Retention properties of wood residues and their potential for soil amelioration

The particle size distribution, the nutrient content and the sorption behaviour of six solid wood and ash/charcoal residues collected in three wood-processing companies in Germany and Brazil were investigated in order to elucidate the potential of these residues for the development of new products for soil amelioration. The absorption of N, P, and K by the residues and the leaching of nutrients from impregnated samples were studied in the laboratory at substrate temperatures of 20 and 300 degrees C. The release of elements by the impregnated samples and the sorption behaviour of ash/charcoal incorporated in the soil were also studied in the field on a temperate site (Hamburg, 53 degrees 32'N 09 degrees 59'E), on a subtropical site (Ivai- 25 degrees 15'S50 degrees 45'W), and on a tropical site (Aripuana, 10 degrees 09'S 59 degrees 26'W). Under laboratory conditions the solid wood residues absorbed 2.0-9.1% of the N, 0.1-0.4% of the P, and 1.0-8.5% of the K available in the impregnation solution. At a temperature of 20 degrees C, selected sieve fractions of the ash/charcoal residues absorbed up to twice as much as N and up to 100 times more K than the treated wood residues. The absorption of N, P, and K to the ash/charcoal residues increased significantly at a substrate temperature of 300 degrees C compared to a substrate temperature of 20 degrees C. In absolute numbers, the leaching of N, P, and K from the impregnated ash/charcoal residues was in the range of the release by the impregnated solid wood residues, whilst the relative rate of nutrient leaching was strongly reduced. The field experiments confirmed the results obtained in the laboratory and indicated that ash/charcoal residues are suitable raw materials for the development of new products for soil amelioration, in particular for application under humid climate conditions.