Berta-Szabó, Emese, et al. “Effects of Long-Term K Fertilization and Liming on the Extractable and Exchangeable K Contents of a Haplic Phaeosem Soil”. Acta Agraria Debreceniensis, no. I, Oct. 2010, pp. 141-5, https://ojs.lib.unideb.hu/actaagrar/article/view/8392.