Collection: A134172873
Full Text COPYRIGHT 2005 American Institute of Biological Sciences
Various organic technologies have been utilized for about 6000 years to make
agriculture sustainable while conserving soil, water, energy, and biological
resources. Among the benefits of organic technologies are higher soil organic
matter and nitrogen, lower fossil energy inputs, yields similar to those of
conventional systems, and conservation of soil moisture and water resources
(especially advantageous under drought conditions). Conventional agriculture
can be made more sustainable and ecologically sound by adopting some
traditional organic farming technologies.
Keywords: organic, agriculture, conventional
Heavy agricultural reliance on synthetic chemical fertilizers and pesticides
is having serious impacts on public health and the environment (Pimentel et
al. 2005). For example, more than 90% of US corn farmers rely on herbicides
for weed control (Pimentel et al. 1993), and one of the most widely used of
those herbicides, atrazine, is also one of the most commonly found pesticides
in streams and groundwater (USGS 2001). The estimated environmental and health
care costs of pesticide use at recommended levels in the United States run
about $12 billion every year (Pimentel 2005).
Other aspects of conventional agriculture also have adverse effects on
environmental and human health, as well as a high price tag. Nutrients from
fertilizer and animal manure have been associated with the deterioration of
some large fisheries in North America (Frankenberger and Turco 2003), and
runoff of soil and nitrogen fertilizer from agricultural production in the
Corn Belt has contributed to the "dead zone" in the Gulf of Mexico. The
National Research Council (BANR/NRC 2003) reports that the cost of excessive
fertilizer use that is, fertilizer inputs that exceed the amount crops can
use--is $2.5 billion per year. Modern agricultural practices can also
contribute to the erosion of soil. The estimated annual costs of public and
environmental health losses related to soil erosion exceed $45 billion
(Pimentel et. al. 1995).
Integrated pest and nutrient management systems and certified organic
agriculture can reduce reliance on agrochemical inputs as well as make
agriculture environmentally and economically sound. Pimentel and Pimentel
(1996) and the National Research Council (BANR/NRC 2003) have demonstrated
that sound management practices can reduce pesticide inputs while maintaining
high crop yields and improving farm economics. Some government programs in
Sweden, Canada, and Indonesia have demonstrated that pesticide use can be
reduced by 50% to 65% without sacrificing high crop yields and quality
The aim of organic agriculture is to augment ecological processes that foster
plant nutrition yet conserve soil and water resources. Organic systems
eliminate agrochemicals and reduce other external inputs to improve the
environment and farm economics. The National Organic Program (a program of the
USDA Agricultural Marketing Service; 7 CFR pt. 205 ) codifies organic
production methods that are based on certified practices verified by
independent third-party reviewers. These systems give consumers assurance of
how their food is produced and enable consumers to choose foods on the basis
of the methods by which they were produced. The National Organic Standards
Program prohibits the use of synthetic chemicals, genetically modified
organisms, and sewage sludge in organically certified production.
Organic agriculture is a fast-growing agricultural section in the United
States. Dimitri and Greene (2002) report a doubling of area in organic
production from 1992 to 1997, currently more than 500,000 hectares (ha).
Organic food sales total more than $7 billion per year and are growing at
double-digit rates (Greene 2000, 2004, ERS 2003). With continuing consumer
concerns about the environment and the chemicals used in food production, and
with the growing availability of certified organic production, the outlook for
continuing growth of organic production is bright (Dimitri and Greene 2002).
Since 1981, the Rodale Institute Farming Systems Trial (FST) has compared
organic and conventional grain-based farming systems. The results presented
here represent a 22-year study of these farming systems, based on
environmental impacts, economic feasibility, energetic efficiency, soil
quality, and other performance criteria. The information from this trial can
be a tool for developing agricultural policies more in tune with the
environment while increasing energy efficiency and economic returns.
The Rodale Institute Farming Systems Trial
From 1981 through 2002, field investigations were conducted at the Rodale
Institute FST in Kutztown, Pennsylvania, on 6.1 ha. The soil at the study site
is a moderately well-drained Comly silt loam. The growing climate is subhumid
temperate (average temperature is 12.4 degrees Celsius and average rainfall is
1105 millimeters [mm] per year).
The experimental design included three cropping systems (main plots). These
systems, detailed below, included (a) conventional, (b) animal manure and
legume-based organic (hereafter organic animal-based), and (c) legume-based
organic systems. The main plots were 18 x 92 meters (m), and these were split
into three 6 x 92 m subplots, which allowed for same-crop comparisons in any
one year. The main plots were separated with a 1.5-m grass strip to minimize
cross movement of soil, fertilizers, and pesticides. The subplots were large
enough that farm-scale equipment could be used for operations and harvesting.
