Interseeding Cover Crops in Michigan Corn Rotations.

Time constraints limit the opportunity to seed cover crops in the fall in Michigan following corn harvest. Interseeding cover crops into corn during the vegetative growth stage may suppress weeds and increase cover crop biomass and soil health benefits. However, cover crops may be competitive with corn if seeded too early. The objectives of this research were to evaluate the establishment and competitiveness of annual ryegrass, crimson clover, and tillage radish interseeded into corn from V1-V6, and to evaluate their effects on weed suppression and soil health. In 2015 and 2016, cover crops were broadcast seeded into corn at the V1, V2, V3, V4, V5, and V6 growth stages at East Lansing, MI. Seeding rates were 17 kg/ha, 17 kg/ha, and 9 kg/ha for annual ryegrass, crimson clover, and tillage radish, respectively. Weed free and no cover control plots were also included. Cover crop and weed density were measured 30 days after each seeding time. Cover crop and weed density and biomass were measured in October prior to corn harvest, and again the following spring in April. Soil chemical and biological health were assessed via carbon mineralization potentials, soil nutrient availability, and extracellular enzyme activities in late summer and the following spring. Weed density in corn was greatest at V1 and decreased for each successive seeding time. In October, annual rye biomass exceeded biomass of tillage radish and crimson clover for all seeding times except V1. Cover crop biomass in October was generally the greatest when seeded at the V4 and V5 stage of corn. Corn yield was reduced for the V1 seeding time but was unaffected by all other cover crop seeding times.