Vaitkutė, D., E. Baltrėnaitė, C. A. Booth, and M. A. Fullen. “Does Sewage Sludge Amendment to Soil Enhance the Development of Silver Birch and Scots Pine?”. Hungarian Geographical Bulletin, vol. 59, no. 4, Dec. 2010, pp. 393-10, https://ojs.mtak.hu/index.php/hungeobull/article/view/3118.