Each of the three cropping systems was replicated eight times.
Conventional cropping. The conventional cropping system, based on synthetic
fertilizer and herbicide use, represented a typical cash-grain, row-crop
farming unit and used a simple 5-year crop rotation (corn, corn, soybeans,
corn, soybeans) that reflects commercial conventional operations in the region
and throughout the Midwest (more than 40 million ha are in this production
system in North America; USDA 2003). Fertilizer and pesticide applications for
corn and soybeans followed Pennsylvania State University Cooperative Extension
recommendations. Crop residues were left on the surface of the land to
conserve soil and water resources. Thus, during the growing season, the
conventional system had no more exposed soil than in either the organic
animal-based or the organic legume-based systems. However, it did not have
cover crops during the nongrowing season.
Organic animal-based cropping. This system represented a typical livestock
operation in which grain crops were grown for animal feed, not cash sale. This
rotation was more complex than the rotation used in the conventional system.
The grain-rotation system included corn, soybeans, corn silage, wheat, and red
clover--alfalfa hay, as well as a rye cover crop before corn silage and
Aged cattle manure served as the nitrogen source and was applied at a rate of
5.6 metric tons (t) per ha (dry), 2 years out of every 5, immediately before
plowing the soil for corn. Additional nitrogen was supplied by the plow-down
of legume-hay crops. The total nitrogen applied per ha with the combined
sources was about 40 kilograms (kg) per year (or 198 kg per ha for any given
year with a corn crop). The system did not use herbicides for weed control; it
relied instead on mechanical cultivation, weed-suppressing crop rotations, and
relay cropping, in which one crop acted as a living mulch for another.
Organic legume-based cropping. This system represented a cash grain operation,
without livestock. Like the conventional system, it produced a cash grain crop
every year; however, it used no commercial synthetic fertilizers, relying
instead on nitrogen-fixing green manure crops as the nitrogen source. The
final rotation system included hairy vetch (winter cover crop used as a green
manure), corn, rye (winter cover crop), soybeans, and winter wheat. The hairy
vetch winter cover crop was incorporated before corn planting as a green
manure. The initial 5-year crop rotation in the legume-based system was
modified twice to improve the rotation. The total nitrogen added to this
system per ha per year averaged 49 kg (or 140 kg per ha for any given year
with a corn crop). Both organic systems (animal based and legume based)
included a small grain, such as wheat, grown alone or interseeded with a
legume. Weed control practices were similar in both organic systems, neither
of which used herbicides for weed control.
Measurements recorded in the experimental treatments
Cover crop biomass, crop biomass, weed biomass, grain yields, nitrate
leaching, herbicide leaching, percolated water volumes, soil carbon, soil
nitrogen, and soil water content were measured in all systems. In addition,
seasonal total rainfall, energy inputs and returns, and economic inputs and
returns were determined.
A lysimeter, a steel cylinder 76 centimeters (cm) long by 76 cm in diameter,
was installed in four of the eight replications in each cropping system in
fall 1990 to enable the collection of percolated water. The top of each
lysimeter was approximately 36 cm below the soil surface to allow normal field
operations to be carried out directly over the lysimeters. Water could not
escape from the lysimeter system, and leachate samples were collected
throughout the year.
Levels of nitrogen as nitrate in leachate samples were determined by the Soil
and Plant Nutrient Laboratory at Michigan State University in East Lansing.
Herbicides in leachate samples were analyzed by M. J. Reider Associates,
Reading, Pennsylvania. Total soil carbon and nitrogen were determined by the
Agricultural Analytical Services Laboratory at Pennsylvania State University
in University Park. Soil water content was determined gravimetrically on
sieved soil (particles 2 mm in diameter). Statistical analyses were carried
out using SPSS version 10.1.3 General Linear Modal Univariate Analysis of
We examined the data from the 22-year experiments carried out at the Rodale
Institute, which compared the organic animal-based, organic legume-based, and
conventional systems. The following data were considered for all three
systems: crop yields for corn and soybeans, impacts of drought on crop yields,
fossil energy requirements, economic costs and benefits, soil carbon (organic
matter) changes over time, and nitrogen accumulation and nitrate leaching.
