Precision Management Could Lead to Successful Cover Crop Establishment When Interseeded into Soybeans.

In South Dakota, few options exist for seeding cover crops after soybean harvest due to the limited growing season that remains. Interseeding cover crops into a growing soybean crop may provide additional time for growth. However, interseeding too soon may reduce soybean yield and/or interfere with soybean harvest. In 2015, a strip trial was initiated in a soybean production field in northeast South Dakota on a Forman-Buse-Aastad soil with 1-9% slopes. A cool-season mix of 30% annual ryegrass (Lolium multiflorum), 20% forage radish (Raphanus sativus), 20% turnip (Brassica campestris), 20% crimson clover (Trifolium incarnatum L.), and 10% dwarf essex rapeseed (Brassica napus L.) was drilled at 6.2 kg/ha in a single row half-way between 76 cm soybean rows on August 6, 2015 [soybean at R3 (beginning pod)]. Three 15-row wide strips were seeded using a 5-row drill modified for the interrow seeding. Seed was also surface broadcast by hand at 16.8 kg ha-1 onto a 3 m x 3 m area adjacent to the strips at the footslope and backslope landscape positions. The soybean crop was harvested on Sept. 26 using a combine with a 14-row head and equipped with a calibrated yield monitor. Cover crop biomass was collected on Nov. 10. Each cover crop sample consisted of 3 reps where 0.92 m of row length was collected for each rep for the turnip, forage radish, and dwarf essex and 0.31 m of row length for annual ryegrass and crimson clover. For the broadcast treatments, 0.09 m2 was collected for all species. Soybean yields compared to adjacent no cover crop areas had similar yields at all landscape positions. The highest cover crop yields were measured from footslope positions. Biomass was similar in the drilled and broadcast treatments, although seeding rate in the drilled area was one-third the seeding rate. The drilled treatment had almost three times the biomass in the backslope areas compared with the broadcast treatment. Precision species selection also may be beneficial, as turnip biomass was greater in the backslope areas, whereas radish biomass was greater in the footslope position.