<![CDATA[ABSTRACT The low yield of sweet potato tubers often associated with low soil organic fertilizer content. This research was conducted in Desa Namo Gajah, Medan Tuntungan with altitude ± 25 meters above sea level began from Mei up to October 2015. The research was arranged with non factorial randomized block design with P0 (Control), P1 (manure of cattle (7.5 tons/ha), P2 (manure of cattle (15 tons/ha), P3 (manure of cattle (22.5 tons/ha), P4 (empty fruit bunches composts (7.5 tons/ha), P5 (empty fruit bunches composts (15 tons/ha), P6 (empty fruit bunches composts (22.5 tons/ha), P7 (rice straw composts (7.5 tons/ha), P8 (rice straw composts (15 tons/ha) and P9 (rice straw compost (22.5 tons/ha). Parameter observed were length of plants, length of tuber per sample, the number of tubers per sample, the weight of plant biomass per sample, the average weight of tubers, and harvest index. The results showed that the number of tuber per sample, weight of tuber per sample, the average weight of tuber per sample, and harvest index were significantly effected by organic fertilizer. P3 (manure of cattle (22.5 ton/ha) produces the highest number of tubers that was 1.17 tuber, weight of tuber heaviest was 450.23 grams, the average weight of tuber was 388.88 grams and the haviest harvest index was 0.34. Key words : organic fertilizer, purple varieties, sweet potato ABSTRAK Rendahnya hasil umbi ubi jalar sering dihubungkandengan rendahnya kandungan bahan organiktanah.Penelitian ini dilaksanakan di lahan masyarakat Desa Namo Gajah, Medan Tuntungan dengan ketinggian tempat ± 25 meter dpl dari bulan Mei sampai Oktober 2015, menggunakan Rancangan Acak Kelompok Non Faktorial yaitu P0 (Kontrol), P1 (Pupuk kandang sapi (7.5 ton/ha), P2 (Pupuk kandang sapi (15 ton/ha), P3 (Pupuk kandang sapi (22.5 ton/ha), P4 (Kompos TKKS (7.5 ton/ha), P5 (Kompos TKKS (15 ton/ha), P6 (Kompos TKKS (22.5 ton/ha), P7 (Kompos jerami padi (7.5 ton/ha), P8 (Kompos jerami padi (15 ton/ha), dan P9 (Kompos jerami padi (22.5 ton/ha). Parameter yang diamati adalah panjang tanaman, panjang umbi per sampel, jumlah umbi per sampel, bobot umbi per sampel, bobot biomassa tanaman per sampel, rataan bobot umbi, dan index panen.Hasil penelitian menunjukkan bahwaperlakuan pupuk organikberpengaruh nyata terhadap jumlah umbi per sampel, bobot umbi per sampel, rataan bobot umbi, dan indeks panen. P3 (pupuk kandang sapi (22.5 ton/ha) menghasilkan jumlah umbi terbanyak yaitu 1.17 umbi, bobot umbi terberat yaitu 450.23 gram, rataan bobot umbi terberat yaitu 388.88 gram dan index panen yaitu 0.34. Kata Kunci : pupuk organik,ubi jalar, varietas ungu]]>
