Transition Strategies for Post-CRP Certified Organic Grain Production

Post-Conservation Reserve Program (CRP) land may provide an excellent opportunity to satisfy certified organic crop production requirements. However, conversion of CRP or long-term pastureland to certified organic production will require tillage because the use of herbicides is prohibited in organic production. Our objectives were to evaluate stand establishment, weed competition, yield, and grain quality for soybean (Glycine max [L.] Merr.), corn (Zea mays L.), and oat (Avena sativa L.) planted following primary tillage of bromegrass (Bromus inermis L.) and alfalfa (Medicago sativa L.) sod in south-central Iowa. Primary tillage treatments were fall moldboard plowing, fall tillage with a Kverneland(R) plow, fall and spring tillage with a Howard Rotavator(R), and spring moldboard plowing. Type of primary tillage did not affect first-crop soybean yield in the first year of the study, but first-crop soybean yields were greatest with spring moldboard plowing in the second year's evaluation. Corn yields in the second year plots were greater for both the fall and spring moldboard plow treatments than for the fall/spring rotary tillage treatment. Rotary hoeing reduced soybean stand more than expected (∼40%) in the first year, but differences among primary tillage treatments were not significant. In the second year, the rotary tillage treatment had significantly lower soybean stand, possibly because of surface crusting. There were some significant differences in grass and broad leaf weed populations in the corn and soybean each year, but overall weed control was considered sufficient. Insect pressure from corn borer (Ostrinia nubilalis [Hübner]) and beanleaf beetle (Cerotoma trifurcata [Forster]) was below economic threshold levels. Crop yields exceeded the county average each year, suggesting that weed and insect pest competition were negligible. We conclude that organic grain crops can be successfully produced following CRP or other long-term hay/pasture crops regardless of the primary tillage method used to till the sod.