Rye-corn silage double-cropping reduces corn yield but improves environmental impacts

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 highrate 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. Doublecropping addressed each concern but often decreased forage production.