Seedling emergence through soil surface seals under laboratory conditions: effect of mechanical impedance and seal moisture

It is well known that soil sealing strongly affects seedling emergence. The effect of soil sealing on the emergence of flax and turnip seedlings was studied in the laboratory. Seeds were sown in pots, watered, then covered with loamy soil and water was added. Three different doses of water were tested. Soil sealing was obtained with a paste of soil mixed with distilled water, added to each pot as a thick homogeneous, continuous and isotropic layer. The initial water content of the seal was measured. When seedling emergence was observed (or at the end of the experiment in the case of event failure), seal strength was measured in situ by a firmness pressure tester (used as a penetrometer). Relationships between water loss and initial moisture of the seal versus mechanical impedance were obtained. Differences in emergence success between species depended on the initial soil water content as well as on the initial seal moisture. A model of seedling emergence success of the two species, flax and turnip, as a function of the initial seal moisture content was obtained using a binary logistic regression model.