Crop yields under normal rainfall. For the first 5 years of the experiment
(1981-1985), corn grain yields averaged 4222, 4743, and 5903 kg per ha for the
organic animal, organic legume, and conventional systems, respectively, with
the yields for the conventional system being significantly higher than for the
two organic systems. After this transition period, corn grain yields were
similar for all systems: 6431, 6368, and 6553 kg per ha for the organic
animal, organic legume, and conventional systems, respectively (Pimentel et
al. 2005). Overall, soybean yields from 1981 through 2001 were 2461, 2235, and
2546 kg per ha for the organic animal, organic legume, and conventional
systems, respectively (Pimentel et al. 2005). The lower yield for the organic
legume system is attributable to the failure of the soybean crop in 1988, when
climate conditions were too dry to support relay intercropping of barley and
soybeans. If 1988 is taken out of the analysis, soybean yields are similar for
Crop yields under drought conditions. The 10-year period from 1988 to 1998 had
5 years in which the total rainfall from April to August was less than 350 mm
(compared with 500 mm in average years). Average corn yields in those 5 dry
years were significantly higher (28% to 34%) in the two organic systems: 6938
and 7235 kg per ha in the organic animal and the organic legume systems,
respectively, compared with 5333 kg per ha in the conventional system. During
the dry years, the two organic systems were not statistically different from
each other in terms of corn yields.
During the extreme drought of 1999 (total rainfall between April and August
was only 224 mm compared with the normal average of 500 mm), the organic
animal system had significantly higher corn yields (1511 kg per ha) than
either the organic legume (421 kg per ha) or the conventional system (1100 kg
per ha). Crop yields in the organic legume system were much lower in 1999
because the high biomass of the hairy vetch winter cover crop used up a large
amount of the soil water (Lotter et al. 2003).
Soybean yields responded differently than the corn during the 1999 drought.
Specifically, soybean yields were about 1800, 1400, and 900 kg per ha for the
organic legume, the organic animal, and the conventional systems,
respectively. These treatments were significantly different (p = 0.05) from
each other (Pimentel et al. 2005).
Over a 12-year period, water volumes percolating through each system
(collected in lysimeters) were 15% and 20% higher in the organic legume and
organic animal systems, respectively, than in the conventional system. This
indicated an increased groundwater recharge and reduced runoff in the organic
systems compared with the conventional system. During the growing seasons of
1995, 1996, 1998, and 1999, soil water content was measured for the organic
legume and conventional systems. The measurements showed significantly more
water in the soil farmed using the organic legume system than in the
conventional system (Pimentel et al. 2005). This accounted for the higher
soybean yields in the organic legume system in 1999 (Pimentel et al. 2005).
Energy inputs. The energy inputs in the organic animal, organic legume, and
conventional corn production systems were assessed. The inputs included fossil
fuels for farm machinery, fertilizers, seeds, and herbicides. About 5.2
million kilocalories (kcal) of energy per ha were invested in the production
of corn in the conventional system. The energy inputs for the organic animal
and organic legume systems were 28% and 32% less than those of the
conventional system, respectively (figure 1). Commercial fertilizers for the
conventional system were produced employing fossil energy, whereas the
nitrogen nutrients for the organic systems were obtained from legumes or
cattle manure, or both. The intensive reliance on fossil fuel energy in the
conventional corn production system is why that system requires more overall
energy inputs than do organic production systems. Fossil energy inputs were
also required to transport and apply the manure to the field.
[FIGURE 1 OMITTED]
The energy inputs for soybean production in the organic animal, organic
legume, and conventional systems were similar: 2.3 million kcal, 2.3 million
kcal, and 2.1 million kcal per ha, respectively (figure 1).
Economics. Two economic studies of the FST were completed, evaluating its
first 9 years (Hanson et al. 1990) and first 15 years of operation (Hanson et
al. 1997). These two studies captured the experiences of organic farmers as
they develop over time a rotation that best fits their farm. With the
development of the final rotation, a third evaluation was completed comparing
this rotation with its conventional alternative (Hanson and Musser 2003). Many
organic grain farmers in the mid-Atlantic region have been adopting this
"Rodale rotation" on their farms, and there was strong interest in an economic
evaluation of this rotation alone (i.e., without the transition period or
The third economic comparison of the organic corn-soybean rotation and
conventional corn-soybean systems covered the period 1991 to 2001 (figure 2).
Without price premiums for the organic rotation, the net returns for both
rotations were similar. The annual net return for the conventional system
averaged about $184 per ha, while the organic legume system for cash grain
production averaged $176 per ha. The annual costs per ha for the conventional
versus organic rotations, respectively, were (a) seed, $73 versus $103; (b)
fertilizers and lime, $79 versus $18; (c) pesticides, $76 versus $0; (d)
machinery costs, $117 versus $154; and (e) hired labor, $9 versus $6. Similar
revenue comparisons are $538 per ha and $457 per ha (conventional versus
organic). The net returns for the conventional rotation were more variable
(i.e., risky). The standard deviation for net returns over the 10-year period
was $127 for the conventional rotation and $109 for the organic rotation.
