| September 19,
2003: Some interesting patterns have emerged
from another long-term organic vs. conventional management
trial, published this year in Agronomy Journal. The research
was carried out at the University of Minnesota and has
been running since 1989. This research complements similar
organic vs. conventional management comparative research
on corn-soy done at The Rodale Institute Farming Systems
Trial (FST), and several other universities.
The treatments were: 2-year and 4-year rotations, each
with zero (ZI), organic (OI), low (LI), and high inputs
(HI) management strategies. All of these combinations
(i.e. 2-yr ZI, 4-yr ZI, 2-yr OI, etc.) were carried
out on both a previously intensively farmed site as
well as a previously non-intensively farmed site. The
2-year rotation was corn-soy, and the 4-year was corn-soy-oat-alfalfa.
Organic fertilizer used on OI was steer and swine manure
at recommended rates, and was comparable to the LI fertility
levels. Via replication and staggered rotations, every
crop in every treatment combination produced yield in
every year. The 2-yr HI is used as a yield standard,
since this strategy typifies conventional agriculture.
Averaged over 1993-1999, corn yields in the 4-yr OI
treatment were 95% of the 2-yr HI treatment, while OI
soybean yields were 82% relative to HI. The larger reduction
in OI soybean yields compared to OI corn, when both
are compared to HI, is a pattern that almost exactly
replicates The Rodale Institute’s long-term corn-soy
organic vs. conventional experiments.
The authors of the study attribute the yield differences
between OI and HI to weed pressure in the OI, which
is another recurring theme in organic vs. conventional
Also similar to The Rodale Institute’s results
was a reduction in OI soy yields in the second half
of the experiment. The Rodale FST has two organic treatments,
a legume and a manure treatment, and the manure treatment
was the one with declining yields. The Minnesota study
uses manure on all of the OI plots, which suggests that
there may be a problem with long-term use of manure
on soybean crops.
Weeds in the 2-yr OI treatment seriously reduced yields
in both corn and soybean, compared to the 4-yr rotation.
The 2-yr rotation OI yields were reduced 40% and 21%,
respectively, in the corn and soy, compared to the 4-yr,
demonstrating the importance of rotations in organic
As demonstrated in other studies, the net returns in
the OI system were equivalent to the HI system, despite
the lower yields, even without organic price premiums.
This is due to the lower input costs of organic systems.
Based on this, the authors conclude that organic crop
systems are a viable management choice for farms.
Porter, P.M. et. al. Organic and Other Management Strategies
with Two- and Four-Year Crop Rotations in Minnesota.
Agronomy.Journal 95: 233-244. 2003
Farming Systems Trial: the first 15 years. The Rodale