Modelling vertical and lateral weed seed movements during mouldboard ploughing with a skim-coulter

Abstract

The vertical distribution of weed seeds in soil is crucial because seedling emergence varies with seed depth, whereas lateral soil displacement during mouldboard ploughing contributes to weed dispersal within the tilled field. In order to model vertical and lateral seed displacements during ploughing, an existing model describing soil particle movements for different ploughing characteristics (depth and width) and soil structures was adapted to integrate the effect of a skim-coulter. This model was tested in two field trials, in Northern France, using coloured plastic beads to imitate weed seeds. The trial in Dijon was set up on an eutric cambisol and comprised both compacted and uncompacted soil. The second trial was set up at Grignon, on an orthic luvisol which was left uncompacted before ploughing. The model correctly simulated the lateral displacement (LD) and the final vertical co-ordinate of the beads as a function of their initial location, soil structure before ploughing and ploughing parameters (ploughing depth and width; skim-coulter depth and width). The model was then used to calculate seed transfer matrixes describing vertical seed movements between seed bank layers and vertical seed distributions for different conditions and plough modes. The results were consistent with those of Cousens and Moss [Weed Res. 30 (1990) 61–70]. Simulations were performed to test the effect of different ploughing modes on the time changes in the vertical distribution of weed seeds and to show how the model can be used to manage weed seed concentration in the top layer by soil tillage. Furthermore, simulations showed that the vertical distribution of the seed bank could be extremely variable, depending on plough characteristics, soil structure or initial seed distribution. Although further studies are needed on the long-term seed movements under the influence of secondary tillage and climate, this model can be useful for evaluating different tillage modes on seed dispersal within the ploughed layers.