Using the SALIMAT technique to establish a willow vegetation cover on wet substrates

Dredging of inland waterways in the Flanders region (Belgium) 'produces' about 1 500 000 million m3 yr-1 of slightly polluted sludge. This material, which consists mainly of soil particles, is hydraulically transported to lagoons where the suspension is dewatered by superficial draining. Due to its wet conditions the sludge deposit is an impassable swampy terrain. As a consequence, normal planting methods cannot be used. Through applied research the SALIMAT technique was developed as a practical, low-cost and mechanized planting method for willow species. SALIMAT consists of a roll of willow rods rolled around a central disposable tube. Biodegradable string is used to tie the rods in place. The SALIMATS are unrolled (horizontally) by dragging them across the lagoon with a crane and drag line. Under its own weight SALIMAT sinks slightly in the sludge and plants itself. It is protected from desiccation by a water and sludge layer. In each SALIMAT, clones from Salix triandra L. and Salix fragilis L. are mixed to avoid the risks of mono-clonal planting. Analysis of growth, vitality and heavy metal take-up are carried out in order to assess ecotoxicological effects. Considering its good growth response (biomass boom), SALIMAT seems at present to be the best available technique to introduce vegetative planting material on recent marshlands and organic or inorganic sludge disposal sites. The technique offers many advantages: (i) off-site mechanical manufacturing, (ii) easy to store and transport and (iii) applicable during several months when field conditions are optimal. 4 figs, 3 tabs