Scientists compare organic and conventional grain yields and address production challenges in organic cropping systems
demand for organic meat and milk is increasing by about 20% per year in
the United States, almost all organic grain and forage to support these
industries in the mid-Atlantic region is imported from other regions.
To meet this demand locally, area farmers need information on expected
crop yields and effective management options.
Scientists in the Sustainable Agricultural Systems Laboratory at the
USDA-Agricultural Research Service (ARS) Beltsville Agricultural
Research Center (BARC) in Maryland have studied the impact of diverse
organic cropping systems on crop yields over a ten year period. Results
from the study, which was funded by USDA-ARS, were published in the
May-June issue of Agronomy Journal.
The researchers collected
data on crop yields, nitrogen inputs, weed densities, and crop
populations from the USDA-ARS Beltsville Farming Systems Project (FSP),
a long-term cropping systems trial with two conventional and three
organic systems that was established in 1996. The three organic systems
differed in crop rotation length and complexity.
revealed that corn and soybean yields in organic systems were, on
average, 76 and 82%, respectively, of those in conventional systems in
years with normal weather. Winter wheat yields were similar among
systems. Corn yields were lower in the organic than in the conventional
systems primarily due to lower nitrogen availability in the organic
systems, which rely on legume crops and animal manures. Weed
competition also contributed to lower corn grain yields in organic
systems. For soybean, weed competition alone accounted for differences
in yield between organic and conventional systems.
systems crop rotation length and complexity had a strong impact on corn
grain yield. A crop rotation that included corn, soybean, wheat and hay
resulted in average corn grain yield 30% greater than in a simple
corn-soybean rotation and 10% greater than in a corn-soybean-wheat
rotation. Differences were due to increased nitrogen availability and
lowered weed competition with increasing crop rotation length and
complexity. Crop rotation length and complexity did not affect soybean
and wheat yields.
Dr. Michel Cavigelli, lead author of the
study, stated, "These research results show that longer, more complex
crop rotations can help address the two most important production
challenges in organic grain crop production: providing adequate
nitrogen for crop needs and decreasing weed competition." This research
should help organic farmers and those considering transitioning to
organic farming select crop rotations best suited for the mid-Atlantic
region. Since the FSP is one of only a handful of long-term cropping
systems trials that includes diverse organic crop rotations, these
results will also be of interest to organic farmers and those working
with organic farmers nationwide.
Ongoing research at the
USDA-ARS Sustainable Agricultural Systems Lab at BARC is designed to
increase soil nitrogen availability and decrease weed pressure in
organic grain crop rotations.
American Society of Agronomy. May 2008.