Winged coulter depth effects on overdrilled red clover seedling emergence

Abstract

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.

Planting depth effects on overdrilled seedling survival in summer

“…DISCUSSION Planting depth in untilled seedbeds apparently needs only to be sufficient to create a moistureretaining groove (Baker 1976) enclosing the seed (i.e., the 13 mm coulter depth for the winged coulter). Overdrilled seedling emergence can be optimised (90-95% of sown seed) at this coulter depth (Campbell 1985) even in dry soil, and results of this study suggest that seedlings are not disadvantaged after emergence by originating higher in the soil profile than they would with deeper drilling. Seedlings were apparently no more vulnerable to environmental stresses with a 13 mm coulter depth than if placed deeper in soil.…”

“…Seeds were spaced at 50 mm intervals to allow easy identification of seedlings. Additional details of drilling technique are given in Campbell (1985).…”

“…Roots developed to similar length (measured from the shoot base) at all 3 depths under the surface, even though deeper planting placed seeds further down the profile initially. If deeper drilling were to counterbalance possible adverse effects of delays in emergence at depth in these seedbeds (Campbell 1985) by improving water relations (or any other environmental factor associated with dry soils) to enhance seedling survival, it should have been expressed in this study. The observed seedling survival response to an increased quantity of RAW in the seedling root zone (0-15cm approximately; Table 1)implies that, as the soil dried, seedlings were sensitive to any improvement in moisture relations that may have resulted from deeper drilling.…”

“…In addition, deeper planting can increase rooting depth (even if root length from seed position stays constant) by initially placing seeds further down the profile (Tadmor & Cohen 1968). Shallow planting to optimise emergence (Campbell 1985) could jeopardise seedling survival in this situation.…”

Sowing Method Effects on Clover Establishment into Permanent Pasture

“…Both no‐till drilling and broadcasting have strengths and weaknesses. The advantage of no‐till drilling is more control over seeding depth to ensure good seed‐to‐soil contact (Campbell, 1985a). A disadvantage of no‐till drilling is that use can be limited by steep topography.…”