10-year study on organic corn yields

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.

The study 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.

Among
organic 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.

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