“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), vol. 29, no. 2, Aug. 2013, https://doi.org/10.22302/iccri.jur.pelitaperkebunan.v29i2.57.