MODELING THE EFFECT OF WEED-SEED DISTRIBUTION IN THE SOIL-PROFILE ON SEEDLING EMERGENCE

Experiments to monitor weed seedling emergence from various soil depth s were begun in 1989. Recently shed seeds were buried in either narrow bands at a range of depths in the soil or mixed evenly between the so il surface and each of these depths. Total emergence of Stellaria medi a (L.) Vill., Matricaria spp., Veronica persica Poiret, Veronica arven sis L. and Polygonum aviculare L., declined with increasing depth of b urial. A similar pattern was observed for Chenopodium album L. with th e exception of emergence from the surface layer. The reduction in emer gence with increasing soil depth was greater for seeds in the narrow-b anded treatments than for those in broad layers. A model was developed using the data from the narrow-banded treatments to predict emergence from distributions over broad layers. Predictions from the model clos ely agree with the data from the present broad-layer treatments and th ose from a similar experiment made in the 1960s. By including the effe cts of depth of seed burial on seedling emergence, this model could be combined with models that determine the effects of cultivation on see d distribution, and therefore improve precision of predictions of seed ling emergence from the seedbank.