Winged coulter depth effects on overdrilled red clover seedling emergence

The effect of depth variation of the winged ‘chisel’ coulter on overdrilled red clover ( Trifolium pratense L.) seedling emergence was studied by controlling depth at 0, 13, and 39 mm below the soil surface in a dry soil in autumn and at 0, 13, 26, and 39 mm in 3 different soils in spring. Near full emergence (90‐95%) at 13 mm depth and lower emergence at 0, 26, and 39 mm was observed in all soils, despite a 3‐fold increase in soil gravimetric water content and an almost doubling of soil strength. Red clover seedling emergence was the same after spraying either paraquat or glyphosate in 50 mm wide bands ahead of the coulter. Few seeds survived more than 5 weeks below ground. Some seedlings at 0 mm failed to penetrate the soil surface with a rootlet before expanding their cotyledons, particularly when sown in autumn. Patterns of seed germination, seedling emergence, and seed loss in autumn are used to discuss problems associated with surface placement and planting at depth. It is concluded that seed placement should be given higher priority than at present in programmes developing overdrilling and direct drilling machinery.