Rye–Corn Silage Double‐Cropping Reduces Corn Yield but Improves Environmental Impacts

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Recent proliferation of large dairies has prompted concern regarding environmental impacts of associated corn silage production and high‐rate manure application. Our objectives were to compare environmental impacts and forage production of monocrop corn (Zea mays L.) silage and rye (Secale cereal L.)–corn silage double‐crop systems with multiple corn planting dates and high‐rate manure application near Morris, MN. From 2007 to 2009, corn for silage was seeded into a silt loam as a monocrop in early and mid‐May and as a double‐crop after rye in mid‐May and early June. Manure was fall applied annually at average total N and P rates of 393 and 109 kg ha−1, respectively. Double‐cropping reduced total forage dry matter (DM) yield 2 of 3 yr and reduced corn DM yield 15 to 25%. Soil NO3–N to 90 cm accumulated at an average rate of 71 kg N ha−1 yr−1 with monocropping, but accumulation was not observed with double‐cropping. Soil organic C concentration from 0 to 5 cm increased in the monocrop (18%) and double‐crop (26%) systems over 3 yr. Average soil solution NO3–N concentration was high with monocropping (52 mg L−1) and double‐cropping (37 mg L−1), but estimated leaching load averaged only 8 kg ha−1 yr−1. Fall and spring ground cover was often less than 10% with monocropping but was usually greater than 30% with double‐cropping. The primary environmental concerns identified for monocrop corn silage were soil NO3–N buildup and inadequate ground cover. Double‐cropping addressed each concern but often decreased forage production.