June 2, 2008

 

US studies show lower corn yields in organic systems than in conventional

   

  

A 10-year study by the USDA-Agricultural Research Service (ARS) revealed that corn yields were lower in the organic than in the conventional systems primarily due to lower nitrogen availability.

 

Scientists in the Sustainable Agricultural Systems Laboratory at the ARS Beltsville Agricultural Research Center (BARC) in Maryland have looked into the impact of diverse organic cropping systems on crop yields over a ten-year period.

 

The researchers gathered 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.

 

US researchers found that corn and soy 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.

 

The group noted that 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 soy, 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, soy, wheat and hay resulted in average corn grain yield 30 percent greater than in a simple corn-soy rotation and 10 percent greater than in a corn-soy-wheat rotation.

 

Differences were attributed to increased nitrogen availability and lowered weed competition with increasing crop rotation length and complexity.

 

Results from the study were published in the May-June issue of Agronomy Journal.