Emergence of sugar beet (Beta vulgaris L.) from seedbeds after glass waste deposition on soil

One part of the collected bottle glass cannot be recycled because small fragments cannot be separated from organic matters and metal residues. One possible way of getting rid of this unrecycled glass is to incorporate it into the ploughed layer of the soil. The incorporated glass fragments will alter the physical state of the soil, particularly the seedbed. We studied the consequences of such a change in soil physical properties on sugar beet emergence in laboratory experiments and using a model for estimating the effects on emergence under more realistic sowing conditions. We examined the effects of fine (<6 mm) and coarse (6–15 mm) glass fragments used as (i) a 2 cm thick mulch, (ii) incorporated into a glass–soil mixture (40% or 80% glass), or (iii) into 20, 30 and 40 mm diameter clods. The glass used as mulch or in the glass–soil mixture did not reduce the emergence final rate. The seedling tortuosity was not significantly higher with mulch, emergence was only slowed by the increased (soil+glass) depth. High glass–soil content (80%) also slowed emergence, but because of the reduced seed–soil contact, which slowed imbibition. Moreover, many seedlings remained trapped under the 80% glass clods because of their very rough surface. The SIMPLE model was parameterized using these experimental data. It was run to evaluate the combined impact of the change in clod roughness taking into account numbers, sizes and spatial arrangements of clods from field observations of seedbeds, the increase in temperature due to the glass (about 2 °C per day), and the increased sowing depth due to the mulch. The simulated consequences of glass waste deposition on seedling emergence in field conditions were limited, except for the advance in seedling emergence due to the thermal effect.