Penelitian ini bertujuan untuk mengetahui pertumbuhan dan produktivitas (produksi, komposisi kimia, dan kecernaan secara in vitro) tanaman Sorghum bicolor (L.) Moench yang ditanam pada tanah erupsi Merapi dengan berbagai level penambahan pupuk organik. Media tanam adalah polybag yang diisi dengan tanah dari Karangmalang (kontrol eksternal), tanah erupsi Merapi penambahan pupuk organik 0, 5, dan 10 ton/ha. Pupuk SP36 100 kg/ha diberikan sekali saat penyiapan media tanah, urea 200 kg/ha diberikan dua kali selama penanaman, dan jarak tanam 50x30 cm. Pengamatan tinggi dan jumlah daun tanaman dilakukan setiap minggu selama 13 minggu. Sorghum dipanen stadium masak susu, dipotong, ditimbang, dioven 55oC dan digiling. Setelah itu dianalisis proksimat dan uji kecernaan in vitro Tilley and Terry dua tahap meliputi kecernaan bahan kering dan bahan organik. Data dianalisis dengan analisis variansi menurut metode rancangan acak lengkap pola searah (CRD) dilanjutkan Least Significant Difference (LSD) test. Hasil penelitian menunjukkan penambahan pupuk organik pada tanah erupsi Merapi secara nyata (P<0,05) mampu meningkatkan tinggi tanaman, produksi bahan kering, dan kecernaan bahan kering secara in vitro. Tinggi tanaman dari 87,55 cm menjadi 118,12 - 126,00 cm, produksi bahan kering dari 2,82 ton/ha menjadi 5,20 - 5,68 ton/ha, dan kecernaan bahan kering dari 65,39% menjadi 66,37 - 69,20%. Berdasarkan penelitian dapat disimpulkan bahwa tanah erupsi Merapi dengan penambahan pupuk organik 5 dan 10 ton/ha mampu menaikkan pertumbuhan dan produksi tanaman sorghum, walaupun belum sama dengan tanah dari Karangmalang.

The aims of this study were to determine the growth and the productivity (production, chemical composition and in vitro digestibility) of Sorghum bicolor (L.) Moench planted in Merapi eruption soil and were added with various levels of organic fertilizier. Polybag was filled using soil from Karangmalang (as external control) and Merapi eruption soil added with 0, 5 and 10 ton/ha organic fertilizer as planting media. SP36 100 kg/ha was added once during preparation of planting media, urea 200kg/ha was added two times during the cultivation, and planting space was 50x30 cm. Observations of plant growth and number of leaf were observed every week during 13 week. Harvest at milk stage, cutted, weighed, sample in oven 55oC and gried. Before analyzed proximate and in vitro digestibility Tilley and Terry two stages included dry matter digestibility and organic matter were done. Data was analyzed using analyzed of various for Completely Randomized Design (CRD) and the differend betweent means was using Least Significant Difference (LSD) test. The result showed that plant height, dry matter production, in vitro digestibility dry matter affected (P<0,05) by addict of organic fertilizer in Merapi eruption soil. Plant height increase for 87,55 cm to 118,12 - 126,00 cm, dry matter production for 2,82 ton/ha to 5,20 - 5,68 ton/ha, and in vitro digestibility dry matter for 65,39% to 66,37 - 69,20%. Based in the study included the addition of organic fertilizers 5 and 10 ton/ha on Merapi eruption soil increased the growth and the productivity sorghum, however not equal than sorghum planted in soil from Karangmalang.

Kata Kunci : Tanah erupsi Merapi, Pupuk organik, Sorghum bicolor (L.) Moench, Analisis proksimat, Kecernaan in vitro Tilley and Terry dua tahap.