[FIGURE 2 OMITTED]
When the costs of the biological transition for the organic rotation
(1982-1984) were included, the net returns for the organic rotation were
reduced to $162 per ha, while the conventional net returns remained unchanged.
Including the costs of family labor for both rotations reduced the net returns
of conventional farming to $162 and organic farming to $127. However, even
with the inclusion of the biological transition and family labor costs, the
organic price premium required to equalize the organic and conventional
returns was only 10% above the conventional product. Throughout the 1990s, the
organic price premium for grains has exceeded this level, and premiums now
range between 65% and 140% (New Farm Organization 2003).
The organic system requires 35% more labor, but because it is spread out over
the growing season, the hired labor costs per ha are about equal between the
two systems. Each system was allowed 250 hours of "free" family labor per
month. When labor requirements exceeded this level, labor was hired at $13 per
hour. With the organic system, the farmer was busy throughout the summer with
the wheat crop, hairy vetch cover crop, and mechanical weed control (but
worked less than 250 hours per month). In contrast, the conventional farmer
had large labor requirements in the spring and fall, planting and harvesting,
but little in the summer months. This may have implications for the growing
number of part-time farmers for whom the availability of family farm labor is
severely limited. Other organic systems have been shown to require more labor
per hectare than conventional crop production. On average, organic systems
require about 15% more labor (Sorby 2002, Granatstein 2003), but the increase
in labor input may range from 7% (Brumfield et al. 2000) to a high of 75%
(Karlen et al. 1995, Nguyen and Haynes 1995).
[Graphic omitted]Over the 10-year period, organic corn (without price
premiums) was 25% more profitable than conventional corn ($221 per ha versus
$178 per ha). This was possible because organic corn yields were only 3% less
than conventional yields (5843 kg per ha versus 6011 kg per ha), while costs
were 15% less ($351 per ha versus $412 per ha). However, the organic grain
rotation required a legume cover crop before the corn. This was established
after the wheat harvest. Thus, corn was grown 60% of the time in the
conventional rotation, but only 33% of the time in the organic rotation.
Stated in another way, the yields per ha between organic and conventional corn
for grain may be similar within a given year; however, overall production of
organic corn is diminished over a multiple-year period because it is grown
less frequently. On the other hand, the reduced amount of corn grown in the
organic rotation is partly compensated for with the additional crop of wheat.
[Graphic omitted]Soil carbon, Soil carbon, which correlates with soil organic
matter levels, was measured in 1981 and 2002 (figure 3). In 1981, soil carbon
levels were not different (p = 0.05) between the three systems. In 2002,
however, soil carbon levels in the organic animal and organic legume systems
were significantly higher than in the conventional system: 2.5% and 2.4%
versus 2.0%, respectively (figure 3). The annual net aboveground carbon input
(based on plant biomass and manure) was the same in the organic legume system
and the conventional system (about 9000 kg per ha) but close to 12% higher in
the organic animal system (about 10,000 kg per ha). However, the two organic
systems retained more of that carbon in the soil, resulting in an annual soil
carbon increase of 981 and 574 kg per ha in the organic animal and organic
legume systems, compared with only 293 kg per ha in the conventional system
(calculated on the basis of about 4 million kg per ha of soil in the top 30
cm). The increased carbon was also associated with higher water content of the
soils in these systems compared with the conventional system. The higher soil
water content in the organic systems accounted for the higher corn and soybean
yields in the drought years in these systems compared with the conventional
system (Lotter et al. 2003).
[FIGURE 3 OMITTED]
Soil nitrogen. Soil nitrogen levels were measured in 1981 and 2002 in the
organic animal, organic legume, and conventional systems (figure 3). Initially
the three systems had similar percentages of soil nitrogen, or approximately
0.31%. By 2002, the conventional system remained unchanged at 0.31%, while
nitrogen levels in the organic animal and organic legume systems significantly
increased to 0.35% and 0.33%, respectively. Harris and colleagues (1994) used
15N (nitrogen-15) to demonstrate that 47%, 38%, and 17% of the nitrogen from
the organic animal, organic legume, and conventional systems, respectively,
was retained in the soil a year after application.
