Techniques for separation of green parts, and nutrient content in green parts

Collection of wood residues such as branches, twigs and needles after felling leads to the removal of nutrients from the site, which in general is a negative effect. Against this background a number of studies have been conducted to examine the technical possibilities and ecological value of separating the green parts. The following studies have been made and the results are presented in this report: * Separation of needles and twigs, with a conventional chipper, in connection with comminution of piled and dried tree residues with low moisture content, * Removal of green parts of fresh tree residues with a chipper fitted with a modified infeed device, * Study of the nutrient content of needles and twigs. Fresh tree residues were chipped with a specially-designed adjustable infeed device. The equipment was found capable of separating the desired fraction, namely needles and twigs. Of the total amount of material, 5-20 per cent by weight were separated. The material largely consisted of green parts. Well adapted separation of green material may also be of importance for the potential fuel availability since land which should not be utilized for removal of wood fuel because of ecological reasons can be made available if the green parts are left on the site. The study of the nutrient content in the green parts was made on both fresh and piled, dry material. During the storage period in the pile, the nutrient content decreased by half. Calculations show that the amount of plant nutrients possible to return via the separated green parts is small in comparison with the supply occurring through both deposition and weathering as well as litterfall. 6 refs., 10 figs., 6 tabs