Natural weed seed burial: effect of soil texture, rain and seed characteristics

Trials were carried out to investigate natural weed seed burial in a no-till agricultural system. With this aim, 30 important weed species were selected to explore if, and to what extent, seed vertical movement is conditioned by soil texture, cumulative rainfall or by seed characteristics. Without soil tillage, the vertical position of the seeds was only a few millimetres below the surface, but it was dependent on soil texture. Seed burial was much slower (and to lesser depths) in clay soils than in sandy soils. Seeds reached greater depths after 1 year in sandy soil (10% > 6 mm) than in clay soils (2% > 6mm), Burial dynamics were also influenced by rainfall and seed weight. The amount of rain necessary to halve weed seeds observable on the soil surface was a function of the soil texture and seed weight; linear regressions between total rainfall amounts and seed weight showed that the slope of the relationship increased as the sand component of the soil decreased (21.1, 35.4 and 39.4 in sandy, loam and silty-clay soil, respectively). A polynomial regression, carried out in sandy soil, between 1000-seed weight and their burial capacity showed an inverse relation (P > 0.05) between these two parameters. Seed shape and coat microsculpture also influenced movement, but only minimally.