Nitrate leaching. Overall, the concentrations of nitrogen as nitrate in
leachates from the farming systems varied between 0 and 28 parts per million
(ppm) throughout the year (Pimentel et al. 2005). Leachate concentrations were
usually highest in June and July, shortly after applying fertilizer in the
conventional systems or plowing down the animal manure and legume cover crop.
In all systems, increased soil microbial activity during the growing season
appears to have contributed to increased nitrate leaching.
Water leachate samples from the conventional system sometimes exceeded the
regulatory limit of 10 ppm for nitrate concentration in drinking water. A
total of 20% of the conventional system samples were above the 10-ppm limit,
while 10% and 16% of the samples from the organic animal and organic legume
systems, respectively, exceeded the nitrate limit.
Over the 12-year period of monitoring (1991-2002), all three systems leached
between 16 and 18 kg of nitrogen as nitrate per ha per year. These rates were
low compared with the results from other experiments with similar nitrogen
inputs, in which leaching of nitrogen as nitrate ranged from 30 to 146 kg per
ha per year (Fox et al. 2001, Power et al. 2001). When measuring these
nitrogen losses as a percentage of the nitrogen originally applied to the
crops in each system, the organic animal, organic legume, and conventional
systems lost about 20%, 32%, and 20%, respectively, of the total nitrogen as
The high nitrate leaching in the organic legume system was not steady over the
entire period of the study; instead, it occurred sporadically, especially
during a few years of extreme weather. For example, in 1995 and 1999, the
hairy vetch green manure supplied approximately twice as much nitrogen as
needed for the corn crop that followed, contributing excess nitrogen to the
soil and making it available for leaching. In 1999, the heavy nitrogen input
from hairy vetch was followed by a severe drought that stunted corn growth and
reduced the corn's demand for nitrogen. In both years, these nitrogen-rich
soils were also subjected to unusually heavy fall and winter rains that
leached the excess nitrogen into the lower soil layers. Monitoring of soil
nitrogen and cover crop production is needed to manage the potential for
excessive nitrate in all systems.
These data contrast with the results of experiments in Denmark, which
indicated that nitrogen leaching from the conventional treatments was twice
that in the organic agricultural systems (Hansen et al. 2001). Overall,
nitrogen leaching levels were lower in the FST rotation study than in those
reported by Hansen and others.
Herbicide leaching. Four herbicides were applied in the conventional system:
atrazine (to corn), pendimethalin (to corn), metolachlor (to corn and
soybeans), and metribuzin (to soybeans). From 2001 to 2003, atrazine and
metolachlor were only detected in water leachate samples collected from the
conventional system. No metribuzin or pendimethalin were detected after
application (Pimentel et al. 2005).
[Graphic omitted]In the conventional plots where corn was planted after corn,
and atrazine was applied two years in a row, atrazine in the leachate
sometimes exceeded 3 parts per billion (ppb), the maximum contaminant level
(MCL) set by the US Environmental Protection Agency (EPA) for drinking water.
These atrazine levels were higher than those in the corn-after-soybean
treatment (Pimentel et al. 2005). In the conventional system, metolachlor was
also detected at 0.2 to 0.6 ppb. When metolachlor was applied two years in a
row in a corn-after-corn treatment, it peaked at 3 ppb (Pimentel et al. 2005).
The EPA has not yet established an MCL for metolachlor in drinking water.
Soil biology. Among the natural biological processes on which the organic
rotations depend is symbiosis of arbuscular mycorrhizae, and this aspect was
investigated in the FST experiments. Arbuscular mycorrhizal (AM) fungi are
beneficial and indigenous to most soils. They colonize the roots of most crop
plants, forming a mutualistic symbiosis (the mycorrhiza). The fungus receives
sugars from the root of the host plant, and the plant benefits primarily from
enhanced nutrient uptake from the fungus. The extraradical mycelia of the AM
fungi act, in effect, as extensions of the root system, more thoroughly
exploring the soil for immobile mineral nutrients such as phosphate (Smith and
Read 1997). Arbuscular mycorrhizae have been shown to enhance disease
resistance, improve water relations, and increase soil aggregation (Miller and
Jastrow 1990, Hooker et al. 1994, Wright et al. 1999, Auge 2000). Efficient
utilization of this symbiosis contributes to the success of organic production
Soils of the Rodale Institute FST have been sampled to study the impact of
conventional and organic agricultural management on indigenous populations of
AM fungi. Soils farmed with the two organic systems had greater populations of
spores of AM fungi and produced greater colonization of plant roots than in
the conventional system (Douds et al. 1993). Most of this difference was
ascribed to greater plant cover (70%) on the organic systems compared with the
conventional corn--soybean rotation (40%). This was due to overwintering cover
crops in the organic rotation (Galvez et al. 1995). In addition to fixing or
retaining soil nitrogen, these cover crops provide roots for the AM fungi to
colonize and maintain the fungi's viability during the interval from cash crop
senescence to next year's planting. Though levels of AM fungi were greater in
the organically farmed soils, indices of ecological species diversity were
similar in the farming systems (Franke-Snyder et al. 2001).
