---

EFEKTIVITAS BRACHIARIA, MIKORIZA DAN KOMPOS JERAMI PADI DIPERKAYA KALIUM DALAM PERBAIKAN KUALITAS
TANAH MASAM DAN HASIL UBIKAYU
(Effectiveness of Brachiaria, Mycorrhiza and Rice Straw Compost Enriched with Potassium in Improving Acid Soil Quality and Cassava Yield)

Bariot Hafif1), Supiandi Sabiham2), Iswandi Anas2), Atang Sutandi2), Suyamto3)
1)Mahasiswa Program Doktoral Bidang Studi Ilmu Tanah Sekolah Pascasarjana IPB
2)Dep. Ilmu Tanah dan Sumberdaya Lahan, Fakultas Pertanian IPB
3)Puslitbang Tanaman Pangan Badan Litbang Pertanian

ABSTRAK

Keracunan Al. kekurangan K dan hara-hara penting lainnya, rusaknya struktur tanah oleh kehilangan bahan organik adalah faktor-faktor penyebab rendahnya kualitas tanah masam. Eksudat akar Brachiaria berpotensi untuk detoksi Al dan memperbaiki ketersediaan hara. Arbuscular mycorrhiza (AM) meningkatkan serapan hara akar tanaman pada tanah-tanah miskin. Penelitian dilaksanakan untuk menguji potensi eksudat akar Brachiaria dalam kelatisasi Al3+ dan penurunan Al dapat ditukar (Al-dd) dan mengevaluasi efektivitas perlakuan Brachiaria, mikoriza dan kompos jerami padi diperkaya kalium dalam perbaikan kualitas tanah masam terkait ketersediaan K, dan peningkatan hasil, kadar pati serta penurunan senyawa sianogen ubikayu. Setelah dua bulan penelitian rumah kaca, asam malat, asam sitrat dan asam oksalat yang di hasilkan oleh akar tiga spesies Brachiaria diukur. Asam malat terukur lebih banyak dibanding asam sitrat dan oksalat. Asam-asam organik tersebut efektif mengkelat Al. Brachiaria decumbens (BD) (Brachiaria terpilih dalam penelitian rumah kaca) menurunkan Al-dd tanah masam sampai 33%. Eksudat akar dan pangkasan daun BD yang dikembalikan ke tanah dan interaksi BD dengan AM efektif meningkatkan ketersediaan K tanah. BD dan interaksi BD dengan AM memperbaiki hasil, pati dan mengurangi kadar senyawa sianogen (cyanogenic glucosides) ubikayu. Perlakuan interaksi BD, AM dan kompos jerami diperkaya K (KCl) 200 kg ha-1 meningkatkan kadar pati dan menurunkan kadar senyawa sianogen ubikayu masing-masing 13% dan 42%.     

Al toxicity, deficiency in K and other essential nutrients, damaged soil structures due to loss of organic matters are factors inducing low acid soil quality. Brachiaria root exudates have potential in detoxifying Al and improving availability of nutrients and arbuscular mycorrhiza (AM) could increase nutrient uptake by plant roots in poor soils. The experiments were conducted to examine potensial of Brachiaria root-exudates in chelating Al and reducing exchangeable Al of soil, and to evaluate the effectiveness of Brachiaria, AM and potassium enriched rice straw compost in improving the quality of acid soil connected with available K, and in increasing yield, starch and suppressing cyanogenic glucosides of cassava as well. After two months of the greenhouse experiment, malic, citric, and oxalic acids produced by the three Brachiaria root-exudates were determined. The production of malic acid was higher than that of citric and oxalic acid. The organic acids chelated Al effectively. Brachiaria decumbens (BD) (the selected Brachiaria in the greenhouse experiment) decreased exchangeable Al of the acid soil as much as 33 %. The root-exudates and leave-cut of BD returned to the soil, and the interaction of BD and AM effectively increased the availability of K. BD and interaction of BD and AM improved yield, starch, and reduced cyanogenic glucosides of cassava. The treatment of BD, AM and rice straw compost enriched with 200 kg KCl ha-1 interaction resulted in a 13% increase of starch and a 42% decrease of cyanogenic glucosides.