Organic and other management strategies with two- and four-year crop rotations in Minnesota

In the USA, the corn (Zea mays L.)-soybean [Glycine mar (L.) Meir.] rotation depends on high levels of external inputs. Few research data exist comparing conventional production practices with practices involving reduced external inputs and expanded rotations. Two trials initiated in 1989 near Lamberton, MN, evaluated a 2-yr corn-soybean rotation and a 4-yr corn-soybean-oat (Avena sativa L.)/alfalfa (Medicago saliva L.)-alfalfa rotation under four management strategies. The four management strategies were zero (ZI), low (LI), high (HI), and organic (OI) inputs. One trial (V1) was on land with a history of no fertilizer and pesticide usage. The other trial (V2) was on land with a history of conventional fertilizer and pesticide usage. From 1993 through 1999, average corn yield in the 2-yr HI strategy was 8.96 Mg ha(-1) in V1 and 8.72 Mg ha(-1) in V2. Corn yield in the 4-yr HI strategy was 4% less than in the 2-yr HI strategy in V1, whereas in V2, the yields were not different. Soybean yield in the 2-yr HI strategy was 2.90 Mg ha(-1) in V1 and 2.74 Mg ha(-1) in V2. Soybean yield in the 4-yr compared with the 2-yr HI strategy was 3% greater in V1 and 6% greater in V2. These results suggest soybean was more responsive than corn to the expanded rotation length in the HI strategy. Corn yield in the 4-yr OI strategy compared with the 2-yr HI strategy was 9% less in V1 and 7% less in V2 while soybean yield in the 4-yr OI strategy compared with the 2-yr HI strategy was 19% less in V1 and 16% less in V2. These results suggest that yield of organically produced soybean was reduced to a greater extent than that of organically produced corn relative to conventional production practices.' By comparing yields of the 2- and 4-yr rotations for each management strategy, this research documents the beneficial yield effects of the expanded crop rotation, which can be masked by external inputs in the LI and HI treatments.