KasnoA.; RachimA.; IskandarI.; AdiningsihJ. S. Relationship between K/Ca Ratios in the Soil Solution with the Dynamic of K in Ultisol and Vertisol of Upland Area. Jurnal Ilmu Tanah dan Lingkungan, v. 6, n. 1, p. 7-13, 1 Apr. 2004.