Wander and colleagues (1994) demonstrated that soil respiration was 50% higher
in the organic animal system, compared with the conventional system, 10 years
after initiation of the Rodale Institute FST. Microbial activity in the
organic soils may be higher than in the conventional system's soils and hence
could explain the higher metabolism rates in the organic systems (Lavelle and
The crop yields and economics of organic systems, compared with conventional
systems, appear to vary based on the crops, regions, and technologies employed
in the studies. However, the environmental benefits attributable to reduced
chemical inputs, less soil erosion, water conservation, and improved soil
organic matter and biodiversity were consistently greater in the organic
systems than in the conventional systems.
Soil organic matter and biodiversity. Soil organic matter provides the base
for productive organic farming and sustainable agriculture. After 22 years of
separate management, soil carbon (soil organic matter) was significantly
higher in both the organic animal and the organic legume systems than in the
conventional system. Soil carbon increased 27.9%, 15.1%, and 8.6% in the
organic animal, organic legume, and conventional systems, respectively (figure
The amount of organic matter in the upper 15 cm of soil in the organic farming
systems was approximately 110,000 kg per ha. The soil of the upper 15 cm
weighed about 2.2 million kg per ha. Approximately 41% of the volume of the
organic matter in the organic systems consisted of water, compared with only
35% in the conventional systems (Sullivan 2002). The amount of water held in
both of the organic systems is estimated at 816,000 liters per ha. The large
amount of soil organic matter present in the organic systems aided in making
the systems more tolerant of droughts, such as those that occurred in 1999 and
other drought years.
Large amounts of biomass (soil organic matter) are expected to significantly
increase soil biodiversity (Pimentel et al. 1992, Troeh and Thompson 1993,
Lavelle and Spain 2001, Mader et al. 2002). The arthropods per ha can number
from two million to five million, and earthworms from one million to five
million (Lavelle and Spain 2001, Gray 2003). The microarthropods and
earthworms were reported to be twice as abundant in organic versus
conventional agricultural systems in Denmark (Hansen et al. 2001). The weight
of the earthworms per ha in agricultural soils can range from 2000 to 4000 kg
(Lavelle and Spain 2001). There can be as many as 1000 earthworm and insect
holes per [m.sup.2] of land. Earthworms and insects are particularly helpful
in constructing large holes in the soil that increase the percolation of water
into the soil and decrease runoff.
Soil organic matter is an important source of nutrients and can help increase
biodiversity, which provides vital ecological services, including crop
protection (Pimentel et al. 2005). For example, adding compost and other
organic matter reduces crop diseases (Cook 1988, Hoitink et al. 1991) and
increases the number of species of microbes in the agroecosystem (van Elsen
2000). In addition, in the organic systems, not using synthetic pesticides and
commercial fertilizers minimizes the harmful effects of these chemicals on
nontarget organisms (Pimentel 2005).
In conventional crop management in New Zealand, Nguyen and Haynes (1995) did
not report any adverse effect on soil microbial activity. These conventional
systems, however, were part of a rotation pastoral-arable system with a
relatively high level of soil organic matter (carbon content of the soil
ranged from 2.9% to 3.5%).
Overall, environmental damage from agricultural chemicals was reduced in the
organic systems because no commercial fertilizers or pesticides were applied
to the organic systems. As a result, overall public health and ecological
integrity could be improved through the adoption of these practices, which
decrease the quantities of pesticides and commercial fertilizers applied in
agriculture (BANR/NRC 2003, Pimentel 2005).
Oil and natural gas inputs. Significantly less fossil energy was expended to
produce corn in the Rodale Institutes organic animal and organic legume
systems than in the conventional production system (figure 1). There was
little difference in energy input between the different treatments for
producing soybeans. In the organic systems, synthetic fertilizers and
pesticides were generally not used. Other investigators have reported similar
findings (Karlen et al. 1995, Smolik et al. 1995, Dalgaard et al. 2001, Mader
et al. 2002, Core 4 2003, Pimentel et al. 2005). In general, the use of less
fossil energy by organic agricultural systems reduces the amount of carbon
dioxide released to the atmosphere, and therefore the problem of global
climate change (FAO 2003).
