D. Lazdiņa, A. Lazdiņš, Z. Kariņš, and V. Kāposts, “Effect of sewage sludge fertilization in short‐rotation willow plantations”, JEELM, vol. 15, no. 2, pp. 105–111, Jun. 2007, doi: 10.3846/16486897.2007.9636916.