Dredged sediment as a substrate for biomass production of willow trees established using the SALIMAT technique

The periodic dredging of inland waterways and the subsequent disposal of the dredged sediment result in the continuous establishment of contaminated sites. As this dredged sediment is rich in nutrients, occupies extended areas and is often unsuitable for agriculture and public works due to the presence of contaminants, planting energy crops is one option for the remediation of this waste material. To evaluate dredged sediment as a substrate for growing willows, a 20×150 m disposal depot was successfully planted using rolls of connected willow rods (SALIMAT). Rods of a Salix fragilis clone and a Salix triandra clone were equally mixed in each mat. This SALIMAT proved to be an economic and effective planting technique for large areas of wet substrate. Leaf nutrient contents were determined to identify potential limiting growth factors Biomass production and tree survival over 4 years of stand development were assessed for three different planting spacings (10, 20 and 40 cm). Results of the foliar analyses indicated that both species were supplied with sufficient N, P, K and Ca to ensure optimal growth. The introduction of SALIMAT resulted in the rapid development of a high-density fast growing stand characterised by shoot densities of up to 54 shoots/m2. An average annual production of 13.4 ton DM/ha was measured. The mixture of the two clones did not result in a polyclonal stand as Salix triandra was suppressed by Salix fragilis. The development of a willow stand was unsuccessful on parts of the depot with a sand fraction of 60%.