Effects of depth of seed burial and soil aggregate size on seedling emergence of Alopecurus myosuroides, Gallium aparine, Stellaria media and wheat

Seedling emergence of Alopecurus myosuroides Huds., Stellaria media L. (Vill.), Galium aparine L. and wheat (Triticum aestivum L.) was compared at a range of depths of soil cover from 2 to 11 cm, The covering soil was a fertile agricultural soil with 60% clay content which had been sieved into four aggregate sizes. The aggregate sizes used were 26-50 mm, 14-25 mm, 6-13 mm and below 6 mm. Total emergence of all species was reduced with increased depth of soil cover. With A. myosuroides and S. media, total emergence was lowest in fine soil conditions. Alopecurus myosuroides showed a marked interaction whereby response to depth of sowing was least with fine tilth. The time to 50% emergence showed a similar response. With all four species, seedling emergence was slowest at greater depths of sowing and with the finest tilth, the differences tending to increase with increasing depth of sowing. A very high proportion of the time to 50% emergence was accounted for by the lag time between sowing and the first recorded emergence.