Agroecosystem performance during transition to certified organic grain production

The 2002 U.S. Farm Bill offers incentives to support the transition from conventional to certified organic production. Research-based recommendations must be developed for suitable crop rotations that provide high yields, grain quality, and adequate soil fertility during the transition. We compared replicated conventional and organic systems, using identical crop varieties, during the 3-yr transition period and the fourth year following a full rotation of organic corn (Zea mays L.)-soybean [Glycine max (L.) Merr.]-oat (Avena sativa L.)-alfalfa (Medicago sativa L.) to determine which rotation was associated with the lowest risk during transition. Organic feed corn yields at the Neely-Kinyon long-term agroecological research (LTAR) site in Greenfield, IA, were equivalent to conventional yields in the transition years, and in the fourth year, the organic corn yield of 8.1 Mg ha(-1) in the longest rotation was greater than the conventional corn yield of 7.1 Mg ha(-1) in the conventional corn-soybean rotation. Organic and conventional soybean yields were similar in the 3 yr of transition. Organic soybean yield of 3.0 Mg ha(-1) exceeded the conventional yield of 2.7 Mg ha(-1) in the fourth year of organic production. Pre- and postharvest soil fertility values were responsive to manure application, but few differences between systems were observed. Grass and broadleaf weed populations varied between the organic and conventional systems each year, but the impact on yield was considered negligible. Corn borer (Ostrinia nubilalis) and bean leaf beetle (Ceratoma trifurcata) populations were similar between systems, with no effect on yield. We conclude that organic grain crops can be successfully produced in the 3 yr of transition to organic, and additional economic benefits can be derived from expanded crop rotations.