Crop yields and economics. Except for the 1999 drought year, the crop yields
for corn and soybeans were similar in the organic animal, organic legume, and
conventional farming systems. In contrast, Smolik and colleagues (1995) found
that corn yields in South Dakota were somewhat higher in the conventional
system, with an average yield of 5708 kg per ha, compared with an average of
4767 kg per ha for the organic legume system. However, the soybean yields in
both systems were similar at 1814 kg per ha. In a second study comparing wheat
and soybean yields, the wheat yields were fairly similar, averaging 2600 kg
per ha in the conventional system and 2822 kg per ha in the organic legume
system. Soybean yields were 1949 kg per ha and 2016 kg per ha for the
conventional and the organic legume systems, respectively (Smolik et al.
1995). In the Rodale experiments, corn, soybean, and wheat yields were
considerably higher than those reported in South Dakota. These results might
be expected, given the shorter growing season (146 days) and lower
precipitation (460 mm) in South Dakota.
European field tests indicate that yields of organically grown wheat and other
cereal grains average from 30% to 50% lower than conventional cereal grain
production (Mader et al. 2002). The lower yields for the organic system in
these experiments, compared with the conventional system, appear to be caused
by lower nitrogen-nutrient inputs in the organic system. In New Zealand, wheat
yields were reported to average 38% lower than those in the conventional
system, a finding similar to the results in Europe (Nguyen and Haynes 1995).
In New Jersey, organically produced sweet corn yields were reported to be 7%
lower than in a conventional system (Brumfield et al. 2000). In the Rodale
experiments, nitrogen levels in the organic systems have improved and have not
limited the crop yields except for the first 3 years. In the short term,
organic systems may create nitrogen shortages that reduce crop yields
temporarily, but these can be eliminated by raising the soil nitrogen level
through the use of animal manure or legume cropping systems, or both.
In a subsequent field test in South Dakota, corn yields in the conventional
system and the organic alternative system were 7652 and 7276 kg per ha,
respectively (Dobbs and Smolik 1996). Soybean yields were significantly higher
in the conventional system, averaging 2486 kg per ha, compared with only 1919
kg per ha in the organic alternative system.
The Rodale crop yields were similar to the results in the conventional and
organic legume farming system experiments conducted in Iowa (Delate et al.
2002). In the Iowa experiments, corn yields were 8655 and 8342 kg per ha for
the conventional and organic legume systems, respectively. Soybean yields
averaged 2890 kg per ha for the conventional farming system and 2957 kg per ha
for the organic legume system.
Although the inputs for the organic legume and conventional farming systems
were quite different, the overall economic net returns were similar without
premiums (figure 2). Comparative net returns in the Rodale experiments differ
from those of Dobbs and Smolik (1996), who reported a 38% higher gross income
for the conventional than for the organic alternative system. However, Smolik
and colleagues (1995) reported higher net returns for the organic alternative
system in their study with alfalfa and nearly equal returns in the green
Prices for organic corn and soybeans in the marketplace often range from 20%
to 140% higher than for conventional corn, soybeans, and other grains (Dobbs
1998, Bertramsen and Dobbs 2002, New Farm Organization 2003). Thus, when the
market price differential was factored in, the differences between the organic
alternative and conventional farming would be relatively small, and in most
cases the returns on the organic produce would be higher, as in the results
here for the FST.
In contrast to these results for corn and soybeans, the economic returns
(dollar return per unit) for organic sweet corn production in New Jersey were
slightly higher (2%) than for conventional sweet corn production (Brumfield et
al. 2000). In the Netherlands, organic agricultural systems producing cereal
grains, legumes, and sugar beets reported a net return of EUR 953 per ha,
compared with conventional agricultural systems producing the same crops that
reported EUR 902 per ha (Pacini et al. 2003).
In a California investigation of four crops (tomato, soybean, safflower, and
corn) grown organically and conventionally, production costs for all four
crops were 53% higher in the organic system than in the conventional system
(Sean et al. 1999). However, the profits for the four crops were only 25%
higher in the conventional system compared with the organic system. If the 44%
price advantage of the four organically grown crops were included, the organic
crops would be slightly more profitable than the conventional ones (Sean et
One of the longest-running organic agricultural trials (ongoing for more than
150 years) is the Broadbalk experiment at Rothamsted (formerly the Rothamsted
Experimental Station) in the United Kingdom. The trials compared a
manure-based organic farming system with a system based on synthetic chemical
fertilizer. Wheat yields were slightly higher on average in the manured
organic plots (3.45 t per ha) than in the plots receiving chemical fertilizers
(3.40 t per ha). The soil quality improved more in the manured plots than in
those receiving chemical fertilizer, based on greater accumulations of soil
carbon (Vasilikiotis 2004).
