ISIS Report 09/12/04
Organic Production Works
A new study shows organic production outperforms conventional in crop
yield, soil fertility, pest reduction and economic return.
Rhea Gala reports
this report are posted on ISIS members website.
Transition to organic production
Increasing public demand for organic products attracts premiums for the
certified organic farmer, causing hard-pressed conventional farmers to consider
In the US, a 20% annual growth rate caused sales of organic produce to
reach $8 billion in 2001; and incentives to farmers to go organic are offered
in the 2002 Farm Bill, including cost sharing, and direct payments for
conservation practices, such as longer crop rotations.
Scientists Kathleen Delate of Iowa State University and Cynthia A.
Cambardella of the US Department of Agriculture assessed the agroecosystem
performance of farms during the three-year transition it takes to switch from
conventional to certified organic grain production. Strategies for lowering the
risk of yield loss during this period have been researched, as productivity has
been found to decrease initially when fertilizer and pesticide applications are
withheld. But productivity generally improves in successive years under organic
management to equal that in conventional farms. The study found that organic
grain crops can be successfully produced in the third year of transition and
that additional economic benefits can be derived from expanded crop
The experiment, lasting four years (three years transition and first
year of organic certification), tested the hypothesis that organic systems
relying on locally derived inputs are capable of providing stable yields while
maintaining soil quality and plant protection compared with conventional
systems with less diverse crop rotations and greater levels of external,
fossil-fuel based inputs. The experimental design involved a completely
randomized four replications of four different cropping system treatments.
The researchers looked at the effects of organic farming practices,
including crop rotation, cover cropping, compost application, and non-chemical
weed control on soil fertility, crop yield, and grain quality compared with the
conventional system. They assessed pests and plant response under various crop
rotations, and determined which certified organic drop rotations reduced the
risks from low yield and improved soil properties and economic returns.
Organics performed as well or better
During the four-year period, corn yield in the organic system averaged
91.8% of conventional corn yield and soybean yield in the organic system
averaged 99.6% of conventional soybean yield. By year three, there was no
significant difference between organic and conventional yields; and both
organic corn and soybeans exceeded conventional yields in the fourth year (the
first year after certification).
In the initial year of transition, an economic advantage could be
gained by planting legume hay crops or crops with a low nitrogen demand in
fields with low productivity, to increase fertility for the following corn
crop. In the second year, yield differences were mitigated by rotation effects
and compost application, providing sufficient nutrients for the organic grain
crop. The yields in year three were similar, but the importance of a
soil-building cover crop, or legume grass mixture such as the oat-alfalfa
mixture used in this study was apparent in the fourth year when organic corn
and soybean yields out-performed the conventional crops.
The researchers thought that timely weed management and sufficient
levels of nitrogen, phosphate and potassium in the organic system contributed
to good yields during transition. Yield increases were obtained after three
years because of available nitrogen due to organic amendments, such as
composted pig manure and the inclusion of forage legumes and other green
manures in extended crop rotations.
Soil fertility depends on the constant renewal of biologically available
nitrogen to replenish the organic nitrogen pools for plants to absorb. Total
nitrogen levels showed an increase of 457 kg per hectare in organic soil over
four years, or an average increase of 114 kg N per ha per annum, sufficient to
maintain organic nitrogen pools in this system. Total organic calcium increased
9% in organic soil over the transition period, with no significant increase in
The researchers found weed pressure in the organic corn and soybean
systems was manageable, and that it was less in organic soybean than in corn
plots where rye was not used as a cover crop. In the soybean-rye rotation, weed
densities were equivalent to conventional systems in the first two years, and
significantly less in the third year. Grass and broadleaf weed populations
varied between the organic and conventional systems each year, but the impact
on yield was considered negligible. Corn borer and bean leaf beetle populations
were similar between systems, again with no effect on yield.
Economic returns in the organic corn-soybean-oats/alfalfa and the
organic corn-soybean-oats/alfalfa-alfalfa rotations were significantly greater
than those in the conventional corn-soybean rotation, as organic soybean
commands premium prices in the organic rotation due to increased demand.
A previous study had found enhanced soil fertility and higher
biodiversity were correlated with less dependence on inputs in the organic
systems, reducing fertilizer and energy inputs by 44% and pesticide by 97%.
The study continues
This study is ongoing, and will continue to examine the effect of crop
sequence and length of rotation on long-term pest disruption and attraction of
beneficial insects into the organic systems. Earlier work by Miguel Altieri at
University of California, Berkeley, showed that greater biological control
should occur in organic systems that maintain diverse biota through minimal
pesticide use (see "Agroecology vs ecoagriculture", ISIS report
Potential food quality changes will also be monitored over time, so that
assessments of the advantages of organic production over conventional systems
can be brought more to the foreground of the debate on organic versus
conventional production. As organic farmers produce high quality food without
conventional inputs from agribusiness, agribusiness has a vested interest in
denigrating organic systems on any account. This research is essential in
countering the corporate disinformation campaign.