SSSAJ: Volume 76: Number 2 • March–April 2012 733 Soil Sci. Soc. Am. J. 76:733–747 Posted online 3 Jan. 2012 doi:10.2136/sssaj 2011.0305 Received 7 Sept. 2011 *Corresponding author (Markusanda@yahoo.com) © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. Mineralogy, Chemical Composition, and Dissolution of Fresh Ash Eruption: New Potential Source of Nutrients Soil Minerology T he Merapi stratovolcano, with a height of 2965 m above sea level, is located 30 km to the north of Yogyakarta, central Java, Indonesia. It has had more than 81 historical eruptions since the 16th century (Voight et al., 2000) and is known as the most dangerous volcano, with a history of deadly eruption, in Indonesia. e Merapi volcano has erupted many times during the last century (1872, 1883, 1906, 1930, 1954, 1957, 1992, 1994, and 1998) (Gertisser and Keller, 2003) and in 2006 (Charbonnier and Gertisser, 2008). Its latest eruption occurred on 26 Oct. to 30 Nov. 2010, with the peak eruption on 15 November 2010, and was recorded as the largest eruption in the series of events starting in 1872. e volume of eruptive materials in 2010 was estimated to be 150 × 10 6 m 3 . Based on Landsat TM satellite image (acquired 15 Nov. 2010) interpretation and field observation, the eruption covered an area of about 435,000 ha, mostly agricultural lands. Mineralogical compositions of volcanic ash vary, depending on the rock type. According to Dahlgren et al. (1993), volcanic ash with a rhyolite, dasite, or an- Markus Anda* Muhrizal Sarwani Indonesian Center for Agricultural Land Resource Research and Development Jalan Tentara Pelajar no. 12 Cimanggu Bogor 16114 Jawa Barat, Indonesia Unusually huge amounts of fresh ashfall from the eruption of the Merapi vol- cano (occurring October–November 2010) resulted in severe deposition problems (1–29-cm thickness) on many agricultural lands. The objectives of the study were (i) to determine the mineralogy and elemental compositions of the fresh ash, (ii) to assess solvent-extracted cations and the composition of pris- tine ash leachates in water, and (iii) to anticipate the possibility of using fresh ash as a new source of nutrients. Mineralogical composition was determined by a polarization microscope and total elemental composition by x-ray fluo- rescence. Dissolved elements were measured from the solid phase (extracted by NH 4 AOc) and water from river stream flow and canals. Results showed that the mineralogical composition was relatively uniform and dominated by volca- nic glass (49% on average) followed by labradorite (26%) and augite (13%), with trace amounts of bytownite, hypersthene, hornblende, and opaque. This indicates that the fresh ash contains mainly easily weatherable minerals. Total element contents consisted of macronutrients in the order of Ca >> Na > K > Mg > P > S and micronutrients of Zn, Fe, Mn, Cu, and Co. Findings from study of pristine ash leachates from river and canal waters, representing natural con- ditions, clearly demonstrated the high concentrations of base cations (Ca >> Na >> Mg > K) and anions (SO 4 >> Cl > NO 3 >> PO 4 ). Base cations extracted by NH 4 OAc were in the order Ca >> Mg > Na > K and the base saturation was >100% (114–484%), confirming that cations in rivers and canals are from sol- uble salts. The high amounts of ions released from fresh volcanic ash indicated its potential as a source of nutrients. Abbreviations: CEC, cation exchange capacity; EC, electrical conductivity; TSS, total suspended solids; XRF, x-ray fluorescence.