Challenges for organic agriculture. Two primary problems with the organic
system in the California study were nitrogen deficiency and weed competition
(Sean et al. 1999). This was also noted for the organic faming systems in the
US Midwest. Although the Rodale experiment overcame nitrogen deficiency
challenges through legume cover crop management, other researchers have been
less successful in maintaining and improving soil fertility levels in organic
systems. Rodale's results could also be influenced by geographical soil
characteristics and may not be universally applicable.
In organic production systems, pest control can be of heightened importance
and impact. Weed control is frequently a problem in organic crops because the
farmer is limited to mechanical and biological weed control, whereas under
conventional production mechanical, biological, and chemical weed control
options often are employed. Also, weather conditions can limit the efficacy of
weed control. Mechanical weed control is usually more effective than chemical
weed control under dry conditions, while the reverse holds true under wet
conditions. In the Rodale experiments, only the organic soybeans suffered
negative impacts from weed competition.
Insect pests and plant pathogens can be effectively controlled in corn and
soybean production by employing crop rotations. Some insect pests can be
effectively controlled by an increase in parasitoids; reports in organic
tomato production indicate nearly twice as many parasitoids in the organic
compared with the conventional system (Letourneau and Goldstein 2001).
However, increased plant diversity in tomato production was found to increase
the incidence of plant disease (Kotcon et al. 2001). With other crops, like
potatoes and apples, dealing with pest insects and plant pathogens that
adversely affect yields is a major problem in organic crop production.
Adoption of organic technologies. Several organic technologies, if adopted in
current conventional production systems, would most likely be beneficial.
These include (a) employing off-season cover crops; (b) using more extended
crop rotations, which act both to conserve soil and water resources and also
to reduce insect, disease, and weed problems; (c) increasing the level of soil
organic matter, which helps conserve water resources and mitigates drought
effects on crops; and (d) employing natural biodiversity to reduce or
eliminate the use of nitrogen fertilizers, herbicides, insecticides, and
fungicides. Some or all of these technologies have the potential to increase
the ecological, energetic, and economic sustainability of all agricultural
cropping systems, not only organic systems.
Various organic agricultural technologies have been used for about 6000 years
to make agriculture sustainable while conserving soil, water, energy, and
biological resources. The following are some of the benefits of organic
technologies identified in this investigation:
* Soil organic matter (soil carbon) and nitrogen were higher in the organic
farming systems, providing many benefits to the overall sustainability of
* Although higher soil organic matter and nitrogen levels were identified for
the organic systems, similar rates of nitrate leaching were found to those in
conventional corn and soybean production.
* The high levels of soil organic matter helped conserve soil and water
resources and proved beneficial during drought years.
* Fossil energy inputs for organic crop production were about 30% lower than
for conventionally produced corn.
* Depending on the crop, soil, and weather conditions, organically managed
crop yields on a per-ha basis can equal those from conventional agriculture,
although it is likely that organic cash crops cannot be grown as frequently
over time because of the dependence on cultural practices to supply nutrients
and control pests.
* Although labor inputs average about 15% higher in organic farming systems
(ranging from 7% to 75% higher), they are more evenly distributed over the
year in organic farming systems than in conventional production systems.
* Because organic foods frequently bring higher prices in the marketplace, the
net economic return per ha is often equal to or higher than that of
conventionally produced crops.
* Crop rotations and cover cropping typical of organic agriculture reduce soil
erosion, pest problems, and pesticide use.
* The recycling of livestock wastes reduces pollution while benefiting organic
* Abundant biomass both above and below the ground (soil organic matter) also
increases biodiversity, which helps in the biological control of pests and
increases crop pollination by insects.
* Traditional organic farming technologies may be adopted in conventional
agriculture to make it more sustainable and ecologically sound.
We thank the following people for reading a draft of this article and for
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Sinica, Shenyang, China; Tomek De Ponti, Visiting Fulbright Scholar, Cornell
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David Pimentel (e-mail: email@example.com) works in the Department of
Entomology, College of Agriculture and Life Sciences, at Cornell University,
Ithaca, NY 14853. Paul Hepperly and Rita Seidel are with the Rodale Institute,
611 Siegfriedale Road, Kutztown, PA 19530. James Hanson works in the
Department of Agricultural and Resource Economics at the University of
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Research Service, Eastern Regional Research Center, 600 E. Mermaid Lane,
Wyndmoor, PA 19038.