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 th e dredged sediment result in the continuous establishment of contaminated s ites. As this dredged sediment is rich in nutrients, occupies extended area s and is often unsuitable for agriculture and public works due to the prese nce of contaminants, planting energy crops is one option for the remediatio n of this waste material. To evaluate dredged sediment as a substrate for g rowing willows, a 20 x 150 m disposal depot was successfully planted using rolls of connected willow rods (SALIMAT). Rods of a Salix fragilis clone an d a Salix triandra clone were equally mixed in each mat. This SALIMAT prove d to be an economic and effective planting technique for large areas of wet substrate. Leaf nutrient contents were determined to identify potential li miting 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 w ere supplied with sufficient N, P, K and Ca to ensure optimal growth. The i ntroduction of SALIMAT resulted in the rapid development of a high-density fast growing stand characterised by shoot densities of up to 54 shoots/m(2) . 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 wa s suppressed by Salix fragilis. The development of a willow stand was unsuc cessful on parts of the depot with a sand fraction of 60%. (C) 2001 Elsevie r Science Ltd. All rights reserved.