“Distribution of Soil Fertility of Smallholding Arabica Coffee Farms at Ijen-Raung Highland Areas Based on Altitude and Shade Trees”. Pelita Perkebunan (a Coffee and Cocoa Research Journal) 29, no. 2 (August 31, 2013). Accessed May 1, 2026. https://mail.ccrjournal.com/index.php/ccrj/article/view/57.